Speed Line Computation of a Transonic Compressor Stage With Unsteady CFD Methods

Abstract

The flow through a transonic compressor stage is dominated by unsteady effects such as shock propagation and wake shedding. An accurate prediction of the performance of a compressor, i.e. operating range and efficiency, may require the modeling of unsteady effects. Steady CFD methods cease to converge too early when the stall limit is approached. Efficient unsteady CFD methods such as the transient time-inclining (TI) method and the perturbation based non-linear harmonic (NLH) method perform better and are becoming increasingly popular in the industry. Both methods consider the actual blade count ratio for each passage while using a single passage model. The main objective of this paper is to explain these methods and benchmark their performance with respect to reliable near stall predictions. Computed compressor characteristics and blade row interaction effects of the Purdue Transonic Research Compressor are compared to measurement data. The stator row is found to be limited at the casing in all of the unsteady simulation results. This effect is also qualitatively predicted by steady results calculated at a lower back pressure level. The NLH method is significantly faster than the other transient methods and the TI method resolves more flow detail on identical meshes.