Experimental Investigation of Turning Flow Effects on Innovative Trailing Edge Cooling Configurations With Enlarged Pedestals and Square or Semicircular Ribs

Abstract

In this paper the experimental measurements concerning the heat transfer capabilities of several trailing edge (TE) cooling configurations that are based on the combination of enlarged pedestals and small rib turbulators are presented. The baseline geometry consists of a converging duct, reproducing the typical shape of a high pressure turbine blade TE, with two rows of enlarged pedestals. Three rows of square or semicircular turbulators were arranged in between the pedestals on the pressure side (PS) surface; the ribs height is e = 1 mm and the pitch is P/e = 10. The airflow pattern inside the test rig simulates the rotor blade cooling scheme with a 90deg turning flow from the hub inlet to the TE outlet. For each configuration heat transfer measurements were made keeping Mach number fixed at 0.3 and varying Reynolds number from 9000 to 27000 in the TE throat section. The effect of a varying tip massflow rate was tested considering 0%, 12.5% and 25% of the TE massflow. The detailed HTC maps were measured using the transient technique with TLC and a PMMA test article. As expected, by comparison with the baseline geometry, test results show that the HTC distribution and the average Nusselt number over the PS surface are affected by the presence of the ribs which promote the airstream turbulence. However, no remarkable difference between the results from different rib shapes can be highlighted. The tip massflow rate alters the HTC distribution in the radial direction over the whole TE. The results are compared with previous experiments, performed on the same geometries, but with an axial inlet.