Energy Separation in High Subsonic Turbine Cascade

Abstract

Trailing edge vortex shedding from a turbine cascade was numerically simulated for an exit isentropic Mach number of 0.79 and a Reynolds number of 2:8 Â 106 . The objective of this study is to clarify the time evolution of the vortex shedding process from a turbine blade and the mechanism of energy separation appearing in the wake. Calculations used a locally developed numerical code, employing a second-order AUSM scheme for inviscid numerical fluxes, a secondorder implicit dual time method for time integration, and Detached Eddy Simulation for turbulence. Calculated results confirmed a non-uniform pressure distribution along the trailing edge, which was observed experimentally and different from a uniform distribution at low subsonic Mach number. The energy separation where instantaneous total temperature splits into hot and cold spots in the wake is caused by convection and vortex rotation. In addition, the formation and dissipation phases of vortices affect the energy separation.

Influences of trailing boundary layer velocity profiles on wake vortex formation in a high-subsonic-turbine cascade

“…Ning et al 17 suggests that the vortex-shedding unsteady stresses can be modeled in Navier-Stokes equations to achieve a vortex-shedding time-independent solution. In recent unsteady calculations of the flows in a high subsonic range, uRANS, 18 a delayed detached eddy simulation, 19 and large-eddy simulations (LESs) 6,20 were employed, but none of the uRANS results yielded a good trailing edge pressure distribution. Although the LES was better able to reproduce the trailing edge pressure distribution than uRANS, the mesh used appeared to be too coarse; further, preliminary LES results predicted a poor representation of experimental data at the trailing edge because the near-wall turbulence structure could not be resolved, which made the models of the wake turbulence flow ambiguous.…”

Comparison between Hot and Cold Flow Conditions of Turbine Cascade

“…In both cases, the instantaneous total temperatures in the wake split into hot and cold spots, which is known as the energy separation phenomenon. 32,33) El-Gendi et al 28) noticed that the combination of the convective and rotational velocities of the vortex makes a main contribution for energy separation. Therefore, the phenomenon is observed in both cases.…”

“…The origin of the X and Y axes was taken at the trailing edge. 28) The distributions of time-averaged velocity normalized by the speed of sound (c 1 ), see Appendix A, for HC and CC are shown in Fig. 11.…”