A systematic study on the turbulent flow of surfactant solutions in different wide-rib rectangular microgroove channels was carried out by direct numerical simulation. The results showed that the drag reduction performance of surfactant solutions could be further enhanced in the grooved channel with a suitable groove size. The optimal size of microgroove for drag reduction could be enlarged in the surfactant solution. The collaborative drag reduction effect of surfactant solution in grooved channel was mainly the competition result of the “restriction effect” and the “tip effect” of the microgroove. There was a higher shear stress near the grooved tips

but the stress was very small within the grooved valley. If the microgroove not only prevents the near-wall vortices from intruding into the grooved valley effectively

but also presents a better restriction effect on the spanwise motions of the near-wall streamwise vortices

the microgroove will show a drag reduction enhancement effect. On the contrary

if the size of microgroove increases too large to prevent the near-wall vortices from intruding into the grooved valley

the shear stress near grooved tip and within grooved valley will increase

and the microgroove will show drag-increasing performance. The fact that a large number of small and weak secondary streamwise vortices induced in the grooved valley is the key factor to increase the restriction effect and thus enhance the drag reduction of surfactant solutions.