DNS of secondary flows over oscillating low-pressure turbine using spectral/hp element method

摘要

This paper investigates the secondary vortex flows over an oscillating low-pressure turbine blade using a direct numerical simulation (DNS) method. The unsteady flow governing equations over the oscillating blade are discretized and solved using a spectral/hp element method. The method employs high-degree piecewise polynomial basis functions which results in a very high-order finite element approach. The results show that the blade oscillation can significantly influence the transitional flow structure and the wake profile. It was observed that the separation point over vibrating T106A blades was delayed 4.71% compared to the stationary one at Re = 51,800. Moreover, in the oscillating case, the separated shear layers roll up, break down and shed from the trailing edge. However, the blade vibration imposes additional flow disturbances on the suction surface of the blade before leaving from the trailing edge. Momentum thickness calculations revealed that after flow separation point, the momentum thickness grows rapidly which is due to the inverse flow gradients which generate vortex flows in this area. It was concluded that the additional vortex generations due to the blade vibrations cause higher momentum thickness increment compared to the conventional stationary LPT blade.