The Influence Of Dynamic Mesh Updating Method On Accuracy Of Numerical Computation

Computational Fluid Dynamics(CFD)has been widely used as a basic research and design method in aviation,aerospace,ship engineering and many other areas,in which the practical engineering problems are very complex,often involving the movement of single object or multi-object inter movement phenomenon.The numerical solution of such problems involving moving boundaries has became a hot research topic in modern computational fluid mechanics.The moving mesh method can be adapted to simulate the real situation of the boundary movement,and has been widely used in solving such practical problems.However,in the process of simulating actual conditions by using moving mesh method,the update grid usually reach a higher distortion level and calculation results usually possess a bad stability.To conquer the above problems and improve the quality of the update mesh,this paper discussed different moving mesh updating methods,and compared them in several numerical examples to verify the effect of mesh updating methods on accuracy and convergence of numerical calculation.The detail research is summarized as follows:First,the motion of a circle in the two-dimensional flow field is taken into computing.Six kinds of moving mesh updating methods are applied in the computation and their results are compared from three aspects:mesh update distortion degree,calculation time and hydrodynamic calculation accuracy.Finally the calculation results of three methods among them are relatively good in the two-dimensional flow field-spring method with a small spring constant factor,diffusion method based on boundary distance and diffusion method based on cell volume.Second,the movement in straight line of AUV is studied.Compared with the two-dimensional flow field,the three-dimensional flow field is more complex,in which the number of grid nodes increases sharply and the updating process becomes much slower.In this application,three kinds of grid updating methods which are validated in two-dimensional flow field,are used to calculate.By comparison,it is found that the calculation time of spring method is less,while the result used with diffusion based on the boundary distance method is better.Finally,the calculation of the self propulsion process of an AUV using moving mesh is carried out.In the course of self propulsion,it is necessary to consider the process of thrust generation by propeller rotation,which increases the difficulty of grid updating and hydrodynamic calculation,where six degree of freedoms(SDOF)is calculated by using spring method and diffusion method to simulate its acceleration from zero to a constant speed.The results show that the spring method is still fast in calculation,its resistance fluctuates greatly.Although the diffusion method based on the boundary distance is still relatively slower,the stability of the result is much better.