Numerical investigations of the flow bifurcations, transition scenario and heat transfer enhancement in asymmetric grooved channels are performed by direct numerical simulations of the mass, momentum and energy equations. The governing equations are solved for laminar and time-dependent transitional flow regimes by the spectral element method in a periodic computational domain with appropriated boundary conditions. Numerical results show a flow transition scenario with two Hopf bifurcations B1 and B2, occurring in critical Reynolds numbers Rec1 y Rec2, respectively. Fundamental frequencies ω1 and ω2, and super harmonic combinations of both develop as the Reynolds number increases from a laminar to higher transitional flow regime. Numerical calculations demonstrate that the time-average mean Nusselt number (the non-dimensional heat transfer rate), increases significantly as the flow passes from a laminar to a periodic—and then to a quasi-periodic flow regime. This increase is accompanied by a reasonable increase in both the friction factor and the pumping power. The obtained behavior is comparable to other geometries and configurations as well as to previously reported numerical results for the studied geometry. This numerical investigation shows a transition scenario at the onset of turbulence, similar to the Ruelle-Takens-Newhouse scenario, which has not been found or reported by other researchers using this geometry. The numerical simulation results also show the existence of a bifurcation scenario that develops a path-dependent flow and heat transport behavior. In the vicinity of the first Hopf flow bifurcation (and consequently, the critical Reynolds number Rec1), the resulting stable time periodic flow depends on both the initial flow conditions and the way in which the incremental process to higher flow regimes is carried out.
Influence of forced flow pulsations on heat transfer behind a rib in a channel in transitional flow regimes
