Modeling and optimization of shark-inspired riblet geometries for low drag applications

Discovery of riblets in a bird beak (Rynchops) for low fluid drag

“…Riblets can help lift vortices from the surface, decreasing drag; however, because vortices have diameter smaller than the spacing, vortices can also fall into riblet valleys. [25].…”

“…For example, Nature has Riblets on the skin of a mako shark (adapted from [15]) shown at two magnifications. (c) Vortices generated in turbulent flow shown on a flat and on a shark-inspired riblet surface (adapted from [25]). On the flat surface, a vortex is near the surface and generates drag.…”

Flow Control Methods and Their Applicability in Low-Reynolds-Number Centrifugal Compressors—A Review

“…A recent review of the drag reduction performance of riblets, which was written by Dean and Bhushan [118], concluded that the blade-shaped riblets provide the optimum drag reduction; however, due to their fragile nature, trapezoidal or scalloped riblets are recommended. In addition, the recent research shows that the blade-shaped riblets produce the best drag reduction [97]. Examples of the riblet shapes are shown in Figure 7.…”

“…The drag reducing riblet structures found in nature (shark skin [97] and bird beak [98]) have inspired researchers to reduce drag in engineering applications. Riblets are small streamwise aligned grooves that shift turbulent vortices farther away from the surface resulting in decreased momentum transfer and wall shear stress [99,100].…”

“…Year Application Reynolds Number β = δ * τ w,0 dp dx Effect on Drag [97] 2016 Transportation, medical, industry 4180 0 −11.6% [98] 2016 Transportation, industry 4200 0 −3.9% [108] The drag reduction performance of riblets is higher at low Reynolds numbers than at high Reynolds numbers [115,116] and ice, fouling, and wearing weakens the drag reduction capability of riblets [10].…”