Investigation for the improvement of film cooling effectiveness on a high pressure Turbine aerofoil with shaped film holes

Modern day gas turbines are operating at gas temperatures which are close to melting temperature of the turbine aerofoil materials. It is essential to cool High Pressure Turbine (HPT) aerofoils such as Nozzle guide vane (NGV) and Rotor blades to improve their creep life to achieve safe life and reliability. Film cooling protects the blade surface from hot gas by providing a cool insulating layer between hot gas stream and the airfoil metal surface. Film cooling effectiveness is a measure of how well the metal surface is protected from the hot gas stream by the layer of cool secondary air. Cooling hole geometry is one of the key parameters which influences the film cooling coverage. Earlier aerofoils were with cylindrical holes, whereas current advanced aero engines are using shaped holes to achive higher effectiveness and better spanwise coverage. The current study is carried out with one of the shaped hole configuration namely, laid back fan shaped hole configuration on HPT turbine rotor blade without rotation. The advantage of using shaped hole over cylindrical hole is brought out in this paper. CFD analysis is carried out using FloEFD software for prediction of film cooling effectiveness for the film holes at one of the peak operating condition. The CFD analysis is validated with measured film cooling effectiveness data. The advantage of using laid back fan shaped hole is brought out from cooling effectiveness point of view. Parametric analysis is carried out for film cooling effectiveness at different blowing ratio (BR) = 1.0 to 2.5, turbulence intensity (Tu) = 5%, 7%, 9 % and fan angle (γ) = 10 ͦ & 12 ͦ of shaped film hole.