Twenty-Second Symposium on Naval Hydrodynamics (1999) / Chapter Skim
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4 Propulsor Hydrodynamics/Hydroacoustics
4 Propulsor Hydrodynamics/Hydroacoustics
Pages 110-238
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From page 110... ...
,r) Unit vector normal to blade camber surface Number of chordwise control points The number of design constraints Static pressure at infinity Vapor pressure Pressure on blade Propeller torque Radial coordinate from propeller axis Radius of propeller boss Radial coordinates of control point Perturbed parameter in SUMT method Radial coordinates of loading point Propeller radius Chordwise coordinate for blade section Unit vector tangent to blade camber surface Propeller Thrust Cartesian coordinates Velocity Speed of advance Induced velocity vector Induced velocity vector due to vortices Induced velocity vector due to sources Velocity vector of relative inflow Weighted coefficients Design variable Difference between objective and calculated pressure at control point Divided chord length Angular coordinate from generator line of propeller Fluid density Angular velocity Cavitation number at propeller center = pot - PV/-~ 2 D2 Chordwise station at blade section Camber distribution Thickness distribution
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From page 111... ...
For example, surface pressure distributions are prescribed as minimizing the occurrence of local suction peaks at the section leading edge. It is possible to derive the blade sections, which have a superior cavitation performance to those based on the NACA series.
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From page 112... ...
By using this chart, the principal dimensions, such as optimum propeller diameter, blade-expanded area and the number of propeller blades are easily decided. Step2: Design of initial propeller with NACA blade section The detailed geometry design follows, using existing propeller lifting-line and lifting-surface theories, to achieve the higher propeller efficiency and better cavitation performance.
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From page 113... ...
It is possible to derive blade sections, which have a superior cavitation performance to those based on the NACA series. This step is described specifically in section 5.
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From page 114... ...
and control point The free vortices shed from the bound vortices on the mean camber surfaces are considered to leave the trailing edge of the blade and flow into the slipstream with the local velocity at that position. Usual approach is to approximate the trailing vortex sheet by a prescribed helical surface, in order to avoid the time consuming calculation of the slipstream velocities.
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From page 115... ...
4.Numerical Method for Initial Propeller Design 4.1. Determination of Vortex and Source Distributions The radial circulation distribution can be obtained from a lifting-line theory such as the Lerbs' induction factor method[16]
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From page 116... ...
is the chordwise coordinate of the trailing edge of the blade. If the pitch angle correction and the camber correction are obtained, a new blade surface is formed by correcting the original pitch angle ,BO(r)
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From page 117... ...
5.3. Propeller Design by SUMT Method The new blade sections with the three-dimensional prescribed pressure distribution over blade surface are designed by using the SUMT method.
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From page 118... ...
Part 2: Set up the objective pressure distribution The objective pressure distributions on the blade sections at the severe] radial positions are given by the polynomial coefficients.
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From page 119... ...
It is considered that giving a priority to the fairness causes these small errors. The optimized blade sections for triangular and semi-flat pressure distributions have thin thickness near the trailing edge as shown in Fig6 (a)
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From page 120... ...
The pressure distributions on the back-side of new blade sections were prescribed as the flat with high pressure at the leading edge. Table 1 Principal particulars of PCC Length between perpendiculars Breadth Draft Power of engine(BHP)
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From page 121... ...
Fig.9 Panel arrangement for PCC2 used in the panel method Fig.10 Panel arrangement for PCC2S used in the panel method The cavity extents of PCC2 and PCC2S with new blade sections are smaller than those of other propellers with MAU and NACA66 a=0.8 blade sections. The cavity of PCC2 is observed unstable.
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From page 122... ...
were designed for evaluating the new blade sections based on the initial propeller (CS1) with NACA66 a=0.8 blade section.
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From page 123... ...
The pressure distributions for CS2 were prescribed as the flat pressure distribution with slightly decreasing near the leading edge.
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From page 124... ...
was presented. In order to improve the cavitation performance as compared with the propeller with NACA series blade section, the new blade sections with the prescribed three-dimensional pressure distribution over blade surface are designed by the present system.
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From page 125... ...
Chen, J and Tang, D., "A Design Method of Highly Skewed Propellers with New Blade Sections in Circumferentially Non-uniform Ship Wake," China Sip Scientific Research Center Report English version 92004, 1992.
