Adiabatic and Overall Effectiveness for the Showerhead Film Cooling of a Turbine Vane

Abstract

There have been a number of previous studies of the adiabatic film effectiveness for the showerhead region of a turbine vane, but no previous studies of the overall cooling effectiveness. The overall cooling effectiveness is a measure of the external surface temperature relative to the mainstream temperature and the inlet coolant temperature, and consequently is a direct measure of how effectively the surface is cooled. This can be determined experimentally when the model is constructed so that the Biot number is similar to that of engine components, and the internal cooling is designed so that the ratio of the external to internal heat transfer coefficient is matched to that of the engine. In this study, the overall effectiveness was experimentally measured on a model turbine vane constructed of a material to match Bi for engine conditions. The model incorporated an internal impingement cooling configuration. The cooling design consisted of a showerhead composed of five rows of holes with one additional row on both pressure and suction sides of the vane. An identical model was also constructed out of low conductivity foam to measure adiabatic film effectiveness. Of particular interest in this study was to use the overall cooling effectiveness measurements to identify local hot spots which might lead to failure of the vane. Furthermore, the experimental measurements provided an important database for evaluation of computational fluid dynamics simulations of the conjugate heat transfer effects that occur in the showerhead region. Continuous improvement in both measures of performance was demonstrated with increasing momentum flux ratio.

Conjugate Heat Transfer Analysis of the Aero-Thermal Impact of Different Feeding Geometries for Internal Cooling in Lifetime Extension Processes for Heavy-Duty Gas Turbines

“…The adiabatic and overall cooling effectiveness are evaluated under different coolant-to-main flow momentum ratios, showing that while the former tends to decrease with an increasing momentum ratio, due to coolant jet separation the latter undergoes a stable increase, thanks to the augmented internal cooling effects. The same trends are reported by Nathan et al [11], who investigated a turbine airfoil with flow impingement for the internal cooling and a showerhead configuration of five rows of holes for the external cooling. In this case, the adiabatic effectiveness increases up to a maximum value with increasing momentum ratio.…”

Evaluation of Superposition Predictions for Showerhead Film Cooling on a Vane

“…This, in effect, created a "wall" of coolant which prevented the hot mainstream flow from contacting the vane surface. Since then, other researchers including Nathan et al [5] have confirmed these results using higherresolution infrared (IR) thermography, and Albert and Bogard [6] observed similar results on a vane with a different showerhead cooling configuration.…”

Experimental Study of Impingement Effusion-Cooled Double-Wall Combustor Liners: Thermal Analysis

“…through a wall with the thickness t and heat conductivity k. For a correct thermal scaling, Equation (3) shows the necessity of respecting the hot gas Biot number and the ratio of h f/h c,int . Coolant warming can be accounted for if needed [30]. Depending on the operating parameters in the experiment, it can be reasonable and necessary to substitute the specimen materials to achieve Biot number similarity.…”