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Non-uniform inlet flow has come back into focus of research during the last years due to the need of increasing the operational range of airborne engines. Higher climbing rates for lower noise pollution at airports as well as boundary layer ingesting inlet designs lead to the demand of inlet distortion resistant engines and compressors, in particular. To fulfill this design task, a deep understanding of the dominant flow physics of the distortion transport through the compressor as well as the influence of the compressor on the upstream flow field is needed. This paper starts with the transport of a circumferential total pressure distortion through a compressor stage. Using numerical results, previously validated by experimental data, a phenomenological approach for the transport is presented. The most important finding is the essential role of the different propagation speeds of the static pressure distortion and the inflow velocity distortion and its decoupling. A static pressure and an inflow velocity distortion are present for all kinds of total pressure distortions caused by the upstream flow field redistribution of the compressor. This decoupling causes not only a significant circumferential increase of the distorted sector but also a strong variation of the distortion magnitude downstream of the compressor stage. All relevant phenomena are present in the phenomenological approach as well as in the numerical and the referred experimental results. Inlet distortions result in a decrease of stability margin [1],[2]. The crucial area for the stability of most modern transonic compressors is the tip region; therefore, the tip region was under particular investigation. The numerical results show that the flow field in the distorted area is shifted toward the stall line. The shock system and the tip clearance vortex behave similar to the results near stall with uniform inflow. No local stall can be observed, although the local operating points within the distorted sector travel beyond the stall line of the compressor map with uniform inflow. Finally, a new analytical approach for the critical distortion angle is presented. The main finding is the circumferential extent has to be big enough to separate the zones of decoupled distortion quantities.

This paper deals with the numerical flow-simulation of a transonic compressor stage, which has been investigated for baseline as well as distorted inflow conditions at the Institute of Propulsion Technology of the DLR in Cologne (Dunker [1] and Lecht [2]). The inlet distortions are generated in the experiment upstream of the compressor stage by non-rotating steel bars, while in the numerical calculations the total pressure and inflow angle distribution measured downstream of the bars are taken as inflow boundary conditions. The circumferential extent of the generated total pressure and inflow angle distortion is 120 degrees. Numerical simulations were performed for uniform inflow conditions at 85% and 100% rotational speed. For disturbed inflow conditions, a full-annulus calculation has been carried out for an operational point at peak efficiency. The object of the investigations is to validate the flow solver for compressor flow with distorted inflow. The results from time-averaged numerical and experimental data are compared extensively. The experimental trends are qualitativly and in the most part also quantitativly well reproduced in the numerical calculations.

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In order to meet the targets set out in the Paris climate agreement of 2015, the energy sector needs to be restructured. In Germany for example the goal is to move out of both nuclear and coal-fired power. In order to fulfil more demanding energy requests alternative sources of energy must be found and made available. One component is the usage of Waste Heat Recovery. This paper deals with the evaluation simulation of an Elektra turbine, which concept is a velocity compounded radial re-entry single wheel turbine. Based on the first turbine design, multiple simulations were carried out in order to maximize the efficiency. With these simulations, optimization opportunities are described and identified. The paper concludes with a comparison of the results achieved by numerical simulation and on the experimental test bench. The main focus for this paper is to analyze the actual flow phenomena to identify possibilities for further improvements. All simulations were calculated with the commercial software FINETM/TURBO 15.1.