The application of jet flaps to ship propellers and thrusters

NOV. 192

ÀRCH1F

Ref.:PAPER 1/1 SESSiON 4

Lab.

y. ScheepbouwkuntIe

Technische Hogeschool

Deift

SYMPOSIUM ON

"HYDRODYNAMICS OF SHIP AND OFFSHORE PROPULSION SYSTEMS"

H0VIK OUTSIDE OSLO, MARCH 20. 25., 1977

"THE APPLICATION OF JET FLAPS TO SHIP PROPELLERS AND THRUSTERS"

By

Paul Kaplan arid August F. Lehman Oceancs, Inc., Plainview, N.Y., New York

THE APPLICATION

OF JET FLAPS TO SHIP

PROPELLERS AND THRUSTERS

. by

Paul Kaplan and August

F,

Leh Oceanics, Inc., Plainviéw, N. Y.,

Abs traàt

The use of jet flaps. as a means of controlling the pressure

on hydrofoils in order to avoid cavitation is described. The concept is then

applied to ship propellerS in order to produce an effciènt propeller design,

which can operáte in a heavily loaded condition without any deleterious

cavi-tation effects, including operation in wake regions. Applications to thruster

design using this concept are exhibited, with the system benefits.eçplained

primarily with referénce to the cavitation resistance of sucha design. Overall

benefits for such' a propulsion system are described in termS of radiated

pro-peller pressure disturbances, number of propro-pellers for a particular applIcation,

and noise characteriética. .

Introduction

The advent of high powered and/or high speed large ships, such as

tankers and container ships as well as specialized chemical carriers, has

introduced a number of problems related to propulsion fór modern merchant ships.

These particular véssels operate with propellers that have not had any

Corn-ntensurate increase in diaméter, resulting in heavily loaded blades. A symposium

devoted to the various problems associated with these ships (see (li) has

indi-cate4 that the main disturbing effect is due to the occurrence of cavitation, primarily during the passage through the upper portion ofthe wake field., While

the degree of cavitation may not have a very significant effect on the ship

overall propulsion efficiency as long as there is not a very large region of

cavitation about the blades, the resulting radiated pressura field and

eubea-quant vthatory forces on the hull produce significant structural vibration

and nOise that are objectionable. Similarly the influence of cavitation' may also result in changes in vibratory bearing forces that are also transmitted

to the ship, which in turn can effect the vibratory characteristics of the

shafting and the' main hull.

In addition to. the problems associated with a small degree, of

cavita-tion, there is often a prOblem when dealing with ships of this type to select

the number of propellers that tust be fitted in order to absorb the power

required to propel the ship at its desired speed in an efficient

manner.

The propellers

cannot

be so heavily loaded such that thrust breakdown and resultant

decreases n efficiency, erosion, etc. will occur, and that often requires the

eek van d-Mdelìng Schee _{- en}

artunde nische HogQscho0j, De DOCÚMENIATIE

_2is

choice of multi-screw confiurationS. The inhérent trade-of fs associate'd

with

this choice have a significant influence on the resulting ship design and the investment required to construct the final configuration, so tha

an obvioús means

of

producing a môre effective ship-propulsion arrangement would aim at minimizing the ntunber of propellers required for a particular

operating condition. The limitations oF cavitation in determining such designs are obvious to ship designers, thereby making cavitation

considera-tions a significant aspect of propeller design for modern large ships.

. In application to offshoresystenls used in various phases of oil ex-ploration and production, the employment of thrusters as part of a dynamic

positioning system is another recent development. Since theoperation of

these control systems involves the use of acoustic reference signals that

indicate the relative position of a controlled ship with respect to its

desired Operating point, minimum influence due to the local environment and.

other disturbances that would affect the acoustiç signals is of paramount

importance. One of the problems associated with thruster operation, especially for large disturbance influence on the ship in the open sea, is the requirement

of qencration of large. control. forces (and hence large powers) which are often

provided by thrusters that have either controllabló pitch or rotatable

orienta-,tion mechanisms. These thrusters will also experience problems due to

cavitation when operating in this manner, which have an influence óñ the radiated noise level that Could interfer with the effective

functioning

of these dynamic positioning control systems (e.g. see (2]).

