Film Cooling Effect of Rotor-Stator Purge Flow on Endwall Heat/Mass Transfer

Mass transfer measurements on the endwall and blade suction surfaces are performed in a five-blade linear cascade with a high-performance rotor blade profile. The effects of purge flow from the wheelspace cavity entering the hot gas path are simulated by injecting naphthalene-free and naphthalene-saturated air through a slot upstream of the blade row at 45 deg to the endwall, for a Reynolds number of $6×105$ based on blade true chord and cascade exit velocity, and blowing ratios of 0.5, 1, and 1.5. Oil-dot visualization indicates that with injection, a recirculation region is set up upstream of the leading edge, and the growth of the passage vortex is altered. The coolant exiting from the slot is drawn to the suction side of the blade and is pushed up along the suction surface of the blade by the secondary flow. For blowing ratios of 0.5 and 1.0, only a little coolant reaches the pressure side in the aft part of the passage. However, at a blowing ratio of 1.5, there is a dramatic change in the flow structure. Both the oil-dot visualization and the cooling effectiveness maps indicate that at this blowing ratio, the coolant exiting the slot has sufficient momentum to closely follow the blade profile and is not significantly entrained into the passage vortex. As a result, high cooling effectiveness values are obtained at the pressure side of the endwall, well into the midchord and aft portions of the blade passage.