Flow visualization in liquids

by

Enzo 0. Macagno

Sponsored by

U.S. Army Rock IslandArsenal

Contract DAAF01-69-C-0169

and

National Science Foundation

Grant GK-2818

IIHR Report No. 114

Iowa Institute of Hydraulic Research

The University of Iowa

Iowa City, Iowa

February 1969

ibliotheek van d

heepvaartkunde

nische Hogeschoo ,

DOCUMENTATIE Afdeling Schee 11111 DATUM'

INTRODUCTION

DYES

Injection

In-situ solution of dye Coatings

Electrical-dying techniques

"Lustre Cream" PARTICLES, DROPS, BUBBLES

Solid particles Microscopic particles Colloidal particles Drops Air bubbles Hydrogen bubbles COATINGS ON BOUNDARIES REFRACTION DOUBLE REFRACTION CHEMICAL REACTIONS ACKNOWLEDGEMENTS

APPENDIX A - SOME FLOW VISUALIZATIONS AT THE IOWA INSTITUTE OF HYDRAULIC RESEARCH

INTRODUCTION

Those procedures or devices by means of which the flow patterns

of a fluid (gas or liquid) can be made visible are called

flow-visualiza-tion techniques. In nature, one finds a good number of spontaneous flow

visUalizations and one may surmise that the oldest visualization method

em-ployed by man was suggested by the observation of air and water

transport-ing solid objects and particles. Leonardo da Vinci used solid particles

suspended in water to visualize flows in a glass flume and very

artistical-ly depicted many of his observations (da Vinci, c. l500)*; since then,

many researchers have used solid particles suspended in water, or floatihg

at the air-water interface, as a simple and effective means of visualizing

flows. The basic idea of this method is to give identity to a small region of fluid and observe where it goes; Many other techniques based on this

fundamental concept have been developed, but other principles can be used. If the stress field in a fluid in motion happens to affect noticeably the

optical properties of the fluid, the possibility of visualizing the stress

patterns is open to the researcher. Unfortunately, pressure modifies the

density of liquids only slightly, and a method based on refraction of light,

which is very successful in flow of gases, would only find application in

liquids if tremendous pressure variations and velocities were to be observed.

Certain liquids, however, have been shown to possess birefringence when

flowing, and a method based on obtaining patterns due to passage of

polar-ized light through liquids has been under development for many years. A

much simpler way of using optical properties is the marking of small

por-tions of fluid by heating them slightly and thereby giving them different

density; simple refraction phenomena then allow visualization of the flow. Flow visualization is an experimental method which may appear to many as

essentially qualitative, but it is not always so; in the following sections,

several techniques which have been developed and improved to provide

quan-titative data are described or referred to.

DYES

The most popular method of flow visualization in liquids is that

in which a dye is used as a tracer. TWO procedures are widely used; in

one the aye is separately dissolved in a small quantity of the same liquid

used in the experimental apparatus, and then brought to the desired point

by means of hypodermic tubing, or through orifices in the solid boundaries;

in the other, crystals which dissolve slowly in the flowing liquid are

lo-cated on the solid boundaries or, sometimes, attached to wires. Solid

boundaries may also be coated, either in spots or wholly, with dyed

sub-stances which in turn will aye the fluid; this method ensures

visualiza-tion very close to the wall. When a fluid is very viscous and accessible

through a free surface, lines or small lumps of the fluid can be colored

when the fluid is at rest and then when it is set into motion the flaw

be-comes visible (G. I. Taylor,

1966);

this rarely employed technique is es-pecially usefUl in observing transients starting from rest. The dying of

lines, surfaces, or regions of the fluid is easier when there is density

stratification. A thin layer of dyed fluid of intermediate density can be

squeezed between two layers of different density to Visualize interfacial

phenomena (Macagno and Rouse,

1961;

Macagno and Hinwood,

1964);

or, if there are several layers, they can be dyed alternately to show their

rela-tive motion (Thorpe,

1967).

When the density varies continuously, dye can also be introduced to identify certain regions (Alonso,

1967);

but then the operation is much more difficult to perform without disturbing the

stratification.

Injection

Introduction by injection of a filament of aye in a flow without

disturbing it is not an easy operation. If the flow is steady, this can be

accomplished if some patience is exercized in shaping the tube through which

the aye enters the flow, and in adjusting the velocity of the flow of aye.

Exudation of aye from orifices or thin slots in the boundaries may seem

easier, but it is also a delicate operation, and optimum location and

orien-tation of the orifice may constitute a problem.

of .flow visualization; they work very well in laminar stable flow, may be quite useful in transitional flow, and in some cases of incipient

turbu-lence, But if the dye is rapidly diffused, it soon becomes too diluted

to be visually observable.

Interpretation of data obtained from flow visualizations made

with dye injections at one or more points is straightforward if the flow

is steady. The lines obtained are streaklines, and also pathlines and

streamlines because all three coincide if the flow is steady. In general, when the flow is unsteady, these three kinds of lines are different. There

is however, a class of flows in which the streamlines are fixed because the unsteadiness affects only the magnitude and not the direction of the

velocity vector; for these flows, pathlines are still observable, but

velo-city variation with time must be determined by special additional means.

In flow of gases, smoke is used instead of dye, and it has been

found feasible to interrupt rythmically the smoke filaments thus making

possible a quantitative indication of the velocity. Such a procedure is

much less effective in liquids because it produces unacceptable

distur-bances of the flow.

In general, injections of dye at fixed points in unsteady flows

generate streaklines and not pathlines or streamlines; the information is

still valuable, but incomplete, because from the knowledge of streaklines

alone one cannot in general obtain the usually desired information on the

flow characteristics. Cyclically interrupted streaklines are much more

useful; but they are only obtainable in stable form by other means.

Dyes commonly used are potassium permanganate, methylene blue,

india ink, milk, food colors, and aniline. Other 'Ayes reported in the literature are pyrogallic acid with iron sulphate and ammonia (Hele-Shaw,

1897), fucsin red (Toussaint and Carafoli, 1926), white and colored ink

(Fage and Preston, 1941), nigrosin black, acid chrome blue (F. Hama, 1960), and fluorescein (Woods, 1968). Woods' application was at a very large

scale in a study of the summer thermocline in the Mediterranean Sea around

Malta.

time than others under the same conditions of disturbed flaw; milk seems

to be preferred by some researchers for this reason, and yellow food dye

seems -- to the author -- to diffuse less rapidly than blue food color.

Injection of dye in a captive eddy in a zone of separation may

be used to define the boundaries of the zone of separation (Macagno, 1953);

if done at a series of points, it may serve to determine the point of re-attachment of a separation zone (Macagno and Hung, 1967L Dye may also be

injected in boundary layers and serve to indicate regimes of flaw as well

as transitional three-dimensional phenomena, as was done by Kline and

Run-stadler (1958), who injected dye with 6-inch long, 0.01 diameter hypodermic

needles, and also through a 0.003-inch slot in the wall. The slot was made by cutting and shimming a single sheet of lucite to minimize the

turbances introduced. In both cases a strong downstream angle of injection

was maintained to avoid spurious upstream flaw.

In-situ solution of dye

When single dissolvable crystals are used, the orientation of

the dye filament is somewhat automatic, but the crystal, or the crystal

and its supporting wire, are obstacles and they are seldom so small that

they do not disturb the flow which they must visualize. If the crystal

is too small, not enough aye may be carried away from it. The Reynolds number of a tube, or wire, inserted in a flow, should be rather low; if

possible, less than fifty.