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From page 126... ...
AUTHORS' REPLY Thank you for your discussion. We think the best pressure distribution for the cavitation performance is the flat pressure with higher pressure at leading edge.
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From page 127... ...
A Study on a Propulsion System by Peristaltic Motion in Highly Viscous Fluid M.-C.
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From page 128... ...
analysis coded] is developed with artificial compressibility method which has been established by Sohi8]
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From page 129... ...
Fig.3 shows the experimental apparatus for the measurement of the flow field. A partickle tracking velocimetry(PTV)
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From page 130... ...
The average velocity profiles around waving surface are shown in Fig.9 which are obtained from sequentially measured frames during 20 seconds. The model is fixed during the experiment.
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From page 131... ...
10 Comparison of velocity vectors between the experiment and the computation(figures shown at every 60° increment over a period)
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From page 132... ...
over this control volume yields j+4 k+3 i+3 k+4A Ak+2 j+S~ Y - ~>j+2 k+5\~_ k+1 :, ,: \/ ;-i i-l a) Control volume of point i b)
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From page 133... ...
dV = 0 (ll) where Vi is the control volume and h= ~u~,q= OR= ~ G I
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From page 134... ...
The velocity profiles at ~ = 0 at different times during a cycle are compared between the computed result and analytic solution in Fig.13. An excellent agreement is seen between the two.
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From page 135... ...
Zero-gradient condition is imposed as pressure boundary condition and the x-directional velocity at outer boundary is set to be the model speed. The number of physical time step(At)
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From page 136... ...
Computed velocity vectors and pressure contours are shown in Fig.16 which are obtained after 5 cycles of motion. The disturbed velocity by the waving surface is clearly seen in the figure of velocity vectors and the difference of pressure between the uphill region and the downhill region is also seen in the profile of pressure contour.
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From page 137... ...
The computed velocity vectors of the case of depth 0.03m are shown in Fig.10 compared with those of experiment. The mean flux at the section of x = 10 is compared in Table 2.
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From page 138... ...
pressure contours Fig.23 Computed velocity vectors and pressure con tours around the body in unbounded fluid with the trochoidal motion at after 5 cycles of computing time.
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From page 139... ...
by pressure contours Fig.25 Computed velocity vectors and pressure contours around the body in narrow channel with the sinusoidal motion at after 5 cycles or computing time.
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From page 140... ...
Mizuta~i, "The Visualization Analysis of High Viscous Flow Field Induced by Peristaltic Propelling Device," Journal of the Visualization Society of Japan, Vol.
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From page 141... ...
DISCUSSION C Johannsen Hamburg Ship Model Basin, Germany Can He author give us an idea about He overall efficiency of He peristaltic propulsion system in comparison to a conventional propeller drive?
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From page 142... ...
Next the calculated results for the 2-D steady and unsteady wing problems are shown and the accuracy of SQCM is discussed emphasizing the wing thickness effects on the calculated results. Then the steady and unsteady calculations for Seiun-Maru conventional and highly skewed propellers are made, and the calculated pressure distributions on the propeller blades and the propeller open characteristics are compared to the experimental data.
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From page 143... ...
The trailing vortices flow out as ring vortices from the trailing edge every time step. We assume that the trailing vortices leave the trailing edge in the direction tangential to the mean camber surfaces and the pitch of trailing vortices reaches an ultimate value, which is the mean of geometrical pitch distribution of the propeller blade, within a half revolution.
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From page 144... ...
When He control points are on He blade surface, the ring vortices are close to He control points especially for thin wing. In this case we treat the ring vortices on the mean camber surface and the shed vortex nearest to TO.
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From page 145... ...
<7' where po = the static pressure in the undist~d inflow p = the density of the fluid 145
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From page 146... ...
= 8_ component of resultant flow velocity averaged in the chordwise direction car) = chord length of the propeller blade TO rH t/c = propeller radius = hub radius = thickness ratio The forces Fx, Fy, Fz and moments Mx, My, Mz agog on the propeller in the X, Y
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From page 147... ...
It is also seen that the Kutta condition at the trailing edge is satisfied.
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From page 148... ...
