Effect of bleed slots on turbocharger centrifugal compressor stability

The compressor with open bleed slot showed lower instability levels at low mfr when not experiencing deep surge. Spectral analysis at low mfr showed that the bleed slot suppresses broadband frequencies linked to piping resonance and below the rpm frequency, thus improving the overall stability. When excited, these frequencies create periodic flow disturbances that originate from the low pressure region below the tongue, at low mfr. The low pressure perturbations are then convected by the flow and propagate around part of or the entire perimeter, depending on the compressor speed.