Interaction of Rotational Wakes and Coolant Film in a Sector-Annular Duct

Abstract

In the effort to increase turbine inlet temperature for greater efficiencies, more focus has been placed on the secondary and unsteady flow structures in gas turbine components. One such area that has seen great interest in past decades is the effect of unsteady wakes on film cooling. These wakes are primarily shed by upstream guide vanes or rotors. Relatively little data exists for annular endwall cooling in the presence of these wakes. Time resolved measurements of the film cooling-wake interaction were obtained using hot wire anemometry in a low speed, 30 degree annular sector open loop wind tunnel. In addition, time averaged measurements of the adiabatic film cooling effectiveness were determined for cylindrical holes. The film cooling effectiveness at three blowing ratios (0.25, 0.5, and 1.0) is reported at three wake Strouhal numbers (0, 0.1, and 0.3). Temperature Sensitive Paint was used to obtain spatially resolved temperature measurements. The experimental results are compared to numerical studies as well as experimental literature for several cases. The rotating wake is characterized by a velocity detriment and a local increase in turbulence. The effect of this wake is a reduction in film cooling effectiveness with increasing Strouhal number at weak injection rates (I < 0.3). For strong injection that would lead to liftoff, the effect of the wake is to promote reattachment and increase lateral spreading of the jet, resulting in increased effectiveness. Potential for active flow control exists for strong injection resulting in equal or better effectiveness at lower coolant flow rates.