Active control of Friction and turbulent Heat Transfer at low Prandtl number

The aim of this thesis is to investigate the effect of spanwise wall oscillation on con- vective heat transfer in turbulent flows at low Prandtl numbers. Direct Numerical Simulations (DNS) of a fully developed turbulent channel flow are performed at a fixed friction Reynolds number of Reτ = 180. The temperature field is modelled using two passive scalars, solved simultaneously and characterized by the following Prandtl numbers: P r = 0.71 (representative of air) and P r = 0.025 (representative of liquid metals). While spanwise forcing is a well-established active control technique for skin-friction drag reduction, its influence on thermal transport-particularly in the low-Prandtl regime where the conductive sublayer extends significantly beyond the viscous sublayer- requires detailed investigation. The analysis focuses on evaluating the Heat-Transfer Reduction (HR) relative to Drag Reduction (DR). The results indicate that for P r < 1, the convective heat transfer is reduced less than the frictional drag (HR < DR). This dissimilar behavior implies a breakdown of the Reynolds analogy, highlighting the potential of spanwise wall oscillations to achieve significant drag savings with a mitigated penalty on heat exchange efficiency in liquid metal applications.