Investigation of Circular and Shaped Effusion Cooling Arrays for Combustor Liner Application—Part 1: Experimental Analysis

An experimental analysis of two different effusion cooled plates, with a feasible arrangement for combustor liner application, is presented in this paper. Though having the same porosity and very shallow injection angle (17 deg), the first configuration presents a “standard” circular drilling (D = 2.65 mm; L/D = 16.4), while the other has “shaped” holes with such an elliptical cross-section that leads to a circular imprint on the cooled surface (D_h = 3.39 mm; L/D_h = 12.8). Either geometry is to be studied on two different samples made of both an adiabatic and a high conductivity material. Tests performed on the adiabatic plates were required to obtain adiabatic effectiveness bidimensional distributions; a full 3D FEM post-processing procedure for the evaluation of the remnant and undesired heat fluxes across the surface was employed as well. Objective of the tests carried out on the conductive samples, having the same flow parameters as the adiabatic ones, was the estimation of overall efficiency, given by the combined effect of film protection and heat removal by convection inside the holes. Hot gas side heat transfer coefficient spanwise averaged values have been evaluated employing the outcome of both adiabatic and conductive tests. Experimental measurements were performed imposing two different coolant jet Reynolds numbers, 12500 and 20000, and varying blowing ratio from 5.0 to 9.0; effectiveness was evaluated with a steady-state technique, using TLC (Thermochromic Liquid Crystals) wide band formulation. Results reveal that the reduced coolant jet penetration achievable by means of shaped configuration leads to an increased wall protection in terms of both peak and spanwise averaged values, even if circular holes guarantee a more uniform effectiveness distribution.