Experimental Study on the Collaborative Drag Reduction Performance of a Surfactant Solution in Grooved Channels

Abstract

Turbulence with a relatively larger vortex is obtained in drag-reducing surfactant solution, which provides an excellent condition for the application of small scale grooves. In this work, the coupling drag reduction performance of surfactant solution and grooves was experimentally investigated to explore the complementary possibility between their drag reduction mechanisms. The cationic surfactant cetyltrimethyl ammonium chloride (CTAC) mixed with the counterion salt sodium salicylate (NaSal) was experimented in smooth or grooved channel, respectively, at the mass concentrations of 50-150 ppm. It was found that the surfactant solutions gave more effective drag reduction in the grooved channel by the interaction between the "restriction effect" and "peak effect" of grooves. Moreover, the critical temperature and critical Reynolds number of the surfactant solution were smaller in the grooved channel, and the friction factor in the grooved channel increased much more rapidly than that in the smooth channel when Re is larger than a critical value.

Direct numerical simulation of surfactant solution flow in the wide‐rib rectangular grooved channel

“…Furthermore, Figure 5b also shows that compared with water, the drag-reducing and drag-increasing performance of microgroove are both inhibited in the surfactant solution at the present Reynolds number, which is consistent with the experimental results obtained by Huang et al 27,28 The reason may be that the scale of near-wall turbulent vortices is enlarged in the surfactant solution and the drag reduction mechanism of microgroove is related to the near-wall vortex scale. The larger scale turbulent vortices are not conducive to the restriction of microgrooves on their spanwise motions and weaken the "restriction effect" of microgrooves on the near-wall vortices.…”

“…Moreover, it can be also seen from Figure 5a that in surfactant solution, the drag reduction rates of microgrooves are much larger than that in water. Moreover, it can also be found from the results of Cases 5-7 (s 1 514.1, 16.9, 22.5) that the drag reduction rates of surfactant solution in these grooved channels are larger than that in the smooth channel, indicating that the drag reduction performance of surfactant solution can be further enhanced by microgrooves, which verifies the experimental discoveries of Huang et al 27,28 and the speculation about the complementarity between the drag reduction mechanisms of surfactants and microgrooves. To study more intuitively the difference between the drag reduction performance of microgroove in water and surfactant solution, Figure 5b portrays the comparison between the drag reduction enhancement performance (DRE listed in Table 2) of surfactant solution in the grooved channel and the drag reduction performance of microgrooves in water (DR obtained by Huang et al 30 ) It is also seen from Figure 5b that in water, the optimal drag-reducing size of microgroove is s 1 516.9, but in the surfactant solution, its optimal drag-reducing size is s 1 522.5, meaning that the real optimal drag-reducing size of microgroove is enlarged in the surfactant solution.…”

“…The present numerical results verify the experimental phenomena discovered by Huang et al 27,28 that the drag reduction performance of surfactant solution can be further enhanced in the grooved channels, and the optimal dragreducing size of microgrooves is enlarged in the surfactant solution as the surfactant solution can inhibit the formation of small vortices and enlarge their scales. The present numerical results verify the experimental phenomena discovered by Huang et al 27,28 that the drag reduction performance of surfactant solution can be further enhanced in the grooved channels, and the optimal dragreducing size of microgrooves is enlarged in the surfactant solution as the surfactant solution can inhibit the formation of small vortices and enlarge their scales.…”

“…In the recent years, Huang et al 27,28 performed some experiments on the collaborative drag reduction of surfactant solutions and microgrooves, and they found that the drag reduction performance of surfactant solutions could further increase in the grooved channel and the drag-reducing sizes and ranges of microgrooves could also be enlarged in the surfactant solutions, which verified the above speculation. Moreover, the drag-reducing surfactant solutions can inhibit the formation of small scale turbulent vortices and enlarge the near-wall vortices scale, providing the environment with relatively larger vortices, which is beneficial to the drag reduction of microgroove.…”

“…In the recent years, Huang et al 27,28 performed some experiments on the collaborative drag reduction of surfactant solutions and microgrooves, and they found that the drag reduction performance of surfactant solutions could further increase in the grooved channel and the drag-reducing sizes and ranges of microgrooves could also be enlarged in the surfactant solutions, which verified the above speculation. However, due to the limitation of experiment, Huang et al 27,28 could not obtain the visual information of near-wall turbulent structures. Therefore, the collaborative drag reduction mechanism of surfactants and microgrooves is unclear so far.…”