Rows Of Fan-shaped Holes Research Articles

Study on Additive Effect of Film Cooling Effectiveness in Two Rows of Fan-Shaped Holes

Abstract The coolant jet interaction has a great influence on the superposition prediction of multirow film cooling. Although there have been many efforts to reveal the mechanics of additive effect in multirow film cooling, the available knowledge about developing the superposition method is still limited. The present work examines the film cooling effectiveness in two rows of fan-shaped holes by pressure sensitive paint technique, at the blowing ratios of 0.5–2.0 and the density ratio of 1.0. It is found that the impact of upstream flow on the downstream cooling film is reflected in the variation of turbulence intensity. The enhanced turbulence intensity is detrimental to the downstream film cooling effectiveness especially at the far away region. The mixing of upstream flow and coolant ejection starts at the leading edge of the hole exit. Thus, the streamwise width of the hole exit should be taken into consideration for better predicting the film cooling effectiveness around the holes. The cause of additive effect is that the coolant ejection at the second row affects the local mainstream entrainment. Then, a new correction factor, which characterizes the influence of coolant ejection on the mainstream entrainment of the upper row, is proposed for improving the classical Sellers method. The final result shows a good agreement with experimental data.

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.