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.

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.

Impingement cooling is widely used in cooling configurations for gas turbine components. Relatively high local heat transfer rates and the possibility of jet adjustment to specific geometries are advantageous for internal turbine blade cooling designs. In this paper a confined impingement cooling configuration is investigated. 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 flow extraction is realized through two staggered rows of holes opposing the impingement holes wall. Heat transfer experiments were carried out using a transient liquid crystal technique for a series of jet Reynolds numbers between 10,000 and 75,000. The obtained local heat transfer data was evaluated regarding spatially resolved Nusselt numbers as well as line and area averaged values. The results include measurements of the discharge coefficients for the flow through the impingement holes. Numerical simulations of the flow field were carried out, complementary to the experiments. The simulations yield information for a better understanding of the main flow structures. The jets cause high heat transfer in the flow impinging regions with Nusselt numbers up to 180 for Re = 45,000. By contrast, for the same Reynolds number the Nusselt number drops below 20 in flow recirculation regions. For area-averaged Nusselt numbers, the correlation Nu ∝ Rex was found to be valid with slightly modified exponents for each passage wall.