Direct numerical simulation of turbulent thermal boundary layers

In this paper, a method of generating realistic turbulent temperature fluct uations at a computational inlet is proposed and direct numerical simulatio ns of turbulent thermal boundary layers developing on a flat plate with iso thermal and isoflux wall boundary conditions are carried out. Governing equ ations are integrated using a fully implicit fractional-step method with 35 2x64x128 grids for the Reynolds number of 300, based on the free-stream vel ocity and the inlet momentum thickness, and the Prandtl number of 0.71. The computed Stanton numbers for the isothermal and isoflux walls are in good agreement with power-law relations without transient region from the inlet. The mean statistical quantities including root-mean-square temperature flu ctuations, turbulent heat fluxes, turbulent Prandtl number, and skewness an d flatness of temperature fluctuations agree well with existing experimenta l and numerical data. A quadrant analysis is performed to investigate the c oherence between the velocity and temperature fluctuations. It is shown tha t the behavior of the wall-normal heat flux is similar to that of the Reyno lds shear stress, indicating close correlation between the streamwise veloc ity and temperature. The effect of different thermal boundary conditions at the wall on the near-wall turbulence statistics is also discussed. (C) 200 0 American Institute of Physics. [S1070-6631(00)50510-8].