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

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

Modern gas turbines have to meet the highest requirements in terms of environmental compatibility and economic efficiency. Reducing specific fuel consumption is of central importance and can be achieved by increasing the pressure build-up per stage. Another possibility is to reduce the number of blades within a stage. Both approaches increase the aerodynamic load on the compressor blades.

Conventional compressor blades are thus pushed to the limit. Due to the large positive pressure gradient in the rear area of the blade, the boundary layer grows strongly, the flow can no longer follow the profile contour and detaches. A high increase in losses and a collapse of the pressure build-up are the result. Tandem blades can provide a remedy here. On tandem blades, the flow at the rear blade is re-energised by the resulting slot flow and a new, thinner boundary layer is formed.

The investigations deal specifically with tandem blades with tip clearance. The flow through the gap rolls up into a vortex which has a large influence on the losses and the stability of the passage flow. If the angle of attack is too high, tip clearance vortex breakdown can occur. This leads to blockage of the flow passage, which can cause the development of stall cells and a premature reaching of the surge line.

On tandem blades, there is the additional complexity of having a system of at least two vortices in the gap area, as each blade has its own tip clearance vortex. With this project, an understanding of the complex interaction behavior of the wall gap vortex system on a tandem compressor blade is being achieved. The main focus is on the question of whether the tip clearance vortices burst individually or together and what influence the existence of one vortex has on the behaviur of the other.

Person of contact: M.Sc. Liesbeth Konrath

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An Analysis of the Secondary Flow Around a Tandem Blade Under the Presence of a Tip Gap in a High-Speed Linear Compressor Cascade
L. Konrath, D. Peitsch, A. Heinrich
Proceedings of the ASME Turbo Expo 2020:
Turbine Technical Conference and Exposition
Virtual, Online, September 21–25 2020, GT2020-14175
DOI: 10.1115/GT2020-14175

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