Flow structure and surface heat transfer around a single small obstacle of rectangular cross-section mounted on a smooth plane surface are investigated. The obstacle is considered to be submerged in the viscous layer so that the far field flow may be viewed as uniform shear. The obstacle is considered to be at a temperature higher than that of the surrounding fluid and the flat surface is insulated. The unsteady Navier-Stokes equations and heat transport equation are solved numerically through a finite volume method on a staggered grid system. Solutions are obtained over a range of Reynolds number Re, which is based on the obstacle height and the incident uniform shear and Grashof number Gr. An investigation of the influence of buoyancy on the upstream and downstream flow separation from the obstacle and the interaction of the separation with the thermal field is also made. Numerical results reveal that in absence of the buoyancy force, the recirculating eddy upstream of the obstacle elongates with increasing Re. It is found that the buoyancy effect reduces the size of the upstream eddy when Re ≤ 200 with Gr (which is a measure of buoyancy) equal to 100. At an increased value of buoyancy force, Gr = 104, the upstream separation zone shifts further close to the obstacle. It is also found that the downstream separation length (which increases with increasing Re) further increases with increasing Gr as long as Re ≤ 200. Buoyancy effects on the flow are not prominent when Re is above 200. The surface heat transfer is quite high at the protruding corners and it increases with increase in Re. Increase of Grashof number produces an increment on surface heat transfer.

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