Investigation of turbulence stimulation of the boundary layer of ship model tested in towing tanks

J.LP1U3CHEZUHIN A..Poo3IXfl1rrY

INYL$TIGÀION O1

URBUL]UJ

_fl

THE

BCU1fl)#Y LATh'R OP 3H12 MODEL$ TE3TET) IN 2OW11G 1NI(3

LN TR() DU

T I C) N

'During the leìt thirty years various methods of artifi-alci tu.rbuience atinulation have been u3ed at the towing tanks.

However, because of the absence

of auitcble mean3 to detemine

the efficiny of the3e

methods, their choice has

been nade

emiriuiiy, and they did not

always ensure the required

tìti-mulatlon effect. 3oientific

approach to studying stimulation

problem under

tank conditions became

possible only due to

the application of phical methods of investigation which are wi..

aely

used in aera nainl's practice. This work

carried out at

the towing tanks of the Kryloff Institute was intended for jtu-. dying conditions ceusing natura].

transition

in the bou.ndary layer of

ship modl

du.ring resistance experiments

in a towing.

tank,

investigation of efficiency of various types of

turbu-lence stinulat,ors uc

r

towir.

tanks; determination of

op-tirnum sizes of the most

effective type of stimuletors

and

their looation on. model surface.

The investigation of

stimu-lator efficiency has been

carried out

mainly by mezi$, of

expe-rimental methods

besad on the determination of

boundary layer

flow chcr8cteristics of models.

Oving to

these nethods it is

possible to determine

the edges of laminer and transition re glans in the boundary layer of

a model measure mean velocity

profiles, estimate the intensity of fluctuations at different points of the boundary

layer, and measure local

friction toroe acting upon a smell element of moddi surface.

-3

I. LxerImentel Methods for Investiatin

Boundary

Layer øf Models In e

Towing Tank

or inve igations carried out et the towing tanks of

tue Institute thc following experimental methods end

appare-tus were purposely developed end used: hot-wire anemometer

technique for determinIng velocity fluctuations in the

bound-ery layer of models, method of Indicating chemical filins to

determine the

extent of laminar

area in

the boundary layer of models, method of measuring

meen velocity orofiles in

the

boundary layer of models using total head tube end special

smell inertia iiiuromanometers,

direct

method for measuring

tangential forces on a model

surface with the use of smell

-sized high-sensitive dynamometers of electrical

type, direct

method for measuring

stimulator own resistance by means of e

special electroinductive type

dynamometer,

method of

estimat-ing smell values

of the resistance of

large ship models.

Hot-wire measuring technique et the towing tanks of the

Institute was used to detetn1ne the nature of velociy

fuotu-ations and degree of turbulence in the boundary layer of models

tested.

A thii platinum wire was selected for

a transducer,

the proper diameter and length of which were determined by

ex-perimen-t provided that they ensured high sensitivity end

reh-ability du'ing the me ureine:its. Platinum wire was mounted

on

a special removable sutport which makes It possible to fix it

In a required position with

regards to streamlines, et a given

-4-distance from the iodel surface. The support was set at dif-ferent points of the model surface on the foundations primarily mounted

flush with

model surface. after installation the

support by

means of a switch

arranged on the towing carriage was connected to e measuring bridge which in. turn through the

amplifier

was connected eIther to a magnetic oscillograph or to a cathode-ray oscilloscope. 1or recording the magnitude of

the effective voltage during

the exooriment In parallel to a cathode-ray oscilloscope, a valve voltmeter was connected.

The relationship between the

degree of stream turbulence end the magnitude of the effective voltage et the output of the

amplifier was estebleshed by oelibmtion.

3ince

the character-.

istics of oaì!bretion curve of transducer

= f (Uy) was

li-near, it was sufficient to know

the magnitude of

the effective

h7oltae Uy fo

stIrnation of the turbulence degree in

the boun-dary leyer of modele i?ig.I shows

a sample of

fluctuation

re-cords in laminar area (cur're I), In transition region (curves

11,111) and In fully turbulent region (curve IY) respectively

for a model tested In the towing tank.

The

most suitable method which would afford the

determina-tion of laminar area In the boundary layer of ship models test-ed in e towing tank to be ¡nade is that of an indicating chemie.. al 'films. As an Indicator materiel

at the towing tanks of the

Institute acetone aolution of hydroquinone diecetyl /010H1004/

Is applied which Is sufficient to check laminar flow In the boundary layer of a

model, Is harinless for the staff and can

be easily menufectured from cheap meter1al. aomperion of

the

reult

obtained when carrying cut thi3 work u3ing differeit

methode fo &nvetigation of the boundary layer on a model,

LIOW that the chemical

method whioh

doe3 not require a oomp

heated aparau end too much labour ha

proved to be a good

one.

Previously, meaurement of mean velocity in the

boundary

layer of mode]. wcre carried out with the ue of total head

tubes rid water menometer, and thi3 naturally retrioted the application of thi3

method. The

ue in thi3 work of purpo3ely

develoed smell inertia electric micronienometer3 and a

coordi-meting device for total heed tube3 we conditioned by the ne-m

ceaiity of

perforniing

meaureinentì in the laminar boundary

layer a.t-the bow

ef-e model where ihickne33 of-layer 13 3mall

enough

end preure renge

lie within LO

5.0 mn of water.

.L're3ure ojok-up of

niloromenometer which i

made in the fO

of a pletic cylinder

1 SI mm diameter and 72 mm long. In-.

stalled inside of this cylinder are a diaphragm, to be an

ela-tic measuring element, and en electroinductance tran3ducer

r't1ch enab1e the deflection of the

diaphragm

during

the tests

to be meajtirrd. linoe the

deformation of the diaphragm we$

3rna1l, it we po3ible to avoid a large amount of water to

be

3hifted end to ensure

inell inertia of ceratu in the ooure

o Jnea3u.re1rtent. when te3ting, the pre.iure pick.u.p wa placed

inboard of the model, cic3e to the coordinating device of the total head tube, and by means of

rubber pipes wa

connected to

e _* ¿ ê

t b 4b I

e

4/)

i

h%9

Vf 't: ;

?igIb

_{eof velocity}

_r1ttustion

_{in the bounry}

1yer of moe1b

T

1niinr region;

2 tø

₅

_{trnidtion region;}

4

- turbu1ent regione.

¿E ¿0

Jo Io

III Il

!,:

_Iuili

giiggggip

Ï

Ìí1_Ill.I

lit

_i

o

4Z 43 S ¿?6 ? ¿'S

-ó ,i-ie ,nz4eva aOsec

-' jime mtezvaé' 8n,i1

-0--

iirie ,,nLç,Wt 3, llirnn

-- j ne

,»ezJ(4

-

¿Ç ''/c

?ig.2. Varitjon

in

_{er&e of turbu1en,e ¿'-}

_{Uy in the}

boundary 1yer of

rnoe1

_{epenrUrig on time}

it a well a to the pipe connection of atatiei orifiGe o1 the model hull. The total bead tube through the coordinating device being operated from

the towing carriage was

projected outside the model, at a given distance normal to its surface. Its traverse waS found by means of e special counter within

an accuracy of 0.05 mm. The output voltage of the transducer was varied and recorded on a 250 mm wide øaper tebe of en

electronic

automatic potentiometer. In order to increase the

accurec' of measurements, pressure range which lles between

C and 200 inn of water was divided into several subranges, on

of which permitted measurements to be made within O - IO mm of

water. he accuracy of pressure measurements in the upper ii

mit of each subrartg was + 24.

