Arrangement effects of inclined teardrop-shaped dimples on film cooling performance of dimpled cutback surface at airfoil trailing edge

Cooling at trailing edge of gas turbine airfoil is one of the most difficult problems because of its thin shape: high thermal load from both surfaces, hard-to-cool geometry of narrow passages, and at the same time demand for structural strength are the reasons. In this study, heat transfer coefficient and film cooling effectiveness on pressure-side cutback surface were measured by a transient infrared thermography technique with consideration of three-dimensional heat conduction. The cutback surface was roughened by teardrop-shaped dimples. Three different rotation angles (30, 45, and 60 deg) of the dimpled surface with in-line and staggered arrangements were examined for blowing ratio of 0.5, 1.0, 1.5, and 2.0. Within the present arrangements, the film cooling effectiveness remained almost constant, although the heat transfer coefficient became a maximum at 30 deg in-line arrangement. The overall film cooling performance evaluated by net heat flux reduction was the highest for the 30 deg in-line arrangement and it was 14-24% higher than the 30 deg staggered arrangement. Three-component PTV results explained this effect by the suppression of flow separation in the 30 deg in-line arrangement and it attained the favorable inflow condition on the downstream dimples.