HEAT TRANSFER IN AN OBLIQUE JET IMPINGEMENT CONFIGURATION WITH VARYING JET GEOMETRIES

Experimental and numerical heat transfer results in a trapezoidal duct with two staggered rows of inclined impingement jets are presented. The influence of changes in the jet bore geometry on the wall heat transfer is examined. The goal of this project is to minimize the thermal load in an internal gas turbine blade channel and to provide sufficient cooling for local hot spots. The dimensionless pitch is varied between p/d(jet) = 3 - 6. For p/d(jet) = 3, cylindrical as well as conically narrowing bores with a cross section reduction of 25% and 50%, respectively, are investigated. The studies are conducted at 10,000 <= Re <= 75,000. Experimental results are obtained using a transient thermochromic liquid crystal technique. The numerical simulations are performed solving the RANS equations with FLUENT using the low-Re k-omega-SST turbulence model. The results show that for greater pitch, the decreasing interaction between the jets leads to diminished local wall heat transfer The area averaged Nusselt numbers decrease by up to 15 % for p/d(jet) = 4.5, and up to 30 % for p/d(jet) = 6, respectively, if compared to the baseline pitch of p/d(jet) = 3. The conical bore design accelerates the jets, thus increasing the area-averaged heat transfer for identical mass-flow by up to 15% and 30% for the moderately and strongly narrowing jets, respectively. A dependency of the displacement between the Nu maximum and the geometric stagnation point from the jet shear layer is shown.