Experimental Study of Impingement Jet Cooling Above Pedestal Roughened Channels

An experimental investigation has been conducted into the use of a combined impingement-pedestal cooling geometry to improve uniformity of surface heat transfer coefficient over traditional combustor liner impingement arrays. Various pedestal arrangements have been investigated by altering the height-to-diameter (H/D) and pitch-to-diameter (P/D) ratios and measurements have been made over a range of impingement jet Reynolds numbers between ∼20 and 40×103. The surface heat transfer coefficient has been determined using a transient liquid crystal thermography measurement technique and the data presented in terms of Nusselt number. A ‘shielded impingement’ concept has also been defined featuring full-height pedestals positioned upstream of each impingement jet and arranged to shield the impingement jets from the developing cross-flow. Aerodynamic measurements have also been made to evaluate the influence of changes to the pedestal geometry on the pressure drop incurred across the different cooling patterns. The analysis indicates superior heat transfer performance can be achieved for the shielded impingement arrangements, with the greatest improvement over equivalent geometries displayed towards the rear of the cooling channel.