The effects of radial inlet with splitters on the performance of variable inlet guide vanes in a centrifugal compressor stage

Abstract

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 industrial centrifugal compressors. However, previous investigations on VIGVs in centrifugal compressors were mostly conducted under the condition of axial inlets, and this study aims to focus on the effects of radial inlet on the VIGVs performance of a centrifugal compressor stage. The axial inlet stage model is compared with the radial inlet stage model with splitters using numerical flow simulation. The flow from the radial inlet was nonuniform in both circumferential and radial directions; thus, the VIGVs, the impeller, the vaneless diffuser, and the return vane channel are modelled with fully 360 passages. The three-dimensional (3D) flow field is numerically simulated at VIGVs setting angles ranging from À20 to 60 . The overall stage performance parameters are obtained by integrating the field quantities. Though the splitters are equipped in the radial inlet, the overall stage polytropic efficiency decreases by an average of 4 per cent and total pressure ratio decreases by an average of 3.3 per cent in comparison with the axial stage model. This can be attributed to the effect of both flow non-uniformity induced by radial inlet and flow loss in the radial inlet at different VIGV setting angles. The flow loss in the radial inlet with splitters is the main reason of the stage performance decrease compared with the flow non-uniformity. The simulation results show that the performance of VIGVs is degraded by its inlet flow distortions resulting from a radial inlet. The results in this study can be applied to centrifugal compressor design and optimization.

A review of prewhirl regulation by inlet guide vanes for compressor and pump

“…Because of its high calculation efficiency, various operation conditions can be studied within limited time. Not only the energy performance of compressor and pump but also the detailed description of internal flow field can be obtained by means of commercial CFD codes, such as Numeca, 6 CFX, 8 Fluent, 30 and Tasc-flow. 31…”

“…Figure 1 shows a typical sketch of inlet guide vanes for a centrifugal pump, 5 and Figure 2 shows the pictures of inlet guide vanes equipment. 6,7

Figure 1.Centrifugal pump with inlet guide vanes (IGVs). 5

Figure 2.Geometry of variable IGVs.

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Numerical investigation of influence of inlet guide vanes on unsteady flow in a centrifugal pump

“…1 Many works have been carried out to investigate the influence of IGVs on energy performance, 2,3 internal flow field, 4,5 and unsteady interaction 6,7 for centrifugal compressors.…”

A 1D mean line model for centrifugal compressors with variable inlet guide vanes

“…Early experimental and computational fluid dynamics (CFD) studies 4,6 showed that introducing preswirl increases the efficiency at lower mass flow rates and improves the surge limit. More recent studies have applied CFD simulations to investigate features such as performance, 7,8 unsteady interactions between the IGVs and the impellers, 9,10 pressure fluctuations at large IGV angles, 11 and the effect of IGV geometry. 1,12 A review of preswirl in from IGVs can be found in the work of Liu et al 13 Both experimental [14][15][16] and numerical 3,9,[17][18][19][20][21][22] approaches have been used to study compressor flow, with and without IGVs.…”