Improvement of Unstable Flow in a Low Solidity Cascade Diffuser of Centrifugal Compressor by Multi-Objective Optimization

Abstract

A compressor for turbochargers is commonly required improving efficiency and expanding the operating flow rate range. Though an aerofoil type diffuser shows better pressure recovery than conventional vaneless diffuser, it is difficult to design the aerofoil type diffuser under conditions of wide change of the flow angle. An innovative design of a Low Solidity circular cascade Diffuser (LSD) was proposed for flow range enhancement of cascade diffuser¸ and an interesting function of the LSD is introduced. At small flow rate conditions, low energy fluid near the diffuser side wall spread between the diffuser blade, and low energy fluid moves to the leading edge of the adjacent blade, then low energy fluid merged with main flow and suppress the flow separation. The phenomena spread to circumferential direction, and whole of the LSD blades show high stability for separation under a large angle of attack. In this study, LSD is designed for compressors of turbocharger by using a Genetic Algorithms (GA) with meta-model of an Artificial Neural Networks (ANN). The final goal of this study is to optimize the LSD with having secondary flow effect under low flow rate conditions.