Recent German Research on Periodical Unsteady Flow in Turbomachinery

Abstract

The main source of flow unsteadiness in turbomachinery is the aerodynamical interaction of the rotor and stator blade rows. The blades and vanes, moving relatively to each other, interact because of the viscous wakes and the potential effects of the blades. In addition, the wakes and potential effects superimpose with other flow patterns, for instance the tip clearance vortices and other secondary flow phenomena. Furthermore in transonic compressors the interaction of wakes and shocks plays an important role. As a result, the real flow field is highly periodically unsteady and very complex, especially in multistage turbomachinery. Although this fact has received increasing attention within recent years, blade row interactions effects are not yet typically addressed in current design systems of turbomachinery. Actually, there is a requirement of the ability of modern design methods to predict unsteady flow features. With increasing aerodynamic loading of the blades and higher Mach numbers the consideration of rotor-stator-interactions gains in importance. It is therefore one of the challenges of the present and future design of compressors and turbines to include beneficial unsteady effects to improve the engine parameters. This requires a detailed physical understanding of the unsteady flow field and the resulting effects on the performance and flow stability. In 2000 the joint research program "Periodical Unsteady Flow in Turbomachinery" was initiated. Partners of this project are five research groups from four german universities:

Near-Wall Flow in Turbomachinery Cascades—Results of a German Collaborative Project

“…While in current design processes the flow is mostly considered in its temporal average [11], the real flow in axial compressors and turbines is strongly unsteady, with turbulence and periodic contributions resulting from the aerodynamic interaction of the blade rows moving relative to each other [12][13][14][15]. It exhibits high complexity due to the inner and outer sidewalls and the effects generated by rotation.…”