Simulation experiment of drag reduction on non-smooth surfaces based on Fluent
In the pursuit of enhancing the efficiency of ships and underwater vehicles,overcoming fluid drag is a pivotal challenge.Among the many drag reduction strategies,the bionic nonsmooth surface drag reduction technique is promising.In the initial phases of surface drag reduction technology development,the prevailing belief was that smoother surfaces would yield superior drag reduction.However,as under standing of drag reduction mechanisms improved,it became evident that surface fluid resistance is intricately linked to the boundary layer.Consequently,research shifted focus toward delaying surface turbulence transition and mitigating turbulence bursts.Inspired by the nonsmooth epidermis of pufferfish,this study designed nonsmooth surfaces for drag reduction experiments,and the circulating water tunnel experimental method based on particle image velocimetry technology yielded satisfactory experimental outcomes in measuring the drag reduction rate of nonsmooth surfaces.However,this methodology faces limitations in terms of time consumption and complex data processing,particularly with large sample sizes.To overcome these challenges,this study investigated the relationship between the spreading spacing,the friction drag reduction rate,and the total drag reduction rate based on the nonsmooth surface drag reduction simulation experiment of Fluent.The process involved designing nonsmooth surface models with different parameters in SolidWorks,followed by mesh delineation in the integrated computer engineering and manttfacturing(ICEM),and subsequent importation into ANSYS for finite element analysis using the Fluent module.The shear stress tramsfer(SST)k-ω turbulence model was adopted for the numerical simulation of drag reduction on these surfaces,and the results of the numerical simulation were obtained using the postprocessing module CFD-post.The results showed the following.With the increase in the spreading spacing of the conical microstructures,the total drag reduction rate of the nonsmooth surface increased.At low flow velocities,the spreading spacing did not have much influence on the total drag reduction rate;at high flow velocities,the larger the spreading spacing,the higher the total drag reduction rate.If the spreading spacing was unchanged,the total drag reduction rate decreased with the increase in the flow velocity.At the same time,with the increase in the spreading distance of the conical microstructures,the friction drag reduction rate of the nonsmooth surfaces decreased,and the friction drag reduction rate showed a decreasing trend when the incoming flow rate was accelerated with the constant spreading distance of the conical microstructures.Further analysis of cloud diagrams indicated that the bionic cone microstructures disrupted large-scale vortex structures in the turbulent boundary layer,transforming them into smaller vortices while absorbing turbulence energy.This process curtailed momentum transfer within the layer and inhibited turbulence bursting,which led to the higher flow velocity,pressure,and turbulence kinetic energy upstream of the cone microstructure and the lower flow velocity,pressure,and turbulence kinetic energy in the two sides and the backside.The nonsmooth surfaces investigated in this study provide not only a new highlight for the design of drag-reducing surfaces but also a novel method of fluid drag reduction for ship,underwater vehicle,and pipeline transportation applications.
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