Impingement Flow Heat Transfer Measurements of Turbine Blades Using a Jet Array

The requirement for increased gas turbine engine performance has led to the use of much higher turbine entry temperature (TET). The higher temperatures require active cooling of the turbine blade using compressor bleed air. Arrays of impinging jets are one method currently used to reduce the blade temperature on the midspan and leading edge. Air flows through small holes in a blade insert and is directed on the inside surface of a turbine blade to reduce local surface temperature. The engine situation was represented by a 10-20 times scale model tested in the internal cooling transient facility at the University of Oxford. The geometry chosen was for a widely spaced array with a jet spacing of 8d and a plate thickness to jet diameter of 1.2. Experiments were accomplished for a range of impingement plate to target surface spacings, z/d, (1, 2 and 4) and jet Reynolds numbers, Re sub j, (10,000 - 40,000) with both staggered and inline array hole configurations. The transient liquid crystal technique, both peak intensity narrowband and hue temperature history wideband, enabled the determination of heat transfer coefficient and adiabatic wall temperature. For the first time, local detail of heat transfer on the target surface as well as observation of the crossflow influence on the jet at the target surface are possible. A large variation in heat transfer exists between the stagnation point and channel passage between jets (2-4 times) which was unknown in previous experiments. Original contains color plates: All DTIC and NTIS reproductions will be in black and white.