Crystals which have been used with advantage by the author in

small-scale experiments are those of green malachite and potassium

per-manganate, both soluble in water. R. Hide (1968), in his study of

source-sink flow in rotating fluids, used nigrosin crystals to visualize Ekman

layers. Sometimes it is desired to remove the color from the fluid; in

the case of potassium permanganate, it can be done with sodium bisulphite.

When one's hands become dyed with potassium permanganate, oxygenated water

may help remove the stain.

The above mentioned applications were at small scale; at very

large scale, the use Of padketsful of dye has been found suitable. J. D.

Woods (1968) has Used packets of dye as either point or line sources to .

Electrical-dying techniques

--Iodine, which react and can be injected in water duced by electrolysis. This

s in water with starch to give a blue color,

tb create dyed streaklines, may also be

pro-idea was proposed by Miss kathalie Gamberoni

(Douglas Aircraft Company, see Clutter et al.,

1959),

and provides a

means of generating periodically interrupted dye filaments. In this method,

iodine is liberated at an anodic wire by electrolysis of a

potassium-iodide solution. The reaction is

11-1" + e + (1/2)H2 at the cathode

I- - e -4" (1/2)12 at the anode.

If there is starch in suspension, a blue color is formed. The anode Vire

should be of platinum; as one can use a 0.001 to 0.002 inch wire, the

dis-turbance introduced in the flow is relatively small. The time lag in the The existence of laminar layers and of turbulent zones was put in evidence

in this field investigation in the Mediterranean Sea. Dye dispersed in

laminar shear layers lasted for several hours, and its motion was registered

photographically.

Coatings

In

1910,

C. G. Eden coated with condensed milk his plates and models; the milk was slowly carried away by the water flowing.around them

and thus visualization of the boundary flow was achieved by a rather simple

means. To reveal the second .laminar regime between rotating cylinders, G. I. Taylor

(1923)

applied dye prior to experiment on the inner cylinder in a coating which could be slowly dissolved by the liquid in between the

cylinders; in this manner the appearance of cellular motion was perfectly

detected by dye which was carried through the fluid at the onset of

insta-bility. Coatings or "smears" which introduce dye in the flowing liquid have also been made with carbo wax in which methylene blue or

methyl-violet were dissolved (Clutter et al.,

1959).

Other coatings are also used for boundary flow visualization,

and they may be dyed, but the principle is not essentially that of dying

production of the blue filament is one of the drawbacks of this method

(Clutter et al.,

1959);

another is the difficulty in properly illuminating the filaments because of some lack of transparency of the liquid. The

method has been suggested as more suitable for the study of wakes and other

mixing zones (Clutter et al.,

1959),

but R. Hide

(1968)

has been able to use Gamberoni's technique in determinations of the velocity distribution

in rotating fluids.

Another technique for introducing aye in a liquid is due to

D. J. Baker

(1966).

The technique uses a.pH indicator, and is applicable in aqueous solutions. Two electrodes are placed in a solution of thymol

blue titrated to the end point. If the voltage is pulsed, a small

cylin-der of the acidic form of thymol (which is yellow) is formed and carried

away by the flow. In this way a neutrally buoyant marker which reverts

to the original color with time is formed. Baker has used the technique

for flow visualization and for measurement of low velocities (in the range

0-5 am/sec.). Electroytical release of dye has also been used by R. Hide

et al.

(1968);

their experimental liquids can also be used

indefinitely.-"Lustre Cream"

A technique based on dissolving a commercial shampoo -- "Lustre

Cream" -- is due to E. 0. Macagno (Iowa Institute of Hydraulic Research).

A first application was made by Professor Rouse to illustrate turbulence

in water in one of his instructional fluid mechanics films (Rouse,

1964).

Hinwood also used the technique in flow visualizations in his doctoral

work on stability of flows with stratification of density (Hinwood,

1966).

Macagno

(1968)

has also used the lustre-cream technique in his work

on intereffects of curvilinearity of flow and density stratificatibn. J. Aguirre applied the method in research for his M.S-, thesis on confined ro-tation of fluids with and without density stratification (Aguirre,

1969).

The lustre-cream technique can be considered as a combination of

dye and particle flow vizualization. It gives, if proper illumination is

used, a good three-dimensional view of flow details, especially near the

liquid-air interface, or close to transparent solid boundaries of the flow.

density by secondary curvilinear currents are now being repeated with

lustre-cream added to one of the liquids; the measurements of conductivity

(which provide the pattern of variable density distribution) show little

difference due to the presence of this shampoo. It is believed, hoWever, that the lustre-cream confers some non-Newtonian properties to the water;

caution seems in order when interpreting flaw visualizations achieved

with this technique.

PARTICLES, DROPS, BUBBLES

Solid particles, liquid drdps, and small gas bubbles may be used

to visualize the motion of liquids. An obvious requirement seems to be

that the difference in density between the tracer and the fluid be as

small as possible, but in practice experimenters have rarely shown much

concern about mismatch of densities in flow visualization with solid

par-ticles or gaseous bubbles. There is a hydrodynamic explanation for this

attitude; the path followed by a small particle depends on the viscous,

inertial, buoyancy, and gravitational forces, and if there is a

predomi-nance of the first, the particle may follow the fluid flow quite well.

In the case of gas bubbles in a liquid, the ratio of densities is really

extreme; but if a gas bubble is so small that its velocity of ascent is

only one hundredth or one thousandth of the fluid velocity, one can

ex-pect satisfactory flow visualization, unless very high local or convective

accelerations are present. For similar reasons, aluminum flakes may also

serve well in flow visualization.

Solid particles

Mention was just made of the aluminum flakes or aluminum powder.

In oil they have been used in recent years by Macagno and Hung (1967), for

visualizing steady non-uniform axisymmetric flow in a conduit expansion,

and by Macagno

(1964)

in non-uniform accelerated flows. In the first case, a comparison was made between the observed and calculated flow patterns;

the agreement was very satisfactory. In the second case, a motion picture

was made (at the Iowa Institute of Hydraulic Research) of different cases

of accelerated flow, but no comparison has yet been made with calculations.

with the oil in the experimental apparatus which was essentially a pump

and pipe loop into which the lucite conduit expansion was mounted. The

external shape of the conduit expansion was chosen to minimize refractive

deformation of the photographed images of the pathlines.

About forty years ago, Camichel (1925) was already using

metal-lic particles in his chronophotographic method of flow visualization.

Fine metallic particles were dropped in the liquid in such a way that they

entrained small air bubbles; most of the powder settled (up or down) out

of the observation region, but what was left in suspension was very

effec-tive for flow visualization. By strongly illuminating a plane (or two in

succession), the path followed by the particles were made visible and

photographed. Camichel used intermittent illumination of the particles

to achieve measurement of the velocity from the traces left by the images

of the particles in photographic plates obtained with suitable time

expo-sure. Aluminum flakes, observed with a stroboscopic light, were also used by Camichel and collaborators to determine periodicity in

two-dimen-sional wakes, (P. Dupin, 1930).

In spite of the abundant literature on flow visualization, very

Thy authors seem to be concerned about the possible disagreement between

the motion of the tracer particles and that of the fluid transporting them.

