NUMERICAL INVESTIGATION OF THE FLOW DISTORTION IMPACT ON A REFRIGERATION CENTRIFUGAL COMPRESSOR

摘要

The inlet pipe to a centrifugal compressor in a water-cooled chiller can cause complexities in designing a compact unit. Flow distortion caused by the inlet pipe shape and non-uniformity of the flow from the evaporator can affect the compressor performance. Inlet guide vanes (IGVs) used for capacity control may help reduce the distortion by forcing a redistribution of the flow. However, the guide vanes themselves result in increased losses and can introduce flow distortion due to the clearance between the movable vane and stationary housing. In this effort, the influence of the flow distortion on the impeller performance and the losses caused by IGVs were investigated using a commercial code dealing with real gas. The CFD model was first verified by comparison to test data. Further investigation showed that the hub-to-shroud flow distortion, especially shroud side distortion, has a major effect on stage performance. IGVs are necessary for straightening the incoming flow to benefit stall margin but generate high losses themselves. The tip clearance of the IGV decreases the deswirl capability and introduces additional local separation loss. Distortion intensity was calculated according to ARP-1420 methods to justify the usage of the mixing plane in the CFD modeling. The extent of distortion indicated that the steady simulation served as a preferable choice for balancing computational cost & prediction accuracy.