Arrangement Effects of 30 deg Inclined Teardrop-Shaped Dimples on Film Cooling Flow Over Dimpled Cutback Surface at Airfoil Trailing Edge Investigated by 2D3C-PTV

Abstract

The objective of this study is to determine the differences in flow fields between the 30 deg in-line and staggered arrangements of teardrop-shaped dimples, and to explain why the surface-averaged Nusselt number with the 30 deg in-line arrangement was 28.7% higher than that with the 30 deg staggered arrangement in our previous study. Measurements of the instantaneous velocity fields over the dimpled cutback surfaces in the two arrangements were performed at five spanwise cross sections using two-dimensional three-component particle tracking velocimetry (2D3C-PTV). Recirculation flows were observed only inside the dimples in the in-line arrangement, and the region above the recirculation flows exhibited a higher Reynolds shear stress. In this region, turbulent mixing between the high-speed cooling-flow and the low-speed recirculation-flow can be promoted. Streamlines of the time-averaged velocities showed that approximately half the fluid flowing out of a teardrop-shaped dimple in the in-line arrangement hardly flowed into the ones downstream. The remainder of the fluid mostly flowed into the dimple immediately downstream, and the inflow of the fluid into further downstream dimples decreased gradually. From the PTV results, we can deduce that the fluid motions in the in-line arrangement leads to a larger temperature-difference between the dimple wall and the fluid because the inflow of fluid heated inside upstream dimples into the downstream ones is less than in the staggered arrangement. Consequently, the Nusselt number in the in-line arrangement was higher.