Vadiraj Katti

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.

Heat Transfer Distribution of Semicylindrical Concave Surface Impinged by Circular Jet Rows

The impingement cooling of the leading edge of a gas turbine airfoil is modeled by considering impingement of three rows of jets on a semicylindrical concave surface. Experimental investigations are conducted to study the influence of jet-to-jet distance (s/d = 2.83, 4, and 6) and jet-to-plate distance (z/d = 2, 4, 6, and 8) on the local heat transfer of a semicylindrical concave surface impinged by three rows of multiple jets for different Reynolds numbers (12,000, 15,000, and 18,000). The local heat transfer coefficient is estimated using thermal images obtained by infrared thermal imaging technique. The local distribution of Nusselt numbers and the overall average Nusselt numbers were computed and compared. It was observed that the local heat transfer coefficients at 0 = 0° decrease with increase in z/d, whereas the heat transfer coefficients at θ = 60 and 80° increase with an increase in z/d at all Reynolds numbers. The configuration with s/d = 2.83 and z/d = 4 is observed to have the maximum heat transfer distribution with minimum coefficient of variance compared to other configurations at all Reynolds numbers covered in this study.

Experimental Study on Local Heat Transfer Distribution between Smooth Semi-Cylindrical Concave Surface and Impinging Air Jet from a Circular Straight Pipe Nozzle

An experimental investigation is performed to study the effect of jet-to-plate spacing and Reynolds number on the local heat transfer distribution to normally impinging submerged circular air jet on a smooth semi-cylindrical concave surface. A single jet from a straight circular nozzle of length-to-diameter ratio (l/d) of 83 is tested. Reynolds number based on nozzle exit condition is varied between 11000 and 28000 and jet-to-plate spacing between 0.5 to 8 nozzle diameters. Experiments were carried out for two relative curvatures (D/d) of 4.4 and 6 by changing the jet tube diameter. The local heat transfer characteristics are estimated using thermal images obtained by infrared thermal imaging technique. Effect of curvature on heat transfer distribution is studied and compare with the flat plate results. Curvature results in decrease of Nusselt number compared to flat plate values.