The interaction of the tip clearance vortex system of tandem blades in a high-speed linear cascade

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The aim of this project is to contribute to the understanding of the tip clearance vortex system of tandem blades. The necessarily existing clearances between rotating and stationary elements in turbomachinery cause significant losses. Conventional compressor blades feature a single tip clearance vortex, which has a majorinfluence on flow losses and stability. In contrast to that, tandem blades develop a system of at least two vortices, which result due to tip clearance vortices forming on each, individual tandem blade. In this project a detailed analysis of the flow field in the tip clearance region of tandem blades is planned. Experimental investigations will be conducted in a high-speed linear compressor cascade. The first point of focus lies on theanalysis of the interaction of the two tandem tip clearance vortices with the flow field close to the side wall.The phenomenon of vortex break down (VBD) - known from tip clearance vortices on conventional blades - shall be investigated in its occurance on tandem blades. Previous investigations have revealed an operating point in which most probably, only the front tip clearance vortex experiences VBD. Instationary wall pressure measurments shall be done to confirm this and to allow for a more detailed understanding. Following, it willbe analyzed whether an operating point at higher incidences can be identified at which both tip clearance vortices are showing VBD and how this impinges on the flow field and its associated losses. In the next step, configurations will be analyzed in which only the tandem front or rear blade exhibits a tip clearance. Thus, a vortex’ behavior without the presence and influence of the other vortex can be assessed. The results willshow if flow phenomena (such as the individual point of VBD) are shifted towards different incidences by the mutual influence. Furthermore, the loss sources and loss development are investigated. The results shall reveal whether certain losses result from the front tip clearance vortex, the rear one or the interaction of the two of them. The experiments are conducted using instationary wall pressure measurements and by the application of a novel surface fence probe, which is used to determine the wall shear stresses.