Effect of blowing ratio on film-cooling effectiveness of ginkgo shaped holes: a numerical approach

Modern gas turbine engines operate at high temperatures to improve thermal efficiency and power output. Increased rotor inlet temperatures increase the rate of heat transfer to the turbine blades, which requires sophisticated cooling schemes to keep the blade temperature at acceptable levels. This work is a numerical investigation of film cooling techniques as applied to gas turbines. The cooling performance of two differently shaped holes, namely, Ginkgo Forward and Ginkgo Reverse, were investigated in terms of centerline and local lateral cooling effectiveness, and a comprehensive comparison was made with the cooling performance of a cylindrical hole. The investigations were performed at a constant density ratio (DR = 2.0) and three different blowing ratios (BR = 1.0, 1.5, and 2.0). Under all of the operating conditions, the results demonstrated significant augmentation in centerline and lateral cooling effectiveness when the Ginkgo Reverse shaped hole was used, followed by the Ginkgo Forward and cylindrical cooling holes. For the shaped cooling holes, the low velocity gradient through the film alleviated the jet lift-off and turbulence, resulting in decreased entrainment of hot gas to the bottom surface. To conclude, the prominent lateral dispersal of the coolant due to the shaped cooling holes significantly enhanced thermal protection and the overall cooling performance.