Steady and unsteady mixed convection flow in a cubical open cavity with the bottom wall heated

In this study we analyze experiments and numerical simulations of steady and unsteady mixed convection flow in a cubical cavity located at the bottom of a square channel. The Reynolds numbers based on the mean flow velocity and the channel width are in the range 100 ⩽ Re ⩽ 1500 and the Richardson numbers vary within 0.1 ⩽ Ri ⩽ 10. Particle Image Velocimetry has been used for the measurements in a water channel. Three-dimensional direct numerical simulations have been carried out with a second order finite volume code considering the Boussinesq approximation since, for the experimental conditions considered, the variation of the physical properties with temperature has no significant influence on the overall flow topology. For 100 ⩽ Re ⩽ 1500 and Ri ⩽ 0.1 the flow is steady and it consists in a single roll that exhibits larger velocities as the Richardson number is increased. An unsteady periodic flow is found at Re = 100 and Ri = 10. Alternate flow ejections from the cavity to the channel occur near the lateral walls while the flow enters the cavity from the channel through the central part of the cavity. A conditional sampling technique has been used to elucidate the evolution of the mean unsteady turbulent flow at Ri = 10. It has been found that the alternate flow ejections persist for all the Reynolds analyzed. The computed Nusselt numbers are in general agreement with a previously reported correlation, valid for two dimensional cavities of different aspects ratios.