Effects of Efficiency Techniques on Accuracy of Dynamic-Overlapped Grids for Unsteady Flows

Abstract

There is a strong need for advancements to compute unsteady flows involving moving boundaries and bodies. Currently, there appear to be two dynamic approaches and their variants proposed for this problem: unstructured and domain decomposition methods. The present objective was to further explore the overlapped grids when it was enhanced with several enabling and efficiency techniques. Their effect on the accuracy was studied primarily from a qualitative point of view. Unsteady Euler equations were solved by a characteristic-based alternating-direction-implicit scheme on overlapped subdomains capable of moving with respect to each other. Initially, the errors due to discretization, Courant number, and interpolations, were studied by solving the Riemann problem and comparing with its exact solution. It was concluded, that a second- or higher-order method, temporally and spatially, was needed even in the dynamic interpolation regions. Secondly, the effects of intermediate grids and diagonal inversions were demonstrated by simulating the 2-D flowfield history of a store separating from a wing section along a prescribed trajectory. For computational efficiency, using approximate diagonal inversions for the discrete equations produced less accurate but acceptable results. However, to ease the grid generation, overlaying an intermediate subdomain in a region of high flow gradients had significant impact on the accuracy.