Buoyancy induced flow in an enclosure is frequently investigated
because of its application in electronic packaging, nuclear reactors
and heat exchangers.Many studies had been reported addressing the
geometric influences of the enclosure and the immersed object. The
commonly investigated cases can be heat transferwithin the annulus
of horizontally concentric circular cylinders [1e10] or the natural
convection in concentric annulus between an inner circular object
and an outer rectangular enclosure [11e18].
Focusing on the natural convection within the annulus of horizontally
concentric circular cylinders, Cheddadi et al. [6] indicated
that flow bifurcationwith two different dynamic flow structures can
be obtained depending on the initial conditions and the Rayleigh
number. Thetwoflows are basically crescent-shaped ‘unicellular flow’
and a ‘bicellular flow’ with a pair of counter-rotating eddies at the top
of the annulus. Similar results were obtained by Yoo [7], Desrayaud
et al. [8] with different Rayleigh number, Prandtl number and radius
ratio. For simplified geometry, analytical solutions for steady state
were available [9]. A critical review of buoyancy-induced flow transitions
in cylindrical configuration can be found in Angeli et al. [10].
On the other hand, natural convection within rectangular
enclosure has been studied extensively for different wall heating
arrangement. Recently, attentions had focused on the flows induced