Efforts towards the production of neutrally buoyant particles is, of course,

one practical way of minimizing the divergence. Camichel's "natural

se-lection" of particles is certainly a move in this direction. For low

speeds, Macagno and Aguirre have, respectively, devised and used particles

which were made of a carefully mixed paste of plaster's putty and wax; to

achieve a selection of particles they used a nearly linearly, stratified liquid in which the particles would float at different levels depending

on their density. Temperature effects and occluded or attached air bubbles

were found to be quite a nuissance, and particles smaller than one

milli-meter could not be made (Aguirre,

_1969).

Particles also play a role in experiments in which they are

used at the interface of air and water. If heavier than water they may

still float because of surface tension effects. Free surface flows can

shock absorbers (Newsham et al., 1965). This method was developed to a

high degree of perfection by L. Prandtl and his collaborators during the

first quarter of this century. Some excellent pictures obtained by them

can be seen in Prandtl andTietjers' book onhydro- and. aeromechanics. Films with extraordinarily good quality of flow visualization were

pro-duced by Prandtl's group using Professor E. Ahlborn's method. The

de-scription of the special camera shutter used to obtain those films is

given in a paper by Prandtl and Tietjens (1925). The type of flow

visu-alization shown in those films was used by Schwabe (1935) to obtain

pres-sure distributions in nonuniform unsteady two-dimensional flows; the

method for the integration of the data shown by the pictures was suggested

by Prandtl.

When using aluminum particles to spray free surfaces for

visuali-zation purposes, the particles or flakes should be washed previousIT in

alcohol to eliminate the estearate which they usually carry. Aluminum

particles which reportedly are quite free of aluminum estearate are the

Alcoa Aluminum Standard Unpolished Powder No. 606, (a fine-flaked

alumi-num powder). Washing with alcohol provides a powder which does not tend

to collect in clusters on the water surface, and helps in obtaining more

stable suspensions. The powder should first be suspended in a bit of

alcohol, and then mixed with the experimental liquid (water or oil);

direct introduction of the aluminum powder into the liquid should be

avoid-ed. Clutter et al. (1959) concluded that glass or plastic beads give more stable suspension of particles in liquids than aluminum powder and refer

to Roberson (1955). Bourot et al. (1960, 1962) have used an electrostatic

field to orient the aluminum flakes during flow visualization, and report

an important improvement.

Plastic spheroids with densities quite close to those of liquids

used in studies of fluid flow have been used in recent years.

Polyethy-lene (a-98 gr/cm3) and polystyrene (1.05 gr/cm3) are two plastics with

densities close to that of water. Other materials used in flow

visualiza-tion are nylon, perspex, bakelite, ebonite, (with densities from 1.14 to

be less than the density for solid material. _{For instance, polystyrene}

.beads with air bubbles have a density from

_0.98

_{to 1.02 gr/cm3.}

1

Allen and Yerman

₍₁₉₆₀₎

_{used polysterene spheres in water to} achieve flow Visualization. _{They consider matching of densities a very}

important reqUirement, and describe and suggest procedures to lower the density of plastic spheres. _{Some plastics, like polystyrene,}

expand'per-manently when heated. _{Allen and Yerman recommend the use of a moving belt}

to pass the beads under a bank of heatlamps; variations of belt speed

distance from beads to lamps control the amount of expansion. Another

meth-od, requiring extensive equipment and knowhow, is spray drying of holloW plastics, also mentioned by Allen and Yerman. _{These authors consider that}

matching of densities within 0.001 to 0.0001 gr/cm' is necessary for

ac=

curate quantitatiia flow visualization.

A very ingeneous technique in which multi-color photograph is

used to achieve a three-dimensional record of the motion of an opaque 1

spherical tracer has been developed by Van Meel and Vermij

_(1960).

By means of a parabolic mirror and color filters they produce ten planes of 1

light with different colors, thus creating a kind of "color" third coordi-nate for the trace of the particle image in the photographic _plates.

1

Microscopic particles

Most fluids contain very small particles unless they have been produced under exceptionally "clean" conditions. Fage and Townend apPlied

the idea of observing precisely the particulate "impurities" usually present in water, and which supposedly do not disturb the flow and follow it vex* closely. (Today, with more _{awareness of Tom's effect on fluid flow, one}

r

would be less sure about the inflUence of microscopical particles!) _They

,

illuminated the minuscule particles with _{very intense light and used an}

ultramicroscope to observe their motion against a dark background. To

measure the velocity of a particle, use was made of the principle thatitne

particle would appear as a bright point if viewed from a system at a speed at which the particle is moving. _{Fage and Townend (see S. Goldstein,}

_1943),

instead of moving the whole microscope, moved the objective which _was

Seems to be difficult.:

Although not intended as a flaw-visualization method,

Bugliarel-lo and Hayden's high-speed microcinematographic studies of bBugliarel-lood fBugliarel-low in

vitro may contain useful aspects in connection with the observations of

microscopic particles as tracers of fluid flow (Bugliarello et al., 1962).

Colloidal particles

A technique which ressembles Gamberoni's procedure for dying

fluid filaments, is Wortmann's tellurium wire electro-chemical technique.

This technique allows controlled introduction of colloidal particles of

tellurium. Wortmann (1953) applied the method to laminar flow and to flow

in boundary layers. In his method, water acts as the electrolyte, the

tellurium wire as the cathode, and any other metallic surface in contact

with the water as the anode. When an electric pulse passes through the

wire, tellurium ions are discharged and become transformed into colloidal

tellurium suspended in the liquid as a hydrosol. The settling velocity

of the cloud of colloidal tellurium can easily be kept under 0.1 mm/sec;

the diffusion velocity, according to Wortmann, is less than 0.001 mm/sec.

Tellurium wires were made by Wortmann by the Wollanston technique, and

are reported to be easily breakable, although if treated with care they can

be used for many hours. When a number of streamlines, or streaklines, is

desired, tellurium pearls soldered to a wire can be used (Wortmann, 1953).

Tellurium is somewhat toxic and gives offensive breath to those who

in-hale its vapors (Clutter et al., 1959).

Drops

Liquid drops may appear as the ideal tracer for flow

visualiza-tion in liquids, but they are subject to requirements similar to, and as

difficult to achieve as, those for solid particles. To use two immiscible

liquids of the same density is not feasible, but suitable drops can be

prepared by mixing two liquids of densities respectively larger and smaller

than the density of the liquid for which the flow must be visualized. If

of dispersing fine drops of, e.g., oil

in

water; this .ressembles

thetech-1

nique of emulsified air in water which will be described in a further sec

tion.

Uniform liquid drops can be produced by different techniques

(Rayner,

1955),

but if they must be introduced in flawing liquid, distur-bances of the flow must be avoided, and this rules out most of the

availa-ble procedures. The simple techniques used by Vanoni et al. (1950),Iand

by Macagno and Rouse

(1961)

lead to emission of droplets immisicible with water which are introduced in a controlled manner and with little

distUr-bences into fluid flaws. 1

The tracer droplets used by Vanoni were prepared with mixtures

1

of benzene and carbon tetrachloride, heptane and carbon tetrachloride,

and heptane and ethylenechloride. The droplets were injected into steady

turbulent

flow,

and instantaneous photographs were taken of the tracers Photographs were of three types: first, single exposure of droplets

which were injected at a point; Second, multiple exposures with droplets

over the entire field; and third, a large number of exposures on a single

plate with only a few droplets in the field. Stereoscopic pictures were

also taken. Valudble quantitative information was obtained from the

photographs by Vanoni and his collaborators. Stereoscopic photography was

also used by Girard and Robert

(1956),

but for particles in suspension' in air.

