Simulating Unsteady Turbomachinery Flows on Unstructured Meshes Which Adapt Both in Time and Space

Abstract

The objective of this paper is to stimulate study of application of solution-adaptive methods to unsteady turbomachinery flows. First, the extension of an existing 3D unstructured mesh Navier-Stokes solver to cover unsteady flows is described. Then the basic method is validated for the classic case of vortex shedding from a cylinder. Next, the modification of the data structures of the algorithm into a strict parent-child hierarchy are described; this enables refinement and derefinement to take place sufficiently economically for mesh adaption to take place over time scales significantly smaller than the characteristic time scales of the unsteady flow. Application to the vortex shedding from a cylinder showed that the unsteady solution obtained on an adaptively (locally) refined mesh was essentially the same as that from a reference, uniformly (globally) refined mesh, both simulations predicting a Strouhal number of 0.20. By contrast, a basic unrefined mesh predicted a small but systematically lower shedding frequency and Strouhal number of 0.17. Finally, both Euler and Navier-Stokes solutions are obtained for the standard problem of the interaction of stator wakes with the following rotor row. The adaptively refined solution displays very good control over the wake resolution and minimises false smoothing of the wake structures as they propagate. Good qualitative agreement is observed in comparison with other published numerical simulations. It is concluded that the application of unstructured mesh methods which adapt both in time and space to unsteady flow problems is both viable and promising.