Experimental assessment of the aero-thermal performance of rib roughened trailing edge cooling channels for gas turbine blades

Based on the combined analysis of detailed flow field and heat transfer experimental data, the aero-thermal behaviour of different trailing edge cooling channels is reported. The reference geometry (GO) is characterized by a trapezoidal cross section of high aspect-ratio, inlet radial flow, and coolant discharge at both model tip and trailing edge, where seven elongated pedestals are also installed. Two variations of the reference geometry have squared ribs installed inside the channel radial central portion (G1) or inside the trailing edge exit region (G2). The forced convection heat transfer coefficient has been measured by means of a steady state Liquid Crystal Thermography (LCT) technique, while reliable and detailed flow measurements have been performed by means of Particle Image Velocimetry (PIV) or Stereo-Ply techniques. The experimental Reynolds number has been fixed at 20,000. The heat transfer data for the three configurations have been analyzed and compared considering both local and channel-averaged features of the heat transfer fields. In particular, the flow mechanisms responsible for the existence of high or low heat transfer regions have been identified and explained. The effects of the different turbulence promoters on both the flow and heat transfer fields have been put in evidence as well. With the aim to determine the most effective configuration, area averaged heat transfer data have been compared, together with information about the channels pressure losses. Configuration G1 turned out to be the most promising, giving rise to a significant heat transfer enhancement associated to a moderate increase in pressure losses.