Large eddy simulation of a sheet/cloud cavitation on a NACA0015 hydrofoil

A single fluid model of sheet/cloud cavitation is developed and applied to a NACA0015 hydrofoil. First, a cavity formation model is set up, based on a three-dimensional (313) non-cavitation model of Navier-Stokes equations with a large eddy simulation (LES) scheme for weakly compressible flows. A fifth-order polynomial curve is adopted to describe the relationship between density coefficient ratio and pressure coefficient when cavitation occurs. The Navier-Stokes equations including cavitation bubble clusters are solved using the finite-volume approach with time-marching scheme, and MacCormack's explicit-corrector scheme is adopted. Simulations are carried out in a 3D field acting on a hydrofoil NACA0015 at angles of attack 4 degrees, 8 degrees and 20 degrees, with cavitation numbers sigma= 1.0, 1.5 and 2.0, Re = 10(6), and a 360 x 63 x 29 meshing system. We study time-dependent sheet/cloud cavitation structures, caused by the interaction of viscous objects, such as vortices, and cavitation bubbles. At small angles of attack (4 degrees), the sheet cavity is relatively stable just by oscillating in size at the accumulation stage; at 8 degrees it has a tendency to break away from the upper foil section, with the cloud cavitation structure becoming apparent; at 20 degrees, the flow separates fully from the leading edge of the hydrofoil, and the vortex cavitation occurs. Comparisons with other studies, carried out mainly in the context of flow patterns on which prior experiments and simulations were done, demonstrate the power of our model. Overall, it can snapshot the collapse of cloud cavitation, and allow a study of flow patterns and their instabilities, such as "crescent-shaped regions." (c) 2005 Elsevier Inc. All rights reserved.