Abstracts - KTH Mechanics

176
Modeling Cavitation on a Wing Section using LES
T. Persson a, N. Berchiche a, G. Bark a, N. Wikström b and C. Fureby a,b
Cavitation can occur in a wide range of liquid flows, especially in marine
applications e.g. around rudders and propellers and consequently cavitation research is
a very important topic for the marine industry. To enable modelling of the complex
behaviour of cavitating flow, time accurate, high resolution simulation of a two phase
flow problem with mass transfer is required. Presently the flow dynamics is captured
by employing Large Eddy Simulation1 (LES) of the incompressible flow equations,
whereas water and vapour is separated using an interface capturing two phase model.
The mass transfer model used is based on the work by Kunz et al. 2. In this model
proportionality between the liquid volume fraction and the amount by which the
pressure is below the vapour pressure is used to model the transformation from liquid
to vapour. The transformation of vapour to liquid is modelled using a simplified form
of the Ginzburg-Landau potential.
The aim of this ongoing work is to study the possibility to simulate early and large
scale developments that by experimental studies3 are confirmed to result in cavitation
erosion.
The proposed model is tested on the flow around a NACA0015 wing profile at 10o angle of attack. Two flow conditions are tested, cavitation number 0.
69 and
1.
07 , giving different cavitation behaviour on the suction side of the wing. At
0.
69 a thick cavity is shed from the main sheet and a stable tip vortex cavity is
present, see figure 1a. At 1.
07 a thinner sheet cavity, behaving differently, is
located near the leading edge of the wing and only a very short tip vortex cavity is
present. The instantaneous pressure coefficient for 1.
07 given at z/L=0.59, where
L is the length of wing section and z=0 is at the tip of the wing, is shown in figure 1b.
a
Chalmers, Shipping and Marine Technology, SE-412 96 Göteborg, Sweden.
b
FOI, Div . of Weapons & Protection, Warheads & Propulsion, SE-147 25 Tumba, Sweden.
1 Sagaut P. (2001) Springer Verlag.
2 R. Kunz et al. (1997) 14th AIAA CFD Conference, Norfolk, June, 1999
3 Berchiche et al. (2003), 5th Int. symp. on Cav., Nov. 1-4, 2003, Osaka, Japan
(a) (b)
Figure 1: (a) Isosurface of the instantaneous volume fraction at 0.
69 . (b)
Instantaneous pressure coefficient on the surface of the wing section at 1.
07 .