Flow instability in baffled channel flow

Flow instability in baffled channel flow, where thin baffles are mounted on both channel walls periodically in the direction of the main flow, has been numerically investigated. The geometry considered here can be regarded as a simple model for finned heat exchangers. The aim of this investigation is to understand how baffle interval (L) and Reynolds number (Re) influence the flow instability. With a fixed baffle length of one quarter of channel height (H), ratios of baffle interval to channel height (RB = L/H) between 1 and 4 are considered. The critical Reynolds number of the primary instability, a Hopf bifurcation from steady flow to time-periodic flow, turned out to be minimum when RB = 3.08. The friction factor (f) is strongly correlated with the critical Reynolds number for RB ⩽ 2.5. For the particular cases of RB = 1.456 and RB = 1.0, we performed Floquet stability analysis in order to study the secondary instability through which time-periodic two-dimensional flow bifurcates into three-dimensional flow. The results obtained in this investigation are in good agreement with those computed from full simulations, and shed light on understanding and controlling flow characteristics in a finned heat exchanger, quite beneficial to its design.

► Baffles in channel flow alter flow topology, resulting in change of stability characteristics.
► The primary instability (Hopf bifurcation) depends upon baffle interval.
► The critical Reynolds number has close correlation with friction factor.
► The 3D modes predicted by Floquet stability analysis are confirmed by full DNS.