Macagno used also a mixture of two fluids of different density

to obtain neutrally buoyant droplets to be used as tracers in

density-stratified flows. His description of the technique is: "For each

experi-ment three mixtures of n-butyl phthalate and xylene with a bit of white

paint were prepared to match the densities of fresh water, salt water, end

the intermediate mixture. The mixture was injected by means of hypoderMic

needles in such a way as to produce small clusters of droplets essentially

instantaneously but with practically no disturbance, as was verified under

conditions of laminar flow. To take pictures of the droplets, a narrow

strip was illuminated with both continuous and intermittent light. The channel was made of black plastic, so that the droplets moved againsta

corresponding to the flashes emitted by the Strobolume. Usually some 30 to 50 pictures were taken in each run in order to ensure a good average,

especially in the case of turbulent motion. The traces left on the film

generally appeared to have a head and a tail of unequal length, And this

helped to determine the direction of the motion. No effort was made to

synchronize the camera shutter and the flashing light in such a way as to

make different heads and tails, because it was found that mere chance was

enough to obtain the desired result in most of the pictures.

"The frequency of the flashing light was controlled first by

means of a mechanical contactor and then by a combination of an electric

clock operating a notched aluminum disk and an electric circuit with a

photocell. A beam of light passing through the notches excited the

photo-cell, which in turn operated the Strobolume. Both timers were built at

the Iowa Institute using standard equipment and instruments."

The above described technique was also used by J. B. Hinwood

(1966) in his doctoral research on stability of stratified flows at the Iowa Institute of Hydraulic Research. Part of his work involved flow

es-tablishment of a liquid of uniform density for which an analytical solution

existed already; this enabled Hinwood to check and evaluate his measurements

of fluid velocities using droplets as tracers.

In some cases, the drops have been introduced in a continuous

stream into the liquid to be studied. Kalinske (1946) used a mixture of

carbon tetrachloride and benzine, the proportions being adjusted so that

the mixture had a density equal to that of the water. Powdered anthracene

was added to the mixture to give it a milky appearence. Kalinske

illumi-nated the drops with a carbon-arc light, and used a motion-picture camera

to make records of turbulent flows through conduit expansions. In this

way, he determined not only mean velocity distributions but also turbulent

velocity fluctuations in both longitudinal and transverse directions.

Mehmel (1962) also used continuous injection of liquid with drops in

sus-pension in his investigation of flow around turbine blades. He used double

mirrors to photograph the droplets stereoscopically.

An already classic application of neutrally buoyant droplets to

Apparently, Simple mechanicist (Dr. August experiment Raspet liquid

illustrated by the excellent photographs published in

1950 in La Houille Blanche

(Vol. V, no.

4).

Air bubbles

Air bubbles have been used by some researchers to visualize the

flow of liquids. _{Air must be introduced in streams of very small bubbles,}

or can be emulsified separately and then ducted into the liquid. BirkhOff

and Cagwood

(1949)

used equally spaced rising air bubbles in their inveSti-gations of the flow field due to the entry of a body in water. The bublr

bules were photographed against a. black background with intermittent light. Velocities were determined from plates, on which the position of the bulp- .

bles were recorded using two flashes separated by a known interval of time.

Another researcher who has used air bubbles is H. Werld (1963).

He used air emulsified in water and obtained good three-dimensional

visuali-, I

zations of flows around airfoils. The method was also applied to flow in

boundary layers and regions of separation.

Hydrogen bubbles

of using the principle to introduce gas

flow. The first with hydrogen bubbles was Geiler's

(1954, 1955).

0.001-inch in diameter installed across a duct as rows of bubbles by pulsing the electrical current

rows of bubbles rendered Visible the fluid lines.,

electrolysis of water using two wires as electrodes

years

a in high schools for many yes before a flUid

of Mississippi State College in

1963)

thOught

1 I

bubbles at desired points andlai

I I

in a _{reported flow visualization}

He used a platinum wire

a cathode, and obtained

through the wire. Those or time lines,

which

in-dicated velocity profiles of his steady flows. Several illustrations,ofl hydrogen-bubble time lines can be seen in one of the Iowa Institute of

Hy-draluic Research instructional films (Rouse,

1964).

A very good illustration of Clever use of the .hydrogen-bubble

1

technique is found in a motion-picture film by S. J. Kline

₍₁₉₆₃₎

in which the differences between streamlines, pathlines, and streaklines are very

clearly shown. Schraub et al.

(1964, 1965)

_{also illustrate the three} dif-ferent kinds of lines very well in a paper on quantitative determination convenient times

of unsteady flaws by using hydrogen-bubble techniques. The possibility of

misinterpretation of flows visualized with streaklines is discussed

analy-tically by F. Hama (1962). Another contribution to theoretical limitations

of visualization techniques is due to J. Faure (1963).

Very good photographic records obtained using the

hydrogen-bub-ble technique can also be found in a report by G. E. Mattingly (1966) who

adapted the technique to the 12-inch variable pressure water tunnel of the

David Taylor Model Basin (now Naval Ship Research and Development Center).

Mattingly discusses the velocity limitations which seem to be inherent to

this method, and warns about distortion of the flow which may result if

the wire Reynolds number is too large. In his study he did not use

velo-cities greater than about 6 inch/sec. Mattingly used a combination of

straight and kinked wires to obtain two families of lines, time-lines and

streaklines. The reSulting net of lines makes possible quantitative flow

visualization in unsteady flows. Mattingly's report is very comprehensive,

and should be very useful to any researcher trying to use the H-bubble

technique in low velocity flows. The same must be said of the paper by

Schraub et al.(1964).

Very few papers in the literature on flow visualization deal with

flow of liquids at relatively high velocities, or with high accelerations.

E. 0. Hansen (1968) describes use of hydrogen bubbles generated by water

electrolysis to visualize high-speed two-dimensional flows. Hansen's

photographs are not as good as those which have become so popular in

re-cent years, but he worked with speeds as high as 25 ft/sec, and his results

are not less of an accomplishment because they lack the esthetic values of

photographs of stable laminar flaws.

Hansen had not only background turbulence to make his flow

dif-ficult to visualize, but he also worked with flows with cavitation numbers

as low as

0.6.

Beyond

0.6,

the cavitation effects were too strong and the method failed to render the flow pattern visible. Hansen used wire

dia-meters from 0.001 to 0.005 inch, in tap water to which sodium nitrate was

added to increase bubble formation. Wires were mounted without tension;

than if they had been mounted under tension. Sbme of the problems which

presented theMSelVes were breakage of wires

in

turbulent regions, and' burning Wires in stagnant regions. Because of the electrical field

present In the water, eddy currents occurred in metal objects

in

contaat with water, and thus bubbles appeared at the edges of metallic boundaries

where they were not Wanted.

In the flows studied by Hansen, there was dispersion of bubbles

and the lines of bubbles generated by successive pulses became

progressive-ly less well defined as they were carried away. In wake regions,

thervisuali-zation was lost at six inches from the wire. Because it was necessary to

dearate the water when tests with cavitation were performed, there was also

the problem of redissolution of gas into water avid of it. Dirt particles

tended to accumulate in wires and spoil the uniformity of bubble formation.

