Today, turbocharged engines are becoming very popular to meet the vehicles' stringent emission norms in the automotive industry. The compressor plays a vital role in the performance of a turbocharger. The compressor consists of two main parts, a wheel (or impeller) and a housing, including the diffuser and a volute. The high-speed flow from the wheel is diffused throughout the diffuser and volute, before being delivered to the engine. Hence, the housing flow characteristics (particularly pressure losses) affect the overall performance of the compressor and its operating range. Generally, the housing has noticeable surface roughness, especially in the volute, because of manufacturing methods, erosion, and particle deposition during operation. The surface roughness of the volute significantly affects the compressor performance. Thereby, its understanding is very much essential in modern applications using turbochargers. This study evaluates the effect of the volute surface roughness level on the compressor performance by experimental and numerical analysis.
In this study, first, experimental analysis is done using a compressor with vaneless diffuser and an overhung volute with three volute surface roughness levels. The experiments are done to measure the compressor pressure ratio and efficiency at various mass flow rates and speeds. Also, steady-state numerical simulations are performed at the same mass flow rates with design and off-design speeds to analyze the flow mechanisms, causing pressure losses because of volute surface roughness. Then, a numerical analysis is also done to understand the effect of surface roughness of the diffuser hub and shroud walls on the performance of the compressor. From the results, it is found that increased levels of volute surface roughness reduced the compressor efficiency by about 1% to 2.5% compared to that of a smooth surface volute. Also, it is found that the pressure losses are more sensitive to the surface roughness of the diffuser shroud-wall than that of the hub-wall.