Over-all performance analysis of a dual-entry turbocharger compressor with variable geometry orifice

Abstract

A dual-entry turbocharger compressor has a dual-entry impeller with the same blades on both sides of an impeller disc. Flows merge into a common diffuser from two sides of the disc, contributing to over-all mass flow rate of the compressor, and the mass flow rate at either side is distributed with self-adaptation. With the self-adaptive distribution, the difference in the mass flow rates between two impeller sides is slight at the near choke point and gradually raises with the reduction of the compressor over-all mass flow rate. The increased mass flow rate difference can prematurely trigger compressor instability, even surge. When a turbocharged engine operates at high-altitude locations, this becomes a serious issue so that the engine fails to work. To overcome the problem, we propose a new method of using a variable geometry orifice plate at the rear entry of the dual-entry impeller. The orifice can improve the mas flow rate distribution at both impeller sides. The dual-entry compressor performance variations prove the effectiveness of the orifice in terms of the compressor stability boundary extension and suggest a control strategy of variable geometry orifice. The mechanism of the orifice extending the compressor stall margin is the pressure gradient change in front of the rear inducer. An experiment was conducted on a centrifugal compressor, and the test results support the numerical findings.