Acoustic characterisation of a small high-speed centrifugal compressor with casing treatment: An experimental study

Abstract

With the advancements in manufacturing, materials and computational methods, turbomachinery designs have become more efficient providing higher specific power and reliability with lower weight and cost. The rotational speed of turbomachines has increased while the overall machine size has decreased for a similar power output leading to the pervasive presence of small, high-speed turbomachines, specifically centrifugal compressors in helicopters, unmanned aerial vehicles (UAVs), auxiliary power units (APUs), turbochargers and micro gas turbines. In addition to superior aerodynamic performance over a wide range, increased operating speeds have made the acoustic emissions of small centrifugal compressors a critical aspect of design. Therefore, this work presents an experimental campaign to characterise the acoustic behaviour of a compressor with an intent to quantify the dominant features of the flow-induced noise for design and near surge operating conditions. Furthermore, the campaign is extended to establish the impact of the ported shroud casing treatment and operating speed on the acoustic emission of the compressor. The induct noise measurement method is used in this work to quantify the noise generated in the compressor by measuring pressure fluctuations near the inducer and diffuser while the propagation of the generated noise to the ducts is computed from an array of piezoelectric sensors. Spectra at the design operating point are dominated by tonal noise while broadband noise content is the dominant feature of spectra for near surge operation. Although the ported shroud cavity does not significantly alter the overall noise levels of the compressor operating at design condition, it does seem to propagate tonal noise. For near surge operation, the casing treatment positively impacts the acoustic emission with a reduction of approximately 10 dB in the range up to the blade pass frequency. Furthermore, various broadband features are also observed to be alleviated by the casing treatment.

Effects of ported shroud casing treatment on the acoustic and flow behaviour of a centrifugal compressor

“…This observation from the measured results is accurately captured by the numerical model. This being said, the measured inducer spectrum of the open configuration does show increased levels compared with the corresponding spectrum for the blocked configuration at higher frequencies 33 which is not captured in the numerical results. The opposite trend is observed in the diffuser probes.…”

“…In addition to the sensors positioned in the inlet and outlet ducts, the instrumentation to measure the noise generated by the impeller using two miniaturised pressure probes positioned in the inducer and diffuser of the compressor are also highlighted in the figure. Further details on the flow bench and measurement methodology are already presented in Sharma et al 33,39 . Fig.…”

“…This investigation focused on predicting the differences between the two compressor configurations in the ranges sensitive to the human ear (0.5–10 kHz) 32 that were observed in the experimental measurements. 33 In order to achieve this, a numerical configuration based on the stress blended eddy simulation (SBES) 34 turbulence formulation with time steps corresponding to 4° rotation of the impeller per iteration was employed. The grid consisted of approximately 10 million cells and the boundary layer region was modelled using 12 prism layers growing exponentially with a growth ratio of 1.3 so as to obtain y + values closer to unity.…”

“…The literature on the acoustic impact of casing treatment is scarce, and the general perception 20,21 is that the casing treatment deteriorates the acoustic spectra of the compressor. Chen and Yin 20 The complete length of the inlet and outlet ducts used in the measurement rig (see This investigation focused on predicting the differences between the two compressor configurations in the ranges sensitive to the human ear (0.5-10 kHz 32 ) that were observed in the experimental measurements 33 . In order to achieve this, a numerical configuration based on the Stress Blended Eddy Simulation (SBES) 34 include the inability to accurately capture the overall levels and decay rates.…”

Effects of blade surface roughness on compressor performance and tonal noise emission in a marine diesel engine turbocharger

“…The total-to-total pressure ratio π tt and the isentropic efficiency η is were used to evaluate the accuracy of CFD models and simulations, and analyze variations of the compressor performance in different cases. The standard definitions of the two compressor global variables are as follows, 22 and all parameters used in the following equations were obtained using average sensor data from numerical simulations…”