Abstract
Impeller tip clearance is a key parameter in design process of a centrifugal compressor which has influential effects on its aerodynamic and thermodynamic performances. Interaction of tip leakage flow with the main stream could be the major source for occurrence of stall phenomenon. In the present investigation, two impeller tip clearances of small and large sizes are investigated under different flow coefficients assigned to “design”, “low flow” and “high flow” conditions. Flow field is precisely simulated utilizing solution of the Reynolds-Averaged Navier-Stokes equations. Influence of the impeller stall on the volute flow field is studied. Structure of vortical flows within the impeller passages and volute are demonstrated in details. Numerical results showed that the flow within the volute becomes stall-prone while the flow within the impeller stalls. In contrast to the high flow case, the low flow condition was more prone for the stall occurrence. Performance tests were also conducted on Iran University of Science and Technology (IUST) centrifugal compressor test rig for validation of the numerical results.
Highlights
Considering tip clearance in compressor blades is inevitable
Rotating stall is one of the flow instability phenomenon in which a circumferentially uniform flow pattern is disturbed by local flow separation
The errors associated with the parameters used for evaluation of the compressor performance were obtained less than 2% for the mass flow rate, 0.5% for the pressure and ±1 rpm for the impeller rotational speed
Summary
Considering tip clearance in compressor blades is inevitable. These gaps are associated with flow instabilities, which may lead to poor thermo-dynamical and fluid-dynamical performances, when being inappropriately designed. Chriss et al [8], have studied impeller flow field of NASA Large Scale Centrifugal Compressor (LSCC) at its design point and lower mass flow rates conditions They illustrated throughflow velocity magnitudes as well as the secondary flow structures inside the impeller utilizing laser Doppler velocimetry. Detailed measurements of swirling flow inside a centrifugal compressor volute with elliptical cross section have been carried out by Ayder et al [10] They showed that the flow inside the volute is highly three dimensional, and that the swirling velocity component has an important influence on the crosswise and circumferential variation of the static pressure and velocity distribution. The volute flow field is studied before and after the impeller stall, in order to find out that if it is stall-prone or not
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