PhD Defence Guru Sreevanshu Yerragolam | Sheared Thermal Convection

Sheared Thermal Convection

Guru Sreevanshu Yerragolam is a PhD student in the department Physics of Fluids. (Co)Promotors are prof.dr. D. Lohse, prof.dr. R. Verzicco and dr. R.J.A.M. Stevens from the faculty of Science and Technology.

In many natural phenomena and industrial processes, thermal convection is often driven by the combination of buoyancy and shear. Therefore, in this dissertation, thermal convection with imposed shear forcing has been studied using direct numerical simulations of Rayleigh–Bénard convection and vertical convection with imposed Couette or Poiseuille type forcing, with a focus on transport of heat, momentum, and scalars. The Nusselt number , which gives the non-dimensional heat transport through these mixed systems, and the friction coefficient  are functions of the thermal forcing given by the Rayleigh number , the shear forcing given by the Reynolds number  and the fluid properties determined by the Prandtl number . Scaling relations of  for passive transport of heat in Couette flow provide insights into the behaviour of heat transport in mixed systems in the limit of very high shear. Using this information, scaling laws for  and  are proposed by extending the Grossmann–Lohse theory for thermal convection. Additional analysis of the spectra of the flow structures in sheared Rayleigh–Bénard convection shows that small-scale structures are crucial to the effective transport of heat and momentum. Disruption to these structures, whether through application of shear forcing, or through confinement, is detrimental for the transport of heat and momentum through sheared Rayleigh–Bénard convection. The scaling relations derived for sheared Rayleigh–Bénard convection are also found to be applicable to the sheared vertical convection even though the theoretical extension cannot be directly applied to this mixed system. However, the many similarities between sheared Rayleigh–Bénard convection and sheared vertical convection hint at the fact that heat and momentum transport through these mixed systems could be independent of geometry. The final chapter focuses on a particular application – transport of  concentration in indoor environments driven by a combination of buoyant thermal plume originating from the occupant and the inflow from the ventilation, which has implications on spread of airborne diseases.