Thermogravitational and hybrid convection in an obstructed compact cavity

The flow over a topography or a step is a fundamental problem in fluid dynamics with relevance to many fields and circumstances. In the present analysis direct numerical simulation (DNS) is used to examine the properties of the thermofluid-dynamic field in a square cavity with a heated obstruction located on the bottom. The involved dynamics include forced flow driven by injection of cold fluid through an orifice and the buoyancy convection of thermal origin, which naturally emerges in the considered cavity as a result of the prevailing temperature gradients. The relative importance of these mechanisms is assessed by considering different values of the Rayleigh number (spanning several orders of magnitude) and using a peculiar analysis hierarchy where selected effects are intentionally switched on or off depending on the targeted regime. In particular, first, attention is paid to pure thermogravitational convection driven by the presence of vertical and horizontal heated surfaces (the hot sides of the obstruction); then, the hybrid regime is examined where buoyancy convection is modulated by currents of forced flow for values of the Richardson number = 1. We also explore the resulting patterning behavior for different thermal and kinematic boundary conditions (distinct thermal behaviors of the top wall and alternate positions of the inflow and outflow sections). For each case, the Nusselt number relating to the vertical and horizontal sides of the obstruction is evaluated and put in relation with the flow topology. The study is also supported by analysis of the frequency spectrum for the situations in which relatively chaotic states emerge