The propeller blade surface and the mean camber surface are divided into 1200 panels (M = 2O, Nor = 30) and 580 lme segments (M = 20,N~ = 29)
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From page 149... ...
On the other hand, some discrepancies between the calculated results and the experimental data are observed on the bacic side at 0.9R section of HSP. These disagreements between the calculated results and the experimental data of the pressure fluctuation and the chordwise pressure distribution on the back side at O.9R section of HSP might be caused by the tip vortex stemmed Tom the leading edge separation[17~.
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From page 150... ...
t16~) Highly Skewed Propeller -- -~; (n=90 r.p.m.)
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From page 151... ...
LE. Chordwise Coordinate Fig.17 a~ordwise pressure distributions at 0.7R and O.9R (Seiun-Maru HSP)
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From page 152... ...
agreement between calculated results experimental data is generally good. Table 2 Principal particulars of DTMB P4118 ~ 0 05 O ~-0.05 -0.1 ~-0.15 6-°~90V180 ' 270 ' \~60 Angular Position, ~ my DIAMETER (inch)
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From page 153... ...
. 0.6 0.8 1 1 2 Advance Coefficient, ~ Fig.25 Companson of thrust and torque in 3 cycle wake 0.03 0.02 1~: 0.01 ~I I I I -- I r SQCM Exp.
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From page 154... ...
[17] Ukon, Y., Kudo, T., Kurobe, Y., Yuasa, H., Kamiirisa, H., Kubo, H., "Measurement of Pressure Distribution on a Full Scale Propeller - Measurement on a Highly Skewed Propeller-", Joumal of the Society of Naval Architects of Japan, Vol.
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From page 155... ...
The predicted pressure distribution near the trailing edge showed a consistent difference between the SQCM and the panel method by Hoshino as shown in Figs. 9 and 10 for steady flow and in Figs.
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From page 156... ...
NOMENCLATURE Cp Pressure coefficient, 1 - ( V/ VOO ) 2 D Propeller diameter, 402.7 mm F Maximum blade section camber i, Total blade rake J Propeller advance coefficient, Us, I nD KQ Torque coefficient, torque/( p n 2 D s KT Thrust coefficient, thrust/( p n 2 D 4 n Propeller rotational speed, rev/s P Propeller pitch p Static pressure in tunnel pa Vapor pressure of water q Root-mean-square (RMS)
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From page 157... ...
Blade sections are non-standard.
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From page 158... ...
At all advance coefficients, measurements were made at an upstream location, x/R = -0.4049 as measured from the propeller mid plane, and at a downstream location, Jc/R = 0.2386. Coincident measurements were made only at these two planes, and only for J = 1.10.
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From page 159... ...
The secondary velocities are then the orthogonal velocity component in the x-t plane, Vc, and the radial velocity, Vr. Since the pitch angle is different at each radius, the coordinate system is different at each radius as well.
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From page 160... ...
The first, case 1, is a point in the "inviscid" flow between the blade wakes. In this region, the turbulence intensity is low and the flow gradients are small.
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From page 161... ...
Cavitation Performance Fundamental cavitation inception tests were performed in the 36-inch water tunnel. The propeller was driven from upstream and run over a range of speeds and advance coefficients to identify the inception of suction and pressure-side ti~vortex cavitation.
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From page 162... ...
Axial velocity matches well on bow sides of the tunnel centerline, but tangential velocity is slightly lower on the side away from the window insert than near it. It is believed that the discrepancy in flow conditions between the two sets of measurements is due to the window insert which was present for the hybrid measurements and not present for the fiber-optic measurements.
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From page 163... ...
The results of these calculations are shown in Figure 14. Figure 14 shows the streamwise vorticity for the four measured advance coefficients at x/R = 0.2386.
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From page 164... ...
The method calculates the blade pressure distribution, spanwise loading, and overall propeller thrust and torque. From the measured circumferential-average tangential velocity, the blade spanwise circulation can be derived3.
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From page 165... ...
and Kerwin, J.E., "Numerical Methods for Propeller Design and Analysis In Steady Flow," Transactions SNA ME, Vol.
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From page 167... ...
Figure 9. Tip vortex on blade 3, contours of V/V,O TV secondary flow vectors.
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From page 168... ...
Contours of VsVc, with cuts Croup Me vortex core, x/R = D.23 86, J= 1.10.