In all, of these developments that characterize modern shipping and offshore operations the coimon element that creates difficulties is the

ever present problem of cavitation. What would be most beneficial to all of.

these cases would be a propeller design that coutd operate under heavily

loaded conditions and

which would be

much more resistent than conventional propeller systems to the occurrence of cavitatiofl. A particular concept has

boon ovolvód which can provide this capabitity, and it Lnvolves a' special design, that incorporates a jet flap within the propeller blade. A descriptton

of the jet flap propeller and its prospects of reducing 'the influence of

cavitation is described, in the present paper.

The 7et Flap - What and _Why '

The jet

flap is a high

lift device that was originally applied to aircraft wings. It is 'essentially represented as a conventional wing with a

thin jet blowing near the trailing edge at some angle relative to the foil

chord. The downward component of jet momentum produces a reaction that leads

-3-induces a soca11ed "supe.rcirculation" about the foil which produces an additional (and larger) inçreznental lift fOrce. On this basis a high lift

. . can be achLevedby izicreasing either thejet momentum or the jet angle, or both. A number of publications in the áeronautical literature describe

the jet flap fâr that application, and a source of general information aboit

this type of high lift system is given in (3] . ,

:

Most of the analytical and experimental work that has been published

on jet flaps has beén concerned with sytnznetric foil sections, with the. basic

theory initially developed in (4] using two-dimensional thin airfoil theory.

Further work has been done :to generalize these results to include the effects

of thickness . (see (5) ) , from which both the resultant lift and the pressure

..

.

distribution on the foil were also determined. One of the features of jet

flap operation is that the pressure distribution resulting from jet deflection is saddle-backed, as illustrated in Fig. l,.and there is a pressure peak

near both the leading and trailing edgewhich is shown in this case for a symmetric foil section. This pressure distribution characteristic is in contrast to that asSociated with an angle of attack, which has a pressure

peak only at the leading edge, with the leading edge pressure peak for the

jet flapped foil not as high for the same tòtál lift as shown by the

com-parative pressure diStributiondue to angle of attack in Fig. 1.

From the nature of these pressure variations, it then follows that the

adverse pressure gradient over the jet flapped foil is smaller, and hence

the occurrence of separation (and stall) are postponed to higher lifts tha

those that can be achieved without the jet. Furthermore, of greater signi-ftcnce o hydrodynaxnic applications wherein cavitation of lifting elements

is.. important, as a result of the reduced pressure peak the occurrence of

cavitation is also postponed in comparison to that of a conventional foil.

M analysis of the uso of jet f lapped hydrofoils for an application to ship

anti-pitching fina, which

was based upon this

resistance to the occurrence of cavitatiOn, was presented in CG]. Xn that case the particular application of a symmetric hydofóil with an elliptic thickness distributioñ was analytically dóvelopad and applied to evolve a proposed solution to that particular problem.

Estimates of power requirements were also made, based upon theory, which

indi-çated the possible utility for that case. Subsequent work of an experimental

nature was carried out in [73, also for symmetric foils, wherein measurements

of the lift and drag forces on a jet flapped foil were made in a water tunnel,

including determination of the power reqpurements, velocity distribution in.

the jet mixing region, etc. In addition the variation of lift force was determined for unsteady motions of the jet deflection angle, in view of the

pC)SSib]e

application to contro] surface; of a submarine. No experimental

;tudy ot: tite cav.i t.ation eharac:terifr;

t ics of thi; fo i J wrre made

i ri I 7 I

Vi (-'W t)F

tIír proiioutd

pp].i rai- I CHI, although x

tonni vc wi nd t:unno i

t-os t-s br

ronaut.ict I ipp I

iíatidnH (e. q. ,

.lecri hod

and i. li

utrated

in 131)

i.ndirate

that tue pro uren predicted by theory .igree. we-li with those experimentally

measured.

