Finite Difference Calculation of Cavitating Flow around a Finite Span Hydrofoil

Abstract

Characteristics of cavitating flow around a finite span hydrofoil are studied by a finite difference computation using Bubble Two-phase Flow model. The flow with Reynolds number of 103 is calculated at the angle of attack of 10 deg. on a NACA 0012 hydrofoil with elliptic planform of aspect ratio of 3.
The mechanisms of the cavitating flow, particularly the relationships between the vortex system around the hydrofoil and the cavitation, are investigated with the use of the high spatial resolution in the numerical calculation although the Reynolds number is low because of the computation time and memory capacity problem. The discussions on the calculated results give the following results :
(1) Since the planform of the hydrofoil is elliptic, the ratio of cavity length to chord length becomes almost constant along the span when the cavity is small. But as the cavity grows, the tip region begins to generate larger cavity. The reason for this is that the tip vortex expands the separating flow region on the suction side of the hydrofoil near the tip.
(2) The larger cavity weakens the tip vortex because of the reduction of the lift force and/or the diffusion of flow due to cavity. The diffusion due to cavity also increases the width of its wake.
(3) The above calculated results agrees qualitatively with the existing experimental results. It can be said that even the present calculation with low Reynolds number has clarified many of the mechanisms of cavitating flow around a finite span hydrofoil.