Unsteady secondary flow in axial turbines

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The blades and vanes in turbomachinery, moving relatively to each other, aerodynamically interact because of the viscous wakes and the potential effects of the blades. Near the endwalls the influence of the endwall boundary layers and secondary flow phenomena additionally superimpose. Due to the aerodynamic interaction of the blade rows the secondary flow patterns are periodically unsteady. The secondary losses are a significant part of the overall losses of the blade row and the whole engine.The project Unsteady secondary flow in axial turbines is part of the joint project Unsteady secondary flow effects in compressor und turbine blade rows. Main focuses of this joint project are fundamental experimental und numerical investigations in compressor and turbine cascades to detect and describe the significant secondary flow effects. The influence of systematic parameter variations on the unsteady behavior of secondary flow effects and loss generation will be investigated. With these investigations the potential for improving the performance of turbomachinery components using advantageous secondary flow effects will be identified.Aim of the project Unsteady secondary flow in axial turbines is to contribute to an improved physical understanding of unsteady secondary flow effects in the blade rows of axial turbines. Fundamental experimental investigations will show, to what extent the periodical unsteady wakes influence the secondary flows and the loss generation in turbine blade and vane rows. The experiments will be performed in a low-speed axial turbine, using two different builds. For turbine build 1 the periodical unsteady wakes are generated with rotating bars. The influence of the bar wakes ion the secondary flow field and the losses in a subsequent stator will be investigated in detail. For turbine build 2 instead of the rotating bars a turbine rotor blade row will be used. Focuses of these investigations are the influence of real rotor wakes on the secondary flows in the stator as well as additional influences due to the rotating hub. The experiments are supplemented with numerical investigations of the project partners.