An active control strategy for simultaneously achieving turbulent drag reduction and heat transfer enhancement in heat exchangers: Oscillation of micro cuboid vortex generators

Currently, most methods for heat exchangers to achieve flow drag reduction or heat transfer enhancement are passive control strategies. However, the passive control strategy achieves either drag reduction or heat transfer enhancement, and it is difficult to achieve both drag reduction and heat transfer enhancement. In practical application, if both drag reduction and heat transfer can be achieved simultaneously, the energy consumption of the heat exchanger will be reduced, and the heat exchange area will be saved. For this reason, a micro cuboid vortex generator (MCVG) that can oscillate in the normal direction is located in a rectangular channel in the present work. The open-source software OpenFOAM was used to conduct large eddy numerical simulation research. The effects of oscillation at different heights on the fluid velocity, turbulent vortex structure, skin-friction coefficient, and Nusselt number are numerically investigated. The numerical results indicate that the MCVG with normal oscillation reduced the streamwise velocity upstream of its location, with a maximum reduction of 5.04 %. The streamwise velocity downstream of the MCVG is more affected, with all reductions exceeding 27 %. The MCVG with normal oscillation increased the normal velocity of the entire streamwise direction. Compared with the normal velocity upstream of the oscillation area, the normal velocity varies more dramatically downstream of the MCVG. Adding a MCVG with normal oscillation in the channel increased the skin-friction drag in the oscillation area and reduced the skin-friction drag downstream of the MCVG. The average skin-friction drag of the wall decreases up to 6.87 %. In addition, adding a MCVG with normal oscillation in the channel can also achieve enhanced heat transfer, and the average Nusselt number of the wall can be increased by up to 6.12 %. The comprehensive performance coefficient can be increased by up to 7.01 %.