Centrifugal Compressor: The Sound of Surge

Abstract

When a centrifugal compressor operates at low mass flow rates (close to the unstable operating condition called surge), flow instabilities can develop and severe flow reversal may occur in the wheel passage. Under such conditions, noise generation has been reported resulting in a notable discomfort induced to the passengers in the cabin.The aim with this study is to predict the flow field associated with a centrifugal compressor and characterize the acoustic near-field generation and propagation under stable and off-design (near-surge) operating conditions. The Large Eddy Simulation (LES) approach is employed. The unsteady features in the flow field leading to acoustic noise generation are quantified by means of statistical averaging, Fourier data analysis and flow mode decomposition techniques. The decomposition method is performed inside the rotating impeller region for several stable and off-design (including surge and near-surge) operating conditions. The acoustic near-field data are presented in terms of noise directivity maps and sound pressure level spectra.For the near-surge condition an amplified broadband feature at two times the frequency of the rotating order of the shaft (possible whoosh noise) was captured. However, an amplified feature around 50% of the rotating order was captured as well. These features are present also during the investigated surge operating conditions, but occur at lower amplitudes as compared with the captured low surge frequency of 43 Hz.

Acoustic and pressure characteristics of a ported shroud turbocompressor operating at near surge conditions

“…β • , stall initiation and fully developed stall can be observed in the passage 1 and passage 2 respectively while passage 3 and passage 4 are the impeller with a speed of approximately (0.32-0.4)RO which corresponds to the peak seen in the diffuser spectrum at 0.37RO. Similar results identifying a tone at 0.5RO in the spectra of diffuser points for the near surge operation are reported in works of Jyothishkumar et al [17] and Sundström et al [16].…”

“…Recent numerical work presented by the researchers of KTH [15,16,17] investigated the performance and acoustic characteristics of the ported shroud compressor operating near surge. Although authors [16] attempted to predict the value of surge frequency, relatively lower surge frequencies are seen in literature as the upstream and downstream duct volumes were not considered by the authors in the numerical model. Rotating stall is also identified and is shown to propagate circumferentially at 0.5 RO.…”

“…Rotating stall is also identified and is shown to propagate circumferentially at 0.5 RO. Dynamic mode decomposition of the transient numerical data [15,16] pointed the interaction of flow exiting PS cavity as the possible cause of the rotating stall.…”

Analysis of the Turbocharger Compressor Surge Margin Using a Hurst-Exponent-based Criterion

“…It is also possible to apply this methodology to high-fidelity Large Eddy Simulation data, e.g. [17,18], which allows for a much more thorough analysis with respect to which input signals to use, both in location and physical quantity. Other modes of instability, e.g.…”

“…These measurement points are plotted in a standard compressor map, i.e. the corrected mass flow, (17) on the horizontal axis, and the total pressure ratio, (18) on the vertical axis. A speedline consist of all points with the same corrected impeller speed (19) These corrections ensure Mach similarity in the axial and circumferential direction at the compressor inlet.…”