Future trends in energy supply tackling environmental challenges, i.e. using P2G to compensate for the volatility of renewable energy sources, demand efficient gas turbines that quickly adapt to changing load requirements. The compressor as a crucial component is especially affected by this need of flexibility and tends to exhibit three-dimensional unsteady flow phenomena. As a result the necessity for investigation of high speed compressor aerodynamics and performance can be stated. This need is addressed by both, numerical examinations and experiments.The latter are objective of a new transonic compressor test rig (TCD2, see figure 1) at Technical University of Darmstadt, commissioned in 2018, that features high modularity and extensive instrumentation.In a first measurement campaign two different rotors, representative of the front stage of an industrial gas turbine were examined and compared regarding their performance data. The resulting data set also comprises 67 measurements where the compressor was throttled beyond its stability limit. The unsteady data acquisition during these maneuvers was performed by strain gauges in the rotor-fixed and by piezoresistive wall pressure transducers and blade tip timing sensors in the stator-fixed frame of reference. An evaluation of this data shows no stall precursors as observed at a similar test rig at the institute, instead a variety of phenomena occurs.In this report we give an overview of those different manifestations of stall with focus on classification and characterization. For this purpose, a detailed post-processing and data analysis are conducted providing information in terms of operating points, propagation speeds of disturbances, structural behavior of the rotor as well as position and fluctuation of the shock waves and wall pressure fields. Based on these methods, multiple phenomena can be distinguished, all arising in the same compressor:1) Steady rotating stall (SRS),2) Transient rotating stall (TRS), partially occurring as classic surge,3) Low-frequent planar acoustic waves, matching a natural frequency of the main duct (ACS),4) Autogenous compressor recovery and restabilization of the flow (REC),5) Rotating instabilities (RI) and6) Broadband disturbances (DIST).For these phenomena, the tendency of their occurrence is elaborated, depending on rotor speed, guide vane setting, throttle procedure, rotor and tip gap. A preliminary result is illustrated in figure 2. TRS and classic surge have already been described in a previous report by the authors and ACS will be subject to a more detailed investigation as well.This study provides a general overview of events occurring at the stability limit of a transonic compressor test rig. It therefore contains valuable information for both, CFD validation as well as future compressor design and operation.

Overview of Unsteady Phenomena Emerging in a Stalled 1.5-Stage Transonic Compressor

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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