Effect of Reynolds Number on Cylinder Drag Reduction Using Micro-Fiber Coating

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 Reynolds number on drag reduction in turbulent boundary layer flow over liquid–gas interface

Physics of Fluids ◽

10.1063/5.0027727 ◽

2020 ◽

Vol 32 (12) ◽

pp. 122111

Author(s):

Hongyuan Li ◽

SongSong Ji ◽

Xiangkui Tan ◽

Zexiang Li ◽

Yaolei Xiang ◽

...

Keyword(s):

Boundary Layer ◽

Reynolds Number ◽

Turbulent Boundary Layer ◽

Drag Reduction ◽

Boundary Layer Flow ◽

Turbulent Boundary Layer Flow ◽

Layer Flow

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Fibre-induced drag reduction

Journal of Fluid Mechanics ◽

10.1017/s0022112008000967 ◽

2008 ◽

Vol 602 ◽

pp. 209-218 ◽

Cited By ~ 19

Author(s):

J. J. J. GILLISSEN ◽

B. J. BOERSMA ◽

P. H. MORTENSEN ◽

H. I. ANDERSSON

Keyword(s):

Experimental Data ◽

Numerical Simulation ◽

Reynolds Number ◽

Drag Reduction ◽

Elastic Layer ◽

Turbulent Drag Reduction ◽

Rigid Polymer ◽

Fibre Concentration ◽

Induced Drag ◽

Turbulent Drag

We use direct numerical simulation to study turbulent drag reduction by rigid polymer additives, referred to as fibres. The simulations agree with experimental data from the literature in terms of friction factor dependence on Reynolds number and fibre concentration. An expression for drag reduction is derived by adopting the concept of the elastic layer.

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

Physics of Fluids ◽

10.1063/1.4995566 ◽

2017 ◽

Vol 29 (9) ◽

pp. 093605 ◽

Cited By ~ 22

Author(s):

Shabnam Raayai-Ardakani ◽

Gareth H. McKinley

Keyword(s):

Boundary Layer ◽

Reynolds Number ◽

Drag Reduction ◽

Laminar Boundary Layer ◽

High Reynolds Number ◽

Boundary Layer Flows ◽

High Reynolds

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Common features between the Newtonian laminar–turbulent transition and the viscoelastic drag-reducing turbulence

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.567 ◽

2019 ◽

Vol 877 ◽

pp. 405-428 ◽

Cited By ~ 8

Author(s):

Anselmo S. Pereira ◽

Roney L. Thompson ◽

Gilmar Mompean

Keyword(s):

Reynolds Number ◽

Turbulent Flow ◽

Drag Reduction ◽

Turbulent Flows ◽

Temporal Dynamics ◽

Homoclinic Orbits ◽

Theoretical Development ◽

Transitional Flows ◽

Turbulent Transition ◽

Laminar Turbulent Transition

The transition from laminar to turbulent flows has challenged the scientific community since the seminal work of Reynolds (Phil. Trans. R. Soc. Lond. A, vol. 174, 1883, pp. 935–982). Recently, experimental and numerical investigations on this matter have demonstrated that the spatio-temporal dynamics that are associated with transitional flows belong to the directed percolation class. In the present work, we explore the analysis of laminar–turbulent transition from the perspective of the recent theoretical development that concerns viscoelastic turbulence, i.e. the drag-reducing turbulent flow obtained from adding polymers to a Newtonian fluid. We found remarkable fingerprints of the variety of states that are present in both types of flows, as captured by a series of features that are known to be present in drag-reducing viscoelastic turbulence. In particular, when compared to a Newtonian fully turbulent flow, the universal nature of these flows includes: (i) the statistical dynamics of the alternation between active and hibernating turbulence; (ii) the weakening of elliptical and hyperbolic structures; (iii) the existence of high and low drag reduction regimes with the same boundary; (iv) the relative enhancement of the streamwise-normal stress; and (v) the slope of the energy spectrum decay with respect to the wavenumber. The maximum drag reduction profile was attained in a Newtonian flow with a Reynolds number near the boundary of the laminar regime and in a hibernating state. It is generally conjectured that, as the Reynolds number increases, the dynamics of the intermittency that characterises transitional flows migrate from a situation where heteroclinic connections between the upper and the lower branches of solutions are more frequent to another where homoclinic orbits around the upper solution become the general rule.

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Direct simulations of turbulent flow in a pipe rotating about its axis

Journal of Fluid Mechanics ◽

10.1017/s0022112097005715 ◽

1997 ◽

Vol 343 ◽

pp. 43-72 ◽

Cited By ~ 117

Author(s):

P. ORLANDI ◽

M. FATICA

Keyword(s):

Reynolds Number ◽

Drag Reduction ◽

Radial Direction ◽

Uniform Grid ◽

Grid Refinement ◽

Streamwise Vorticity ◽

Vorticity Field ◽

Vortical Structures ◽

The Mean ◽

Grid Points

Flow in a circular pipe rotating about its axis, at low Reynolds number, is investigated. The simulation is performed by a finite difference scheme, second-order accurate in space and in time. A non-uniform grid in the radial direction yields accurate solutions with a reasonable number of grid points. The numerical method has been tested for the non-rotating pipe in the limit ν→0 to prove the energy conservation properties. In the viscous case a grid refinement check has been performed and some conclusions about drag reduction have been reached. The mean and turbulent quantities have been compared with the numerical and experimental non-rotating pipe data of Eggels et al. (1994a, b). When the pipe rotates, a degree of drag reduction is achieved in the numerical simulations just as in the experiments. Through the visualization of the vorticity field the drag reduction has been related to the modification of the vortical structures near the wall. A comparison between the vorticity in the non-rotating and in the high rotation case has shown a spiral motion leading to the transport of streamwise vorticity far from the wall.

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