Heat transfer and thermal pattern around a sphere in a turbulent boundary layer

Direct numerical simulation (DNS) is performed by solving the governing equations for fluid flow and heat transfer. The nondimensional sphere diameters are 17 and 34 wall units and cover several collocation points of the fluid. Two-way coupling is used to account for the effect of the sphere on the structure of the near-wall turbulence and the main stream. The calculation of the thermal field is done with the same grid system used for the velocity field. Water was used as test fluid, with the Prandtl number Pr=5.4. The calculation is performed for a single stationary sphere attached to the bottom of the flume. The heat transfer calculations were carried out at a constant heat flux wall boundary condition. The present DNS results indicate essential enhancement of heat transfer coefficient associated with a flow motion toward the wall. The thermal pattern around the sphere is obtained and compared with the experimental images. A possible mechanism of heat transfer in the presence of coarse particles in the near-wall region of a turbulent boundary layer is discussed.