Optimization of Jet Impingement Channel for Near Wall Cooling in Gas Turbine Airfoils

摘要

The current experimental study focuses on the heat transfer and pressure effects of a single array jet impingement channel. This study is broken down into three parts: 1) varying flow and varying diameters, 2) effects of jet configuration by staggering and angling jets, and 3) the effects of surface roughness on jet impingement. A single row of five jets, individually fed for the varying flow case and plenum fed for all other cases expels air onto the target surface as the spent air is constrained to exit in only one direction, causing jets to encounter maximum crossflow. The baseline jet plate parameters were defined as diameter, D, height to diameter H/D, and jet-to-jet spacing, S/D, are 9.53 mm (0.375 in), 2 and 4, respectively. The Reynolds Number, Re, for these studies ranged from 50,000 to 80,000. A transient liquid crystal technique is employed to determine the local and average heat transfer coefficient distribution on the target plate. Commercially available CFD software, ANSYS CFX, is used to correlate experimental results and to provide detailed insights of the flow field created by the array of jets. Additionally, two stainless steel coupons representing the jet impingement array at realistic size were tested and compared to results reported in literature. udBy varying the jet flow rates by approximately ± 2% over the baseline case, local heat transfer enhancement on the target surface is increased up to 35%. Using the flow rates from the optimum varying flow case, a jet plate with varying diameters was created. Unfortunately, enhancement was not as significant in the varying diameter case due to the nature of flow distribution from the plenum.udStaggered jets, 1D and 2D, and staggered angled jets, 1D and 2D with 30◦ inclination were compared to the baseline case. Staggered jets, because of interactions with the channel side walls show no enhancement over the baseline. However, jets staggered 1D with 30◦ inclination show a heat transfer enhancement of ≈ 20%.udFor the final part, surface roughness is explored. In general, different shaped ribs tend to enhance heat transfer by increasing the surface area of the target plate. As found in this study, and also reported in literature, horizontal ribs can cause entrainment, thus reducing the effectiveness of the jet impingement. If strategically placed, as for the X-shaped ribs, further enhancement can be achieved, especially in the downstream regions of the channel where crossflow tends to affect jet impingement.ud