The characteristics and divergence of fan-shaped and cylindrical holes on the suction side of a turbine blade under rotating conditions

Detailed film cooling effectiveness for fan-shaped and cylindrical holes on the suction side of a turbine blade under rotating conditions was obtained by experimental measurements. The experiments were conducted using a 1-stage turbine installed in a closed-loop, low-speed, thermal wind tunnel. The turbine section was designed to rotate at different settled speeds, and the velocity of the mainstream was adjusted to achieve a zero-incidence angle. In the experiments, a steady-state thermochromic liquid crystal (TLC) technique was used to evaluate the film cooling performance. The row hole was situated at an axial location of 8% with an injection angle of 45°. The diameter of the cylindrical hole was 0.8 mm, and the length-to-diameter ratio was 6. For the fan-shaped hole, the forward expansion angle and the lateral diffusion angle were 12° and 10°, respectively. The effects of blowing ratio (M), rotation speed ( Ω ) and density ratio (DR) on the film cooling performance were analyzed. The blowing ratio was varied from 0.5 to 2.0 with three rotation speeds, 300 rpm, 450 rpm and 600 rpm. CO2 and N2 acted as coolants to achieve the two density ratios of 1.47 and 0.98, respectively. The results showed that the row of fan-shaped holes had better film cooling performance under most operating conditions and especially at low blowing ratios. The length of the coolant trace first increases and then decreases along the spanwise direction, from hub to tip, at all operating conditions. With an increase in the rotation speed, the lateral averaged film cooling effectiveness of both hole geometries decreases. However, fan-shaped holes have better film cooling performance at low rotation speed. In addition, the results for the density ratio showed that CO2, which has a higher density ratio, achieves higher film cooling performance for fan-shaped holes, while the length of the coolant trace is almost constant between the two density ratios.