Computational Flow Field Assessment of the Inlet Region of Centrifugal Compressor Under Unsteady Flow Conditions Near Surge

Abstract

Abstract The centrifugal compressor of a turbocharger is affected by the opening and closing of the engine intake manifold and consequently experiences a pulsating backpressure. The imposed pulsating conditions generate internal losses and reduce the overall compressor performance and efficiency. However, previous studies have shown that these dynamic conditions can also lead to a surge margin improvement, benefiting the lower limit of stability, in certain conditions. The stability of the compressor arises from the flow behaviour in the inlet region and the interaction between the rotating and stationary components at the inlet. In this paper, the computational flow field of the inlet region of a centrifugal compressor under pulsating flow has been studied. A full stage, 3D URANS model of a compressor exposed to pulsating backpressure has been solved using ANSYS-CFX for the near surge operating point. The transient behaviour of this operating point has been studied at six instances in time within one cycle of the pulse. The flow field is assessed using Mach number, static entropy, static pressure and local flow direction in the inlet region. Flow separation regions have been identified. The authors propose that the variation in flow field at the inlet due to the dynamic response to the imposed boundary condition could explain the improvement in surge margin under pulsating flow conditions for this compressor system.