Centrifugal Compressor Stall Control by the Application of Engineered Roughness on Diffuser Shroud

Abstract

Automotive turbochargers consist of two parts; turbine and compressor, Centrifugal compressor is the fundamental part. Downsizing in the engine size is pushing the automotive industry to operate the compressor at a low mass flow rate. However, the operation of the turbocharger centrifugal compressor at a low mass flow rate leads to fluid flow instabilities. These flow instabilities are flow separation and flow recirculation and because of these instabilities, compressor enters the state of the stall and/or surge. To reduce or eliminate these flow instabilities is the focus of turbomachinery aerodynamics and this research. In the current study, surface roughness has been applied on diffuser shroud, as a passive flow control method to reduce the compressor flow instabilities and increase the stall margin and operating range of the centrifugal compressor for the applications of automotive turbochargers. The analysis is carried out using a baseline SRV2-O compressor developed and fabricated by the German Aerospace Center named DLR. The steady-state analysis is carried out in two parts. In the first part, detailed aerodynamics of centrifugal compressor has been performed. Numerical simulations have been performed to validate the experimental data by comparing it with the data obtained from the numerical simulations and performance has been evaluated over a constant rotational speed from stall to choke using both k-ε and k-ω SST turbulence models. In the second part, the application of roughness as a passive flow control method on the diffuser shroud and overall performance has been simulated for different roughness heights from stall to choke using both turbulence models. After the application of surface roughness, a significant reduction in flow instabilities has been observed. The results obtained from this analysis showed significant enhancement inflow structure of the diffuser as flow separation and flow reversal has been reduced.