The determination of tangentisi stresses

during model

tesc-ing in a towtesc-ing tank can be performed either by direct meesu.re

ment of local rictlon Zurces acting upon a smsll

element of

model surface, or by measuring hydrodynamio queiìtitie3 direot

ly associated with skin friction. 1lreot

measurement of

fric-tin forces in. the towing tanks hes been

rarely carried out0

This is due to difficulties arising

from the development of

experimental equipment

designed for carrying out auoh ezperi

xnents. In most cases friction forces ere

determined by indirect

ways, the application of which is based on assumptions not al-ways proved end verified. This letter circumstance was the

wea decided to detlp a

ll-ize

high-

aitive eleotric

dynemometer which could be applied for dIrect measurement

of

tangential stresea acting upon a very aell element of the

ur.fece of a model ttted in e towing teak. It cQn3isted of

a plaatiu cyliidrioal

a3e 45

mm

diaxuter and 30 mm long, in

side of which movable pert

end elastic olòmenta of the

dyne-mometer were placed as weil as en 1ectroinductance

trams-ducer. The dynemometer was placed inboard of a model In

such a way that one of ita bottoms seed as If it were a

pert of the model surface. The bottom had a rectangular out

in its middle, inside of which flush with model surface a

working element - ¡obiit quadrate pie tfor having sides

20 mm x 2° mm ori the elastic elements was mounted. ¶ravu1a

of the platform 3roportional to the forces acting upon lt

were measured by an electric transducer. The gaps between

edges of the platform end the out on its three sides were

a-sumed to be 0.1 mm; the gap between the trailing edge end

the out wa

assumed to be 03 mm.

or recordng electrical

quantities into which the travels of the platform ere

trans-formed, ue was me'e of the electronic automatic potentiometer

with a paper tepe 2i

nr

wide. This tape width Was adequate

to record the forces from each of the four subieages Into

which, as has already been mentIoned, the whole range from O

to 300 mg was divided.

The lower subrange varied

U

to

u

treìe were not covered

by the obtained ranges, a

second

dy-nanometer was manufactured,

which was similar in construction

to the previous one,

bu.t had a much more

rigiI elastic system

enabling me

urexnents to be made in.

the range between 0 end

2 gr. On the basis of numerous

calibrations made for both

in-struments, lt was possible

to deteiiine their error

which in

relation to the upoer limit

of each subrange covered was

found

to be

Ualibration o

the dynenioxneter for tangential

stresses

was made before caun

test and no less then once for a seven

hour test by using a special

device, the dyneinometer

being

immersed in water.

fter calibration, the dynemometer

was

mounted on e model and it was

subjected to testi, in.

the cou.rse

of which measurement and recording

of friction forces were

taken. The megnitudes of the

tangential stresses obtained

from direct measurements at two

points on the surfece of

itodel

o. !O tested

the

owing tank of the Institute are

giien

in Zig. 1.

l'ith e view to deteining the own

resistance of a wire

stimulator at the Towing Tank a

special electroinductence

dy-nanometer hes been developed.

he principal circuit and

the

electric transducer of this instrument are similar to those of

the dynannometer for measuring

tangential stresses. The

sizes

and configuration of the

dynannometer enabled it to

be installed

at the

00W

of a rtodel in such a way

that e piece of 50 mm long

Io

-p1atforn with 10 mm x ni dimenion. Thiring the rejijtance

tet

the 2orces acting u.pon the platform and e part of the trio wire fixed on lt were nieaìured and recorded on the paper

tape of the electronic potentiometer.

The application of modem methothì for investigating the

boundary layer of niodel by no mean3 excluded the nece33ity

for measuring their

rei3tance3 in carrying out

comparative

resistance tests. In these tests the range of low towing soeeds 0.2 1.0 rn/sec was of particular interest when total resistance everiode1s '3 ut 7 ni long did not exceéd 6

-7 kg. Yith size increase and displacement of models there

was a con:3idereble

Increase

of

fluctu.ations In the

resistance

comparable with the mean value of towing résistance

et low

speeds of run. or resistance ineasurentents with large models,

at low speeds of run, test equipment and apparatus have been

developed

which ensured

effective damping of

the

resistance

fluctuations and

nell errors involved.

2. Initial (J,ndidons for Tet in a t2cwin

Tank

Turbulence stimu..Lab.on of the boundary layer

of models

and it experimental Investigation depend to a considerable

extent on the

initiRl

conditions in a tank under which model tests are conducted. These are as

follows: degree of initial

turbulence In tank water, flow

velocities

after

previous run,

model acceleration at the beginning of run, draught of model,

Nuiiierou. d te miìable show that th atent of th

1ew.-uar boundary layer end the critical aize of the Reynolds num ber are fected by the changes in the degree of initiai

tur-bulence. t the same time, there is no information available

at present concevdng

the amount nd the rate of changes in

the degree of initiai turbulence in towing

tank$ When testing

in towing tanks initial turbulence is

produced by disturbances

ceused by e moin, model.

e1coity fluctuations in the

vici-nity of the turbulence trail extending behind a

model can re

sein for some time after the run is över. The degree of

ini-tial turbulence in this case would depend on. the

intensity of

conducting the tests, ehen increasing the

frequency of runs,

the degree of initial turbulence should rise.

This fact has

already been noted, end at several towing tanks attemts have been

made to increase the degree of. initiai turbulence

artifi-cially, by reducing time Intervals between successive runs

with a view to obtaining more consistent results.

¿s the cegree of turbulence in a tank is relatively

low,

direct measurement of its amount and the rate of changes

de-pending on test oonitions present greet difficulties..

s a

resul o speclail:' conducted

experiments the order of initial

turbuleace i. the twng tanks of the Ïnstitute was

estimated

to be about

CO,GI4.

The investigation of the effect of changes

in the degree of initial turbulence on transition was

made in-.

directly, i.e. by measuring the degree

of turbulence in the

12

-beteen runs.

wir

riemoxneter was mounted on

model

long without stimulator, in the fixed

position along the model

length. Ls seen freni the diagram Uv

= f(v) given in

fig. 2,

with reduction of time interval between runs,

i.e. with

in-creasing the degree of initial tubulexie

in e tank

wai;er,tran-ition occurs at lower values of the

1eynoidariuxnber. However,

the influence of the degree of initial turbulenQe

in a tank

wa-ter on naturel

turbulence of the boundary layer for models 6 m

long is smell, which is also oonfined

by the results of tests

conducted with the same aim in view u.sing the

method of

chemic-al films. furthermore, this influence is quite evident mainly

at very low towing speeds.

