Experimental Simulation of Turbine Airfoil Leading Edge Film Cooling

Abstract

Leading edge showerhead cooling designs represent an important feature of certain classes of high-temperature turbine airfoils. This paper outlines a methodology for predicting the surface temperatures of showerhead designs with spanwise injection through an array of discrete holes. The paper describes a series of experiments and analyses on scaled cylinder models with injection through holes inclined at 20, 30, 45, and 90 deg for typical radial and circumferential spacing-to-diameter ratios of 10 and 4, respectively. The experiments were conducted in a wind tunnel on several stainless steel test specimens in which flow and heat transfer parameters were measured over the simulated airfoil leading edge surfaces. Based on the experiments, an engineering design model is proposed that treats the gas-to-surface heat transfer coefficient with film cooling in a manner suggested by a recent Purdue–NASA investigation and includes the important contribution of upstream (coolant inlet face) heat transfer. The experiments suggest that the averaged film cooling effectiveness in the showerhead region is primarily influenced by the inclination of the injection holes. The effectiveness parameter is not strongly affected by variations in coolant-to-gas stream pressure ratio, free-stream Mach number, gas-to-coolant temperature ratio, and gas stream Reynolds number. The model is employed to determine (inferentially) the average Stanton number reduction parameter for a series of pressure ratios varying from 1.004 to 1.3, Mach numbers ranging from 0.1 to 0.2, temperature ratios between 1.6 and 2.0, and Reynolds numbers ranging from 3.5×104 to 9.0×104.

Experimental investigations on showerhead cooling on a blunt body

“…The measurements showed that the film cooling performance depends strongly on the injection geometry and the coolant injection rate. Later, Wadia and Nealy [6] conducted experiments in a wind tunnel on several stainless steel cylindrical models.…”

State-of-the-Art Cooling Technology for a Turbine Rotor Blade

“…Each film cooling hole has a circular cross section and is oriented at a 20 deg angle with respect to the surface. Wadia and Nealy [17] have shown the advantages of using shallow angle (20 deg angle) cooling holes along the leading edge. Wadia and Nealy [17] also proposed an internal heat transfer coefficient for the coolant within these cooling holes based on a conventional correlation (see Eq.…”

“…Effects of partition taper on downstream film effectiveness[45] Fig 17. Trailing edge design modifications[46] Fig.…”