The flow field in a compressor is circumferentially nonuniform. The circumferential variations measured in the absolute reference frame are associated with the wakes from upstream stator row(s), potential field from both upstream and downstream stator rows, and their aerodynamic interactions. Also, stator-stator and rotor-rotor interactions can impact stage performance. Additionally, the circumferentially non-uniform flow can introduce instrumentation errors in calculating compressor performance during rig or engine tests. In a recent study, Chilla et al. investigated the instrumentation errors caused by circumferential flow variations in an 8-stage axial compressor representative small core compressor of an aero-engine. The analysis showed that a baseline probe configuration with 3 equally spaced probes around the annulus yields a maximum of 0.8% error in flow capacity and 2.8 points error in compressor isentropic efficiency. Therefore, it is of great value to resolve the compressor non-uniform circumferential flow for precise calculation of compressor performance, as well as better prediction of blade forced response. Historically, experimental characterization of the circumferential flow variation is achieved by circumferentially traversing the flow, either utilizing a probe traverse mechanism or utilizing fixed instrumentation but actuating the stator rows circumferentially. This involves the design of complex traverse mechanisms which present challenges in sealing and can be costly. To the best knowledge of the authors, there is a dearth of research available in the open literature on reconstructing compressor circumferentially nonuniform flow using spatially under-sampled data from a few probes at fixed circumferential locations. To address this challenge, a novel method is proposed to reconstruct compressor nonuniform circumferential flow using spatially under-sampled data points from a few probes at fixed circumferential locations. The paper is organized into two parts. In the present part of the paper, details of the multi-wavelet approximation for the reconstruction of circumferential flow and Particle Swarm Optimization algorithm for selection of probe positions are presented. Validation of the method is performed using the total pressure field in a multi-stage compressor representative of small core compressors in aero engines. 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. Also, a sensitivity analysis of the method is conducted to investigate the influence of probe spacing on the errors in the reconstructed signal and guidelines for placing probes are drawn. To conclude, a roadmap for reconstructing the nonuniform circumferential flow in a compressor using spatially under-sampled data points was established. The method is shown to be robust and capable of reconstructing compressor circumferential flow with good accuracy.


Reconstructing Compressor Non-Uniform Circumferential Flow Field From Spatially Undersampled Data: Part 1 \u2014 Methodology and Sensitivity Analysis

Division / Sponsor:
International Gas Turbine Institute (IGTI)

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

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