Comparison of Turbine Performance and Flow Loss Mechanism of a Radial/Mixed-Flow Turbine

Aiming at the problem that the efficient operation range of radial turbines is relatively narrow and can not meet the requirements of wide and efficient operation range of turbines when the engine is running at variable altitude, the performance discrepancy and flow loss mechanism between a radial turbine and a mixed-flow turbine with the same swallowing capacity were studied via experimental and numerical methods. Results show that the efficiency of the mixed-flow turbine is 4.5% higher than that of the radial turbine under all turbine loads, although swallowing capacity of the two turbines is quite similar. In addition, the boundary of turbine efficiency for the mixed-flow turbine is 30%—50% narrower than that of the radial turbine, hence turbine performance of the mixed-flow turbine is less sensitive over operation conditions than that of the radial turbine, which indicates that the mixed-flow turbine has stronger off-design load adaptability. Results of loss distribution analysis illustrate that the loss in the shroud passage, tip passage and exit tip part is about 60% lower in the mixed-flow rotor than that in the radial turbine. Flow analysis of the two turbines indicates that the distribution of flow angle at the inlet of mixed-flow rotor is more uniform with the variation of turbine load than that of the radial rotor. Especially, the incidence angle near the tip of the leading edge of the radial rotor is higher than that of the mixed-flow turbine. As a result, the scale of tip leakage flow is shrunk in the mixed-flow turbine and leads to a lower loss in this region. Thus, the flow field in the mixed-flow rotor passage is well improved, and hence the loss is lower and the turbine performance is well improved. © 2024 Chinese Society for Internal Combustion Engines. All rights reserved.