Theoretical expressions for the forçes acting on jet flap hydrofoils

for the two-dimensional steady motion condition show that -the foil lift

coefficient is depéndent on the value of the jt momentum coefficient C.,

defined by - - -

-J

= pv2c

where the jét momentum J is defined by

(2)

with

Ç) the flow rate of tha jet, V the- jet velocity, V the free stream

vc.loity

and c the foil chord. The

two-dimensional

uf coefficient for

a thin foil, due to the vör-ticity effects induced by the. jet- and by an

-angle of attack, is represented by

--- +T

Dct

where the angle of attack' and r is the jet'deflection angle, with the

quantity - givon (approximately) by

--B 2vÇ

- . (4)

far- the range of email C values appropriató t hydradynamic applications,

i

---

-i.e. C <0.25. The valuo of is dnpendont on C1 to some degree, with

an increase above the Convontioniit valuo of 2w by aiout ()% (depend-tut tnt

The. total lift coefficient also cntainf5 the cothpcnent due tO the jet momentum,

and it is given by -- ' -aCL -CL B

'-+

r - (1+6) 4-(1) (3)-T - (5)

-5-where a correction for foil thickñess (represented

by the

term 6, the

thick-ness -

chord ratio)

is

also included.. No effects of camber, are thcluded in

tu i::

(xj)rcY;s ion s i n'c' the foi 1f'; are assumed to be symmetrical.

i n ;i iot. i ; ('mi t t('(I

iroin tIu

ji

t i tap hydroioi i

, t:h

loi I

w i I I

l'xI)er i encc a 1h rtj; L lurco.

WI 1h 1h 1h ru5t COO ii ici i'II t. cle'.l ¡,fl('(I Ly

=

T/pV2c

(6)

where T. is jet thrust, and by application of the momentum theory, itcari

be shown that the net total thrust coefficient is,

= C. (7)

.3

' which is independent of the jetàngle r. Thus complete jet momentum ' recovery. is obtained in the form of thrust, according to theòry. This

tL',..'u.Lt tS based upon neglect of jt tnicing or entrainment and other dl;sipat.ive

(:?ffcct.i, ; well an depending ii,,on the Principle of cnorvation of momntum.

Whon carnbor of u' fofl oction is eonsiderod the rcsultinq liFt is Lncroased by thc camlxr terni in cn essentially additive manner'. Camber linos corresponding to the"constant load" distribution known as NACJ, a=l.Omay be moro reasonable

to expect in the case of a jet flap then for ordinary foils since the occurrence

of separation just upstream of the trailing edge (in ordinary foils) may not

ocóur as severely in the case with a jet. In addition the fore-and-aft

sym-rruetry of this particular camber line fits in weil with the jet flap saddleback

loading.

Another aspect of jet flap foils is the interaction of the effects of

thickness, angle of attaciC, camber and jet effects on the pressure distribution

of such foils. It is not nccessiry to minimizo thø foil thickness in order

to obtain minimum pressure peak for a given CL value. n fact thora is, an

optimum thickness valuo for any design (seo

_C6I),

which is a function of the desired pressure âoofficient (Cr) value, and the thickness is often n

siqnifi-cant value that provides additional structural strength to the foil section.

Experimental data (Bee (3], (7] and other sources in aeronautical

literature) shows generally good agreement with theory for, the lift force

variation. The agreement in regard to Full thrust momentum recovery is not ci'

good but nevertheless a very large portion of' the jet momentum i recovered in

the form of thrust. A workable featuró is the lack of influence of the jet

anglo on this jet momentum recovery. A particular important feature of jet

oscillatory motions of the jet angle, as shown

in [7].

This

particular aspect of small lag effects

is

important for

üse of

the

jet

flap concept

asa

control surface,

s well a

indicatinq the quasi-steady lift force

bohavior oF thi; Lype of foil.

