Experimental Investigation of a Complex System of Impinging Jets Using Infrared Thermography

A central task in aviation technology is the development of efficient cooling techniques for thermal highly loaded engine components. For an optimal design of the cooling mechanisms, the heat transfer characteristics have to be known and need to be describable. As a cooling concept for low-pressure turbine casings, complex systems of impinging jets are used in order to reduce blade tip clearances during the flight mission. In order to improve established theoretical model approaches, this paper presents a novel method for the experimental investigation of such a complex system with 200 impinging jets using infrared thermography. The presented experimental method uses a thin electrically heated chrome-aluminum foil as target plate. Modeling the transient effects inside the foil, small structures and high gradients in the heat transfer coefficient can be reproduced with good accuracy. Experimental results of the local heat transfer characteristics are reported for jet Reynolds numbers of Re=2000...6000. The influence of the jet-to-jet distance and the jet Reynolds number on the Nusselt numbers are quantified with Nu∼(S/D)−0.47 and Nu∼Re0.7. The results indicate a dependency of the flow regime for the relatively low jet Reynolds numbers, as it is known from literature.