The application of implicit time iterative method to parallel computing is a hot issue in CFD research. It is found that LU-SGS scheme is sensitive to partition boundary in the rotating reference frame, and thus the problem of computational divergence is encountered in parallel calculation of the hovering rotor. To solve this problem, three implicit time iterative schemes based on LU decomposition (namely LU-SGS, DP-LUR, and HLU-SGS) are studied comparatively, and a rotating grid example is designed to test these calculation methods. Results show that as the LU-SGS scheme uses a simplified method to deal with boundary cells, numerical errors increases in proportion to the rotating speed and accumulation of errors leads to divergence of calculation. DP-LUR and HLU-SGS schemes can effectively eliminate the influence of partition boundaries by using Jacobian iterations in boundary cells, and both keep the scheme stable with large CFL number. HLU-SGS inherits the high efficiency of LU-SGS scheme. Parallel computations of the Caradonna-Tung rotor are then carried out by the three schemes, where coarse and fine background meshes are studied comparatively. Although complex partition boundaries are produced for parallel computation, fully converged results of the aerodynamic force and wake are obtained. The computation results are in good agreement with experimental data, showing that current implicit time stepping methods are applicable for parallel computation in rotating reference frame, and can be furtherly extended to other large scale parallel computations.
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