Another f!aturc of? thc$e

förces in the

(;('ncral })r('ciómirulnce Of jot effects on the

total lift (dependent

Ln C. und

1 ) , which can sometiineschange the sensitivity of the lift to angle of attack changes, i.e. lift changes can be reduced due to a change in angle

of incidence as compared to an ordinary foil (see (3] for discussion of

such experimental results). . . .

Application to Ship Propellers .

Ìn view of these characteristics of the jet flap, a natural extension

would be to the case of ship propellers wherein cavitation limits for

par-ticular desired loadings would be of importance. The jet flap propeller

design would allow increased.propeller thrust by means of achieving larger

propeller section lift coefficients then can, normally be employed, because

of cavitation limit's imposed by angle of attack variations when the propeller

operates in a spatially varying wake field. In general, 'as a result of thé.

ìnìreasod lift. coo ffcient, a smaller diameter slower turning propeller can be

used tor the caso where the same tôtal thrust must be developed. Since the

moment arm to the center of lift and the rotational speed of 'the propeller

are both decreased relative to a conventional propeller, there is the

pos-sibility of an increase in efficiency due to the relative redúced torque.

Howevér it io necessary to conSider the additional power required for pumping

the jet fluid through the system and out at the trailing edge, and the

resultant efficiency must therefore be determined from consideration of the

total power requirements for this particular concept (i.e. the sum of shaft

power and pump power).

The design of a propeller

employing a jot flap invOlves satisfying the

thrust.roquirement

from

two individual contributions, one part from the pro-1i1tor foil soctjc,n without jot. action and the other part supplied by the

oupnrcirculation induced by the jot. The thrust supplied by jot action is

determined by the jet exit velocity, jet anglo, jt slot width and the length

of the jet along the trailing edge of the blade. The design of auch a pro-puller involves combining conventional propeller theory and that from jot flap

theory, as well as experimental and/or computational evaluation hc determine

the optimum characteristics of each'contributing element.

The original intent in any design is to establish the propeller

orienta-tion so that the non-jet acorienta-tion is supplie4 by a cambered foil whose secorienta-tions

of attack, using the mean values

of

inflow velocity obtained from

the measured wake field. Te jet contribution is then determined so that the resultant pressure distribution was relatively flat and also satisfied the

lift coefficient requirements of each particular section. The design is also baséd

upon an attémpt to induce a minimum axial induced velocity, since the

shaft torque requirements of a propeller are a direct function of the axial

velocity component. However that cannot be exactly. achieved in principle

since the induced velocities from a jet flap are significantly different

from that of a conventional airfoil section due to the nature of the f].ow associated

with the sheet emitted in the trailing edge region. This is

another reason for the dependence upon experimental evaluations to establish

an optimum design, based upon the state-of-the-art employed

in

the ànalysis fôr this t:ypr of propeller system.

Lor thu caso of a jet flap propeller the fluid for the jet flap cntors

'

t:)ic )vorR41Cr through a hollow drive shaft, under a pressure supplied by an

auxil.ary pump. This fluid passes throuqh various passageways within

th

blade and then exits from a slot in the trailing edge region. The glot has a

specific angular orientatiön relative to thé blade surface, which is

distri-butod radially

in

accordance to the desired lift characteristics at each section. Anillustratiön of.such a representative propeller blade, with an indication of the resulting lift forces, is shown in Fig. 2.

As indicated in the above, the basic design of the jet flap propeller

is essentially made up of a combination of blade element sectional

character-istics which are combined to produce the required steady thrust output based

upon the average flow velocity values when operating in a wake. The variations

in anqin nf attack that are experienced when operating in a wake, as the pro_:

p1.ier rc,ttes, produca changes in the flow characteristics that aro oxpoctcd

Li

have tc.,rnier effects on the prtpellor section

characteristics and rusuLtthq

risura of e jet flap propeller so that a reduced. sensitivity tu the

occur-renca of cavitation

is expected, b&nt'il upon the

resulta indicated fcr et flap hydrcfoils described in the preceding onction. A particul@r

design can be

eMteblished which produces the desired average thrust,

together with prewiurti

distribution

valuas whose peaks

are somewhat less than those for cavitation

incet,tion. Somó degree of angle cf attack change can be tolerated during the

coursa of the propeller paasage through the wake, with the extent of the

influence of the particular angle of attack in altering the pressure peaks

determined from computations from the theories in

(5] and (6].

