Aerothermal comparison of a diffuser hole and a slot geometry: thermal performance and jet stability

Abstract

Numerous experimental investigations, predominantly determining the adiabatic film cooling effectiveness and the heat transfer coefficient with film cooling dependent on parameters such as blowing ratio (M), density ratio (DR), velocity ratio (VR) and momentum flux ratio (IR) have been conducted in the past for a vast variety of geometries. To fully characterize a jet in cross-flow for its application in film cooling, thermal and aerodynamic parameters have to be analysed in conjunction. In the present work, detailed flow field measurements using Stereoscopic Particle Image Velocimetry (SPIV) are conducted at engine-realistic operating conditions in a test rig at the Institute of Thermal Turbomachinery (ITS) at the Karlsruhe Institute of Technology (KIT). Additionally, thermal measurements using Infrared Thermography (IRT) are carried out to determine the adiabatic film cooling effectiveness and the heat transfer coefficient with film cooling. Two film cooling hole geometries are analysed: A 10°-10°-10° laidback fan-shaped shaped film cooling hole (LFH10) and a slot geometry with a plenum-like inlet. Flow field data, and thermal film cooling quantities are analysed to quantify and characterize their aero-thermal behaviour. The significance of the stability and continuity of the exiting film cooling jets for the thermal performance is demonstrated to comprehend the differences in how efficiently the provided cooling air is used. It is shown that the absence of the counter-rotating vortex pair may not necessarily lead to an improved adiabatic film cooling effectiveness <inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:msub><mml:mi>η</mml:mi><mml:mrow><mml:mrow><mml:mi mathvariant="normal">a</mml:mi><mml:mo>,</mml:mo><mml:mi mathvariant="normal">W</mml:mi></mml:mrow></mml:mrow></mml:msub></mml:math></inline-formula>.