Session: 40-02 Axial Compressor Instabilities and Stall

Paper Number: 123043

123043 - Analysis of Pre-Stall Pressure Disturbances in an Axial Compressor 

Rotating pre-stall pressure disturbances were observed at off-design conditions in an axial compressor. Unsteady pressure measurements from twelve uniformly-spaced casing pressure transducers were analyzed to characterize these rotating disturbances. Specifically, the temporal and spectral characteristics of the rotating disturbances were studied as a function of mass flow rate, at four steady operating conditions along the part-speed compressor characteristic. In terms of spectral characteristics, the auto-spectral density (ASD) of the pressure measurements was characterized by a broadband local maximum with distinct peaks superimposed, each corresponding to a different circumferential wavenumber, consistent with observations in the literature of pre-stall rotating disturbances, or “rotating instabilities.” At one operating condition, the highest-amplitude peak occurred around half of the blade-passing frequency. The location of the highest-amplitude peak shifted as mass flow rate was reduced to different operating conditions. Using the wavenumber-dependent ASD, the amplitude, center frequency, and local width of each peak were characterized as a function of circumferential wavenumber for the four distinct operating points. Furthermore, temporal analysis of the pressure signals indicated that the rotating disturbances had compact support in both space and time. Motivated by the compact nature of the disturbances, an empirical model of circumferentially-propagating Morlet wavelets was developed. The model showed good agreement with the experimental data, in terms of both the temporal characteristics and the wavenumber-dependent ASD characteristics. The empirical model demonstrated that the complex spectral characteristics of the rotating disturbances could correspond to a handful of physically relevant parameters such as a disturbance size, shape, and circumferential propagation speed.

Presenting Author: Valerie Hernley University of Notre Dame

Presenting Author Biography: Val graduated with her PhD from the University of Notre Dame in August, 2023. This work is a subset of her dissertation, "Identification of Aerodynamic Forcing Mechanisms From Experimental Measurements of Compressor Blade Vibration". She is now employed as a dynamics engineer at the Johns Hopkins University Applied Physics Lab.

Authors:

Valerie Hernley Johns Hopkins University Applied Physics Laboratory
Jeongseek Kang University of Notre Dame
Matthew Montgomery Doosan Enerbility
Aleksandar Jemcov University of Notre Dame
Scott C. Morris University of Notre Dame