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From page 169... ...
Comparison of measured and calculated blade wake pitch.
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From page 170... ...
Also, on another propeller of quite similar blade shape, we performed measurements of the tipvortex flowfield with the small probe volume used here, and with a probe volume several times larger. We saw no difference in the measured flowf~eld; therefore, we believe no correction is necessary.
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From page 171... ...
The viscous blade wake, originated by the boundary layer on the blade surfaces, the trailing vortec sheets, due to the radial gradient of the bound circulation, as well as the turbulence distribution are resowed in the trailing edge pow and discussed The near wake geometry is ch~racterised by marked deformation processes, due to the bending of the blade wake sheets, the contraction of the slipstream and the trajectory of the tip vortex. Furthermore, the turbulent diffusion and the viscous dissipation lead rapidly to marked broadening and decay of the trailing edge wake.
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From page 172... ...
Wake analysis is developed considering three regions in the flow field behind the propeller: the trailing edge wake, the near wake (within the first diameter) and the far wake (up to wake breakdown)
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From page 173... ...
Different test conditions were adopted for the flow visualizations and will be specified for each presented result. 2.4 Phase Sampling Measurements were worked out in poorly seeded water conditions, as required in a cavitation tunnel in order to accurately test propeller cavitation performances.
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From page 174... ...
A neighboring region of slow flow, which extends in the pressure side of the blade, can be also noticed. This flow distribution in the inns radii is due to the increasing thickness of the blade sections toward the root, as well as to the fact that the LDV measurement points are closer to the blade trailing edge.
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From page 175... ...
This is primarily due to the low aspect ratio and the skew of marine propellers, which cause strong threedimensional effects. The knowledge of the wake geometry along downstream convection from the blade trailing edge is required in order to Fulfill this goal.
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From page 176... ...
in figure 16 the radial variations of the mean axial velocity for different angles in the trailing edge flow are shown. The figure indicates that the slipstream axial acceleration stops, that is VX/V',,f= 1, at the same radius along the circumference.
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From page 177... ...
Moreover, in the trailing edge measurement disk, the angular variation of the CIr at the boundary of the slipstream with the outer flow (r/R=0.9) is rather smooth and the minimum values of the turbulence intensity reduces at almost the free stream level 2%.
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From page 178... ...
"Hydrodynamic analysis of propellers in steady pow using a surface panel method ", Journal of the Society of Naval Architects of Japan, 1989.
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From page 179... ...
Testedpropeller model '(p trigger I digits Encoder signals ~ ataIogic ~ ' /~: ! "', ~ Figure 4 Coordinate systems 2.15R 1.65R 1.05R 1 0.95 Q9 0.85 Qua 0.7 Q6 0.5 0.4 TIC , 0 65R 0 20R _.
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From page 180... ...
241 281 321 Figure 6. Angular variations of the mean axial velocity.
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From page 181... ...
7 and velocity PDF atX/R=0.2 Blade wake flow 8.E-O1 6.E-O1 4.E-0 1 2.E-0 1 O.E+~) O -2.E-0 1 Rx ~R`r Rrr Far from blade flow 2.E-02 1.E-02 8.E-03 4.E-O]
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From page 182... ...
Mean' axial velocity d~sh~ibution In the near wake Figure 14. Axial turbulence distribution it?
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From page 183... ...
450 400 350 300 250 2(10 150 100 50 O · Up vortex 0,8 0.60 : - 0.25 ~c propeller ptch , ~ .
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From page 184... ...
1° 11° 21° 31° 4I° 51° 61° 71° 81° 91° 1° 11° 21° 31° 41° 51° 61° 71° 81° 91° Figurel9. Angular variations of the Brat the tip region -X/R=0.65 andX/R=2.15 Trailing vortici~ Figure20.
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From page 185... ...
Figure 24. Deformation of hub and tip vortices system.
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From page 186... ...
Cenedese Rome University "La Sapienza," Italy In 1985 I was working at C.E.I.M.M. implementing an experimental set-up for the measurement of the velocity field in the wake of operating marine propellers (see reference 9 of the paper)
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From page 187... ...
The availability of a long test section allows study of the far wake. The use of LDV in the study of the far wake, as the authors have discovered, is difficult due to the passage of the blade's wake downstream in the turbulent flow field of the water tunnel.
