Nusselt number-turbulent strain rate relationship: Forced convection of a flat surface downstream of a pair of side-by-side rectangular strips

Abstract

The turbulent strain rate generated by a pair of 25.4 mm tall and 12.7 mm wide (W) rectangular strips at a Reynolds number based on the strip width of 8500 was measured using a 3D hotwire probe in a wind tunnel. The strips were placed side-by-side separated by 3 W, 2 W, and 1 W. The convective heat transfer enhancement, denoted by the normalized Nusselt number (Nu/Nu0), was correlated with turbulence fluctuation, Taylor microscale, turbulent strain rate and integral-Taylor scale ratio. With the effects of both turbulence fluctuation and eddy scale incorporated, the turbulent strain rate correlated most strongly with Nu/Nu0, with an R-square value of 0.82. Comparatively, the R-square for Nu/Nu0 - velocity fluctuation and Nu/Nu0 - Taylor microscale were 0.77 and 0.64, respectively. Furthermore, the turbulent strain rate was found to have the most significant impact on heat transfer augmentation, more so than the individual effects of turbulent fluctuation and Taylor microscale.