Drag reduction using wrinkled surfaces in high Reynolds number laminar boundary layer flows

Abstract

Inspired by the design of the ribbed structure of shark skin, passive drag reduction methods using stream-wise riblet surfaces have previously been developed and tested over a wide range of flow conditions. Such textures aligned in the flow direction have been shown to be able to reduce skin friction drag by 4 − 8%. Here, we explore the effects of periodic sinusoidal riblet surfaces aligned in the flow direction (also known as a "wrinkled" texture) on the evolution of a laminar boundary layer flow. Using numerical analysis with the open source CFD solver OpenFOAM, boundary layer flow over sinusoidal wrinkled plates with a range of wavelength to plate length ratios (λ/L), aspect ratios (2A/λ), and inlet velocities are examined. It is shown that in the laminar boundary layer regime the riblets are able to retard the viscous flow inside the grooves creating a cushion of stagnant fluid which the high speed fluid above can partially slide over, thus reducing the shear stress inside the grooves and the total integrated viscous drag force on the plate. Additionally, we explore how the boundary layer thickness, local average shear stress distribution, and total drag force on the wrinkled plate vary with the aspect ratio of the riblets as well as the length of the plate. We show that riblets with an aspect ratio of close to unity lead to the highest reduction in the total drag, and that because of the interplay between the local stress distribution on the plate and stream-wise evolution of the boundary layer the plate has to exceed a critical length to give a net decrease in the total drag force.

Diversity of dermal denticle structure in sharks: Skin surface roughness and three‐dimensional morphology

“…SA5 Surface area, Volume.Crown5 Volume of the crown, SA.Crown5 Surface area of the crown, Volume.Base5 Volume of the base, SA.Base5 Surface area of the base, Volume.CB Ratio5 Ratio of the volume of the crown to the volume of the base, PerVolC Ratio5 Ratio of the volume of the crown to the volume of the whole denticle. -Ardakani & McKinley, 2017). We discuss issues relating to denticle ridges and fluid dynamics in more detail below, but here we note that our measurements of the height and spacing of mid-body ridges on six species of sharks showed that smooth dogfish and shortfin mako sharks are the most similar (Tables 2 and 5) while species such as spiny dogfish and leopard sharks have relatively widely spaced and higher ridges on the surfaces of denticles.…”

“…Shark denticle ridges (often termed riblets by analogy to engineered ridge‐like structures) have been the subject of considerable focus due to their possible association with fluid dynamic drag reduction and both biologists and engineers have focused intensively on the spacing of ridges (e.g., Bechert, Bruse, & Hage, ; Motta et al, ; Raayai‐Ardakani & McKinley, ). We discuss issues relating to denticle ridges and fluid dynamics in more detail below, but here we note that our measurements of the height and spacing of mid‐body ridges on six species of sharks showed that smooth dogfish and shortfin mako sharks are the most similar (Tables and ) while species such as spiny dogfish and leopard sharks have relatively widely spaced and higher ridges on the surfaces of denticles.…”

Investigation of Drag Coefficient at Subcritical and Critical Reynolds Number Region for Circular Cylinder with Helical Grooves

“…Therefore, one observation from the Figure 9 is that the critical Reynolds number decreases for the increases of the roughness. For example the critical Reynolds number for single start is around 1.4×10 5 and gradually decreases for higher number of starts and for 6 starts the critical Reynolds number is found around 4×10 4 . Similar findings are also obtained by Adachi [22] and Hojo [23].…”

“…It is well-known that the drag in a cylinder decreases when the wake behind it changes laminar flow with turbulent including a narrow wake width. RaayaiArdakani and McKinley [5] includes wrinkled surface and show that the surface texture can be able to reduce the skin friction drag. Massumoto et al [6] proposed apple shape geometry and compared with sphere and different hollow shaped geometries like U-shaped, Vshaped grooves and find that apple shape geometry can reduce the drag up to 23% as compared with sphere and 13% with circular cylinder.…”

Interpolation of Turbulent Boundary Layer Profiles Measured in Flight Using Response Surface Methodology

“…Among a number of boundary layer controlling devices such as suction [2,3], blowing [4], synthetic jets [5], vortex generators [6], and riblets [1,[7][8][9][10][11][12], riblets are one of the methodologies used to reduce aircraft surface drag [1,[7][8][9][10][11][12]. Riblets are a passive means of turbulent flow control by which skin friction drag is reduced, and were first employed at the NASA Langley Research Center back in the 1970s [8,13] in imitation of the skin structure of a shark that swims long distances at high speed.…”