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From page 188... ...
The present experimental results suggest He conjecture that the dominant form of destabilization is He azimuthal one. Replying to the final question, for our experience the process of slipstream instability and final breakdown is considered to be independent of the tunnel features for low test section blockage ratios.
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From page 189... ...
NOMENCLATURE a C C' Cp CpO CPOLamb CPOnum Poo Po PIc VOO Va Vt x y Y+ z £ V p tip vortex core radius mid span chord lift coefficient pressure coefficient pressure coeff~cient at the tip vortex center Cp0 predicted by the Lamb profile Cp0 predicted directly by the code turbulence intensity free stream pressure tip vortex center pressure local cut-off pressure local radius free stream velocity axial velocity tangential velocity axial coordinate spanwise coordinate non-dimensional distance to the wall vertical coordinate turbulence dissipation rate kinematic viscosity liquid density cavitation number
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From page 190... ...
The asymmetric character of the tip vortex in the region close to the tip has been highlighted. The author has shown that the excessive increase of the core radius prevents from a correct prediction of the static pressure in the viscous core.
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From page 191... ...
It consisted in the extraction, from the computed flow field, of tangential and axial velocity profiles along a line parallel to the span of the hydrofoil centred on the local axis of the tip vortex, Figure 1. The position of the tip vortex axis was localized by searching, first, the minimum of the pressure in each plane normal to the free stream velocity, and, then, by searching the zero of the tangential velocity along a vertical line very close to the minimum pressure location.
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From page 192... ...
Then, the pressure distribution on a plane normal to the free stream velocity situated at one chord downstream the tip is set as a boundary condition on the exit plane (at two and a half chord from the tip)
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From page 193... ...
Then, the axial and tangential velocities are determined along the y axis for positions within 8 mm from the vortex center. The exact position of the vortex center which corresponds to the zero tangential velocity is then evaluated.
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From page 194... ...
~ ) 0 ~ 411^ A ~ ~ O O O O -ex pen mental r mm 1 It's therefore obvious that, even in this very near region, the numerical results predict a core radius larger and a maximum tangential velocity lower than the experimental ones, thus an over diffused tip vortex.
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From page 195... ...
Position downstream the tip: x/C=0.5. ~ ha ~ ~ ~ | o | UD, l~ninar | _ 0 UD, k - £ _ UD, RNG r mm 1 1' In Figure 8 we have plotted the core radius divided by the thickness of the turbulent boundary layer, 6, computed as for a flat plate of length equal to the midspan chord, C, 6' 037C(V~c)
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From page 196... ...
We are still far from the experimental predictions of the core radius and improving the mesh refinement seems to be of limited value to fill the remaining gap. Let us see next how other changes improve the results.
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From page 197... ...
It was expected that the non-linear k-£ model would improve the results and decrease considerably the vortex core dimension. The obtained predictions may be due to the lack of accuracy of the UD scheme, which has to be replaced with a second-order discretization scheme.
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From page 198... ...
The tangential velocity profiles obtained at x/C=0. 1 and x/C=0.5 with both exit boundary conditions are shown on Figures 17 and 18.
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From page 199... ...
The static pressure profiles through the tip vortex, shown on Figure 23, are very slightly disturbed by this change of the condition at the exit. This is not surprising taking into account the changes observed in the velocity profiles.
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From page 200... ...
the higher order discretization scheme strongly decreases the local core radius as compared to the first order scheme; , the exit pressure condition has a very slight effect on the tangential velocity distribution in the core, but a slightly larger one on the axial velocity distribution. The numerical computation results have allowed to show that the methodology used by the ACC partners to evaluate the pressure on the vortex core using the experimental tangential velocity profile obtained along a line parallel to the foil span seems to be fully justified, even if the absolute values are not in close agreement.
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From page 201... ...
, , [12] Dacles-Mariani J., Rogers S., Kwak D., Zilliac G., Chow J., "A computational study of wingtip vortex flow field", AIAA 24th Fluid Dynamics Conference, July 1993, Orlando.
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From page 202... ...
DISCUSSION M Billet Applied Research Laboratory, USA The scientific program of the "Action Concertee Cavitation" into the physics of tip vortices roll-up has provided significant insight to the cavitation and propeller design communities.