This

concept is the basis for expecting a reduced cavitation

influence

for propetlers of this type, which

can

be verified for particular cases by direct comparison of experimental measureentB for a convetional propeller design

and

that of a jet flap propeller.

-i.

-8-A numbér of water tunnel experimental studies were carried out sometime

ago at Oceanics (of proprietary nature) which were aimed at determining the basic performance characteristics

of

the jet flap propeller, primarily from the point of view òf increased efficiency for tanker applications. Some of

the

results obtained in these studies provide important illustrations of

the

characteristics of a jet flap propeller, and they are presented here in order to demonstrate experimental data that verifies a number of aspects that

äan be achieved by a jet flap propeller. The particular data presented here

is only to be vièwed as illustrative, and not necessarily final data for

particular designs, and is therefore only shown for that purpoSe. The

vari-ation of thrust and effióiericy for a particular model' (as a function of

pro-peller rotational speed) is shownin Fig. 3, illustrating the results for a

fixed jet slot width and jet anglespanwise distribution for dfferentvalues

of jet flow. Sorne of these resultS are also: shown in Table ]. in tabular form, which exhibits the effect of jet action as compared to the basic propeller

itself without any jet. The determiriation of pump power is obtained from

knowledge of the f low rate and the pressure,head of the pump, together with

an assumed pump efficiency of 87%. The efficiency of the propeller is then

define by:

n velocity x thrust_{shaft pöwer + pump power} (8)

It can be seen from these results that there is a significant increase

in the thrust due to the jet action, with only a small relative increment

in the pump power as compared to that of the normal Shaf t power. In addition

it can be seen that there does not appear to be a significant change in torque

relative to the torque without a jet, for such a larga increase in thrust. This interesting aspect of the torque rouiroment, whichdid not seem to chango

very much with largo increases of thrust due to the jot action, has boon found

to hold in a number of dif feront invoetigationa employing the et flap principio, and sorne posBiblo explanations for it have been considered. Similarly some

reasons for the small pump power incremont have also seen determinad. In regard

to the torque requirement, there are two influences present that contribute to

the foneficial results1 One of these

i8

due to the effect of the jet momentum recovery which acts in the direction along the foil chord, as shown in the

representation of section force coefficients (including the experimental support

for this jet momentum recovery action).

Another

effect that assists in reducinq the driving torque is that associated with the combined effects of fluid being

emitted radially within the propeller. blade, together with the rotation

about the longitudinal axis, which can be shown to result in a Coriolis

force against the internal wall sections of the prope-l-ler blade that acts

to reduce the torque. A means of explaining a beneficial influence on the pump power is the effect of centrifical force, which acts to aid the motion

of the fluid thatis being;emitted from the propeller bláde which it is

rotating about the longitudinal axis. Precise evaluation of all of these beneficial effects cannot be presently made, but nevertheless their ctïon

can be qualitatively understood in order to explain how the results obtained

in experimental studies have a certain technical basis that can lead to

ex-pected beneficial results for any basic application of the jet flap principle

to a propeller.

The results discussed above provide a basis for obtaining increased

propéller thrust without a significant added power penalty. The overall

efficiency of the propeller, when employing a jet flap, is generally

com-parable to that of a Conventional propeller design, in spite of a requirement

for an additional source of power for the pump to supply the jet fluid emission.

With regard to cavitation performance, nO direct experimental studies have been

completed (at the time of this writing) in sufficient depth to illustrate the

benefits of a jet flap propeller as compared to a conventional propeller.

