Causes of Acoustic Resonance in a High-Speed Axial Compressor

Abstract

Nonharmonic acoustic resonance was detected in the static pressure and sound signals in a four-stage high-speed axial compressor when the compressor was operating close to the surge limit. Based on prior research reported in the literature and measurements of the resonance frequency, Mach number of the mean flow, and the axial and circumferential phase shifts of the pressure signal during resonance, it is shown that the acoustic resonance is an axial standing wave of a spinning acoustic mode with three periods around the circumference of the compressor. This phenomenon occurs only if the aerodynamic load in the compressor is high, because the mode needs a high circumferential Mach number for resonance conditions. Mathematics of existing analyses of acoustic resonances in turbomachinery complex and have therefore rarely resulted in published examples of good agreement with real engine data. The present paper provides suitable, physically based simplifications of the existing mathematical models which are applicable for modes with circumferential wavelengths of more than two blade pitches and resonance frequencies considerably higher than the rotor speed.

Numerical simulation of rotating stall in a subsonic compressor

“…The acoustic wave resonance in the compressor is proposed as a possibility (B. Hellmich [9]). Structures observed on Fig.…”

Sound generation by non-synchronously oscillating rotor blades in turbomachinery

“…8(a) and (b). Though the mode is cut-off, its amplitude level is comparatively high since its cut-off ratio is close to one, and the mode is probable to cause complex sound phenomenon related to the acoustic resonance in turbomachinery [17]. Therefore, if the results measured in the far field are barely adopted without considering this factor, certain sound modes that generated by oscillating blades might not be detected and the relative analysis might be unreliable.…”

Study of the acoustic resonance occurring in a multistage high-speed axial compressor

“…20 In 2008, Hellmich 12 proposed a methodology to evaluate the transmissions/reflections occurring at the rows interfaces in a high-speed compressor. The same methodology has been applied to CREATE but will not be presented here: a detailed description is available in the work of Courtiade.…”

“…To plot the estimated amplitude, a propagation method has been used: the maximum amplitude has been set to 1 in section 280, and relation (6) has been used to propagate the amplitude in the whole machine. The damping factor has been calculated for a circumferential mode 18.…”