Abstract
Automotive turbochargers improve the performance, reduce emissions and improve fuel efficiency. Improving the efficiency of the compressor in a turbocharger has a direct impact on the overall efficiency, torque and compressor exit temperatures. Any improvement in compressor efficiency over a wide range of operating speeds is beneficial since a turbocharger is expected to cover a range of mass flows and speeds. A typical automotive compressor is connected to the turbine shaft by a standard hexagonal nut. The presence of the nut and the extended shaft causes disturbances to the incoming flow. This results in a relatively large recirculation zone which increases the blockage as well as adds to flow losses. In a typical Computational Fluid Dynamics (CFD) simulation these effects are ignored and a smooth hub is assumed. When the presence of nut and extended shaft are included in the CFD simulations the loss of efficiency is predicted. In this study numerical simulations of compressors with realistic hub geometry incorporating the extended shaft and nut are carried out. Considering this as a baseline several concepts for smoothening the hub geometry are studied taking into consideration the ease of manufacturing. Test results from a few configurations illustrating the effects of a smooth hub geometry are also presented. Improving the smoothness of the hub can provide efficiency improvements in the order of 0.5-1% depending on the size of the compressor wheel.