1rom the experience gained in towing tank

lt is known.

that the flow remaining behind a towed model,

since the model

returns

o its initiai. position,

remains for

long time after

the run is over and can

affect tue magnitude of the model

re-sistance In subsequent runs et

low speeds. 3ince many tests

in this work have been carried out at low speeds

of run and

analysis of the results was often nade by comparison of the

measured resistance coefficients, it was necessary

to estimate

the magnitude of the residuary flow velocity in

the tank end

its dependence oi the thne interval between

successive runs

taking into account sizes of model and speeds

of return run.

special accurate measurements of the resi8uar

flow velolty

13

-intervals between

runs

carried out in. the towing tank of the

Institute

have &town that

taie

velocity of the residuary flow may attain 3 4 orn/seo ivd varies depending on time interval between

runs end speed of model

on

its return. Therefore,

lest

the results of resistance tests be effected by the

residuary

flow et the toving speeds Yo=(.,3-0.0 rn/icc, it was necessary

that the interval between runs should not be less than 6 minu-tes, with

speed of

model return equal tcI.0 rn/sec and that

in the range of towing

speeds Vo=0.2O.4 rn/sec there

houlc3

b en additional reduction in speed of return to 0.5

rn/sec.

The influence of model acceleration at the beginning of

run on the boundary layer stizaulation hes not

been

investigat-ed

specially,

however,

all the model testa in the tank were

oar-ned out at given velues of acceleration equal to 0.03 - 0.05

i 2

m,sec

e result of the experimental investigation dealing

with the effect of model draught on stimulation o! the boundary

layer (see fig. 4), lt found thct with decrease of draught some itimuiat&on

effect beenie evident. This la chiefly due

to the lnfluew,c o2 ve-ne1ciixg on transition, and it occurs

at relatively high values of

roide number when

eveloped

weveincking occurs.

The roughness cf the surface of tested models

manufactur-ed of paraffin-wax

in usual way was specially measured on a

XL L

43',

- ,;7kG

,rn'ezvae ¿. "n.

Nature cf i1ngs in. re$ithiary flow depending

on time

_{nterv1 between iucceive run}

Mßû?/ ,Vo

₄

-2---.

G---

_4J7Çg1

--

- "

ig.4 iffect cf vrition in c{ught

on the extent of

1&iinr hounry layers

f

awt

-15..

it wea fou.n

that tio aeeege degree

of surface roughness

of

the modela tested

amounted to 3.0

5.5 micron.

3uoh a

sur-face may be considered as

hydrodynamically smooth

in the

range of Reynolds

numbers

lle=O.5.106..1.5.I0'7.

3. Natural ¶1arbu.lence

of the Bond.ary Layer

on

}Qde1

Te8ted i

a Towlng

Tank

The questions as tO the need for application

of

stimulat-ing devices end estlmaion

of their efficiency

should be

decid-ed upon on the basis

of inveatigation.of natural turbulence in

the boundary layer of mudel3

testeti in e towing

tank.

The principal parameter

which determines

transition in

the boundary layer of a model la the local

Reynolds number tex.

ehen certain critical values

of the local 3eynolda

number are

reached Re= Re, laminar

boundary loyer becomes

unstable and

after some transition stage,

the flow in. the

boundary layer be.

comes turbulent. The value of Reynolds

number

which in

oondition

of natura. tur1ulence defines the edge of

laminar

aree, is not constant

and depends on the

nature of pressure

distribution along the model

surface

3

well as on the

initial

conditions of teats (see section 2). 3ince the pressure

dis-t-ributlon along the hullis

affected mainly by the

hepe

of

ship linea end the ratio

of its main. dimensions,

it is

consider-ed that the principal

geometrical parameters

of hull

efining

transition in the boundary

layer would be the

following:

16

-waterlixtø, !ozii of teii, 'shape of fore=body sections, apeot

ratio 1,/B and ratio

VB

As long

a each oleas of ahips has its more or less

de-finite ratio of geomtrica1 particulars, a mall nuinber of

shape lines was selected in. these investigiitions with

vari-ation only o! those hull

paranetera vhioh

most affect the flow oondition in the boundary layer o! models. ¿s objects for investigations the following models were seleoted two

se-ries of large models (6m long) of cargo. ships with blook

coef-ficient 8O.6 and

' O.8, differing in each series in forms

of stem and shapes of fore-body sections three small models (1.5 in long) geometrically similar to the large ones; one smell model with block coefficient

SO.7

and two models with

analytical lines. The main particulars and numbers of these

models are indicated in Table I.

The shape of stein r models with

SO.6

is indicated

in fig.5. lJodels with =O,8 have the shape of stem sirrtiler to that of uodel No.1. jxie shape of fore-body seotiona

U - shaped,

sheped

and with bulbous bow (b) is indicated in Table. Models with analytical lines have vertical atem,

rectangular sections and parabolic waterlines.

The teats were carried out under given and controlled initial oondit1on In the tank

(see. sectIon 2), the influ.-.

ence of whIch was allowed

for both in conducting experiments

and In th treatment of uieIr results.

mor?

-deis not all of the

experimental methods considered

in

sec-tion I

were used, and

only in the most

interesting oases

3e-yeral methods under similar conditions were aoplied.

As a rule,

during the teste the edge of the laminar area was determined first by using chemical indicator teohnique and the most typic-al streamline was defined with the use of paint6 Then the

deg-ree of turbulence

&..ong this streamline was measured using

hot-wire

nemometers with a view to

determining the extent

of

tran-sition region anl for checking the results obtained by the

che-mical method4

While testing, pressure

distribution along the

selected typical

streamline of many models was determined as

Wella

ig.5 how the results of tests with series of models

having block coefficient

)ti

On the section along the cen-tre line the edges of laminar boundary layer region are drawn for 3 to 6

speeds of run, and typIcal

streamlines ere indicated along which the measurement of pressure distribution waS made and boundary layer velocity fluctuations were determined. The

results of pressure measurements are given as diagrams = f(x).

The

results

obtained seem to Indicate the existence of the

developed laminar areas in the boundary layer of models un-der conditions of natural turbulence, even at Reynolds num-bers up to Re i.l.107. The form of edges of laminar areas is detertined to a ret extent by stimulation effect of free

stream surface8 epndence of the extent of laminar area on

-?riw1oei cU

'3-

--L; mo4eli

ml1 modelì

1odel

of ana1yt.1irìe

id

bo1iUni$i 3erT

cofficierit

Diaplcement

U'

Length

L

Breadth

B

Drught middle

Wetted

urface

re

Blook coeffi- cient

_{Ltidahip section}

coefficient

Priietic coeffi-

oient of fore-)

body

in prticu1ar3 of rnode1

I

Io

.

356j Q. 356f 0 35

. 75 6,68

I

098

I. 10

622

-0.5U20.582 (.).58

-jo.

73 o. 973 0. 97

LLodel No4

4

708]T,700

.20

62Q

.938 0.938

.375 O375

8.56

0.789

0. 992

-O. 627 o. 625 0. 63

ipeot retic

7.2

?,29

ng1eofent-.

