Characterization of Overall Effectiveness Under the Influence of Two Coolant Temperatures

Abstract

Abstract A conjugate heat transfer analysis of the complex mechanisms of internal and external cooling of turbine blades can present a formidable task. Such an effort may be simplified somewhat by evaluating the normalized metal surface temperature of a turbine blade, also known as the cooling scheme’s overall effectiveness. Investigations of turbine cooling effectiveness for scenarios with multiple rows typically assume a single coolant temperature. However, scenarios may exist in which a region of interest is affected by multiple local coolant temperatures, such as when coolant is injected from different internal passages. The present work develops an appropriate reference temperature for such a situation as well as a new nondimensional parameter indicating the relative difference between coolant temperatures. The effect of this new nondimensional parameter on overall effectiveness and streamwise temperature gradients is evaluated for two double row cooling hole configurations. Each row, consisting of 7-7-7 cooling holes set in an Inconel flat plate, exhausts coolant at independently controlled temperatures; effectiveness is also evaluated at different advective capacity and momentum flux ratios. Circumstances are identified in which different coolant temperatures may present an advantage in overall cooling effectiveness and in reducing streamwise temperature gradients.