Discrete Vortex Method Simulations For The Hydrodynamic Performance Of Hydrofoils At High Reynolds Number

The hydrodynamic performance of the hydrofoil under high Reynolds number has always been a key factor considered in the design of high-performance ships.With researching deeply,the method of predicting the performance has developed from model tests to numerical simulations.Compared with mesh methods,the vortex method can obtain higher calculation accuracy with less cost.However,for non-zero attack angle hydrofoil,its accuracy is greatly reduced.Therefore,this dissertation will propose a new discrete vortex method,semideterministic and semi-random vortex method to handle this problem,which aims to improve the prediction accuracy for a non-zero attack angle hydrofoil without increasing the amount of calculation.This dissertation first proposes an improved discrete vortex method.Compared with the original algorithm,it can generate blobs strictly satisfying the vorticity conservation conditions;effectively prevent them from entering the object,and accurately and quickly predict their convection.After verification,this method can accurately calculate the performance of zero attack angle hydrofoil under high Reynolds numbers,with a low deviation of drag coefficient(within 5%).However,the new method cannot accurately predict the performance of a non-zero attack angle hydrofoil.This is because the algorithm uses random walking to approximate the diffusion,which makes boundary layer on the upper surface of the hydrofoil earlier separate,reducing the calculation accuracy.To solve the problem,this dissertation proposes a new vortex method,semi-deterministic and semi-random vortex method.In this method,the diffusion approximation method depends on the relative location of the blobs and the boundary layer separation point: if a blob’s location is before the separation point,use a deterministic walking method,called boundary layer reorganization method to approximate its diffusion;if not,use random walking.After verification,this new vortex method can accurately predict the performance of a non-zero attack angle hydrofoil,controlling deviation of lift coefficient within6%.Besides,the new vortex method is also more stable than the older.