International Journal of Heat and Mass Transfer, Vol.97, 662-674, 2016
Effects of plate angle on flow bifurcations and heat transfer characteristics in a channel with inclined plates
Oscillatory flows and heat transfer characteristics in a channel with inclined plates have been numerically investigated. For the fully developed channel flow of 10 <= Re <= 800, the inclined plates as a vortex generator are installed at the upper wall. To examine the effects of inclined plates on flow bifurcation and attendant heat transfer rates, unsteady simulations are performed for various plate conditions. The resulting flows are classified into three vortical structures of recirculation bubble (RB), standing vortex (SV), and traveling vortices (TV) depending on the Reynolds number and geometrical conditions. The variation of flow pattern is closely related to the spectral characteristics of steady state, periodic state, and quasi-periodic state. Based on these flow patterns and unsteady features, the transition scenario is proposed with increasing the plate angle. The flow is evolved from the steady state to the periodic and quasi-periodic state, and the frequency-locking phenomenon is observed for specific Reynolds numbers at a certain range of plate angle. In addition, the heat transfer enhancement is discussed with flow patterns and unsteady characteristics. The Nusselt numbers continuously increases from the steady state of RB to the periodic state of SV, while their variations are discontinuous when the periodic state of SV is changed into the quasi-periodic state of TV. The flow analyses show that these discontinuities are related to the supercritical Hopf bifurcation and the additional appearances of fundamental frequency. Also, the frequency-locking state before the development of quasi-periodic state with multiple frequencies brings about a jump increase of heat transfer. The disturbed flows by the inclined plates exhibit the logarithmic variation and Nusselt number correlation similar to the transition flow. (C) 2016 Elsevier Ltd. All rights reserved.