0. 907

6,61

5540

Table I

b

0.O172 o;c27o 00267

1,55

L55

I.55

0.214 10.234 10,234

0089 0094 0.094

0,550

0.560

:0,769

0,769

0. 992

0. 992

j

0,90?

0,90?

6,61

6.61

4,0

55.0

--0.029C

1,695

236 04108

0.576

0.687

0. 988

0.662

7 17

T ( A. -.

-4-0.42

500

o. 5o

0.24

0.82

5.00 1.00

0.24

.985 5.3?

0.70

IOO 1.00

o,70 Q,7Q

_10.0

5.00

8,5

14.0

Denoe

of

water-deg..

l.ine

hap e &

f fo re

re& 4.0 IO.Q

4.0

:42.0

bo4y etìonì

U V

b

U ci

22 6.22

.854 o.854

Ii In

8.58

_O.78i

_{¶o. 992}

L

9071

0.428

0.582

0.973

0.634

7,29

4,0

19

clearly illutrated, for exemple, by model to. 3.

The results of the above tests arid similar experiments

with the other models Indicated in. Table I

are plotted

in

fig. 6 as the ratio between the greatest extent of laminar

boundary layer and the length of corresponding model on

the

base of Reynolds nuriber. It is evident from the above date

that the curtes

f(e) change to e regular way

reflect-Ing the features of the mein geometrical parameters of models

tested. 1ith large models having angle of entrance o

water.-Une o/2

40

_{to m° (models Nos. I,2,3,IC,II)}

_dependence

xl/L

on 9e

has the sanie character differing from that for

mo-dels with angle of entT,rnce of waterline o/2 =

400

_Row

ever, wit.

uell modeli the angle of entrance of waterline

does not itflune

ie

hspe of curves xl/L.

It is supposed

that the alteration In the shape of

ves xl/L and their

mutuel Intersection are due to wavemaking produced by models.

In the range of Reynolds number

e

(I.e-2. 5)

e IO

and

(3.5-7.e).16

for models with small raked stem and romd

Ing at a given

e

with increasing block coefficient the

ex-tent

f lamInar area increases.

Tet with model No.2

con-fi

considerable influenre of stem shape, Increase of stem

rake and radius of rounding Is accompanied by a considerable

extension of laminar erees, There is appreciable ínflu.errne of

shape of fore-body sections:

sheped sections favour

the

earlier boundary layer transition.

A bulbous bow (models Nos.

p

, Q,

/-i:./ZIA'.

/---"!!±c

I'i8m/,g'

/

4Fin/s

¡

/

/

/

-

20

-- Wo. sd,i Model .ìVo i 6 m'odee' ,Ve .3 :

F!!

Yig.50

Ee of 1aminr crea in the

bounthiry 1yer of

inode1.

No-

i,7

0,3

iii-fludel A41

2

I

0,3 0,1

L

-2I.

pect ratio of a model does iot influence markedly the

tren.-ition under condtren.-itionì of natural turbulence.

Table 2. oontain3 the critical vnlue3 cf local teynold3

numbers

_{calculated from the reu1t}

_{of above teìt3.}

Table 2

Values of the critical Reynoldì number e.I05 obtained

frog the test

ren1lt3 b:j chemical method

During the tet with model3 No.I,4 and 5

the extent of 1a

minai' area along

_{no 3elected ìtreaniline on a model hull}

_wai

detemilned not on1r by using the chemical method,

_{but aleo}

when uing not-wire te3hnique. The greexnent between reju.lt

obtained by two quite distinctive experimental methods,

_as

sen from fig, 7, mey be coisidered e

good.

By means of hot-wire technique the extent of transition

odel NO.

I

2 3 4

510

-II

Model

No.

Te

6 -7 8 Sm 9 e. - Sm

2.IQ6

--4,8

-

4.1 4,8

--

6.4

--7,7

-0.6.106

_3.0

_-

_2.6

3.106

_4.6

_-

_{4.2 7,Q 6.(7.I 7.8 Q.8.i06 2.1 2.8 30 3.4}

4.106

_{48 10,9 4.4 8.6 7.7.0 7.1 X.o.I& 1.8 2.3 3.3}

_3.3

5.IQ

4.5 11.4

4.4 9.4 9,..b.8

o.2

1.2.106

1.7 2.2 3,5

3.2

6.106

_{4.0 II.?}

_{4,3 9.1}

_{9.7.2 5.6}

_1.4.106

_{1.8 2.2 3.7}

_3.1

7.I&

-

11.8

3.8 7.6 9.'

-

_-

L.I06

_{"0 2.4 3.8}

-8. I0

-

11.7

3,4 4, 9 7,5 -

-

1.8, I& 2.1 2. 6 3. 9

-11.2

-

-

-

-

2.0.106

_{2,2 2,9 4.0}

-I. IO

Io. 4

-

-

-

2.2.106

_{2.4 3.2 4.1}

-region (see flg.?) on. the models In

qiesticn we

investigated.

The extent or tranuition region in per

cent to model length

when

eynolds number is varied

e(28),IO

anounted to 7

for model Io.i, 6 to 8

for model to.4 and to 5

to 7

for

model flo.5.

Thus, despite the difference in

geometrical

par-ticulera of models, the extent of transition region in

the

boundary layer changes but little and averages

to 48

of

model length.

The determination of the enges of laminar and transition.

regions in. the boundary layer of model Nc.IQ

having analytical

lines was made by all methods available

for boundary layer

in-vestigation.

These included the method of chemical

indicator

films, hotwire rethod, method of measuring mean

velocities

and direct method of riersuring friction

stresses. The results

of the ex'eriments as the relation Rexc

f(1e) are plotted in

fig.8, vtheo the regions

f the critical values of local

Rey-nolds numbers covered by all methods are IndIcated (shaded).

seme

3hown in the figure is a diagram dealing with the extent

of laminar and transition regions in the

boundary layer

of

model Ito. IO, along the waterline situated at 1/2 draught of

model, at the speed of run. LO n/sec.

¿s seen, better agree

ment in the results concerning the extent of

laminar

and

transition regions was obtained ehen mesuring tangential

stresses and fluctuations in the bounaary ieyr,

i.e., the

magnitu.des which to a great extent present physical processes

L

-

O--Model No.f

----flodel # "lode? fr'oj

O,

-frlOo' /10.5

l

-- ft'ode( /10. /0

-.

- .. /'rfj( iVo // oly

flodel

.6

f'lodel ,4'O- 7 friodel ,le-S

/lode N $

?ig.6. Extent of 1minr rea

in the boundrry 1yer of iuo1e1

L. ¶ ¿Zd 1.0 ¿o 2 6

.-Re /O

6

7 89

- Re

/O0

fo

/1

r

a28 aso a i i _/ I 3 4 s o P o g #Q

iig.70 Ectent of transition region. in.

_{the bourulary l9yer of}

model.