Hwever, in the case of the water tunnel experiments carried out previously

at Oceanica, we have visually observed the cavitation characteristics of a particular jet flap propeller whon operating in a wake and have made

compari-son with pictorial data supplied from other water

tunnel

tests (in other facilities) for the comparative conventiònal propeller. A significantly decreased extent of cavitation was found for the jet flap propeller as

com-pared to the conventional propeller,

with

the occurrence of any cavities for the jOt flap propeller only found in outboard rogions where no jot omission

occurred for the particular design being tested. Other

(unpublihud)

inveeti

gationa. have

been

conducted wherein similar behavior has boon observed. On thie basis we can expect that the anticipated benefits cf the jot

flap propeller cañ be realized in regard to cavitation resistance, while

still providing efficient poformance. At the present time arrangomonta for

an experimental evaluation of a conventional propeller in a wake are being.

made at Oceanica in order to obtain test data that would duplicate results

obtained in antoher facility

which

exhibited propeller cavitation, and thereby verify the capabilitiesof the. test facility añd procedure used in the

Oceanica water tunnél. A jet flap propeller will then be designed for operation

lo

-performance, efficiency, degree of cavitation observed, and measured

pressure variations on a nearby hull surface will be compared to that

of

tI

})eVi()tIly

te;.t1

conventional. propti1or under tIu ;arn

cOndi t.i.orìs.

'I'hi; work will be carried out for other propeihr designs in order to

the capability

of

the

jet

flap

propeller in providing the anticipated benefits, when operäting in wake conditions wherein ordinary

popeilers produce objectionable rsults due to cavitation.

Thruster Designwith a Jet Fläp

application of thrusters for offshore operations involves the

capability ofproviding forces in different directions in order to counter

varying forces, as in a dynamic positioning system. Different types of

thruster systems are used, ranging from fixed pitch-variäble orientation

devices to controllable pitch propeller installations.. In order to in

crease the thrust output of süch systems they are often shrouded in a

duet. As shown in (2] the cavitation on these blades, results in a high noise level that interferes with the acoustic sensors for the control

system, and conventIonal design modifications result in penalties to

sys-tem performance in order to decrease the cavitation noise.

This particular situation can also be directed toward the uso of a

jet flap propeller which can deliver syrmnetrical thrust to port and

Htarboard while not requiring añy rotational direction changes,

control-lable pitch mechanisms, etc. The propo$cd concept will òperate wïthin

41 _{a duct, and is pictorially represented in Fig. 4.} The thruster consists of syrmetrical blades mounted on a hub at zero angle of attack. 'The

interior of the blades are hollow and are divided into two chambers, each

chamber, feeding one slot at either side of the trailing edge of the blade.

The slot directs the fluid. jet at an anglo T relative to the bladé chord

line. External controle will permit the selection of a water supply to either chamber and thereby the selection of the side of the blade from

which jot ejection will take place. Tn operation the blade will rotate

at a ccnstant speed. Ejection of water from' either slot will cause the

jet flap action to introduCe a lift in the direction opposite to the aide

from which jet ejection is taking place. The introduction of this lift

results in the croatión of an axial flow through the düct. This axial

flow, in turn, results in the

blade Hoctions oporattnq at a neqativc

angle of attack. Thus, two forces are at work, the force resultinç; f rem

the jit flap action produces thrust in one direction while the force

The net thrust is the dïfference between the twO forces. It is obviow;

that as

long as

the relative

inflow to thc blade,

i.L.

the

angle

t'mains

unii1, th(' Lift qnerited

by th blade section

will

be

small.,

and

the (ffect

cî t1ì

jcL: flap Wi

1.1 predominate

iic1 produce thrust i.n the

required

direction.

. In addition to introducing lift, the jet flap produces a thrust in the directiOn of rotation and consequently adds driving torte to the system.

The fluid emitted from the jet i captured in. the duct and thus adds to the

môrnentum in the duct. Furthermore, a

component

of the lift introduced by

.

the blade section also adds to the driving torque. Therefore, a fair percentage..

of the necessary driving torque is gained from the forceS resulting from the

jet flap thruster action. . . .

