Solution-adaptive structured-unstructured grid method for unsteady turbomachinery analysis. II - Results

Abstract

A solution-adapt ive method for the time-accurate analysis of two-dimension al flows in multistage turboma- chinery is presented. The method employs a hybrid structured-unstructured zonal grid topology in conjunction with appropriate modeling equations and solution techniques in each zone, thus combining the advantages of both structured and unstructured grid methods. An efficient and robust grid adaptation strategy is also used for the unstructured grid regions. The numerical methodology is presented in detail in Part I of this article. Results obtained using this method for different turbomachine flow configurations are presented in this article. The numerical results compare well with available experimental data and other structured grid based simulations. ART I of this article describes a hybrid-grid procedure for the analysis of unsteady turbomachinery flows that combines the advantages of both unstructured and structured grid methodologies. The method is implemented within the zonal framework of Ref. 1, which is generalized to include both structured and unstructured grid domains. The region in the immediate vicinity of the airfoils (inner region) is dis- cretized using structured grids, while the rest of the domain (outer region) is discretized using an unstructured triangular grid. In the viscous inner regions, the Navier-Stokes equations are solved using an implicit, third-order accurate, upwind- biased scheme. In the inviscid outer region, the Euler equa- tions are solved using either a central difference scheme or an upwind scheme that incorporates a linear reconstruction procedure. The solution in the outer unstructured region is advanced in time explicitly using the same time-step values as for the structured regions which are time-advanced in an implicit manner. An efficient and robust grid adaptation strat- egy with both grid refinement and coarsening capabilities is also used for the unstructured grid. For generality, three- dimensional effects of stream-tube contraction are also mod- eled. The present method is capable of treating multistage turbomachinery configurations. Part I of this article described the domain decomposition, grid generation, inner and outer grid solution procedures, grid adaptation strategy, and the various boundary conditions used. Results obtained using this method for different turbomachine flow configurations are presented in this article.