The flow behavior and heat transfer characteristic in a rectangular channel with miniature vibrating device

Abstract

In present work, the miniature vibrating device (MVD) that oscillates along the normal direction is arranged in a rectangular channel. The geometric dimension of MVD is sufficiently small to be immersed in buffer region of turbulent boundary layer. The flow behavior and heat transfer feature in channel with MVD are numerically investigated. The numerical results indicate that the MVD could cut off the streamwise vortex existing in original flow field, and speed up the vortex shedding from the MVD. Consequently, the scales of vortices induced by the MVD decrease. The induced small scale spanwise vortices evolve along the streamwise direction, and then break into plenty of small scale streamwise vortices due to viscous diffusion effect of fluid. The small scale streamwise vortices finally evolve into relatively uniform streamwise vortices. In addition, due to the suppression effect of the induced small scale vortices on the sublayer of turbulent boundary layer, the fluid velocity in viscous sublayer and buffer layer both decrease, and the remarkable drag reduction is achieved. Due to the disturbance caused by induced small scale streamwise vortices occur in outer region of boundary layer, the fluid mixing in logarithmic region enhances, which results in the augment of the Nusselt number. Compared with the channel without MVD, the skin friction coefficient reduces by up to 15.38% while the Nusselt number increases by up to 17.70%. Moreover, the comprehensive performance coefficients of considered cases are greater than 1, and the maximum comprehensive performance coefficient of 1.223 can be achieved at Reynolds number of 9490.