The present study numerically investigates the two-dimensional mixed convective flow of air past a square cylinder placed at an angle of incidence $\alpha ={45}^{\circ }$ to the free stream. We perform direct numerical simulations for a Reynolds number of 100, a range of Richardson numbers (Ri) between 0.0 and 1.0, and a Prandtl number of 0.7. The critical Richardson number at which the near field becomes a steady flow from an unsteady one lies between $0.65$ and $0.7$, along with a simultaneous emergence of the far field unsteadiness. There is no range of Ri for which the entire flow field is seen to be steady. At a relatively moderate Ri, the flow field reveals the presence of vorticity inversion through the momentum addition in the downstream region. We discuss the dual wake-plume nature of the flow behind the cylinder. The wake exhibits characteristics similar to those of a plume, revealing a self-similar behavior in the far field at increased buoyancy. We explore the cause of the far field unsteadiness and discuss the mechanism of the observed flow physics using instantaneous and time-averaged flow fields. The important flow quantities, such as force coefficients, vortex shedding frequency, and Nusselt number, are discussed at various Richardson numbers.

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• Laminar flows
• Thermal convection
• Vortex shedding