In this paper numerical study of cavity over hydrofoils is considered by using boundary element method based on potential flow. For this purpose hydrofoil and cavity surface are approximated by panels. Then sources and doublets are distributed over these surfaces. In this method the length of cavity is assumed constant. A set of equations are obtained by applying boundary conditions over the hydrofoil and cavity surface with closing cavity condition, which they are solved together. An important advantage of this method is getting the answer in a short period of time along with low cost computations. Also, there is a good agreement between numerical and experimental results that shows the accuracy of this method.

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