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From page 203... ...
and our work. In our study, using 2.5 million grid points, the velocity profiles compare well with measured data, but the static pressure is overpredicted only in the viscous region of He vortex core.
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From page 204... ...
This methodology has permitted precise determination of the position of the tip vortex trajectory. Convection scheme: The use of a high order discretization scheme improves the prediction of the local tip vortex core radius but has a very slight effect on Me prediction of the local vortex intensity.
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From page 205... ...
[2] Le Guen A., Ph'D thesis, Separation of turbulence and wandering effects on Laser Doppler Velocime~y analysis of a tip vortex flow, 1998.
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From page 206... ...
ABSTRACT A potential based panel method for the prediction of unsteady sheet cavitation on hydrofoils or propeller blades, is extended to include (a) the effects of a general cross-section tunnel, (b)
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From page 207... ...
= o (1) where ~ is the perturbation potential defined as follows; where ~ is the total velocity vector and UOO the inflow velocity vector.
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From page 208... ...
2 oo · The Kutta condition: the velocity at the trailing edge of the hydrofoil is finite.
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From page 209... ...
r 5 1 0.4 02 C, O . -02 Pressure Convergence (y=0.04)
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From page 210... ...
The predicted cavity planform when the tunnel ejects are included appears to be very close to the observed, shown in Figure 10. However, there are flow phenomena at the root of the blade (re-entrant jet, cloud cavitation at the trailing edge)
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From page 211... ...
. _'; -~ Figure 10: Photograph of the cavitating 4990 hydrofoil inside the DTMB 36inch cavitation tunnel; ~ = 0° = 0.62.
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From page 212... ...
Cavity shape of N4990 Hydrofoil Condition: detachment point=1.25% of chord ~ = 0.62,- a = 1.3 Condition: detachment point=0.6% of chord Condition: Leading edge detachment o= 0.62, a= 1.3 2-D Cavity shape of N4990 Hydrofoil Condition: detachment point=1.25% of chord ~ = 0.62, a = 1.3 1.25 0.75 0.5 0.25 o Condition: detachment point=0.6% of chord is = 0.62, a = 1.3 125 0.75 0.5 0.25 -0.5 0 0.5 1 X .. ~ ,l....' Condition: Leading edge detachment ~ = 0.62, a = 1.3 v-',,, , ~0.5 0 0.5 1 Figure 11: Effect of the cavity detachment location (kept at the same percentage of the local chord at different sections along the span)
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From page 213... ...
These examples show that there is clearly a need for the correct modeling of face cavitation in propeller design. Like back cavitation, face cavitation is not necessarily going to detach at the leading edge.
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From page 214... ...
Even in its present condition, equation (17) does not include the extrapolation terms, namely To at the cavity leading edge, and the source and dipole strength extrapolations for the split panel.
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From page 215... ...
Since the cavities predicted for mid-chord cavitation are so thin, it is dif Figure 17: Wetted pressure distribution on hydrofoil with camber. 50x10 panels.
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From page 216... ...
Ordinate is panel number from leading edge. Abscissa is strip number.
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From page 217... ...
This may be due to a better resolution of the blade near the hub. In general, propeller blades are thicker near the hub.
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From page 218... ...
The surface of the tip vortex cavity will be determined from applying the kinematic boundary condition on the cavity surface. In the present work we have completed the development of a method for determining the cavity shape away from the trailing edge.
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From page 219... ...
4 Conclusions A panel method for the prediction of the unsteady sheet cavitation on hydrofoils or propeller blades was extended to include: · effects of tunnel walls. The effects were found to be critical in predicting the correct cavity shape observed in experiments.
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From page 220... ...
V/Vma2: at section A-A of the "solid body" tip vortex. The panels representing the bulb and the tip vortex cavity are shown at the top.
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From page 221... ...
Cavitation performance evaluation of naval surface ship propellers with standard and advanced blade sections. In Twentieth Symposium on Naval EIydrodynamics, pages 101-116, University of California, Santa Barbara, August 1994.
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From page 222... ...
The flow field around the propeller blades at the two different sizes were compared which allowed the effects of scale to be investigated. Two modern skewed 5 blade propellers were then investigated to see whether or not these propellers exhibited any significant scale effects.
