Noise at the mid to high flow range of a turbocharger compressor

The acoustic and performance characteristics of an automotive centrifugal compressor are studied on a steady-flow turbocharger test bench, with the intention of identifying operating regions associated with flow noise within the compressor and connected ducting. Near choke, discrete tones including rotor-order frequency and its harmonics (bladepass) are observed. As the flow rate is reduced, the current compressor exhibited a broadband elevation of noise in the 4-12 kHz band, which was evident both in the upstream compressor duct and external sound pressure level (SPL) measurement locations. At all rotational speeds studied here, the total SPL in this frequency range demonstrates a strong dependence on the incidence angle of the incoming flow with the blades at the inducer of the impeller. When the incidence angle is further increased (mass flow rate is decreased) beyond a critical value, the temperature near the inducer tips increases sharply, suggesting local flow reversal, and the total SPL in the 4-12 kHz range suddenly reduces.