Characteristic Secondary Flow Behavior in Ultra-Highly Loaded Turbine Cascade Under Transonic Condition

Abstract A gas turbine is increasingly required to be enhanced in quick start capability as well as in aerodynamic performance to support variable energy output from renewable sources such as solar and wind powers. On the other hand, the diameter of core engine of a turbofan engine is demanded to be decreased for the improvement of propulsive efficiency by the increase of bypass ratio. Moreover, for the farther enhancement of the specific work output of micro gas turbines by the increase of the turbine inlet temperature, the application of a thick turbine blade will be required for the installation of any internal and external air-cooling system. These various requirements would be responded by an increase of blade loading of axial turbines. In this study, the 3D computations were performed for the flows in an ultra-highly loaded linear turbine cascade (UHLTC) with the blade turning angle of 160 degrees under transonic condition with the assumption of steady compressible flow. The focus was on the characteristic secondary flow behavior and the associated loss generation. In the computations, the isentropic exit Mach number was varied in the range from 0.6 to 1.3 to examine the effects of the variation of shock wave formation on the secondary flow structure. The computed results for UHLTC were also examined by comparing with those observed in a typical transonic turbine cascade to highlight the characteristic secondary flow behavior caused by the increase of blade loading.