The steady performance of mainly two high pressure ratio mixed flow turbines for an automotive turbocharger (expansion ratio of 2.9) has been investigated and the results indicated superior performance of the rotor with a constant inlet blade angle relative to that with a nominally constant incidence angle. These results have been confirmed by the measurement of the three components of velocity, the Reynolds normal stresses and the flow angle at the inlet and exit of the mixed-flow turbine rotors by laser Doppler velocimetry (LDV) under steady state conditions. The turbine testing conditions corresponded to the 50% and 70% design speeds, equivalent to 29,400 and 41,300 rpm respectively.
The velocity results have indicated that the flow upstream of the rotor varies significantly along the blade inlet plane, and this is more evident at the 50% design speed. The flow in the volute behaves as a free vortex except in regions close to the hub, while the exit flow revealed that the constant incidence design rotor has a significantly higher exit swirl angle than the constant blade design, in agreement with the higher exit kinetic energy loss in the former case.