Influence of Spanwise Pitch on Local Heat Transfer for Multiple Jets with Crossflow

The influence of spanwise jet-to-jet spacing on local heat transfer distribution due to multiple impinging circular air jets from an in-line rectangular array on a surface parallel to the jet plate is studied experimentally. The length-to-diameter ratio of the nozzles of the jet plate is 1.0. The flow, after impingement, is constrained to exit in one direction from the confined passage formed between the jet plate and the target plate. Mean jet Reynolds numbers based on the nozzle-exit diameter d covered are 3000, 5000, 7500, and 10,000, and jet-to-plate spacings studied are d, 2d, and 3d. Spanwise pitches considered are 2d, 4d, and 6d, keeping the streamwise pitch at 5d. For all configurations, the jet plates have ten spanwise rows in the streamwise direction and six jets in each spanwise row. The flat heat transfer surface is made of thin stainless steel metal foil. Local temperature distribution on the target plate is measured using thermal infrared camera. Wall static pressure on the target plate is measured in the streamwise direction to estimate crossflow velocities and individual jet velocities. Heat transfer characteristics are explained on the basis of flow distribution. A simple correlation is developed to predict the streamwise distribution of the Nusselt number averaged over each spanwise strip resolved to one jet hole as a function of jet-flow and crossflow distributions.

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