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This paper presents an experimental and numerical research on the internal flow of a typical radial inlet for centrifugal compressor. Detailed flow measurements were carried out with five-hole probes, consisting of 106 sampling holes and 2178 measuring points. Automatic calibrating and measuring systems, which made the probe calibrations, measurements and data acquisitions controlled by computer, were developed and used to accelerate the flow measurements. Since separations and vortices in the radial inlet were not able to be accurately measured by five-hole probes, numerical simulation was adopted to assist in the flow analysis of the radial inlet in the present study. The investigation indicated that there were five main flow separations and vortices in the present radial inlet. Four of them were generated in the plenum, making the plenum the primary cause of the flow loss and the major factor of the flow distortions in the radial inlet. The last flow separation was generated on the inlet side of the flange at the 90° turning and extended to the exit of the axial duct. Besides, the symmetrical tangential flows in the radial inlet made positive and negative yaw angles with absolute value up to over 15° distributed in the tangential direction of the radial inlet’s exit, which will probably increase the incidence loss in the blade passages and negatively affect the work capability of the impeller. Based on the flow analysis and discussions, preliminary suggestions are proposed to provide references for the improvements of radial inlet. [ABSTRACT FROM PUBLISHER]

Structural vibration and noise radiation of a single-stage centrifugal compressor excited by the internal unsteady flow is investigated experimentally in the first part of our work [Zhou et al. Appl Acoust 2018;131:112–28]. Experimental results for acceleration of vibration and sound pressure under different rotational speeds indicate that the straight discharge pipe connecting the volute is forced to vibrate the most intensively at the blade passing frequency (BPF) and acts as the major contributor to the compressor noise emission. In this paper, a pipe micro-perforated panel (PMPP) is optimally designed with the genetic algorithm to suppress vibration and noise radiation of the straight discharge pipe section. A maximum sound pressure level (SPL) reduction of 20 dB for the BPF component and 8 dB for the overall noise are observed under the tested working conditions, while the influence of the PMPP on the aerodynamic performance of the compressor is negligible. The PMPP may be a promising method for controlling the tonal component of vibro-noises radiated from the centrifugal compressor. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the noise radiated from a centrifugal compressor unit, which mainly consists of a single-stage compressor connected with inlet and outlet pipes, a variable-frequency driving motor, a transmission gearbox and a bearing box. Sound pressure level spectra were measured at three rotational speeds each with several mass flow rates. The experimental results reveal that the overall sound pressure level increases with the rotational speed but varies slightly with the flow rate. The largest overall sound pressure level occurs at the measuring point near the motor, implying that the motor is one of the most important noise sources of the test rig. The frequencies of the tonal components are respectively consistent with the shaft frequency, the blade passing frequency of the compressor impeller and the interaction frequency of the magnetic flux wave with rotor slots in the variable-frequency motor. For sampling points near the connected pipes, the broadband noises mainly arise from the internal random pressure fluctuation through a curve fitting analysis of the squared sound pressure versus the dimensionless frequency. A coherence analysis between the acoustical and vibrational signals implies that the structural vibration induced by the internal pressure loads is the primary contributor for the compressor noise. Particularly, the outlet pipe with the highest vibration level should be a major concern for noise reduction of the centrifugal compressor. [ABSTRACT FROM AUTHOR]