An Experimental Study to Compare the Naphthalene Sublimation With the Liquid Crystal Technique in Compressible Flow

Abstract

The naphthalene sublimation and the liquid crystal technique are two methods being used for measurements of the heat transfer coefficient on turbine airfoils. In this paper the results obtained with the two methods for the same compressible flow conditions are compared. The measurements were performed in a free jet test facility on a flat plate and a cylinder. The free stream Mach number ranged from M=0.4 to 0.8. The naphthalene sublimation technique was applied to obtain the local Nusselt number, based on the Sherwood number, applying a new analogy function (Häring, Weigand (1995)). These results were compared with measurements on the same test arrangement using the transient liquid crystal technique. A good agreement between the two measurement techniques and correlations was found for the entire Mach number range. An application of both techniques on a turbine airfoil confirmed this observation. The sublimation technique was also applied to measure the local heat transfer coefficient on a turbine vane at exit Mach numbers up to M=0.9 and exit Reynolds numbers up to Re=1.8e6. The experimental results were compared with the two dimensional boundary layer code TEXSTAN (Crawford, 1986).