RADIATION EFFECTS ON FILM COOLING IN TURBULENT NONISOTHERMAL AND NONUNIFORM GASES

The effects of gas radiation on film cooling in turbulent nonisothermal and nonuniform pure gases is studied and applied to a 2D channel geometry. The cooled wall temperature results from coupled conduction, radiation, turbulent convection and mass transfer. A random statistical narrow-band (RSNB) model associated with the Curtis-Godson approximation is used for gas radiative properties. A second order Taylor expansion of local blackbody intensity is carried out in order to obtain the expression of time averaged intensity as a function of the mean temperature and its variance. A six supplementary equation model is developed. The turbulent transported quantities are the kinetic energy, temperature variance, mass fraction variance and their respective dissipation rates. The increase in the cooled wall temperature due to gas radiation is studied in two representative industrial applications. It is shown that gas temperature fluctuations increase significantly radiative fluxes especially at moderate mean temperature levels. Finally, the distance over which the film remains efficient is not affected by radiative transfer.