Dehner, R., Selamet, A., Steiger, M., Miazgowicz, K. et al., "The Effect of Ported Shroud Recirculating Casing Treatment on Turbocharger Centrifugal Compressor Acoustics," SAE Int. J. Engines 10(4):2017.
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).