Flow behavior and heat transfer in a rectangular channel with miniature riblets

In this paper, the flow behavior in a rectangular channel with miniature riblets (MRs) is numerically investigated. Specially, the MRs are arranged at the bottom of the channel along streamwise direction, and the height of MRs is much less than the thickness of boundary layer. In addition, the heat transfer feature in such a channel is probed as well. The numerical results indicate that the MRs play a role like a "wall" which effectively restrains the momentum exchange of adjacent speed streaks. In addition, it's found that the MRs can regulate the vortices of their surroundings. Furthermore, the flow structure in channel is extracted with the dynamic modal decomposition (DMD), and the frequency of the dominate mode is obtained, which demonstrates the flow stability in channel is improved by the MRs. Therefore, the drag reduction can be achieved consequently. It's also found that the local drag and heat transfer characteristics present similar features with the distance from MRs. Compared with the rectangular channel without MRs, the rectangular channel with MRs shows excellent drag reduction feature, and drag reduction rate is up to 17.19%, which is obtained at the expense of a degree deterioration in heat transfer performance. Furthermore, the comprehensive performance coefficients of various channel with MRs are all less than 1, which illustrates that the MRs is a device that is beneficial to drag reduction but to heat transfer enhancement.