O O Q

_{edge of 1mincr region E000rding to chernic1 methotL}

edge of 1rninr region. according to hotWire iTlethaci.

edge of tru,iition region

ocording to hotwire

'i,

Rpyjî°

o 1,0 ¿0 40 4D 10 LO D 00 _/0,0

-

Re 1O

¿T o

4

frì inQa 7e.'n's r

stczjjej-JP.77 /77e $IUf '.'ts aJ ,Q7ea'7

Occoìding 'o

n,a' '4d

i r 5 _{19 15}

---

Mû. ,so 'i ,?ooW ,Vo. 5

PS

ReM'

ig.d. (riticcl vclue

of lecci

_{eyìioirL number nd extent of}

lcminar, tt'miition

_{turbu.ient bounry leyer region,}

from the

_{a3Ltlt3 of tet3 with model No.10}

_{in the t2nk.}

o

chêmicl metho

_{-.rneu.reraent of}

tcngen-j.

mneu.rement of

tiiL tree

meen veiooitie

_{-hot--wire rietho}

25

-reult$ of experiment oondu.cted usir..g the chemical method vith

the above reult houla alio be noted.

The invetigatons carried out in thi3 work have 3hown

that when testing under oondition3 of natural

turbulence the

extent3 of laminer a:rea

in the boundary layer of model3

amount to a corl3iderable magnitude (up to 5

of model length)

at Reynolds numbers to

e=(7-9),IO6, and in.

some cases to

'Re=(I2-I3),IC. In this connection there is evidence for ap-lication of the efficient turbulence - producing devices.

4. Iffeotiveness of Turbuience.-Produoin

iDevices used at Thwing Tanks

3tiiaulators which are applIed

in resistance tests at

towing tanks are to ensure that transition in the boundary layer occurs at lower velues of local

eynolds

number compared

with natural transition;

in this case

the edge of laminar

aree should be defined et a given oositiori along the model

length.

The main types of st1mu1etor used at the towing tanks

at present are the

oilowing:

trip wire, stud

and send

strips. These are placed at the bow of models and produce

disturbances iwaediately in the boundary layer. Up to

recent-ly, at a

number of towing tenk

stimuletors in the form of

bed-ly shaped bodies (rods, grids, rough profiles) placed in front

of a model were used intended

for increasing the degree of initial turbulence of tank water.

26

-Inve-tigation of the efficiency of the above stimalator3

in this work ha

been performed by mearil of the experimental

methods con3idered in section I when testing with the

models

e

thoie used for invetigetion cf natu.ral boundary

layer

tui'-bulence, the main partieuler3 of which are given

in Table I.

Trip wires woro I.0 iin, 15 mm and 2.0 mm diameter

res-peotively. The studs uied were o! two types

conical studs

3.0 mm diameter, 2.5 mm projection, those of 1.0 mm diameter,

0.9mm ìrojeotion end studs with semicircular hea&ì 2.5

mm

die-meter, 2.0

mm

projection. 3and strips were IO

mm

wide and 25 mm

reìeotively with grain size 0.6 mm.

Trip wires end send strips were arranged on the models in

accordance with the practice adopted in inot towing

tenks,i.e.

et a distance equal to O.05 of model length from the

forward

perpendicular; the in'f1un'e of alteration in location of

stim-ulator

along the model was also estimated. When armnged

in

orte row studs were fitted at a

distance of 25 mm from the stem

spacing 25 min and 12

mm

respectively; when arranged in two

rows, the first row was fitted at the seine

distance as before,,

but the second row moved vertically at half the interval was

50 mm distant from the first, the spacing in this oase

being

25 mm.

The models with stimuletors of the above types and sizes

fitted in turn were run at several towing speeds using the

chemical method.

27

-During the interia1 betwenteata

meeaurenient of model

reaiatence by meana of purpoaely developed reaiatence dynamo-w meter (iee aection I) wea made. Sometimea teata were

re?eat-ed and uae waa made of

hotwire

enemometera which

were placed

along the

typical

streamlinea on the modeL hull. Inveatigatioi

of the

efficiency of wire

tiniulatora wea alaa

performed by

uaing the method of mean velocity

meaaurenent and

tangential

atreaea in

the boundary lar of models.

The limited acope of this report makea it poeaible to diva only a few of the moat typical reauita of the exper1

mental inveatigatíona made with regarda

to efficiency of ti-mulating devices.

Fig. 9 and IQ show the reaulta of inveatigating

the

efficiency of varioua stimulating devices when testing with

three

large

models (No.I,4 and Io) and with three amall mo deis (No.7,8 and 9) usl..ng tne chemical method. The diagrsm

show the experimental v±ues of the largest relative extent of laminar area in the boundary

layer of modela with

fitted stí

inulators auch eat trip wire, stude and pnd tripa, ana mo

deis without any

stimuiaiora.

ull linea correspond to

the

nature of variation in the

extent of laminar area

depending on Rèynold3 number under

coridition

of natural turbu.lenoe, for

e selected type of stiriiulator. "Jumping0 reduction of laminar

aree during transition, as well as the curves x1/L=f(1e),

when

the number of intenediate points

is not sufficient, are

56

_{Re fO}

co

ig.9. Tì3I11t3 of in.ve3tlgetion of 3timu1etor

efficiency obtine by chemieni

methoL

oòo

no turbulence device

- trip wire

of 2.0 mm

aie-me ter

trip

ie of 1.0 i

meter

çi Ø Ø

- one row

of 3tU3.

the ice of wire when

arranged at a di3tence

of 0.05 L from

the forward perpendicular

i

e10 defined by a

dotted line

drawn parallel to axis

of ab3i33ee.

It appears from the

result3 just dicuaed a

well 83 from

tho3e of 3imilar in1retigation3 with other models that the

na-ture of changes of curve

3if(Re)

for model vith fitted

ti-L

inuletor remains exactly the same

a

that for natural

turbulence4

Only in 3eparate cee

there 13 a sudden

reduction in the extent

of laminar area followed by the gradual change or

fixing of the

latter at the 3timuletor

it3elf.

When under oondition3

of naturel turbulence

there occur

large

nd stable la'ilncr aree3

in the boundary layer

cf certain

model3, laminar regirnd neintalfl.3 1t

tebility even if

3tifllU-lator3 are u3ed. Thu3, in. teiting model No.1 trip

wire of 1.0mm

diameter orove

to be effectIve at the

Reynolds number

Re3.7.IO6(rO.0), wheree3

tud

reduce the extent of

lami-nar region by 5O;

at the 3ame time, trip wire of the

3ame

diameter placed on model3 No3.4

and IO iteadily flxe3

the

edge of laminar region at the place of 3tirnulator

only at the

'eynol4

numbers

e=3. 4. IO(ir0. 13) and

Re=5. 3. IO°(1rO.

I?)

accordingly. 3tud3

(when. 3paced 25 mn and 12 mm

repect1vely)

prove to be quite

ineffective.

In te3t$ with 3rnEll

model3

1.0 mm trip wire epoear3 to

be an in3u.fficiently effective

3timulator over the 'hole range

of !enold

number3

Re

(0.5

1.5)

io6

(r=O.O8-Q.29) end one row of

3tUd3 ±3

not able to cause appreciable

3tlmuletlon effects Only

use

/

/

4.

s

Re /O

1,0

/5

Re 1iT6

Flg..I0.Re8u.1t3 of irivetigetion of

timi1etor'ì

methoL

O O O

- no

turbu.lence deviee

o

o

- trip wire

of 1.0 mm dímeter

- tria

wire of 2.0

hIm

&Liiieter

Hob'e ,$'o.ß

6òo-øçø

L

n.

