Abstract
A new type of nonsmooth surface inspired by the shape of barchan dunes has been proposed and is intended to reduce skin friction, a major cause of overall drag. Simulations were carried out to obtain skin friction reduction characteristics for the nonsmooth surface using the commercial computational fluid dynamics software Fluent. A realizable k‐ε model was employed to assess the influence of the nonsmooth structure on turbulent flow and velocity fields. The numerical simulation results showed that the new nonsmooth surface possesses the desired skin friction reduction effect and that the maximum skin friction reduction percentage reached 33.63% at a fluid speed of 30 m/s. Various aspects of the skin friction reduction mechanism were discussed, including the distribution of velocity vectors and shear stress contours and the variations in boundary layer thickness. The accuracy of the flow field for the nonsmooth unit was further verified by particle image velocimetry test results. The new bionic nonsmooth surface, which exceeds the limitations of existing nonsmooth bionic structures, can effectively reduce skin friction and should provide insights into engineering applications in the future.
Highlights
With the rapid growth in energy consumption, the global energy crisis has been become increasingly serious
From these experiments they observed that bubble drag reduction (BDR) and air-layer drag reduction (ALDR) have significant drag reduction effects; the effects of BDR are limited to the first few meters downstream of the injection location, and ALDR is sensitive to inflow conditions
A new bionic nonsmooth surface inspired by the shape of barchan dunes has been proposed
Summary
With the rapid growth in energy consumption, the global energy crisis has been become increasingly serious. Elbing et al [8] conducted a set of experiments to investigate the phenomenon of skin friction reduction, which includes bubble drag reduction (BDR) and air-layer drag reduction (ALDR) in a turbulent boundary layer at large scales and high Reynolds numbers From these experiments they observed that BDR and ALDR have significant drag reduction effects; the effects of BDR are limited to the first few meters downstream of the injection location, and ALDR is sensitive to inflow conditions. Sanders et al [9] observed that, at lower flow speeds and higher gas injection rates, a layer of gas would form on the underside of a flat plate and persist along its entire length Such air layers lead to skin friction reductions greater than 80%. The friction drag is reduced when the wave travels at slower wave speeds than the bulk-mean velocity, and a maximum drag reduction rate of about 40% is achieved in the case of a stationary control input
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