Performance of a Micro-scale Radial-Flow Compressor Impeller made of Silicon Nitride

Abstract

A micro-scale, high-speed compressor impeller (12 mm diameter, 800,000 rpm) was built and tested for feasibility in regard to aerodynamic performance. The compressor might be applied in a fist-sized gas-turbine-generator. To survive high stresses at such high temperatures, the rotor was manufactured as a single turbine/compressor/shaft unit in silicon nitride. Tests were conducted in a cold-flow rig at reduced speed of 420,000 rpm. Results from a CFD code compared favorably to measured data at this speed. Extrapolation from test conditions to full design speed was accomplished by application of CFD applied at both speeds. The experiments confirm design rules regarding reduction of efficiency at low Reynolds number, and results with several blade-to-shroud clearances were obtained to illustrate the importance of this parameter on micro-scale compressor performance where blade-to-shroud clearances will be relatively large compared to conventional radial-flow compressors.