The Highly Nonlinear Thermal Behavior of Film Cooling

Abstract

The current view of film cooling/heating behavior is largely the result of room temperature experiments in which the high temperatures typical of gas turbines were only simulated. The simulation rests on the assumption/deduction that the effect of temperature on film cooling behavior is due solely to the effect of temperature on fluid density. A few experiments reported in the literature have included wide variation in temperature. In this article, the data from several of these are examined in order to determine the actual, observed effect of temperature on film cooling behavior. Literature data exhibit a highly linear relationship between Taw and Tfc when the film is injected through a slot, and Tfc/Tms lies in the range 0.8 to 1.27. The data also indicate that this relationship is highly nonlinear when Tfc/Tms is less than approximately 0.8. The nonlinearity is so pronounced that Taw may not decrease even though (Tfc/Tms) is decreased from 0.57 to 0.35. Nonlinearity in the relationship between Taw and Tfc has a major impact on optimum system design whenever the thermal designer has design control over the film coolant temperature.