CFD modeling of turbulent boundary layer flow in passive drag-reducing applications

Abstract

In this paper, the turbulence boundary layer, velocity and skin friction coefficient characteristics of grooved surfaces are studied. Flow over surfaces with transverse square, triangular and semicircular grooves are numerically modeled via the finite volume method. Comparisons are made on the basis of the grooved surfaces' skinfriction coefficient, normalized by that of a smooth surface, with Reynolds number in the vicinity of 2 × 10 6 . Results show that square grooves are superior to the two other groove geometries in reducing the drag. Viscous damping in all grooves keeps skin friction inside them well below the surface above. However, the interior geometry of square grooves allows them to balance the net inward momentum due to the sudden absence of the wall in a way that minimizes disturbance of the main flow while taking advantage of the restart of the boundary layer. As a consequence to the separation of the boundary layer, an inevitable stagnation point within the groove must exist. Square grooves had the highest such stagnation point along the backward-facing side of the groove. The shortness of the resulting upward boundary layer from the stagnation point to the corner produces smaller near-wall secondary flow motion and more relaxed merger with the main flow. All this contributes to enhanced drag reduction for the described groove structure.

Drag Reduction on Microstructure Surfaces

“…To examine the effect of the surface shape on the friction resistance, Bourisli and Al-Sahhaf (2008) analyzed friction coefficient and velocity by a series of simulation tests using riblets in three different directions, square, triangular and semi-circular. As a result, they found that three of the rough surfaces gave less resistance to smooth surfaces and that the triangular riblets provided the greatest drag reduction [6]. Using the simulation software, El-Samni et al (2007) determined the pressure gradient to compensate for mass flow on smooth sur-faces such as curved surfaces at different protrusions and grooves.…”

Research on mechanism of drag reduction and efficiency improvement of hydrodynamic torque converter with bionic non-smooth surfaces

“…To study the effect of surface shape on frictional resistance, Bourisli and Al-Sahhaf [3] analyzed the friction coefficient and velocity by a series of simulation tests using grooves in surfaces gave the less resistance compared with three different shapes, including square, triangle, and smooth semi-circle. The results showed that all non-smooth surfaces.…”