A Proposal for Improving Cavitation Model

Abstract

Some issues about cavitation are discussed for improving cavitation model for CFD. Concerning the relatively large cavitation bubbles those are often observed in experiments, combination of grid scale bubbles：GSB and sub grid scale bubble model：SGSB are proposed. GSB shall be computed by using the computational scheme for free surface with phase change model. SGSB can be computed with conventional cavitation model. Breakup of GSB generates SGSB, and coalescence of SGSB makes GSB. Upper limit of void fraction of SGSB is estimated in the range of five or ten percent from the simple speculation of the structure of packed spheres. Two types of cavitation bubble inception model are also discussed. To verify the proposed concepts of cavitation model, a traveling bubble over a hydrofoil is computed by using free surface flow scheme of VOF approach. Computed results show qualitatively similar characteristics of bubble dynamics to those in experimental results.