The influence of wall heating on turbulent boundary layer characteristics during mixed convection

Highlights: • Mixed convection turbulent boundary layer flow characterized using multi-plane PIV technique. • Experiments were performed in inertia-dominated to buoyancy-influenced flow conditions. • Modification to turbulent stresses due to wall heating observed. • Multi-modal distribution wall-normal turbulent velocity component observed. • Thermals bursting are hypothesized as the cause for the modification to the turbulent variables. An investigation on the modification of turbulent boundary layer characteristics by wall heating was conducted on the mixed convection turbulent boundary layer flow. The multi-plane particle image velocimetry (PIV) technique was used to characterize turbulent boundary layer dynamics. Experiments were performed over a range of mixed convection flow conditions, quantified by the Richardson number ($\mathrm{Ri}$), from inertia dominant flow ($R{i}_L=0.01$) to buoyancy-influenced flow ($R{i}_L=0.3$). The implemented PIV technique produced multiple two-dimensional velocity fields from two orthogonal planes with respect to the mean-flow direction. From the computed velocity fields, the low-order turbulent statistics were computed where a significant modification to the wall normal stress was observed. The cause of this modification was investigated via the probability density function (PDF) of the turbulent wall-normal velocity component ($v\text{'}$). Results show that the PDF of $v\text{'}$ is multi-modal in the presence of wall heating, demonstrating that the buoyancy-driven phenomena influence the turbulent boundary layer flow via intermittent bursting and rising of thermals through the boundary layer.