The Effect of Ported Shroud Recirculating Casing Treatment on Turbocharger Centrifugal Compressor Acoustics

Ported shroud compressor covers recirculate low momentum air near the inducer blade tips, and the use of these devices has traditionally been confined to extending the low-flow operating region at elevated rotational speeds for compressors on compression-ignition (CI) engines. Implementation of ported shrouds on compressors for spark-ignition (SI) engines has been generally avoided due to operation at pressure ratios below the region where ported shrouds improve low-flow range, the slight efficiency penalty, and the perception of increased noise. The present study provides an experimental investigation of performance and acoustics for a SI engine turbocharger compressor both with a ported shroud and without (baseline). The objective of implementing the ported shroud was to reduce mid-flow range broadband whoosh noise of the baseline compressor over 4-12 kHz. At the compressor inlet, elevated BPF noise of the ported shroud partially offset the mid-flow range (4-12 kHz) whoosh noise suppression and the maximum overall SPL reduction was 6 dB(A), while elevated 4-12 kHz and BPF noise caused an SPL increase of up to 5 dB(A) at low speed and flow. Since the ported shroud did not significantly increase low-flow 4-12 kHz noise at the compressor outlet, overall SPL was reduced over the mid to low flow range by a maximum of 12 dB(A).