If the angle a remains small the overall effectiveness of the unit

will be high, artd this angle will be small if the induced flow is small

compared to the rotational speed of the blade. On the basis that the induced

flow rate cannot be controlled, it would be possible to maintain a small

angle a by increasing the rotational speed of the blade but high rotatIonal

spoeds require higher absolute jet flap exit velocities which, in turn,

re-quire moro pumping horHepower. The obvious solution is to impart as much

ertorqy into the flow across the. propeller as possible which introducing a

minimum increase in the axial flow. In a longer duct system the necessary

energy can be converted into static pressure because the system will permit

such static pressure increases. With the short duct of a thruster, an increase of the necessary head through a local pressure increase seems

un-likely except if straightener vanes are added. The straightener vanes act

to remove the swirl introduced by the pump, causing the pressure to rise as

the flow passes from the leading to the trailing edge of the stator vanes.

Consequently, this approach (the usa of straightener vanfla) will permit the

necessary introduction of static head With specific control of the axial

flow velocities. Thus there are two actions that can aid in producing an

effective thruster system using the jet. flap concept.

The benefits of reduced cavitation susceptibility by means of the jet

flap concept are expected te reduce the radiated noio level associated

with blade cavitation due to loading. The only prospective acurce of

cavitation could possibly be in the high speed jet itself as it exits from

the blade trailing edge, and that would have to bo obiiirved cxporlmontiUy.

In addition the radiated noise spectrum,

involving

both intcn5ity ¿md

frequency characteristics, would have to be determined, but it is not expected

to be very severe in view of the reduced. cavitation volume and its variation

12

-Another aspectof the jet flap action that is'berieficial for this

thruster application is the rapid change of force developed by a symmetrical

fOil às the jet angle is dhanged in an unsteady manner. This wàsdemow

strated experiiüefltallY th (7]. for a control surface

application, which can

easily carry over to the present design application of a thruster-. Thus the application of a jet flap to a thruster appears o be a use-fu]. prospect

for eliminating noise radiation düe to cavitation while still producing an effective control and propulsion device,

concluding Remarks

The äbove discussiOfl shows the prospects for useful application of

the jet flap concept* for a number of important maritime propulsioz applica-tiOns, where cavitation is 'a limiting factor. Experimental work is now being

pursued in order to demonstrate the benefits of this concept with model. test

data in comparison to similar data for conventional propellers, with emphasis

on radiated pressure on a nearby hull (in a wake field) together with

efficiency and other system öharacteristics. If the results obtained verify

the expectatioñs o. theory and earliér tests, further progreSs toward possible

ship installation (as well as extension to thrusters) can then be considered.

- References

-i.:

Symposium on High Powered Propulsion of Large Ships, NSMB, Wageningen., The Netherlands, December1974.

2. PRONK, 'C. and SCHNEIDER, C.C. Propulsion for 0ffshorC Vessels. Paper presented-at 3rd LIPS Prop. 'Symp., May 1976, also Intl. Ship Building

Frog. 23(1976):264. - -

-3 THWAITES, B. editor Incompressible Aerodynamics. Oxfórd Press, 1960.

4. SPENCE, D.A. The Lift COefficient of a Thin, Jet-Flapped Wing.

Proc. Royal Soc., A238 (1956), pp 46-68.

-. KUCHEMANN, D. 'AMothod for Calculating the Pressure Distribution of

at Flapped Wings. 'Great Britain Aeronautical Res. Council R&M 3036

(1956a- -.

-KAPLAN, P. and GOODMAN, T.R. t3se of Jet-FlappedHydrofoile as Ship

Antipitóhing Fins. J of Aircraft, 4(1967) i2, pp 165-173.

KAPLAN, P. and LEHMAN, A.F. An Experimental and Analytical Study of

Jet Flap Hydrodynamics for Application to Submarine Control Systems.

Oceanico, Inc.' Rpt. NO. 67-41, November l967

-Tha. jet flap application to propeller systems has been patented by Oceanice, Inc. in.the U.S.A. and in 12 other countries.

