The flow field in a compressor is circumferentially nonuniform due to the wakes from upstream stators, the potential field from both upstream and downstream stators, and blade row interactions. Characterization of this nonuniform flow is of great importance since it can affect stage performance and blade forced response. Historically, experimental characterization of the circumferential flow variation is achieved by circumferentially traversing either a probe or the stator rows, which requires complex traverse mechanisms and is costly. In Part 1 of this publication, a novel method to reconstruct the compressor nonuniform circumferential flow using spatially under-sampled data points from a few probes instrumented at fixed circumferential locations is proposed. The methods include two core techniques: a Particle Swarm Optimization algorithm for selection of optimal probe position and a Multi-wavelet approximation method to reconstruct the nonuniform circumferential flow from several dominant wavenumbers. A roadmap for implementation of the method was established including practical guidelines for selection of most important wavenumbers and evaluation of the confidence in the reconstructed circumferential flow. Validation of the method is performed using a representative total pressure field in a multi-stage compressor available in the open literature. The circumferential flow variations are characterized using full-annulus unsteady RANS simulations. The circumferential total pressure field is reconstructed from 8 spatially distributed data points using a triple-wavelet approximation method. Results show good agreement between the reconstructed and the true total pressure fields. In Part 2 of the publication, the method is applied to two rig-level experiments to further demonstrate the capability of the novel method in reconstruction of the circumferentially non-uniform flow in turbomachines. The first experiment was conducted in a high-speed centrifugal compressor for aero-engine applications. The compressor stage features an unshrouded impeller followed by a vaned diffuser. The circumferential pressure field upstream of the diffuser leading edge is reconstructed using measurements from 10 pressure taps distributed at different circumferential locations. Results showed that the circumferential flow variations upstream of the diffuser LE is dominated by the potential field of the diffuser vanes. In addition, the influence of the fixture struts upstream of the impeller is observed in the pressure field upstream of the diffuser leading edge. In the second experiment, the method is applied to resolve the total pressure field downstream of an embedded rotor in a multi-stage environment. The circumferential total pressure field was experimentally characterized by indexing the stators with respect to one another to simulate the annulus using a stationary probe. The full annulus circumferential flow is reconstructed from a small portion of available experimental data acquired at different circumferential locations, and comparisons between the reconstructed circumferential flow and experimental results are made.  


Reconstructing Compressor Non-Uniform Circumferential Flow Field From Spatially Undersampled Data: Part 2 \u2014 Practical Application for Experiments

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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