Vaned Diffuser Effect on Centrifugal Compressor Performance and Stall

Abstract

A centrifugal compressor is a mechanical device that helps to achieve higher pressure ratios at lower mass flow rates. It is used in many applications such as turbochargers, cruise missiles, and turbojet engines where compact high pressure ratio compressors are required. The performance of a centrifugal compressor is greatly influenced by instabilities like stall and surge, which decrease the operating range and the efficiency of a compressor. These instabilities are effected by the geometry of the vaned diffuser used and hence, the present study aims to see both computationally and experimentally the effect of vaned diffuser parameters like the number of vanes (solidity) and the vane setting angle (α) on the performance and stall of a centrifugal compressor. Computational steady-state study is performed for different vaned diffuser geometries with changes in solidity and vane setting angle to understand their effects on performance. These studies show large variations in the performance curves with changes in surge points, choking mass flow rates and efficiencies. A new rotating centrifugal compressor facility is used for the experimental study. This facility uses a connected turbine driven by compressed air to achieve the required rotation rates, with the compressor RPM being controlled by valves in the turbine inlet and the load on the compressor being controlled by valves at the compressor outlet. This facility enables studies of both performance and stall of centrifugal machines as a function of the vaned diffuser geometry, and preliminary experiments have been done to establish the facility.