Abstract
This paper describes an experimental study carried out with the objective of characterizing flow instabilities in turbocharger compressors, specially the distribution of the high-temperature compressed backflow that appears upstream of the impeller at marginal surge conditions. The inlet of a test compressor was fitted with linear and circumferential thermocouple arrays in order to measure the temperature distribution caused by this backflow, whose independence of duct wall temperature was validated through thermographic imaging. Miniaturized pressure probes at the inducer and diffuser showed how pressure spectra varied during the different operating conditions. In-duct acoustic intensity was measured in both the inlet and the outlet to investigate the correlation between a known super-synchronous broadband issue known as whoosh noise and the backflow behaviour as characterized by local pressure and temperature. Analysis of the results points to inlet whoosh noise being boosted by this reversed flow but not caused by it, the source probably being located at or downstream of the compressor impeller.
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