Effect of Aerodynamically Induced Pre-Swirl on Centrifugal Compressor Acoustics and Performance

The effect of aerodynamically induced pre-swirl on the acoustic and performance characteristics of an automotive centrifugal compressor is studied experimentally on a steady-flow turbocharger facility. Accompanying flow separation, broadband noise is generated as the flow rate of the compressor is reduced and the incidence angle of the flow relative to the leading edge of the inducer blades increases. By incorporating an air jet upstream of the inducer, a tangential (swirl) component of velocity is added to the incoming flow, which improves the incidence angle particularly at low to mid-flow rates. Experimental data for a configuration with a swirl jet is then compared to a baseline with no swirl. The induced jet is shown to improve the surge line over the baseline configuration at all rotational speeds examined, while restricting the maximum flow rate. At high flow rates, the swirl jet increases the compressor inlet noise levels over a wide frequency range. At low to mid-flow rates, on the other hand, the swirl jet reduces the broadband whoosh noise in the 4-11 kHz range. Mild surge detected for the baseline configuration in the 15-35 Hz range at mid flow rates and high speeds is also suppressed with the swirl jet configuration due to favorable local changes in slope of the compressor characteristics.