Conjugate Heat Transfer from an Impingement and Film-Cooled Flat Plate

Abstract

The effect of solid thermal conductivity on conjugate heat transfer from a flat plate with combined impingement and film cooling is studied both experimentally and computationally. One side of the plate is exposed to hot mainstream, whereas the other side is impinged with air jets. A flow configuration with multiple staggered rows of cylindrical film holes and a matrix of impingement holes is considered. A thermochromic liquid crystal technique is used in the experiment to measure the surface temperature of the plate. The physical domain is meshed with fine-sized hybrid: hexahedral and tetrahedral grids suitable for the finite volume computations. Reynolds-averaged Navier–Stokes equations are solved with shear-stress transport -omega turbulence modeling. A grid independence study is carried out using a grid convergence index method. A validation exercise of computational results is carried out against the full coverage film cooling data available in literature (“Total Cooling Effectiveness on A Staggered Full-Coverage Film Cooling Plate with Impinging Jet,” ASME-TurboExpo2010, American Soc. of Mechanical Engineers Paper GT2010-23725, Fairfield, NJ, June 2010). Results from the conjugate heat transfer study are presented for three blade materials: A, B, and C with thermal conductivities of 0.2, 1.5, and , respectively, and for three blowing ratios of 0.6, 1.0, and 1.6. Limited by the experimental facility, the mainstream Reynolds number is varied from 49,050 to 130,800; and the coolant jet Reynolds number is kept constant at 825. The computations for the impingement surface reveal multiple peaks and valleys in the heat flux and temperature plots. Material C has experienced significant changes in the values of impingement surface heat flux and temperature with blowing ratio, whereas these changes are only minor for material A. On the interaction surface, convective heat flux values are the lowest for material A and progressively increase with increasing thermal conductivity. However, the effectiveness values vary significantly for material A in the streamwise direction. A good agreement is found between the effectiveness distributions obtained from the measurements and the computations. The Nusselt number variations on the interaction surface are presented by defining a factor that accounts for the direction of heat flux.