Freestream effects on the interaction between near-wall vortex and film ejected from a fan-shaped hole

A flat plate film cooling experiment was conducted to investigate the effects of near-wall vortex on the film cooling performance of a fan-shaped hole. A vane-shaped vortex generator was installed upstream of a fan-shaped hole to simulate a near-wall vortex. Infrared thermography was used to measure the cooling effective-ness and heat transfer coefficient for the blowing ratios from 0.5 to 2.5. Inlet flow properties of turbulence in-tensity and boundary layer thickness were varied to set up different freestream conditions. Results show that the vortex affects the film cooling to varying degree under different freestream conditions. In case of low inlet turbulence, upstream boundary layer thickness is a significant factor on the film cooling performance. With a thin boundary layer, vortex intensifies the mixing of freestream and coolant jet. The decrease in lateral-average film cooling effectiveness ranges from 0.02 to 0.06 depending on the blowing ratios and relative positions of the vortex. The heat flux through the test plate is significantly increased by 20%. Thickened boundary layer pro-motes coolant jet to penetrate the freestream flow, which degrades the film cooling performance. However, thick boundary layer restrains the vortex disturbance on the freestream flow, and the heat flux of the test plate is only increased by 5.6%. In the case of high turbulence intensity, boundary layer plays an insignificant role. The near-wall vortex dissipates quickly and exerts little impact on the film cooling effectiveness and surface heat transfer coefficient.