Numerical Investigation of Laidback Fan-Shaped Film Cooling Holes With Large Eddy Simulation

Abstract

Due to the high demand for the output power and thermal efficiency, the turbine inlet temperature is extremely high which has significantly exceeded the melting point of the blade material. Therefore, the turbine blade cooling system plays a pivotal role in the entire engine. As for the external cooling, film cooling technology has been widely used in the modern advanced design of gas turbines in order to enhance the cooling performance and reducing the cooling air usage. According to the public literature, conventional cylindrical film cooling hole has been studied by many researchers, whereas the laidback fan-shaped film cooling hole, as a cutting-edge technology, is relative novel, advantageous and still under investigation. Thus, large eddy simulation (LES) method was implemented to study the flow field and the thermal performance of shaped film holes at turbulence intensity Tu = 0.5%, density ratio DR = 1.5, blowing ratio M = 0.5–3.0 and momentum flux ratio I = 0.17–6.00. The adiabatic film cooling effectiveness with LES shows a good agreement with the experimental data. A comparison was conducted between the conventional cylindrical film hole and the laidback fan-shaped film hole in the range of M = 0.5–1.5. The results show that shaped film hole obtains better cooling effectiveness with sufficient spread in spanwise direction as the blowing ratio increases, and M = 1.5 can provide a relative better performance for shaped film hole. As for the details of the flow field, the counter-rotating vortex pair (CRVP) and anti-CRVP structures are found in the simulation. Time-averaged Reynolds shear stresses and turbulence viscosity exhibit strong anisotropic properties near the bottom surface. The analyses may help to understand the characteristics of the laidback fan-shaped film cooling and guide the cooling design of the turbine blade.