.uu.

UIl"..

uiiiiII

Re ./Yô

effioiencyobtaine

by hemic1

one row of

tu

two rows of

ìtu3

3mfld

itrip

-31-of a 2.0 mm wire enables in this case to

stimulate

sufficient-ly the boundary layer at 'eynolds

numbers te =

(I.0.-I.2),I0°

By arranging the studi in two rows

their effectiveness is

markedly increased (see fig., model

No,?). 3tuds with semi-a

circular neads are more effective compared with those having

conical heads. Iioweie, in all

models tested trip wire proved

to be the most effective

t1mu1ator.

The investigation of

efficiency of sand strips 25 mm

wide and with grain size 0.6 mm that

has been carried ot on

several models (see, for exemple, model

No.9 in fig. 9) made

it possible to ascertain that this

type

of stimulator was le

efficient comoared with trip wire and studs.

It should be

noted, however, that the effectiveness

of sand strips can

change markedly depending on the size of

grains, vidth and

position of strips in relation to n

model hull.

The question

es to the most suitable location of send strips end the choice

of grain sizes was not

investigated in this work, since as

compared with other stimuintors

sand strios are more com',licat

ed for producing end installing on. a model, end

they do not

en-sure the

required

stimulation effect.

is hes been staed, effectiveness of stimulators was

in-vestige .ed also by ritasuring

the

resistance of

each

model

with

fitted various tiiauiators in siwoession.

s an

example, fig.II

gives the results of resistance measurement for model to.5

ob-tamed by means of a

purposely developed strain-gauge dynamo-meter. When testing,

the following atirnu.letors were placed on

the model in ucoeion

trip rire of 2.0 mm diameter and

1.0 min re3peotively with oonia1 heads, arranged in one row,

pecing 12 ram and

tud. 3tud

proved to be ineffective over the whole range o! ?roude number3 covered including service

p e ed 1.

In

te3tiflg

i3l No.10 when uing the

total head tube

and electrical ìneil inertia manometer (see eot1on I), meeurerient of mean velocity profiles we

aìe et

3ectiofl.

of boundary layer, at a ditence of 0.6 in from the ìtem

end at the depth of 0.12 n

from water jurface.

The reult

of meauremnentr e

curve --

f(Y,v) are given in fig.I2

U

Laminar velocity profile at

he 3ection under consideration

in

cond1tion

of natural turbulence perit up

to the 3peed

of run Vu.3 ni/sec.

When trip wire of 1.0 mm

diameter i

placed t station

I

0.25), at the

pee

of run V=0.4rn/ìeo

there i e slight change

in. velocity di3tribution;

however,

ju3t er

the

3peed increae3, already et

11=0.6 /ec, velocity

profile epproache to turbulent. Coaperiion of the

ecperimen-tel re3ult3 with

theoretical relations for the plate3 (see,

for exemple, the

curves 3howing

the calculated

boundary layer

thickne

in laminer and turbulent regime3

defined by dotted

lines, flg.12), a well a conìi3tenry in the reìult obtained in checking teìts made it

po33ible

to ascertain tht the

re-sult obtained were reliable.

mn.ve-tiget1cn of the wire efficiency wa

ìl3O

made in

tech-.2D ZU 405

33

-flaaL NÒ

Uhu

_au...

¿z,

.-iII

eiit& of QorprEtive reitance tet

of

a3e1.

000 no turbulence device

ÒÖÖ

2O miri trio Wire

il

R_UU*1U111&1 _._In.

II_11111

Ii__-'l'li

III i i_11111i

I!____

I

UUSL___UI1Muu....,g

ull1I_IIIiIIIII!4111F

_{huPA -1111111}

-

V1 _'A

lUI

_{UPI__}

_*W

_l4UIl

r _aaRva,i*.-

_{a._______}

UUEVM_______

uaaui____

0,g

05

f

_¿1,7 0,8 LO 1,i' 1,2 _{1,3 14' 15 Lç L?}

.__ 21._V,'7 #77/

/f

igI2 1ffect cf trip

_{wire on the cimne of}

_veloolty

profile in the bounry layer of moe1 o.I0,

G G G

1.0 mi

r1p wire

lu

l'_

ll

- I

iii

34

-nique. While testing with model No.10 under conditionì of naturel turbulence and with e 1.0 mm wire

fitted,

meeure-ment wa made of tangentiel 3tree on the model

urfece

(see 3ection 5 and fig.13).

3pecielly conducted experimentaffirmeci the validity of

the recoiimended by rlo3t towing tenk3 location of a wire on

modeli of l3rge ies, et a di3tence eque]. to 0.OSL from

the fo'ar1 erp(P-dic.Ller.

The main reason for the restricted

application of rodi,

gridi end rough profiles er'renge' in front of the towed model

ii a wake appearing behind a

tiniulator and reiulting in

de-crease of speed of water 3urrounding

the model.

»ue to

the

change in the wake inteniity with diitence away from the

3t1-muletor, it i

practically impo33ible to apply sufficiently

accurate oorrectionì Rilowing for

ritence

_{to be affected}

by wake. iowever, a

the date available are not adequate to

ae

the megn1tue of wake end effectivene

of

tu.rbuience-producing deviceì dealt

with, it wa

decided to inve3tigate

the

flow behind certain typei of these devicei.

rod of I0rnr

diameter, three roda of the e diameter 3peced 100 mm apart,

iix rods of 3 mm diameter, 3aced 50

mm, a grid with 20mrìx20mm

dimenion

and 1.0 mm diameter of wire, a rough profile were

3electe

for the

tejt'j.

i)uring the

s the magnitude of e wake behind the

ti-mulator we

meauied and

rough eitimetion of the turbulence degree in e wake wea made. Experiment3 have shown that the

-35-ciaíuitude of wake oenind the

_{imlatcr at a ditnce of I.m}

varies from ô.O

to 2

(depending on the configuration of

stimulator used) and decreases appreciably, down to 4.0

- I3

at a ditence equal to 4 in. The assessment of the degree of

initia]. strean turbulence during the experiments

was made

be-hind a rod stimulator from the resistance of sphere, the

dia-meter of rod being 10 mm.

_{The resistance of sphere in water}

was measured 'by a specially develoed

straingauge

dynamo-meter. While treating the results, correction was

_introduced

to allow for the influence

of wake. The

_{magnitudes of the}

deg-ree of initial turbulence are given in

able 3.

