Adiabatic and Overall Effectiveness Measurements of an Effusion Cooling Array for Turbine Endwall Application

Abstract

An experimental analysis for the evaluation of adiabatic and overall effectiveness of an effusion cooling geometry is presented in this paper. Chosen configuration is a flat plate with 98 holes, with a feasible arrangement for a turbine endwall. Fifteen staggered rows with equal spanwise and streamwise pitches (Sx/D=Sy/D=8.0), a length to diameter ratio of 42.9 and an injection angle of 30 deg are investigated. Measurements have been done on two different test samples made both of plastic material and stainless steel. Adiabatic tests were carried out in order to obtain adiabatic effectiveness bidimensional maps. Even if a very low conductivity material polyvinyl chloride was used, adiabatic tests on a typical effusion geometry suffer, undoubtedly, from conductive phenomena: a full three-dimensional finite element method postprocessing procedure for gathered experimental data was therefore developed for reckoning thermal fluxes across the surface and then correctly obtaining adiabatic effectiveness distributions. The objective of the tests performed on the conductive plate, having the same flow parameters as the adiabatic ones, was the estimation of overall efficiency of the cooled region. Experimental measurements were carried out imposing two different crossflow Mach numbers, 0.15 and 0.40, and varying blowing ratio from 0.5 to 1.7; effectiveness of the cooled surface was evaluated with a steady-state technique, using thermochromic liquid crystal wide band formulation. Results show that the postprocessing procedure correctly succeeded in deducting undesired thermal fluxes across the plate in adiabatic effectiveness evaluation. The increasing blowing ratio effect leads to lower adiabatic effectiveness mean values, while it makes overall effectiveness to grow. Finally, Reynolds-averaged Navier–Stokes steady-state calculations were performed employing an open source computational fluid dynamics code: an adiabatic case has been simulated using both a standard and an anisotropic turbulence model. Numerical achievements have then been compared with experimental measurements.