Numerical Study of Active Flow Control for a Transitional Highly Loaded Low-Pressure Turbine

Abstract

Active control was simulated numerically for the subsonic flow through a highly loaded low-pressure turbine. The configuration approximated cascade experiments that were conducted to investigate a reduction in turbine stage blade count, which can decrease both weight and mechanical complexity. At a nominal Reynolds number of 25,000 based upon axial chord and inlet conditions, massive separation occurred on the suction surface of each blade due to uncovered turning. Vortex generating jets were then used to help mitigate separation, thereby reducing wake losses. Computations were performed using both steady blowing and pulsed mass injection to study the effects of active flow control on the transitional flow occurring in the aft-blade and near-wake regions. The numerical method utilized a centered compact finite-difference scheme to represent spatial derivatives, that was used in conjunction with a low-pass Pade-type nondispersive filter operator to maintain stability. An implicit approximately factored time-marching algorithm was employed, and Newton-like subiterations were applied to achieve second-order temporal accuracy. Calculations were carried out on a massively parallel computing platform, using domain decomposition to distribute subzones on individual processors. A high-order overset grid approach preserved spatial accuracy in locally refined embedded regions. Features of the flowfields are described, and simulations are compared with each other, with available experimental data, and with a previously obtained baseline case for the noncontrolled flow. It was found that active flow control was able to maintain attached flow over an additional distance of 19–21% of the blade chord, relative to the baseline case, which resulted in a reduction of the wake total pressure loss coefficient of 53–56%.