Mechanism of Flow Drag Reduction on Non-Smooth Surface

Numerical simulations of air flow were carried out on non-smooth surface where microriblets were distributed uniformly at only one of the walls. An accurate numerical treatment based on k-ε turbulence model was adopted to study flow alteration and to analyze drag reduction and increasing mechanism on non-smooth surface. A modified calculation unit was used to estimate characteristics of flow at the reformed cells. With the microriblets aligned on the surface, the Reynolds shear stress was significantly decreased which was considered the dominant factor resulting in drag reduction. An additional force generating from the deviation of static pressure on the front and rear end of the riblet grooves caused pressure drag increasing exhibiting exponential growth with the flow rate, which was closely related to vortices induced by momentum transfer at the adjacent area of flow inside the grooves and the outer flow. Shear action at groove walls was greatly degraded due to the gradually variational velocity of vortices. Flow alteration on non-smooth surface compared with smooth surface was also analyzed in detail.