Researching how initial value of internal iteration impacts on computational efficiency in unsteady flow solving

On the basis of the dual time stepping method in unsteady flow, we come up with a strategy to improve the efficiency in unsteady flow solving. By means of extrapolating the flow message of a few moments forward, we get the iterative initial value of the next moment to make it closer to the convergent solution and decrease the initial residual value of internal iteration, thus increasing the computational efficiency of unsteady flow. Taylor expand the convective term of flow field in time direction, then we design some kinds of extrapolation schemes. We use the solution of unsteady flow around circular cylinder to verify the computational efficiency of this method, and research on different initial value extrapolation schemes, spatial discretization schemes, and time steps and convergence criteria impacting on the efficiency of initial value extrapolation method. Researches show that based on the dual time stepping method, using the strategy of initial value extrapolation can improve the computational efficiency generally. Of which the alternate extrapolation strategy can doubled the efficiency generally. Compared with upwind scheme, the efficiency of this method increases more when using center scheme; all have obvious effects when using different time steps and convergence criteria.