The Flow and Heat Transfer Enhancement Mechanisms of Autonomous, Aero-Elastically Fluttering Reeds

The limits of low Re forced convection heat transport within high aspect ratio, rectangular mm-scale channels that model air-cooled heat exchangers are overcome by the deliberate formation of unsteady small-scale motions induced by autonomous aero-elastic fluttering of cantilevered, planar thin-film reeds. The coupled flow-structure interactions between the fluttering reeds and the embedding channel flow and the formation, evolution, and advection of the induced unsteady small-scale motions are explored using video imaging and high-resolution PIV. Concave/convex undulations of the reed’s surface that are bounded by the channel’s walls engender the formation and transport of cells of spanwise vorticity concentrations of alternate (CW and CCW) sense. It is shown that the shedding of these vortices is accompanied by energy transfer from large to small flow scales and a concomitant increase in TKE throughout the channel whether the base flow is laminar or turbulent. The TKE increment is accompanied by enhancements in channel heat transfer, as characterized by Nu, which increases with Re. The losses associated with driving the reeds can be effectively managed by reducing the reed’s characteristic flutter frequency with minimal penalty in Nu enhancements