Mechanisms underlying flat surface forced convection enhancement by rectangular flexible strips

Employing turbulence generators, such as rectangular flexible strips, is a simple and effective approach to enhancing forced convection. In the current study, 12.7 mm wide rectangular flexible strips (with thickness of 0.1 mm, 0.2 mm and 0.25 mm, height of 25.4 mm, 38.1 mm and 50.8 mm, transversal spacing of 12.7 mm, 25.4 mm and 38.1 mm) were investigated at Reynolds number (Re) of 8500 and 6000, and freestream turbulence intensity (Tu) of 0.4%, 7%, 9%, and 11%. The convective heat transfer augmentation was analyzed in terms of the normalized Nusselt number (Nu/Nu0). The relationships between the averaged Nu/Nu0 and the strip thickness, height, spacing, Re and Tu were determined using multiple linear regression. The correlations between the local Nu/Nu0 and turbulent flow parameters, including turbulent kinetic energy, downwash velocity and near surface streamwise velocity were also illustrated. The freestream turbulence intensity (Tu) had the most significant effect in augmenting the averaged Nu/Nu0, and the local Nu/Nu0 correlated best with the local ke. The maximal averaged Nu/Nu0 over 23 W downstream, within ± 1 and ± 4 strip widths cross-stream was found for Tu = 7% case and Tu = 11% case, respectively.