Effect of main stream turbulence on the film cooling effectiveness of a circular and a fan-shaped film cooling hole

Abstract

The reliability of turbine blades and vanes of modern high temperature gas turbines is assured by turbine blade cooling technologies. Among the various cooling methods, film cooling has been a key technology to ensure the long-term operation of turbine blades and vanes that are exposed to hot gas-path flows. Therefore, many papers have been published aiming at the improvement of film cooling effectiveness by optimization of film cooling hole geometries. Although the turbulence intensity of the mainstream generated in the gas turbine combustor is very high and may reduce the film cooling effect on the turbine vane and blade, there are few papers investigating quantitatively the effect of the mainstream turbulence on the film cooling. For this reason, the influence of mainstream turbulence intensity on film cooling effectiveness was investigated with an active turbulence generator equipped with electric-motor driven propellers for circular and fan-shaped film cooling holes. Spatial distributions of the turbulent mixing field between turbulent mainstream and film coolant jet were measured with quantitative measurement methods, such as PIV and LIF. As a result, it was revealed that when the mainstream turbulence is high the counter-rotating vortex pair is weakened, the film cooling air spreads in the span-wise direction and the lateral-averaged film cooling effectiveness decreases about 10%.

Keywords

• gas turbine
• film cooling
• heat transfer
• laser induced fluorescence
• particle image velocimetry