A numerical study for correlating performance versus number of blades and investigating flow characteristics and loss generation of an automotive radial flow turbine

Hybridization of engines is the future technology to overcome the increasing emissions of CO2 and pollutants from internal combustion engines. So far, the current technology, called downsizing, involves reducing engine size while maintaining continuous engine boosting with a turbocharger. It is well known that the radial turbine, an essential component of turbochargers, is a seat of various loss mechanisms such as incidence losses which significantly affect performance. As a contribution for further improving performance and reducing loss generation in radial turbines, this study investigates the effect of the blade number on performance and loss generation within a radial turbine of small scale turbocharger. To this end, six radial turbines were designed with several blade numbers ranging from three up to thirteen. The flow solution was computed by solving the Navier-Stokes equations using a CFD solver. The numerical results were validated against experiments. The results revealed that the impeller of 11 blades provides better performance than the other investigated designs. The results showed a substantial effect of the number of blades on the distribution of flow characteristics and loss generation. The efficiency, mass flow rate, output torque, blade loading, and leakage flow through the clearance gap of the turbine were correlated to the number of blades.