Effect of shape of the obstacle in buoyancy-aided mixed convective flows past bluff bodies

Mixed convective buoyancy-aided flows past bluff bodies are of great practical interest due to their numerous aerospace, energy, and structural applications. Direct Numerical Simulation of the mixed convective buoyancy-aided flow past differently shaped bluff bodies is carried out to characterize the flow and heat transfer. The Reynolds number is held constant at 100, the Richardson number is varied in the range 0.0 ≤ Ri ≤ 2.5, and the Prandtl number is taken as 0.7. Four shapes of the bluff body (square, diamond, isosceles triangle in vertex- and base-facing flow configuration) are utilized for the study. The competitive effect of the forced and natural convection in the flow leads to interesting flow physics downstream of the obstacle. At the considered Reynolds number (Re) of 100, the well-known vortex shedding occurs in an isothermal flow (Ri = 0.0). At the same time, the heating of the body induces a natural convective jet-like flow in the wake, which influences the vortex shedding phenomenon. The shedding is observed to be suppressed in the near wake beyond specific critical values of the Richardson number, depending on the shape of the body. At higher Richardson numbers (Ri), the increased thermal buoyancy causes additional transitions far downstream of the obstacle resembling thermal plumes. Even more fascinating is the drastic change in the flow behaviour when the shape of the obstacle is modified. In the present study, the effect of the shape of the obstacle on the near- and far-field flow behaviour is examined in detail. The critical Richardson numbers for the suppression of vortex shedding and the inception of the far-field unsteadiness are compared. The reasons for the difference in the flow patterns due to the varying Richardson number and various shapes are elaborated. The corresponding integral parameters, such as drag coefficient, Strouhal number, etc., are discussed.