Eighteenth Symposium on Naval Hydrodynamics (1991) / Chapter Skim
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Steady and Unsteady Characteristics of a Propeller Operating in a Non-Uniform Wake: Comparisons Between Theory and Experiments
Steady and Unsteady Characteristics of a Propeller Operating in a Non-Uniform Wake: Comparisons Between Theory and Experiments
Pages 607-632
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From page 607... ...
The present paper exposes the latest work conducted at the Bassin d'Essais des Carenes in the theoretical and numerical fields to produce a numerical code able to answer this need, as well as the results issued from an original technology developed at ONERA to give access to the fluctuating pressure field on a blade. The code issued from these efforts is based on a linearized lifting surface theory and is fitted for low and moderate loadings.
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From page 608... ...
Unfortunately, no unified tool based on the linearized lifting surface theory was available to allow the computation of both steady and unsteady characteristics of a propeller operating in a nonuniform flow, within the solving of the inverse problem or of the direct one. The present paper exposes the latest work conducted at Bassin d'Essais des Carenes de Paris in the theoretical and numerical fields to develop a numerical code able to eliminate some of the previously mentioned restrictions, as well as the experimental results obtained in its facilities from an original technology developed at the Office National d'Etudes et de Recherches Aerospatiales aimed at giving access to the fluctuating pressure field on a blade.
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From page 609... ...
Following ITTC standards, one defines a right hand orthogonal system of Cartesian coordinates with the origin O coinciding with the centre of the propeller. The longitudinal axis x coincides with the body axis, positive downstream; the transverse axis, positive part; the third axis z positive upward.
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From page 610... ...
Following ITTC standards, one defines a right hand orthogonal system of Cartesian coordinates with the origin O coinciding with the centre of the propeller. The longitudinal axis x coincides with the body axis, positive downstream; the transverse axis, positive part; the third axis z positive upward.
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From page 611... ...
In the direct mode, the leading edge suction force has to be taken in account and is calculated with the method described in (14)
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From page 612... ...
To solve the problem raised by the time-dependency of the potential, the following procedure has been implemented: - the value of the doublet associated to the jump ~ of potential 6¢ at the trailing edge at a given time is obtained from the integral equation (16) , - the doublet element associated to the potential jump is convected downstream on the helicoid at a speed equal to the steady component of the local at-infinity velocity, - the computation is actually conducted on the first blade only, due to the blade-to-blade periodicity of the solution.
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From page 613... ...
Figure 7 shows that the predictions of fluctuating moments are good in amplitude as well as in trend versus EAR. BASSIN D'ESSAIS DES CARENES EXPERIMENTS In the prediction of unsteady efforts, one of the expected advantage of the linearized lifting surface methods over lifting line theories is to give access to the fluctuating force amplitudes as well to the fluctuating pressure field with a better accuracy.
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From page 614... ...
Thin film pressure transducer technology The objective of the thin film pressure transducers is to give accurate measurements of the fluctuating pressures at specified points located on the surface of a propeller blade with the smallest alterations of the flow around the profiles. Besides, the sensitive part of the captor has to be as small as possible.
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From page 615... ...
The propeller was equiped with six thin film pressure transducers, three on the back and three on the face. They were located mid-chord at three different radii, respectively 0.5R, 0.7R and O.9R.
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From page 616... ...
Such results are accurate enough to allow noise radiation prevision and give credit to the results obtained for the amplitude of fluctuating forces and moments. CONCLUSIONS The code that was developed at Bassin d'Essais des Carenes offers a good reliability, partly due to the use of new collocation techniques insuring the consistency of the method.
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From page 617... ...
283-305 (16) Portat, M., Bruere, A., Godefroy, J.-C., Helias F., "ON ERA developed thin film transducers and their applications," Proceedings of Sensors Symposium, Jan.
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From page 618... ...
4 Propeller NSRDC N° 4133 Open water results ~_ ~_ 0,7 0,8 0,9 Advance coefficient J0 618 ~ ~ KT0 computation ~_ ~ KQ0 computation KT0 experiment O KQ0 experiment
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From page 619... ...
6 Boswell experiments Fluctuating forces 0,9 ~f~ ~ ~_e l 0,6 o,g Expanded Area Ratio 1 ,2 Fig. 7 Boswell experiments Fluctuating moments , , 1 0,3 0,6 0,9 Expanded Area Ratio 619 KTX computation KTY computation ~ KTZ computation O KTX experiment KTY experiment ~ KTZ experiment tIt KQX computation KQY computation KQZ computation O KQX experiment LI KQY experiment ~ KQZ experiment 1 ,2
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From page 620... ...
10 Propeller BA N° 2515 Fluctuating forces acting on one blade ~L 4 5 6 7 8 2 3 Harmonic order Fig. 11 Propeller BA N° 2515 Fluctuating moments acting on one blade 6 7 8 ~_ ~.~ ~.
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From page 621... ...
13 Propeller BA N° 2515 0.5R- Face - Midchord Harmonic Order Fig. 14 Propeller BA N° 2515 0.7R - Back- Midchord Harmonic Order 621 Kp averaged |g Kp computed Kp computed 8 Kp averaged Kp averaged Kp computed
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From page 622... ...
o A ._ ._ o Q y a) ._ ._ ID o C' 100 o 200 100 O 200 180 160 140 120 100 Harmonic Order Fig.
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From page 623... ...
Rake is considered positive downstream, Re is the curvature radius of the blade at the leading edge, ds/dx is the slope of the mean camber line versus the profile mean line at the leading edge Model geometry Model length LM= 6.9 m Model Midsection diameter DM= 0.625 m The meridian equation is given as: if O < x ~ 0.045914 LM, then r / RM= 5.7532* x if 0.045914 < x < 0.40171, then r / RM= Yaft((x-0.005439)
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From page 624... ...
o ° co CM c ~co ~c~0 co ~co ~0 ln ~ o ~)
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From page 625... ...
o o · c~ c~ ~ ~ oo ~ ~n ~ c~ 0 0 ~ c')
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From page 626... ...
cn 0 cr.
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From page 628... ...
o co 0 ~0 ~° CD ° Co o c ~0 {D ° ~o ln O D o ~ o o o ~ o oo o cM o cO ~cSi o cM ~o ~ · co 1 0 0 ~t O cn 0 0 0 ~° ~° 0 °0 ° C ~° ~° ~° O o O ~ O C`1 0 ~ O ~- O ~ O (D O (D O a)
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From page 629... ...
Lo cM o an ~win up 0 ~ cot ~(D w CM w O ~ ~O O ~CM w ~ m ~ ~ we in ~ ~ |
From page 630... ...
~cM cM cM oD CE: ~ ~n co ~co cr7 ~ ~ ~ ~ m ~u~o 0` 0= ~U]
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From page 631... ...
. According to our experience, the simple linearized lifting surface theory is not able to provide results which show satisfactory agreement with experiment, and the nonlinear deformation of the trailing vortex sheet in the slip stream must be taken into account.
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