Fundamentals of Scaling of Overall Cooling Effectiveness With Temperature Ratio

Abstract

In this paper we study the relationship between overall cooling effectiveness (or so-called metal effectiveness) and mainstream-to-coolant total temperature ratio (TR), for typical high-pressure nozzle guide vane (HPNGV) cooling systems. The temperature ratio range studied is that between typical experimental conditions (TR ≅ 1.2) and typical engine conditions (TR ≅ 2.0). The purpose is twofold: firstly, to quantify the difference in overall cooling effectiveness between experimental and engine conditions of temperature ratio; and—secondly—to understand the physical bases for the difference, separated in terms of changes in five local surface boundary conditions. We do this using a bespoke conjugate thermal model which includes models of both the internal cooling and the external film cooling layer. Three typical cooling architectures are studied. The results allow comparison and scaling between situations at different conditions of temperature ratio.