Non-homogeneous thermal boundary conditions in low Prandtl number pipe flows

The effect of non-homogeneous thermal boundary conditions on temperature statistics in low Prandtl number turbulent pipe flows is studied numerically via direct numerical simulations. Two wall heat flux distributions, varying in azimuthal direction and motivated by concentrated solar power systems, are prescribed and their influence on the thermal field is presented. As a reference, also homogeneous thermal boundary conditions are simulated and compared the the non-homogeneous ones. The influence of the azimuthal variation of prescribed wall heat flux is assessed in terms of instantaneous velocity and temperature fields, local and global Nusselt numbers, averaged temperature distributions and the turbulent thermal diffusivity. The global Nusselt number appears to be unaffected by the thermal boundary conditions, whereas the local Nusselt number deviates appreciably.