I Hansen recommends use of extremely clean water, backlight illumination if

I 1

possible, and simultaneous recording of time lines arld,streaklines, far, which two wires are needed. Hansen claims an accuracy of 2.5% in his

measurements of velocities.

Another paper on the use of the H-bubble technique in obseriing

unsteady flow is an article by Weinberg and Heiser.

₍₁₉₆₈₎

on visualizations in unsteady boundary layers. As have most researchers reporting work with

this technique, they added an electrolyte to the water (not considered

I ;

necesbary by same researchers), and used extremely clean water. To aVoid

electrical shorting, they used plastic models and a small plastic

conduits.

Like Mattingly, they found it convenient to imbed platinum wires or strips

In their models flush with the surface of the model. Weinberg and Heiser

also worked with rather low velocities; their maximum Reynolds number for

flow around airfoils was

6,160.

They studied boundary layer development' (a transient phenomenon)in a fluid flow which was initiated from rest.

COATINGS ON BOUNDARIES

Painting, smearing, or coating solid boundaries of fluid flows

to visualize the adjacent flow is an old technique With more applications

(1921)

used oil paint to visualize boundary flow disturbed by an obstacle and by a change in direction in a conduit; two of his photographs are

re-produced in Prandtl's

Essenticas of Fluid Dynamics (p. 147).

The action of the main flow on the motion of the coating fluid

or substance is certainly a complex one, and the technique is very much

at a qualitative stage. The coating, in order to provide a flow vizuali-zation, must also flow or move, and the lines or furrows which appear in

the coating may be revealing the interaction between two fluids rather

than what occurs in the undisturbed flow. For instance, if the line of

separation is desired, it may very well be that separation occurs

differ-ently due to the coating.

According to an analysis by L. C. Squire

(1960),

in a thin oil sheet under the boundary layer of a body, the oil flaws in the direction

of the boundary layer skin-friction except near separation, where the oil

tends to indicate separation too early. These conclusions are independent

of the oil viscosity. Squire also concluded that the effect of the oil

flow on the boundary layer is very small.

Other examples of applications of the coating technique can be

found in papers by F. Gutsche (see Clayton and Massey,

1967),

Duller

(1963),

and J. R. L. Allen

(1966)..

Gutsche used patches of paint applied to the blades of a rotating impeller, and Duller applied a film of fluorescent

oil (Loving et al.,

1959)

to objects in a helium tunnel at Mach numbers of 15 and

20;

he also used a film of oil with white lead. It seems to the author that the coatings used by Duller could be employed in liquids

also. Allen used plaster of Paris

as

coating, and concluded that his method should be restricted to turbulent boundary layers. One drawback

of Allen's technique is the increase in roughness of the boundary as the

visualization progresses.

REFRACTION

In gases, changes in density due to flow ay be high enough to

be detected by optical means, Shlieren and shadawgraph methods (Beams,

companying variations in density. In principle at least, pressure fields

in water also produce variations in density, and ideally a sufficiently1 powerful optical technique could reveal the pressure field through detection

of variations in density.

In liquids, one cannot usually base the method of visualizatiOn

in the variation in density due to pressure, but rather on that due to

changes in temperature: By heating the liquid at a-certain point, or

along a certain line, the fluid is marked. with regard to temperature, alid

wherever it goes it can be visualized because of the modifications induced

in the optical paths of light passing through it. Bland and Pelick (1962)

actually induced density stratification across a fluid to visualize the

flow; the question may then be raised of whether they actually determined

the flow of a stratified fluid instead of the flow of uniform densityi

II

fluid? On the use of Schlieren and shadowgraph methods in the study of; flow patterns in density-stratified liquids, a recent paper by Mowbray

I

(1967) is a valuable contribution, but perhai)s more readily available, for use and more related to common flaw visualization is the fluid-marking

technique due to D. Pierce (1961). Pierce investigated experimentally the

shedding of vorticity from the edges of a plate accelerated normal to !it-self. He used air heated locally, but the method could be used in liquips which could also be heated locally to produce enough density chahge for

I

visualization of a separation region and the formation of vortices. rabula

(1968) has used this type of flow visualization in his study of the respnse

of towed thermameters.

DOUBLE REFRACTION

Some pure fluids and many colloidal suspensions and fluids

with

' I

additives have been found to possess special optical behavior. Streaming

,

birefringence (SBR) has been observed since the time of J. C. Maxwell

(1873). In the past forty years a good number of papers on the techni'quas of flow visualizations based on double refraction or birefringence have

been published, but a theory for the interpretation of the patterns obtained

'

by the SBR technique, not withstanding several contributions over the paSt

on this method was published in

1960

by H. Wayland, who raises the impor-tant question of how non-Newtonian a fluid with SBR must be. He remarks, however, that it is a fact of experience that certain pure fluids show

SBR while still behaving very much as Newtonian fluids. Even some

col-loidal solutions have been found which exhibit, within certain ranges,

Newtonian behavior. Prados and Peebles

(1955, 1957)

who made extensive studies of SBR with milling yellow aye solutions, claim that this fluid

behaves as Newtonian for rates of strain up to 12 sec-1.

Prados and Peebles used plane and circularly polarized light

in their investigations, arid worked with two-dimensional flows. They

ob-tained interference patterns and analyzed them for cases in which the

re-lation between the stresses, or strains, and the streamlines are known. Their procedure is simpler than others in the literature, but not too

ac-curate. Wayland

(1960),

who experimented with ethyl cinnamate (Wayland,

1955)

in a rotating cylinder apparatus, and developed his own procedure

for data reduction, considered that the work with milling yellow was

in-conclusive. D. F. Young

(1956)

stated in his dissertation that he had evidence that milling-yellow solutions show in their hydroaynamic behavior

that the substance induces non-Newtonian properties; this was based on

his use of milling yellow aye in a Hele-Shaw apparatus.

Fluids which have been used in SBR are sesame oil, vanadium

pentoxide sol (Humphrey,

1923),

ethyl celulose (selected among fifty others liquids by Weller et al.,

1942),

bentonite sols, clay Hectorite in water, benzopurpurin sol (used by Binnie,

1945,

and by Lindgren,

1959,

in studies

of transition from laminar to turbulent flow), and tobacco mosaic virus

(Sutera,

1960).

Flow visualization using doubly refracting fluids has been used

as a quantitative technique for two-dimensional flows. If used in

three-dimensional flows, the effects would be integrated along the optical paths

of the polarized light, and it seems that only qualitative or

semiquanti-tative results could then be obtained. Even for two-dimensional flows

the technique requires a good amount of knowhow, and all procedures of

analy-sis published to date seem to be based on tenuous assumptions about the real

behavior of the fluid. Future work may yield more reliable methods of data

believe that analysis of the fringe patterns will never be simple.

CHEMICAL REACTIONS

Theuse of chemical reactions to Visualize flOws seems to be in

a purely qualitative stage. Macagno (1961) used phenolphthalein and sodium

hydroxide added to fresh and salt water to examine the conditions at an

interface in which turbulent conditions could develop and produce mixing.

The stratification of density was purely incidental, and the observation of

a zone of mixing with this procedure is as feasible in jets and wakes in

fluids of Constant density as it is in stratified flaw. Other reactions,

if as quick as those used in titration methods, can be utilized. Direct

introduction of iodine in water with starch, mentioned before in connection

with GaMberoni's method, can also be used.

