Heat transfer measurements of a confined impingement cooling configuration with ribs on the target surfaces are presented. The assembly consists of four non-perpendicular walls of which one holds two rows of staggered inclined jets, each impinging on a different adjacent wall. The ribs are aligned with the inclined jet axes, have the same pitch and are staggered to the impinging jets. The flow exhausts through two staggered rows of holes opposing the impingement wall. The passage geometry is related to a modern gas turbine blade cooling configuration. A transient liquid crystal technique was used to take spatially resolved surface heat transfer measurements for the ground area between the ribs. A comparison with the smooth baseline configuration reveals local differences and a generally reduced heat transfer for the rib-roughened case. Furthermore, lumped heat capacity measurements of the ribs yielded area averaged heat transfer information for the ribs. From the combination of ground and rib heat transfer measurements it is concluded that the overall performance of the ribbed configuration depends on the Reynolds number. Of the five investigated jet Reynolds numbers from 10,000 up to 75,000, only for the highest Re the averaged Nusselt numbers increase slightly compared to the smooth baseline configuration.

For heat transfer measurements on the center blade of a linear cascade, the infrared measurement technique was set up. As a highly challenging condition, the angular dependency of the infrared signal was identified. Beside a shallow angle of view, limited by geometric conditions, the curved blade surface necessitated the consideration of this dependency. Therefore, a powerful in-situ calibration method was set up, which accounts for the angular dependency implicitly. In contrast to usual procedures, the correlation of the measured infrared intensity and the temperature was calibrated by a separate calibration function for each position on the blade. In all, three different calibration approaches were proceeded and assessed. Initial measurements in low-speed test conditions delivered physically more reasonable results, using a local calibration compared to a usual global calibration. By means of these data, an evaluation of the aerodynamic characteristic of the cascade was enabled. With few modifications, the procedure is capable to deliver high-precision heat transfer measurements in the high-speed cascade wind-tunnel at the Institute of Jet Propulsion.

The 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/djet=3 − 6. For p/djet=3, cylindrical and 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- ω -SST turbulence model. The results show that for a 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/djet=4.5, and up to 30% for p/djet=6, respectively, if compared to the baseline pitch of p/djet=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.

Heat transfer measurements of a confined impingement cooling configuration with ribs on the target surfaces are presented. The assembly consists of four nonperpendicular walls of which one holds two rows of staggered inclined jets, each impinging on a different adjacent wall. The ribs are aligned with the inclined jet axes, have the same pitch, and are staggered to the impinging jets. The flow exhausts through two staggered rows of holes opposing the impingement wall. The passage geometry is related to a modern gas turbine blade cooling configuration. A transient liquid crystal technique was used to take spatially resolved surface heat transfer measurements for the ground area between the ribs. A comparison with the smooth baseline configuration reveals local differences and a generally reduced heat transfer for the rib-roughened case. Furthermore, lumped heat capacity measurements of the ribs yielded area averaged heat transfer information for the ribs. From the combination of ground and rib heat transfer measurements, it is concluded that the overall performance of the ribbed configuration depends on the Reynolds number. Of the five investigated jet Reynolds numbers from 10,000 to 75,000, only for the highest Re the averaged Nusselt numbers increase slightly compared with the smooth baseline configuration.

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/djet = 3–6. For p/djet = 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-ω-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/djet = 4.5, and up to 30% for p/djet = 6, respectively, if compared to the baseline pitch of p/djet = 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.