BUOYANCY-INDUCED FLOW TRANSITION IN MIXED CONVECTIVE FLOW OF AIR THROUGH A BOTTOM HEATED HORIZONTAL RECTANGULAR DUCT

A detailed numerical simulation was carried out to study the buoyancy induced flow transition in a mixed convective flow of air through a bottom heated horizontal rectangular duct. The unsteady three-dimensional Navier-Stokes and energy equations were directly solved by a higher order finite difference numerical scheme without using any turbulence modeling. Results were particularly presented for Re = 500 and A = 2 covering a wide range of Gr/Re2 from steady laminar longitudinal vortex now to unsteady chaotic flow. The results indicate that the increasing buoyancy causes the steady laminar flow for Gr/Re2 < 4 to become a periodic laminar flow for 4 less-than-or-equal-to Gr/Re2 < 19, then to a quasiperiodic flow for 19 less-than-or-equal-to Gr/Re2 < 25 and finally to a chaotic flow in the downstream for 25 < Gr/Re2 less-than-or-equal-to 40. Thus, the buoyancy induced laminar to turbulent flow transition follows the Ruelle-Taken route. An empirical equation was proposed to correlate the locations for Hopf bifurcation.