Lattice Boltzmann study on drag reduction of a bluff body by slip boundary

Superhydrophobic surface is a promising technology, but the effect of superhydrophobic surface on flow noise is still unclear. Therefore, we used alternating free-slip and no-slip boundary conditions to study the flow noise of superhydrophobic channel flows with streamwise strips. The numerical calculations of the flow and the sound field have been carried out by the methods of large eddy simulation (LES) and Lighthill analogy, respectively. Under a constant pressure gradient (CPG) condition, the average Reynolds number and the friction Reynolds number are approximately set to 4200 and 180, respectively. The influence on noise of different gas fractions (GF) and strip number in a spanwise period on channel flow have been studied. Our results show that the superhydrophobic surface has noise reduction effect in some cases. Under CPG conditions, the increase in GF increases the bulk velocity and weakens the noise reduction effect. Otherwise, the increase in strip number enhances the lateral energy exchange of the superhydrophobic surface, and results in more transverse vortices and attenuates the noise reduction effect. In our results, the best noise reduction effect is obtained as 10.7 dB under the scenario of the strip number is 4 and GF is 0.5. The best drag reduction effect is 32%, and the result is obtained under the scenario of GF is 0.8 and strip number is 1. In summary, the choice of GF and the number of strips is comprehensively considered to guarantee the performance of drag reduction and noise reduction in this work.

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Effect of Slit Inclusions in Drag Reduction of Flow over Cylinders

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.846.18 ◽

2016 ◽

Vol 846 ◽

pp. 18-22

Author(s):

Rohit Bhattacharya ◽

Abouzar Moshfegh ◽

Ahmad Jabbarzadeh

Keyword(s):

Fluid Flow ◽

Drag Reduction ◽

Drag Coefficient ◽

Finite Volume ◽

Lattice Boltzmann ◽

Circular Cross Section ◽

Finite Volume Methods ◽

Turbulent Regime ◽

Ansys Fluent ◽

Comparison Of The Results

The flow over bluff bodies is separated compared to the flow over streamlined bodies. The investigation of the fluid flow over a cylinder with a streamwise slit has received little attention in the past, however there is some experimental evidence that show for turbulent regime it reduces the drag coefficient. This work helps in understanding the fluid flow over such cylinders in the laminar regime. As the width of the slit increases the drag coefficient keeps on reducing resulting in a narrower wake as compared to what is expected for flow over a cylinder. In this work we have used two different approaches in modelling a 2D flow for Re=10 to compare the results for CFD using finite volume method (ANSYS FLUENTTM) and Lattice Boltzmann methods. In all cases cylinders of circular cross section have been considered while slit width changing from 10% to 40% of the cylinder diameter. . It will be shown that drag coefficient decreases as the slit ratio increases. The effect of slit size on drag reduction is studied and discussed in detail in the paper. We have also made comparison of the results obtained from Lattice Boltzmann and finite volume methods.

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Involving the Navier–Stokes equations in the derivation of boundary conditions for the lattice Boltzmann method

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2011.0045 ◽

2011 ◽

Vol 369 (1944) ◽

pp. 2184-2192 ◽

Cited By ~ 1

Author(s):

Joris C. G. Verschaeve

Keyword(s):

Boundary Condition ◽

Lattice Boltzmann Method ◽

Lattice Boltzmann ◽

Stokes Equations ◽

Slip Boundary Condition ◽

Navier Stokes ◽

Grid Spacing ◽

Navier Stokes Equations ◽

Slip Boundary ◽

Boltzmann Method

By means of the continuity equation of the incompressible Navier–Stokes equations, additional physical arguments for the derivation of a formulation of the no-slip boundary condition for the lattice Boltzmann method for straight walls at rest are obtained. This leads to a boundary condition that is second-order accurate with respect to the grid spacing and conserves mass. In addition, the boundary condition is stable for relaxation frequencies close to two.

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Examination of the Slip Boundary Condition by µ-PIV and Lattice Boltzmann Simulations

Electronic and Photonic Packaging, Electrical Systems Design and Photonics, and Nanotechnology ◽

10.1115/imece2002-33704 ◽

2002 ◽

Cited By ~ 4

Author(s):

Derek C. Tretheway ◽

Luoding Zhu ◽

Linda Petzold ◽

Carl D. Meinhart

Keyword(s):