TABLE 1

TEST DATA FOR JET FLAP PROPELLER

(Slot Width = 0.20 ini., Velocity. = 5.3098 ft/sec)

jet Flow Rate (cfs) = O

*Total pOwer inclúdes shaft power and pumping with an efficiency of 87%.

Jet Net

Prop Flow Pressure Net Net Speed Pressure Head Thrust Torque

(rps) (psi) (ft) (lb) (lb-ft) Shaft Power (f t-lb! sec) Pump Total* Power Pòwer (f t-ib/ (f t-lb! Ef ficiéncy sec) sec) n 9.04 11.02 13.04' 15.02' 16.99 19.04 21.00 23.01 9.02 10.99. 13.00 14.04 15.04 15.99 17.00 18.03 19.02 20.03 o 12.8 12.5 12.0 11.8 11.5 11.2 10.9 10.5 10.1 Jot 9.8. 0 FlOw 24.49 23.79 22.41 21.71 21.02 20.33 19.40 18.48 17.56 16.86 2.8 .15.3 29.9 46.6 64.2' 89.9 110.4 V 137.1 Ratò (cfs) = 21.0 34.2 49.3 57.9 66.9 75.4 83.2 96,3 108.4 120.7 0.92 2.25 3.64 5.35 7.12 9.24 11.46 14.2 0.0395 1.3 2.65 4.27

316

6.05 6.92 7.89 8.97 .10.13 11.31 52.26. 0 155.8 298.2 504.9 760.1 1105. 1512. 2053. (V = 45.87 73.68 60.36 183.0

5864

348.8 55.24 455.2 33.51 371.7 .31.81 695.2 50.11 842.8 47.82 1016. 45.55 1211. 43.28 1423. 41.56 52.26 0.285 155.8 0.522 298.2 0.532 504.9 . 0.490 760.1 0.449 1105. 0.418 1512. 0.388 1 _2053. .0.355

ft/sec, based on SQ/A)

143.1 0.780 250.4 0.725 412.3 0.635 516.7 0.595 631.4 0.563

7528

.0.532 897.8 0.504 1068. 0.479 1261. . 0.456, 1471. 0.436

ÇP

FOIL WITH

FOIL AT INC IENCE

FIG.

3.

COMPARATIVE PRESSURE DISTRIBUTIONS ON FOIL

MAJOR JET

EMMISION

REGION

JET

LIFT

(NÔ JET)

ROTATIONAL

DIRECTION

ADDITIONAL

iTHRUST DUE

TO. JET.

FIG.

2.

DESCRIPTION OF FLÖW EFFECTS WITHIN PROPELLER

BLADE AND SECTION

V

140 130 .120.

EFFICIENCY

110 100 C rd

r

I.-O

o

-o

/-r'

THRUST

10

fl

12

13

14

15

16

17

18

19

.

20

MODEL PROP SPEED n (RPS)

FIG. 3

REPRESENTATIVE MODEL TEST DATA FOR JET FLAP

PROPELLER

.

AQ

0.0395 CTS; V

46 FPS

Q

0.0559 CTS V

65 FP5

O Q

0.0685 CFS.V

85 FPS

Q O

u

.50

.30

.20

. 80....

T

'J rA

I-I.

's o ... 90 .80 .50 40 30 20 lo o

SECTIONAL VIEW

JET INDUCES LIFT

PRODUCES ROTATIONAL TORQUE

)DS MOMENTUM TO THE DUCT FLOW

DRA

COMPONENT RESISTING ROTATION

DRAG COMPONENT

ASSISTING ROTATION

FIG. 4

DESCRIPTION OF PROPOSED JET FLAP THRUSTER

END VIEW

III

V..

(-)THRUST FR4

(-)LIiT FROM

BLADE SECTION

BLADE SECTION

ROTATIONAL DIRECTION

(+)LIFT FROM

JET ACTION

(+) THRUST FROM

JET ACTION

INFLOW INDUCE

BY JET ACTION

AND

ROTATION