Abstract
There is great interest in the usage of ceramic matrix composites (CMC) as a turbine blade material. However, depending on the manufacturing process of the CMC, blades may have a thicker trailing edge. The design space therefore needs to be updated due to the resulting flow physics. Recently, experimental results acquired at the NASA Glenn Transonic Turbine Blade Cascade Rig showed that a loss measure generally increased with increasing trailing edge thickness. For some cases, however, the general downward trend of the loss with increasing Reynolds number (Re) was interrupted by a local loss peak around Re ∼1.24 × 106, and then subsequently dropped to the original pre-peak trend. A possible cause of this intriguing phenomenon was speculated to be transonic vortex shedding, which is the mechanism of vortex shedding promoted by reflected shed pressure waves at the trailing edge at relatively high Reynolds numbers and transonic Mach numbers. A Reynolds-averaged Navier–Stokes analysis or an under-resolved large eddy simulation (LES) does not reproduce this apparent anomaly and thus a highly-resolved LES (the total mesh count of ∼290 million cells) was performed to investigate the aerodynamics of the CMC blade. The numerical results at Re = 1,246,350 show that the pressure waves generated by the vortex shedding in the wake travel upstream and significantly influence the transition and separation on the suction side thus enhancing the vortex shedding in the wake. This feedback does not hold under a low-Re condition (Re = 621,900). The Reynolds number dependence was also examined by numerical perturbation of the pressure waves in the wake and by examining how such perturbation attenuates or endures. It is confirmed that the perturbation of the pressure waves is quickly damped below a set Reynolds number.