Boundary Condition ◽

Shear Rate ◽

Channel Flow ◽

Lattice Boltzmann ◽

Slip Velocity ◽

Slip Length ◽

Slip Boundary Condition ◽

Slip Boundary ◽

Lattice Boltzmann Simulations ◽

Bounce Back

This work examines the slip boundary condition by Lattice Boltzmann simulations, addresses the validity of the Navier’s hypothesis that the slip velocity is proportional to the shear rate and compares the Lattice Boltzmann simulations to the experimental results of Tretheway and Meinhart (Phys. of Fluids, 14, L9–L12). The numerical simulation models the boundary condition as the probability, P, of a particle to bounce-back relative to the probability of specular reflection, 1−P. For channel flow, the numerically calculated velocity profiles are consistent with the experimental profiles for both the no-slip and slip cases. No-slip is obtained for a probability of 100% bounce-back, while a probability of 0.03 is required to generate a slip length and slip velocity consistent with the experimental results of Tretheway and Meinhart for a hydrophobic surface. The simulations indicate that for microchannel flow the slip length is nearly constant along the channel walls, while the slip velocity varies with wall position as a results of variations in shear rate. Thus, the resulting velocity profile in a channel flow is more complex than a simple combination of the no-slip solution and slip velocity as is the case for flow between two infinite parallel plates.

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Immersed boundary (IB) - Lattice Boltzmann Method (LBM) coupled with Adaptive MESH Refinement (AMR) techniques for simulation of Incompressible Viscous Flow

10.32920/ryerson.14664936 ◽

2021 ◽

Author(s):

Xixiong Guo

Keyword(s):

Lattice Boltzmann Method ◽

Lattice Boltzmann ◽

Adaptive Mesh Refinement ◽

Moving Objects ◽

Mesh Refinement ◽

Adaptive Mesh ◽

Slip Boundary Condition ◽

Immersed Boundary ◽

Slip Boundary ◽

Boltzmann Method

This study is aimed at developing a novel computational framework that seamlessly incorporates the feedback forcing model and adaptive mesh refinement mesh refinement (AMR) techniques in the immersed-boundary (IB) lattice Boltzmann method (LBM) approach, so that challenging problems, including the interactions between flowing fluids and moving objects, can be numerically investigated. Owing to the feedback forcing based IB model, the advantages, such as simple mechanics principle, explicit interpolations, and inherent satisfaction of no-slip boundary condition for solid surfaces are fully exhibited. Additionally, the "bubble' function is employed in the local mesh refinement process, so that the solution of second order accuracy at newly generated nodes can be obtained only by the spatial interpolation but no temporal interpolation. Focusing on both steady and unsteady flow around a single cylinder and bi-cylinders, a number of test cases performed in this study have demonstrated the usefulness and effectiveness of the present AMR IB-LBM approach.

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Bionic shape design of electric locomotive and aerodynamic drag reduction

Archives of Transport ◽

10.5604/01.3001.0012.8369 ◽

2018 ◽

Vol 4 (48) ◽

pp. 99-109

Author(s):

Zhenfeng WU ◽

Yanzhong HUO ◽

Wangcai DING ◽

Zihao XIE

Keyword(s):

Flow Field ◽

Drag Reduction ◽

Bluff Body ◽

Aerodynamic Drag ◽

Geometric Characteristic ◽

Shape Design ◽

Shape Optimisation ◽

Electric Locomotive ◽

Geometric Models ◽

Characteristic Lines

Bionics has been widely used in many fields. Previous studies on the application of bionics in locomotives and vehicles mainly focused on shape optimisation of high-speed trains, but the research on bionic shape design in the electric locomotive field is rare. This study investigated a design method for streamlined electric locomotives according to the principles of bionics. The crocodiles were chosen as the bionic object because of their powerful and streamlined head shape. Firstly, geometric characteristic lines were extracted from the head of a crocodile by analysing the head features. Secondly, according to the actual size requirements of the electric locomotive head, a free-hand sketch of the bionic electric locomotive head was completed by adjusting the position and scale of the geometric characteristic lines. Finally, the non-uniform rational B-splines method was used to establish a 3D digital model of the crocodile bionic electric locomotive, and the main and auxiliary control lines were created. To verify the drag reduction effect of the crocodile bionic electric locomotive, numerical simulations of aerodynamic drag were performed for the crocodile bionic and bluff body electric locomotives at different speeds in open air by using the CFD software, ANSYS FLUENT16.0. The geometric models of crocodile bionic and bluff body electric locomotives were both marshalled with three cars, namely, locomotive + middle car + locomotive, and the size of the two geometric models was uniform. Dimensions and grids of the flow field were defined. And then, according to the principle of motion relativity, boundary conditions of flow field were defined. The results indicated that the crocodile bionic electric locomotive demonstrated a good aerodynamic performance. At the six sampling speeds in the range of 40–240 km/h, the aerodynamic drag coefficient of the crocodile bionic electric locomotive decreased by 7.7% on the average compared with that of the bluff body electric locomotive.

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