Danckwerts and Wilson (1963) Used a time-reaction method for flow

visualization. The principle is that a liquid which becomes colored some

time T after entering a fluid system will mark those parts of the liquid which have spent times longer than T in the system. They were able to

change the time T, and deduce further details of the flow studied. They actually used a double reaction: one slow reaction involves sodium

persul-phate and potassium iodide ions, and iodine; the other reaction is

prac-tically instantaneous and involves iodine and sodium thiosulphate. When

all the thiosulphate is used up by the second reaction, free iodine

liberated and can react with starch which has also been added to the water;

this gives an intense blue color. The method is thus based on a ret4rded

effect which depends on the amount of sodium thiosulphate initially

incOr-porated into the system. The method seems to be basically a qualitativ

I

one; the authors recognize that caution should be exercized in interpreting

This study of techniques.of flow visualization in liquids has

been undertaken at the Iowa Institute of Hydraulic Research in view of the

need for such methods in several areas of investigation of the flow of

liquids. The study has been approached in a.broad manner in order to make

a contribution as general as possible; but in response to specific demands

a double emphasis has been incorporated into this work. The emphasis on

unsteady phenomena is due to the interest and support of the U.S. Army

Rodk. Island Arsenal. The emphasis on flows with stratification of density corresponds to the continuing Institute vork on this area; the financial

support of the National Science Foundation has made possible to cover this

Flow visualization by introduction of a thin layer of dye between two li-quid streams flowing in opposite direction. Onset of turbulence in the shear layer can be observed in the third photograph. (Macagno, Iowa Institute of 1;ydraulic Research).

SO,

\

/555arTar.. BO .

23

60

Chemical-reaction technique. Vizualization of turbulent mixing at a shear layer. (Macagno, Iowa Institute of Hydraulic Research).

Confined Karmgh flow due to the rotation of a disk. Dye was massively in-troduced in the central region; part of it was rapidly diffused by secondary currents; the remaining dye illustrates the existence of a laminar core.

Visualization of the three-dimensional boundary layer adjacent to the cylinH der for the same confined flaw, (Macagno, Iowa Institute of Hydraulic Re-search).

Use of crystals- to visualize confined

Kaman

flow. One crystal was attached to a wire, and another to the rotating disk. A third crystal just fell through the liquid. (Alonso, Iowa Institute of Hydraulic Research).

7-=

f

Side and top views of confined Kaman flow of a homogeneous liquid. The flow was driven by a disk rotating at 65 rpm. The flow visualization was obtained by adding

lustre cream to the water. (Macagno, Iowa Institute of Hydraulic Research).

,#)0000Pre

Top view of confined Kgrmgn flow. The angular speed of the disk was 100 rpm. Visualization by the lustre-cream technique. (Macagno, Iowa Institute of Hydraulic Research).

.41

II

Confined Kaman flow of a density-stratified liquid.

The upper layer contains lustre cream.

photograph shows initial disturbances at the interface.

The second and third photographs were taken, one

after the other, with different illumination.

The second photograph shows very clearly that the

distur-bances due to the flow in the lower layer do not penetrate deeply into the

upper layer.

There is also

a strong difference between the average angular speeds of the two layers.

(Macagno, Iowa Institute of

0.8 0.7 0.6

Q5

(Juitt)p 0.4 03 0.2 0.1 0.9 0.0 o

C

0.373

CIF

0.0196

RFC=

298000

Z

= 0.322 1255

<T

<5270

0.0 01 0.2 0.3 0.4 ₀₅

r/d

Angular velocity distribution within the lower of two rotating layers of fluids of different density. The flow was visualized by means of aye and plastic beads. (Aguirre and Macagno, Iowa Institute of Hydraulic Research).

lor:"

Aitralt-- "

Lustre-cream technique. Confined Kerman flow of density-stratified liquid. Initially, two layers of different density and same thickness were at rest. The first photograph shows the interface, which was advancing towards the free surface. The second is a top view of the interface, photographed through the transparent upper layer. (Macagno, Iowa Institute of Hydraulic Research).

.41116.,L

Lustre-cream technique. Confined Kg.rman flow of density-stratified liquid. Lustre cream, dyed with different colors, was added to both layers. The

-photographs show the different scale of turbulence due to different angular speeds of the disk which generates the motion. (Macagno, Iowa Institute of Hydraulic Research).

Lustre-cream technique. The upper photograph shows the onset of turbu-lence in a density-stratified liquid in a conduit. The lower photograph shows onset of turbulence in liquid of uniform density in the same conduit.

7 8 "

:

f

0,827"

From pump

1 IN Or' ..11106 8.4111. wiussaL.v.-t, _ 9,511

74"

2 0"--1

f

1,654"

f

\

To tank

Apparatus used to study flow of oil through an expansion in a circular

conduit.

Note orifices 1 to 18 through which dye was injected to determine the

reattach-ment line for the captive annular eddy.

(Macagno and Hung, Iowa Institute of

Hydraulic Research). t , V

1,2,3

16,17,18

.4% 4

R=198

R 61

;--,

-. .

-R=100

R=101

=

Flow of oil in a conduit expansion visualized by aluminum powder in suspension. The lower part 6f each figure shows, for different Reynolds numbers, streamlines which resulted from numerical inte-gration of the Navier-Stokes equations. (Macagno and Hung, Iowa Institute of Hydraulic Research).

7.1

Accelerated flow of oil in a circular-conduit expansion. _{The flaw was} started from rest and was rapidly established for a Reynolds number of

4500.

A long laminar eddy with secondary cellular motion resulted.

(From a film by E. 0. Macagno, Iowa Institute _{of Hydraulic Research).}

-eAMIT,4

7 - 4.1kee

...047-

011_

,

. ::,,,.... t,:m.... ,

-- - -

----.42E2,_

A, ',,,,

+...asaiNdelik,

__,...,_____-- - 111..&... .zglir__

.:; .,iiz....__._. ..iim..,:.,... .._ _{,.--.- "}

_--.

' --- ^ -'''..tr''"-,'62'''' ---'---..--'-... - '' ,_''''"".'7- ,..., ''''''' 9

-_

.eSSaLr---Unsteady flow around a constriction. The flow was started from rest, and was rapidly accelerated. Visualization by means of aluminum flakes at the air-water interface. (Macagno and Tzeng, Iowa Institute of Hydraulic Research.)

.4

11.-0111.

Ali._ _Aim.

Flow visualization in density-stratified flow by chronophotographic method. Neutrally buoyant droplets were used in each layer. To show flow conditions at the unstable interfaces, droplets of intermediate density were used. (Ma-cagno, Iowa Institute of Hydrualic Research).

Chronophotographic technique. Neutrally buoyant droplets in stratified flow. The upper picture shows a highly disturbed interface still in laminar regime. The lower picture depicts the onset of turbulence between the two layers.

AGUIRRE, J. (1969), "Confined flow of homogeneous and stratified fluids induced by a rotating disk," M.S.

Thesis,

University of Iowa, (available on loan).

Neutrally buoyant plastic particles were prepared and used in this work.

The "lustre-cream" technique,

introduced by E. O. Macagno at the Iowa Institute of Hydraulic Research, was also used to visualize flow near transparent boundaries and at free surfaces. ALLEN, M. and YERMAN, A. J. (1960), "Neutral density beads for flow visualization," ASME Symposium on Flow Visualization, New York, November 30, 1960, p. 4-1 to 4-10. "A truly three dimensional flow visualization tech- nique applicable to flow systems where compressibility effects are small or negligible would have considerable utility.

