Full-coverage film cooling on the curved walls. 3rd report. Cooling effectiveness on concavely and convexly curved walls.

Abstract

The effect of wall curvature on the full-coverage film cooling performance has been studied experimentally by using concave, flat and convex walls. The effect of coolant mass flux has also been investigated. A preliminary consideration, based on the balance of the centrifugal force associated with an injected fluid element and the pressure gradient normal to the wall, leads to the understanding that the trajectory of the injected fluid tends to move away from the concave wall and attach to the convex wall, respectively, under the present experimental conditions. This has been experimentally confirmed by both the boundary layer measurements and the smoke-wire flow-visualization. In accordance with the flow structure observed, the cooling effectiveness measured on the convex and concave walls is higher and lower than that on the flat wall. In addition, the mass flux ratio has little effect on the cooling effectiveness on the concave wall, while it is optimum in the range of 0.4 - 0.5 on the convex wall.