In salte of the possibility of

_{producing the nigh degree}

of initial tarbu.lenc, the stimulators _{just discussed when}

testing in a towing trtnk cannot be used, due to the existence

a wake varying in dircction regarding

the motion of

model

and having great magnitude.

table 3

Vrarieticn In dezree of

treem

turbulence behind a rod stimula tor

a result of numerous model tests carried out in the towing ¶ank with the

use of different end mutually

_checked

)istance from stimulator in

n

1.0

2.5

3.88

experimental methods, it waì futzrid that when reiìatanee et3

were carried out in

tank of irouMe type with inodel

5-6 in

long

hewing main e'ticular ìimilar to those indicated in

r2able I, the 'tosí effeutive

timuletor we

a 1.0 to 1.5 mm

dia--V

meter trip wire located at. 0.05L from the forward perpend1cu.ler

In th1 case, the edge of laminar area waì fixed at the place of

trig wire, at Reyno1d

nuxaber Re34.

10b In

teiting with

illo-deis 1.5 to 2.0 m long having similar

lines arid main.

particu-1ers as mentioned above, trip wire appeared to be also the most

effective stimulator, but with 2.0 mm wire.

Here the

lami-nar edge was estbiishd t the place of wire, at Tenolds

number3 eI.IO6.

5, Investigation of the Trie Vire 11esitance

Tiesistance of a stimulator placed on the surface

of

e. ricôel

tested, though not relatively greet, however introduces some

ele-ment of uncertainty in the results of rei,stance tests

with

large models, and when determining the resistance of small

mo-deis this can give

se to aprecieble errors.

However, it was

1mposs.ble to exi.uie this reiis'tence due

to the inaccurao of

the only prcica1 way for determining the resistance of model

with stinatlator and that without it, at the towing speeds, at

which there are no appreciable 1ininr area i in the boundary

layer of model.

11th

a view to obtaining the. more accurate data about

assessirient of the effect of variation in wire diameter on its

own resistance in carrying out this work,

special resistance

tests with models were run in the towing tank when using

the

electroinductive

nouier developed for this

urpose (

se

section I ). Thìring these tests resistance measurements were

¡nade on the portion of e wire 50 mm long out out

of the wire

stimulator, at the usual location, i.e. at a distance cf e.o5

from the forward

oerpendicular. iesitence of

the dynamometer

platform on which a cut part

of the wire under test was fixed,

was excluded from the results,

after particular

measurement of

this resistance was made, when the stiriu.letor was not connected

with the small platfr,rm

but was located at a distance of

0.05 - 0.10 miri from

t.

The results of measurements for

wires 1.0 mm, [.5 mm

and 2.0 mm

respectively are given in

fig. 14.

In the same figure the resistance of the platform is

also indicated.

s seen in the diagram, the character of

chan-ges in

resistance depending on the speed of run is essentially

the sanie for all

the three of

sizes and starting

from the soeed cf 1.2 rn/sec

it can be assumed to be

propo-tionel to the square of model speed.

?or the models tested in carrying out this work, the

eeL-oulation of wire's

resistance

allowance made in accordance with

the, test results showed that

at the

relatively high speeds of

runt this allowance is only a pert of the tota.l increase in re

siduery resistance coefficient of model when the stimulator is

38

-of model N.I0

tt

roade number r0.2 the allowance for

the reaitance of a

O mm wire i

equal to 4Ct

Io,

while th a1iotRnco fr the re$itance of -the saine wire which i

found to be the difference of reiitanea for the abo'ie

model

with fitted timulator and that without it 13 equal t

Ct

e.oe

The noted difíerenciea in the ai1owance

for

re-3itance of

t1miilator there were oberired in towing tank

end

foiierly in rough etirnetion of the wire re3i3tence.

The cited

data obtained by direct meeurement

of the reitance, combined

with the reìult

of

ounday layer inve'tigation, ìeemed to

iridimte the existence

of some unknown additional

reaon

oaui1ng the increase of the reitence of models when

t1rnuïe

tor3 are fitted.

a v1e

to invetigating 'the hydrodynmical apeot3

f the effect of wire 3timulator

tet3 with model

o.I0 hev

ing parabolic lines were carried

out, In carrying out

the9e

te3t3 tangential tree on the model 3urface were nieaiured

under cov'-.tion

of ntml turbulence end with a 1,0 mm wire

t1mulator fitted

diitanee f O.0L from the 3tem. Thile

tet1ng, the dynanionieter for taxgential

treea (see section

I) we

arranged on the waterline of motel, at, e distance

of

0.12 m from the

atr ur2ace 3pacìng

= o.3

ni

and

c = Qt3

ni

troni 'the item with no

timulator fitted and ipacing4x=O.35m;

x=O.IC m;hO.Q5 in

from the stimulator. ¿.

result

of

the eeriment períoed on the be.e of the measured tangen

-tial stre3es the relation ff(e)

shown in fig. 13 we

ob 39 ob

-taineL In the

ye figure mlue3 of k1n frictien coefficient

for the p1te in laminar end turbulent flows e3

ciculted

ac-cording to formu1ee

0.64

0.370

reìpectistely

plotte&

It i

evident fron the diagram (fig.13) when. testing

u.nder

uondition3 of natural turbulence the coefficient of

tangential

tree

at

ectiom3 x=0.3 and x=0.6 with increeirig the

Reynolds number in the renge cf e(I_) .

varies

equidi-tarrtly to laminar friction line of the

1ate exceeding

the

values of this curve by the

raoint equal te '

1.0 . I0.

ihen

a tiniuletor is fitted on a niodel et th section x0.6 ni,

i.e. at a distance of

x Q.3 ni from the stimulator, skin

friction coefficient varies equidistantly

exceeding the values

of this curve by a definite amount equal to ''I.3.I0.

The

estimation mae to

eterm1ne the local friction forces for

model No.10 when

ìing pressure distribution obtained from

the eperiment dIA not permit to explain the said

ystenietic

increee in

riction

oefficient compere

with that of the

lete due to the curvature influence.

The additional

resist-ance

of the

cthng

element of tne dmemometer due to

the

flow passing in the gas

between the smell piatforzn

and the model hull evidently accounts for this discreoency. The

mentio-ned resistance should vary in proportion to the square of

speed.

In the case under consideration this takes 2lece when.

the

ifference

n

he mee3ured locei. friction coefficient of

2 o

-- RefO

ig.I3.flepen.tnce of the coefficient of tagentia1 tree on Reyno11i number from

eurenent of 1oci friction fcrce

on the roe1

irfce

W,di tz,pw,re

QL CÌJL at ea'

b pa'te

Q---¿ bn-i

xa4m

zO,35'

tii1J'"'

¿ J-¿Z0,/ö'77

¿JXa/''

device X=1?3I"

--fis G

x a 6m

Jot

X«5m

/C8fltr'Ot/

Tiiii

d

"s..

11

q

IVI

01__________

-

--M

-I

3 4 6

7

Q /0 c5 IC3 s o

41

-only in the turbulent 'reime it I

slightly greater.

