NUMERICAL INVESTIGATION OF THE ROTATION ON THE FILM COOLING OVER A FLAT SURFACE

Abstract

ABSTRACT A computational analysis was carried out to comprehend the mechanism of rotation on the film cooling which is important in understanding the mixing process between the film coolant and the hot stream air over the high pressure turbine blades. In this paper, a simple flat surface with a vertical film cooling hole was positioned parallel to the hot main stream and different rotating orientations were selected to simulate the blade pressure or suction sides. A polar coordinate frame was used with the center of the film cooling hole center as the origin point and three parameters S/D, the polar angle and either the adiabatic effectiveness or heat transfer coefficient could be chosen as the control parameters to produce a 2D graph of the effective film cooling areas. The rotation effects were clearly shown with the effective film cooling area graphs. The effective film cooling area was reduced with the rotating speed increasing. INTRODUCTION Film cooling is a cooling technique currently receiving wide application on the high temperature turbines. Although many parameters affecting film cooling have been intensively investigated, there are few studies on the rotation effects. Dring et al. (1980) were among the earliest to study film-cooling performance in a low-speed rotating facility. The rotating speed was about 405rpm. The existence of the radial component of the film coolant was found to have a strong impact on the nature of the effectiveness distribution. Abhari and Epstein (1994) presented the time-resolved measurements of heat transfer on a fully cooled transonic turbine stage in a short duration turbine test facility. Rotor speed was 6190rpm. The suction surface rotor heat transfer was lower than that measured in the cascade. High blowing ratios were shown to provide much less effective cooling than lower ones. Takeshi et al. (1991) used a heat-mass transfer analogy to measure the film cooling effectiveness on a low-speed stationary cascade and the rotating blade with the speed 6260rpm. A low level of effectiveness appeared on the pressure surface of the rotating blade compared to that on the stationary blade. Garg and co-workers (1997) performed the studies of the effect of blade rotation on the adiabati