NEUTRAL DENSITY BEADS FOR FLOW VISUALIZATION

is such a technique." ...chopping the light beam at a controlled frequency so that particle paths would be recorded as broken lines in which the length of each segment would give an indication of the local velocity vector at that point." See also Instruments

and

Control Systems, March 1966.

ANNOTATED REFERENCES

ALLEN, J. R. L. (1966), "Flow visualization using plaster of Paris," J.

of

Sedimentary Petrology, for September

1966, p. 806-811. Scours and furrows left in a coating of plaster of Paris by different flows.

Suggests use in already turbulent

boundary layers.

The roughness of the wall increases

BAKER, J. D.

(1966),

"A technique for the precise

measurement of small fluid velocities," J. Fluid Mechanics, vol.

26,

pt.

3, p. 573-575.

Technique uses a pH indicator, is applicable in aqueous solutions, permits visualization and measurement of three-dimensional fields.

Two electrode configurations,

in which networks of fine platinum wires are used. Range

0-5

cm/sec.

Flows with velocities higher than

5

cm/sec sweep the dye from the wires faster than it can be produced in visible amounts. BINNIE, A. M.

(1945),

"A double-refraction method-of

detecting turbulence in liquids," Proc. Phys. Society,

vol. 67, p. 390-402.

Used SBR to study transition from laminar to turbulent flow.

BEAMS, J. W.

(1954),

"Shadow and Schlieren methods,"

Physical Measurements in Gas Dynamics and Combustion, High Speed Aerodynamics and Jet Propulsion, vol. IX,

p. 26-47,

Princeton University Press.

Introduction.

Schlieren Systems.

Light Sources, Optical Parts, and Photography. Com- parison of Schlieren and Shadow Methods, Cited References. BIRKHOFF, G. and CAGWOOD, N.

(1949),

bubbles," J. Applied Physics, vol. Air bubbles were used as tracers to visualize un- steady flow.

Ref.:

E. Balint (Aircraft Engineering,

June

BLAND, R. E. and PELICK, T. J. (1962), "The schlieren method applied to flow visualization in water tunnel," J. Basic Engineering, vol. 84, p. 587-592. The schlieren method is based upon the variations in density across the medium; they affect the refraction index, and can be optically detected.

The system used

at the Garfield Thomas Water Tunnel is described. "Schlieren" were obtained at first by the effect due to differences in temperature between water and tunnel walls, but as they were reduced after a few hours of con- tinuous flow, three resistance wires were embedded in the models, and a controlled situation was created. Authors are somewhat skeptical about detection of pres- sure field in the flow by schlieren techniques. BUGLIARELLO, G. and HAYDEN, J. W. (1962), "High-speed microcinematographic studies of blood flow in vitro," Science, Nov. 30, 1962, vol. 138, no. 5344, p. 981-983. Used phase-contrast microscope with oil-immersion objective, focused on diametral plane of tubes.

Tubes

were capillaries 35 to 84 microns in diameter.

Micro-scope was connected to a Beckman-Whitley Magnifax camera (up to 3000 frames/sec.).

Magnification 970.

Pre-cautions taken to avoid heating due to carbon arc used for illumination are mentioned. BOOT, J. M., BRUN, R., and MORILLON, B. (1960), tion-d'un champ electrostatique uniforme sur l'orien- tation de lamelles d'aluminium en suspension dans un gaz," C. R. Acad. Sci. Paris vol. 250, no. 12, p. 2118-2120. BOUROT, J. M., COUTANCEAU, M., and MOREAU, J. J., "Sur

theorique et experimentale des phenomenes

d'orientation presentee par une suspension lamellaire dans un 6coulement de Stokes," C. R. Acad. Sci. Paris, vol. 255, no. 25, p. 3357-3359. Electrostatic field used to obtain desired orientation of alluminum flakes during flow visualization. what the authors say, it is not clear how the technique could be used. CAMICHEL, C. (1925), Applications des lois de similitude

a

l'etude des phdnomgnes qui se produisent

a

l'aval

d'un corps immergg dans un fluids visqueux en mouvement, Editions G. Roche d'Estrez, Paris. Description of chronophotographic apparatus.

Fine

metal-lic particles with small air bubbles attached to them were used as tracers.

They were illuminated by a

periodi-cally interrupted light.

Two-dimensional, axisymmetric,

CLAYTON, B. R. and MASSEY, B. S. (1967), "Flow visualization in water:

a review of techniques,"

J. Scient. Instrum.,vol. 44, p. 2-11. Techniques used in flow visualization are reviewed. DANCKWERTS, P. V. and WILSON, R. A. M. (1963), "Flow- visualization by means of time-reaction:' J. Fluid

Mechanics, vol. 16,

pt. 3, p. 412-416.

"A continuous-flow system is fed with a liquid which turns blue a specified time

0

after entering.

A

more or less stationary pattern is thus set up, those parts of the liquid which have spent times longer than

0

in the system being blue while the rest is

colorless.

The value of

6

can be changed at will,

enabling details of the flow-pattern to be deduced. The interpretation of the finer points of the color- pattern is made difficult by the effects of molecular interdiffusion of different parts of the liquid.

1

CLUTTER, D. W., SMITH, A. M. O., and BRAZIER, J. G. (1959), "Techniques of flow visualization using water as the working medium," Douglas Aircraft Division, Long Beach, California, Report No. ES 29075. Techniques used in the water channel built at Douglas El Segundo in 1953 are described, including photography and lighting.

Large number of illustrations given.

DA VINCI, LEONARDO (c. 1500), Del moto e misura deli' acqua, Raccolta di autori che trattano del moth delle acque, vol. X, Bologna, 1826. This book and another with the same title published in Bologna by N. Zanichelli in 1923 contains many drawings of flow visualizations, but they are not due to the hand of da Vinci.

Copies of manuscripts by da Vinci must be

sought to see the original forms of the sketches of flow- ing water.

See, e.g. flows in expansions in

Ravaison-Mollien, Paris, 1889, vol. 4, Folio 91 recto and verso. The account of da Vinci's glass flume is:

"Sia fatto

DULLER, C. E.

(1963), An investigation of flow

visuali-zation techniques in helium at Mach numbers of 15 and 20," NASA TN D-1769, 18 p. "Three techniques are discussed:

(1) the

fluorescent-oil film technique for making surface streamlines visible and for locating flow separation on a test body, (2) the white-lead technique for locating the stagnation point, and streamlines radiating from the stagnation point on a test body face at various angles _{of attack, and (3) the ionization technique for making visible the regions of flow separation and attachment on afterbodies.}

Results indicate that surface

stream-lines, stagnation points, and separated and attached flow, over an afterbody may be made visible on a variety of test body configurations in hypervelocity helium flow." EDEN, C. G. (1910), "Apparatus for the visual and photographic study of the distribution of the flow round plates and models in a current of water," R. a. M. 48, 1910/11. Used coating of condensed milk to visualize flow. See also R. a. M. 95, 1911/12, and R. a. M. 97, 1911/12.

,

DUPIN, P. (1930), "Etude exp6rimentale our les

tourbil-1

ions a1tern6s de B4nard," Thses prasentdes des Sciences de Paris, No, 2133,

Serie

A No. 1264,

Gauthier-Villars, Paris. Stroboscopic observation of aluminum flakes suspended in the fluid.