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From page 223... ...
This method uses global flow parameters giving good overall predictions of total losses. 3 Validation using a 3 Blade Propeller Model propeller DTRC4119 was chosen as part of the validation exercise of the code since extensive laser velocity measurements have been made around this propeller (Jessup 1989)
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From page 224... ...
The accuracy of the RAN S code predicted thrust slowly deteriorates with reduced advance coefficient. As with the model experiments in the Cavitation Tunnel the choice of axial velocity for use in the definition of J is not clear cut for the predictive results.
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From page 225... ...
in the case of the numerical predictions this radial perturbation will not be present, but the effect of a larger boundary layer due to the long cylindrical hub can be seen in the axial velocity predictions. These differences are generally small but can still have an effect on the convected portion of the flow.
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From page 226... ...
0.7 0.6 0.5 0.4 C I ,c ~of Q-O° OO-~-O a 0 0.0 ~=> -02 . 2 0.3 0.4 0 5 0.6 0.7 O.B 0 9 1.O1 1 r/R ,~x- ~,0, 0 MODEL TEST LDV c NUMERICAL PPtEDICTlO}JS Vt Figure 7 Mean Wake Velocities X/C=0.329 The tangential velocity at X/R=0.329 shows generally close agreement between the predicted and measured values, except in the tip region.
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From page 227... ...
At a radius of r/R=0.7, the depth and width of the axial velocity wake shows close agreement between the predicted and measured values. The predicted values show a local peak in the axial velocity on the suction side of the blade wake that is not seen in the measured data.
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From page 228... ...
4.2 Static Pressure Predictions The blade surface static pressure predictions for the suction side of the propeller blade for the two different scaled propellers are given in Figure 15. The colour contours are of-Cp and the higher the value of 228
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From page 229... ...
.. ~ Figure 15 DTRC4119 Suction Face Static Pressure Predictions Figure 16 DT~C4119 Transver .
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From page 230... ...
As the flow developed downstream of the propeller, so the full scale propeller had the higher and lower radial velocities and this is associated with the full scale propeller having the stronger tip vortex flow. 5 Scale Effects on a 5 Blade Propeller The two model propellers used in this section are typical of the modern 5 blade propellers of the controllable pitch propellers (CPP)
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From page 231... ...
Model Scale Full Scale · ~ Figure 18 DTRC4119 Transverse Section X/D=O.1 Radial Velocity Predictions 11_ i_ 1_ Figure 22 C659 Suction Face Static Pressure Predictions Figure 23 C660 Suction Face Static Pressure Predictions 231 _.
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From page 232... ...
5.3 Static Pressure Predictions Blade surface static pressure predictions have been made at one advance coefficient of J=0.8. It should be noted that at this off-design advance coefficient neither of the two skewed propellers showed any significant scale effect on the propulsion predictions, in contrast with the 3 blade propeller.
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From page 233... ...
The scale effects were most noticeable, for the skewed propeller C660, on the blade surface static pressure predictions. Also predicted was the connation of a boundary layer separation near the trailing edge of the Fill scale propeller that was not present at the model scale.
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From page 234... ...
V' Tangential Velocity Component (m/s) DISCUSSION Blade Section Relative Velocity V,,, = ~ [(V0~2+~27rnrO7~2]
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From page 235... ...
A milestone in the use of CFD for design problems will be reached when the user has sufficient confidence in the calculations to make critical decisions based on those solutions, even when results may not pass all tests of intuition. Can the author reflect further on his experience using RANS in propeller design, and for instance, were your conclusions on scale effects on thrust used to impact changes to full scale propulsion hardware?
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From page 236... ...
Does he eventually expect to include cavitation and the change of state from water to vapour in his work? A curious finding is that whereas the 3 bladed straight propeller behaves as expected re scale effect, the 5 bladed skewed propeller does not, as the predicted efficiency of the full scale propeller is slightly less than that of the model.
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From page 237... ...
The results for the skewed propeller win the separation show that significant unexpected scale effect can change the performance of skewed propellers; the propeller designer must be aware of this to prevent poor full scale performance.
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From page 238... ...
Uto. Pressure and Blade Surface Viscous Forces The propulsion coefficients are made up from two components, one pressure, the over wall shear stress.
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Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.