A solution adaptive structured-unstructured grid procedure for unsteady flows
J. C. Tannehill
A solution adaptive hybrid grid method for the computation of two-dimensional, unsteady flows is presented. The method is capable of handling multiple component, complex geometries in relative motion, such as those encountered in turbomachinery analysis. The numerical approach uses a hybrid structured-unstructured zonal grid topology along with modeling equations and solution techniques that are most appropriate in the individual domains, thus combining the advantages of both structured and unstructured grid methods. The viscous flow region in the immediate vicinity of the airfoils is resolved using a third-order accurate, implicit, upwind solution of the Navier-Stokes equations on structured, O-type grids. Explicit solutions of the Euler equations are obtained in the rest of the domain that consists of an unstructured mesh made up of triangular cells. The use of both central- and upwind-differenced flux schemes is investigated for the unstructured domains. Methodologies for accurate, conservative transfer of information at the interface between the structured and unstructured domains as well as that between two unstructured grids in relative motion are developed. An efficient and robust solution adaptation strategy is developed which incorporates both refinement and de-refinement capabilities for the unstructured grid regions. Both time-averaged and time-resolved results are presented for test cases and are compared with available experimental data. The quality of the results obtained by the present method is comparable with those obtained by methods based on fully structured grids. Calculations performed using the solution adaptation capabilities are also presented.