Also used a fine thread attached to the

model, and observed its motion.

Near wake was observed

FAGE, A. and PRESTON, J. H. (1941), "Description of a water tunnel and apparatus for the investigation of flow problems," J. Royal Aeron. Soc., A, vol. 178 Successfully detected transition in boundary layer flow by means of colored ink injected at the nose of the model. GELLER, E. W. (1954), "An electrochemical method of visualizing the boundary layer," M.S. Thesis, Dept. Aeronaut. Engin. Mississippi State College, Aug. 1954. First work on H-bubble technique.

Dr. August Raspet

of Mississippi State College first suggested the method.

See also J. Aeronat. Sci., 1955, vol. 22,

p. 866-870.

GOLDSTEIN, S. (19)43), "Water flow, the ultramicroscope. Ultramicroscope photography," Modern Developments

in

Fluid Driamics, vol. I, p. 294-296, OXfOrd University Press.

HAMA, F. R. (1960), "The injection of dye for flow visualization," ASME Symposium

on

Flow Visualization,

New York, November 30. Use of three dyes is briefly discussed.

Brief account of results reported in several papers by Fage, and Fage and TOwnend.

See Proc. Roy. Soc.,

A, vol. 135 (1932), p. 656-677; vol. 144 (193)4), P. 381-386.

Also Phil. Mag., (6), vol. 46 (1923),

p. 754-768, and paper by Fage in 50 Jahre Grenzschicht-

forschung,

F. Viewig and Sohn, Braunschweig, 1955,

p. 132-142. HAMA, F. R. (1962), "Streaklines in a Perturbed Shear Flow," The Physics

of Fluids, vol. 5,

no. 6, p. 6)414-650. . . .

practically no truth can be obtained from

streakline or pathline observations as to the nature of time-dependent phenomena.

.

.

images, which one

might receive from such observations,can be entirely misleading." HANSEN, O. (1968), "Investigation bubble visualization technique in dimensional flow," Naval Ship R7D 59 P.

of the hydrogen- high-speed two- Center, Report 2626,

"Experimental limitations of the hydrogen-bubble flow- visualization technique have been investigated at the Naval Ship Research and Development Center in the. 12-inch variable-pressure water tunnel using a two- dimensional closed-jet test section.

The

visualiza-tion technique was used in studying the flow around a two-dimensional hydrofoil

It was found that the

HELE-SHAW

(1897),

"Experiments on the nature of the

surface resistance in pipes and on ships," Trans.

Inst.

Naval Architects, vol.

39, p. 145-156.

Hele-Shaw's viscous-flow analogy of irrotational flow, still in use and development, is based on flow visuali- zation of a thin fluid layer between two glass plates. HIDE, R., IBBETSON, A., and LIGHTHILL, M. J.

(1968),

"On slow transverse flow past obstacles in a rapidly rotating fluid," J. Fluid Mechanics, vol,

32, pt, 2,

p. 251-272.

Fluid motion made visible by releasing dye electroly- tically from

0.36

mm wires.

The solution can be

used indefinitely; no replenishment is needed.

A

good number of photographs is given; they show the flow visualization.

Dye was released periodically.

HIDE, R.

(1968),

"On source-sink flows in.!: rotating

fluid," J. Fluid Mechanics, vol.

32,

pt. h

Used aye streaks produced by the iodine-starch tech- nique (with

0.004

inch copper wire), and other dying

techniques, including direct use of crystals, and the phenolphthalein indicator technique.

Seven plates

with photographs of the visualized flows are included in this paper. HINDERKS, A.

(1927),

"Nebenstrdmungen in gekrUmmten Kanglen," Z. V. vol.

71,

no,

51, p. 1779-1783.

Coated boundaries with paint to visualize flow.

See

also Prandtl, L., "Essential's

of

fluid dynamics," p.

1

HINWOOD, J. B. (1966), "The stability of a stratified flow in the region of flow establishment," Ph.D. Dis- sertation, University of Iowa, Feb. 1966. Use of lustre-cream is described on pages 44-48. KALINSKE, A. A. (1946), "Conversion of kinetic to poten- tial energy in flow expansions," Trans. ASCE, vol. III, Paper No. 2273. "The velocity and turbulence measurements were made by photographing on motion-picture film the flow in transparent conduits.

The water herein had suspended

in it small, immiscible droplets which formed streaks in the pictures, from which the direction and mag- nitude of the velocity at any instant in two dimen- sions could be obtained." Size of particles considered suitable:

one to two

millimeters. Data reduction is described with some detail.

HUMPHREY, R. H. (1923), "Demonstration of the double refraction of the vanadium pentoxide sol, and some applications," PPOC. Phys. Soc., London-, vol. 35, p. 217-218. KLINE,

S. J. (1963), Flow visualization, Sound Film,

KLINE, S. J. and RUNSTADLER, P. W,

(1958),

"Some

preliminary results of visual studies of the flow model of the wall layers of the turbulent boundary layer,"

Report MD-3,

Dept. Mech. Eng., Stanford

University, AD

152 187.

Dye used to visualize flow regimes and.three-dimen- sional phenomena in boundary layers. LOVING, D. L. and KATZOFF, S.

(1959),

"The

fluorescent-oil film method and other techniques for boundary-layer flow visualization,"

NASA, Memo. 3-17-59L.

This technique was applied by C. E. Duller in

1963,

in helium, at Mach numbers of

15

and 20.

LINDGREN, E. R.

(1959),

"Liquid flow in tubes, I & II,"

Arkiv fUr Fysik,vol. 15, p. 97-119,

and

503-519.

also vol.

16, p. 101-112.

MACAGNO, E. O.

(1953),

"Andlisis cualitativo del

movimiento de los Ifquidos,"

ACta Otayana de Ingenierta,

vol. I, no. 4, p.

1-36.

Flow visualizations in water using dyes and floating particles.

Zones of separation were detected by

1---MACAGNO,

E. O. and HINWOOD, J. B. (1964), "Instabilite

dans la zone d'etablissement d'un courant avec strati- fication de densite," Huitames Journges de L'Hydrau- lique, Question I, Rapport 10, Lille, 8-10 June 1964. Flow of two layers of different density.

Flow

con-ditions in stratified flow are visualized at the inter- face and within the two layers.

(Translation of this

paper into English available at Iowa Institute of Hy- draulic Research.)

MACAGNO,

E. O. (1964), Film on accelerated and

pul-sating

flow

in a conduit expansion, Iowa Institute

of Hydraulic Research. Aluminum particles suspended in Eureka oil.

Expan-sion 2:1 in circular conduit.

Unreleased film.

MACAGNO, E. 0. (1968), Confined

Kaman

flow

in-homo-geneous and in stratified fluid's.

Color Film, Iowa

Institute of Hydraulic Research. Unreleased film of flow visualizations using dye and lustre-cream techniques,

(It will be available On loan.)

MACAGNO,

E. O. and HUNG, T. K. (1967), "Computational

and experimental study of a captive annular eddy," J. Fluid Mechanics, vol. 28, pt. 1, P. 43-64. Flow visualized with aluminum particles, suspended in "Eureka" oil.

Injection of dye through orifices

in wall served to determine reattachment poikt in conduit flow expansion.

Comparison of calculated and