Experimental and CFD Investigation of inlet fin influence on compressor stability and performance

The operational stability and overall performance of turbocharger compressors are influenced by local as well as global instability phenomena under off-design conditions. This paper investigates the suppression of inlet recirculation and enhancement of surge operating range, using inlet fins. Both experiments and high-fidelity CFD simulations were used to assess the effect of fins on compressor performance, stability, and operating range. Experiments were conducted on a small turbocharger, while numerical simulations were performed using the RANS equations coupled with the k-ω SST turbulence model solved by ANSYS CFX. The numerical approach was validated, and a mesh independence study was conducted to evaluate discretization uncertainty at both design and off-design conditions. The results revealed that fins effectively suppressed upstream recirculation and preswirl, and promoted more uniform and directed flow into the impeller. Under stable, high-flow conditions, fins had a negligible influence on pressure ratio and efficiency. However, at low flow rates near surge, their presence significantly enhanced compressor performance. Pressure ratio increased by up to 5.4%, while the surge mass flow rate decreased by 8.4-10.4%, indicating a substantial extension of the stable operating range. Despite an efficiency penalty of up to 5% at low flow rates, the compressor performance at medium and high flow rates remains unaffected. The flow field analyses revealed that fins reduced swirl velocity, maintained higher incidence angles, and limited upstream momentum exchange, thereby stabilizing near-surge operation.