A surface extraction method of flow feature for shock-fitting scheme

A new surface extraction method named source-rays method is proposed to locate and shape initial shock wave surface for shock-fitting algorithms. In this method, the flow field data acquired by the shock-capturing schemes are used as the observed data, and the grid nodes with the features such as shock waves and contact discontinuities are obtained as a discrete point set according to the parameters of density, pressure and others. The discrete point set is finally assembled into a continuous smooth surface by being segmented into several subsets for fragment fitting. Based on the two-dimensional method, this identification algorithm is extended to three-dimensional application by introducing a unit sphere model. The discrete points are fitted to a series of triangular patches with determined connection relationship by a unit sphere, and a smooth continuous surface can be assembled. The results show that the feature surface (shock wave and contact discontinuity) obtained by the source-rays method coincides with the discontinuous distribution in the flow field calculated by the shock-capturing schemes. By using the extracted feature surface as the initial shock wave surface, the convergence solution can be quickly obtained in shock-fitting algorithm. In addition, this method can also be used in the adaptive mesh refinement procedure. According to different flow parameters, the spatial surfaces of the corresponding flow field structures can be obtained. Based on these surfaces, the mesh grid can be locally refined. This flow field feature surface extraction method has the advantage of grid scale set arbitrarily for mesh adaptation procedure.