Unsteady Pressure Measurement in a Single Stage Axial Transonic Compressor Near the Stability Limit

Abstract

With the help of piezoelectric high frequency pressure probes measurements are undertaken to investigate the flow during stable compressor operation close to the stability limit. Fourteen static pressure probes record the static wall pressure and ten total pressure probes record the total pressure at the rotor exit, both in the absolute frame of reference. The data is then visualised as ensemble averaged contour and spectrum plots. With the help of wall and exit pressure, the tip leakage vortex is localised. Oscillations of the tip leakage vortex are seen as well in terms of high relative standard deviation as well as in an excitation of a frequency band around 1/2 BPF. Further investigation of the frequency spectrum with the help of the pseudo-unsteady wall pressure reveal the occurrence of rotating tip leakage vortex disturbances forming a two-passage periodic vortex pattern. The presented measurements were obtained using Rotor-1 from the TU Darmstadt rotor family. With a sampling rate of 125kHz the pressure field is resolved with 23 measurements per passage (at 20.000 rpm, design speed).