'Iariation in the rneaur d values cf skin friction

coef-ficient with and without 3tiu1ator that takes plaee at

the

1enolds numbers corre3ponding to Prounde numbers lr0.2-0.22

for moel No.I0

iì due to the change in water speed suzrouni3

Ing the hull at the piece of

iarnometer due to waveniaking,

t Reyriol

mrther

. XO, under conditions cf

natural iurbu1ene there I

a sudden increase in the measured

frictiö:i cieient orresïonding to the trenaition region

in the boundar

layer

f the model. friction tresse.3 In this

case somewhat exceed those for the turbulent region, at sec

tion Ax

O.5 w. With subsequent increase of

eynolds numbe,

friction stresses decrease again varying aroxImetely equi

distantly to turbulent friction line of plate.

The validity of the results obtained is confirmed b

number of data, The vuiu* of the critical.

eynolds number

Re

= 5.6

at which a change o! locel friction coeffi

oient typical for transition takes place, approaches values

of the critical

eynolds numbers obtained under conditIons

of natural turbulence in testing

model Tc.IO when using

the chemical method (ie= 5.e

ion)

and hotwire teohniqu

4.8

ie),

_{The values of skin friction coefficient}

for the model In question not fitted with stimulator which

were found by mee

cement at sections

x=0.3 and

_x=0.,

practically coinuid, which is to be execter3 for the model

42

-view to checkIng tLle resu.1ti in these tests showed that

this ooiricine Is pute setisfactory.

The results of me urements of tangential stresses made

on the surface of model No.10, at different dI3tpnces

from

the stimulator are given in the same figure. The rete

of

changes in skin friction coefficient then will be quite

dit-ferent from that at a great distance away from the stimuieto. 11th Teynelds number increasing tangentiel stresses on the model surface immeditely behind a stimulator show e sharp

increase attaining e maxiiriurri velue, which (

et 4x

SO mm)

is 5.5 times as large as compares to that

for laminer regIm.

and apiroximate1y twice for turbulent regime.

As

In-creases, tangential stresses

decrease to values, correapond

Ing to the measured stresses on the surface of model, et a

distance great

enough behind the stimulator.

Then in the

range of the stated 1?roude numbers the effect of free surface

is evident (iee curves

et 4xo.o5 m

end

x

0.10 n).

Then using the test

esiu1ts with model No.10 and extrapo1a

tion diagram for tangential stresses behind a stimulator,

along the waterline, was drawn and shown in f ig.15. The

re-gion of th3 incree.ìed tengexiial stresses behind the wire

stimulator, at the ileynolds nuriber 'e = (1.5 - 4,0) 10°

extends for the distance of

200

ISO rim

behind it.

'ith

Iteynolds number increasing this region is. reduced.

ourfold

increase of 'Re'

decreases the

extent of raised tangential stresses twofold.

¿o

,r. ,77/

t? /S'Ç

iig,T4

T1eu1t

_{f meurement of trip wire}

O O r

-.2.0

cUnnieter wire

I.5 mi

Thameter wire

çç çØ -I.O ini diameter wire

L 4C'/83

44

2 «5 2,5'

o''

3o

reitnce

reitE.rLce cf

tynernoieter

pia tf

t

dZ in mi«,in

?ig.Ii.

urveì of ohenge

in tngentia1 tree

c1iie

to trip wire.

liii

r"

/

.

-iIi

L, o _/5',

44

Taking into account the above results of tangential

sires-ses measured exactly behind the eire, the fact may

be

consider-ed as establishconsider-ed that, aart from the general stimulation

ef

feot exerted on the boundary layer of 'towed model, the stimu

lator is resonsib1e l'cr the local hydrodynamical influence

on the Thiring of models resulting in increase

of tangential

stresses on the model surface in the limited region behinc

the stimulator,

dditlonal resIstance of the model due to this

influence must be regarded es oonionent of the total resistance

of stimulator. Therefore, -the resistance of the stimulator

should be considered to consist of own resistance and resistance

due to its local effect.

The man1tude of te additional resistance coefficient of

model as influenced by the local effect of stimulator

=

0.043.IO

hes been deterined by integration of the measured

tangential stresses, at ?roude number Pr = 0.2. Thus, the

re-sistance

coefficient of a 1,0 i wire for model kto. IO, et

Proude number Pr = 0.2

equel to the sum

of the stimulator's

own resistance and the resistance owing to its local effect,

amounts to

.087

IO, which almost coincides with

the

value of correction for stimulator's resistance 4C,

0.t8

I6

determiuod irin the measurement of thi model re

sistence with stimulator and without it.

The decrease of the resistance coeffic±ent for the mo

dei referred to, due to the effect of fixed laminar area, as shown by the test resultì, et Proude number 1r=0.2, with 1.0mm

45

-wire feund by ce1u1etion i 0.096

I0.

Thus, the re31 tence eugmentetion for the riedel in qu.e3tion due to the re-. 3i3tence of 3timu.letor itself in this ce3e i fully

coinpenet-ed by decree

of the re3istence coeffl1ent due

to the per.

3i3tence of the lniner erea eheed of the 3timulator. The above re3ult3 of the experiment3 an3 celoulation3 cari be ap-.

plied ior etmetin

the trip wire re1stence when uad in re

i3tance te3t3 in to'wíng tank3.

Conclu3ion3

I. Rei3tence teat3 'with model3 in towing tenk3 of rou.e

7

ty?e, at, ieyno1d3 nuniber 3maller then 1.5.10 3hould be cerj-ned ot with th.e ue of turbulence-producing device3.

The nioj

efftive of the

imuletor

u3ed In toiri

tanks et pre3ent 1 e trip wire.

When te3ting in. ternk3 with riodel3 5-7

ri

long e trip

wire of 1.0 1.5 min dimeter 13 recommended. With large rakô

3tem, a weil a with lerge angle3 of entrance of waterl1ne

the dierneter of trio wire hould be 2.0 mm.

The u.3uel practice

in

towing tenk3 of placing e trip

wire at 0.05L frani the forward perpendiculer may be

conider-ed e juitified.

The ue o' th recommended

3ize3 of trip 'wire in te3t

ing with model3 5 to ni long enable3 to obtain reliable

re-3u1t3

of re3i3tence

te3t3

at Reynold3 nurnber varying from

7

6

When carrying out re115tance tet3 ith model len.gths

mel1er then 5 m

In towing tank3 of

roude type, diameter of

trie wire

hou1d be chosen 1.5 to.2.O mn.

4.orrection for

the wire own resi3tenoe ehou.it be introduced ,in the

reu1te

of tet3,

to be determined from the re3ult3 given in

thI3

w o rk.

TrIpwire rei3tance 3hould be con3idered to oonuIt of the atImu.ltor own reeItenae end: that

due to it

local

effect on the tangential 3trese3 In the

re3tricted region

behind the

timu1ator.

whIle testing in a tank

It le neceeìery to take

co

of the ridury

flow after previous run3 maintaining definite

time intervale between iu3ceeive ±1X3,

£. houLi doubt arise

as to reliability of the

re3ulte

of reiìtence

toete, it is recommended tocheck the

flow

In the boundary layer of the model teeted by means

of the che

micel method showing the

recjui?ed accuracy.

It. In view of complexity and variety of phenomenB

000Ur-Ing in the bondary layer of

models tested in towing tanks,

further study of t.iese henornene based on the inve3tigetion of boundary layer o! mod ele 13 necessary.