Variable inlet guide vanes (VIGVs) can regulate pressure ratio and mass flow at constant rotational speed in centrifugal compressors as a result of inducing a controlled prewhirl in front of impellers. Radial inlets and VIGVs are typical upstream components in front of the first-stage impellers in many pipeline and multistage centrifugal compressors. However, previous investigations on VIGVs in centrifugal compressors were mostly conducted under the condition of axial inlets, and present work aims to focus on the effects of radial inlet on the VIGVs performance of a centrifugal compressor stage. The axial inlet stage model was compared with the radial inlet stage model using numerical flow simulation. The flow from the radial inlet was nonuniform in both circumferential and radial direction, thus the VIGVs, the impeller, the vaneless diffuser, and the return vane channel were modeled with fully 360-deg passages. The three-dimensional flow field was numerically simulated with FINE™/Turbo at VIGVs setting angles range from -20° to +60°. The overall stage performance parameters were obtained by integrating the field quantities. The simulation results show that the performance of VIGVs was significantly degraded by its inlet flow distortions resulting from a radial inlet. The stage performance map indicates that the overall stage polytropic efficiency decreased by an average of 2.5% and total pressure ratio decreased by an average of 1% because of the flow distortions at different VIGVs setting angles, in comparison with the axial stage model.
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