Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
Currently Skimming:
Prediction of Unsteady Performance of Marine Propellers with Cavitation Using Surface-Panel Method
Prediction of Unsteady Performance of Marine Propellers with Cavitation Using Surface-Panel Method
Pages 913-929
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 913... ...
Abstract This paper describes a low order potential-based panel method formulated for the prediction of the unsteady performance of a cavitating marine propeller that operates behind a ship. The method employs normal dipoles and sources distributed on the blade, hub and wake surfaces to represent the potential flow around the cavitating propeller.
|
From page 914... ...
Finally we predict the cavity behavior around the blades of two marine propeller operating either in screen-generated wake or in wake generated behind a ship model. Our predictions compares fairly well with the cavitation patterns observed at cavitation tunnels.
|
From page 915... ...
915 Ffom the Green's theorem, we may derive an expression for the potential in the flow field by distributing the normal dipoles and sources on the body and wake surfaces to deal with the cavity flow problem. The sources on the cavitating portion of boundary surfaces will serve as a normal flux generator, which may be integrated in the strenmwise direction to form the cavity shape, in a similar manner as in the thickness problem of the thin wing theory.
|
From page 916... ...
4.l Discretization of propeller blades and wake For numerical computation, the propeller and cavity surfaces are replaced by a set of non-planar quadrilateral panels as shown in Figure 4. The flow near the leading edge and tip of the blades varies more rapidly than any other region around the blade, and hence the surface panel size should be smaller in this region.
|
From page 917... ...
on an arbitrary point with index j and the cavity detachment point~cdp) at the blade leading edge, we obtain the following: (For convenience, all physical variables are to be nondimensionalized; that is, the speed by Vs' the length by R and the velocity potential by Rigs We will use the same symbols after nondimensionalization.)
|
From page 918... ...
dipoles on trailing wake, SW The strength and the position of the trailing dipoles in wake should be determined in principle by satisfying the kinematic and dynamic boundary conditions on the wake surface. In linear theory, the trailing vortices shed downstream with the speed of the oncoming uniform flow, while keeping the strength obtained when leaving the trailing edge of the blade.
|
From page 919... ...
N`d,1' VNC,IP and other known quantities. Applying at the same time the numerical Kutta condition and also rearranging all known terms in the right hand side, we obtain for the i-th control point the final form for the partially cavitating flow as follows: No t: ~ No I, ~jl5Jij + (N..,,,, ~ i3ij, + (ONP —°1)
|
From page 920... ...
. In the present partially cavitating flow, the lower surface coincides with the blade surface.
|
From page 921... ...
For the partially cavitating flow, by applying (32) to the control points on both SB ET and SC, together with the closure condition equation (43)
|
From page 922... ...
Figure 20 shows the nominal velocity contour simulated at the KRISO cavitation tunnel for a 4400TEU conThe time history of the cavitating pattern is shown at selected angular positions in Figure 21 with the cavitation number an = 2.04, the Froude number Fit = 2.072 and the advance coefficient JA = 0.7642. Experimental observations of the cavity extent at the KRISO cavitation tunnel are shown in Figure 22.
|
From page 923... ...
[3] Kinnas, S.A., "Leading edge correction to the linear theory of partially cavitating hydrofoils," J
|
From page 924... ...
· . 30 35 Figure 6: Lift coefficient variation with time for a partially cavitating hydrofoil in heave aor8 norm 0.012 ,¢ To' n ode 0~76 Figure 4: Quadrilateral representation of a propeller Figure 7: Cavity volume variation with time for a blade partially cavitating hydrofoil in heave 924
|
From page 925... ...
an o.o \ / lye Figure 11: Comparison of cavity extent between predictions Slid observations for DTRC Propeller 4381 at JA = 0.7 with an = 1.92 1~ 2~0 2.5 an as t.0 1.5 `/C . Figure 9: Convergence characteristics of cavity extent with the number of panels distributed on a rectangular hydrofoil o.oso~ nix of nova Figure 12: Drawing of 6300 TEU Propeller 0.00 O.tO 020 030 X/C 1/~ y Figure 10: Cavity shape for a partially cavitating Figure 13: Iso-axial velocity (VA/VJ)
|
From page 926... ...
2.4868 0.0~ 0_~0 0.010 0 6 10 16 9, (I-) Figure 16: Cavity volume on the key blade versus blade angle for HSVA Propeller 926
|
From page 927... ...
contours of the Delb~Theta,6 deg. wake simulated at KRISO cavitation tunnel Figure 18: Comparison of cavity extents predicted with /~§p= 12 deg~top)
|
From page 928... ...
Vt ..' ,,-' ~ —'''1' 1 ~ 30 1 u"i Brie, - _~ ~ _~ me, ' 1 ' - 1 - ' 1 ' - i -- - 1 ~ _ L! Figure 21: Predicted cavity pattern for KP325 Propeller at JA = 0.7642 with CT71 = 2.040 find En = 2.072 -;,, f: t.33r ·~33~ t.w ..~ .~.
|
From page 929... ...
Has this been found to be sufficient for predicting He cavity shapes on the propeller, especially since they show that Heir predicted cavity shapes converge slowly with number of panels? It would be nice to include in their reply a convergence study win number of panels for one of the propellers for which they compare their results with measurements.
|
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.