Nanoscale Fluid Flow Over Two Side-by-Side Cylinders With Atomically Rough Surface

2006 ◽  
Vol 129 (3) ◽  
pp. 325-332 ◽  
Author(s):  
A. S. Ziarani ◽  
A. A. Mohamad
Keyword(s):  
Surface Roughness ◽  
Lift Force ◽  
Liquid Argon ◽  
Dynamics Simulation ◽  
Two Dimensional ◽  
Drag Forces ◽  
Roughness Amplitude ◽  
Drag And Lift ◽  
Nanoscale Fluid Flow ◽  
Real Solid

A molecular dynamics simulation of flow over two side-by-side cylinders with atomically rough surfaces is presented. The model is two-dimensional with 3×105 liquid argon atoms. The surface roughness is constructed by external protrusion of atoms on the surface of the cylinders with specified amplitude and width. Two cylinders, with diameters of d=79.44 (molecular units), are placed at a distance of D in a vertical line. The solids atoms are allowed to vibrate around their equilibrium coordinates to mimic the real solid structure. The influence of various parameters, such as roughness amplitude, topology, periodicity, and the gap between cylinders on the hydrodynamics of flow, especially drag and lift forces, is studied. It was noted that even very little surface roughness, with amplitude on the order of a few nanometers, can influence the drag forces. Both roughness texture and the number of roughening elements affects the drag and lift coefficients. The gap between the cylinders showed to be an effective parameter, especially on the lift force for flow over the nanoscale cylinders.

Wake Flow of Single and Multiple Yawed Cylinders

2004 ◽  
Vol 126 (5) ◽  
pp. 861-870 ◽  
Author(s):  
A. Thakur ◽  
X. Liu ◽  
J. S. Marshall
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Side Wall ◽  
Wake Flow ◽  
Upstream Region ◽  
Two Dimensional ◽  
Cylinder Wake ◽  
Dimensional Approximation ◽  
The Face ◽  
Drag And Lift

An experimental and computational study is performed of the wake flow behind a single yawed cylinder and a pair of parallel yawed cylinders placed in tandem. The experiments are performed for a yawed cylinder and a pair of yawed cylinders towed in a tank. Laser-induced fluorescence is used for flow visualization and particle-image velocimetry is used for quantitative velocity and vorticity measurement. Computations are performed using a second-order accurate block-structured finite-volume method with periodic boundary conditions along the cylinder axis. Results are applied to assess the applicability of a quasi-two-dimensional approximation, which assumes that the flow field is the same for any slice of the flow over the cylinder cross section. For a single cylinder, it is found that the cylinder wake vortices approach a quasi-two-dimensional state away from the cylinder upstream end for all cases examined (in which the cylinder yaw angle covers the range 0⩽ϕ⩽60°). Within the upstream region, the vortex orientation is found to be influenced by the tank side-wall boundary condition relative to the cylinder. For the case of two parallel yawed cylinders, vortices shed from the upstream cylinder are found to remain nearly quasi-two-dimensional as they are advected back and reach within about a cylinder diameter from the face of the downstream cylinder. As the vortices advect closer to the cylinder, the vortex cores become highly deformed and wrap around the downstream cylinder face. Three-dimensional perturbations of the upstream vortices are amplified as the vortices impact upon the downstream cylinder, such that during the final stages of vortex impact the quasi-two-dimensional nature of the flow breaks down and the vorticity field for the impacting vortices acquire significant three-dimensional perturbations. Quasi-two-dimensional and fully three-dimensional computational results are compared to assess the accuracy of the quasi-two-dimensional approximation in prediction of drag and lift coefficients of the cylinders.

Effects of active crowder size and activity-crowding coupling on polymer translocation

Soft Matter ◽  
2020 ◽  
Author(s):  
Fei Tan ◽  
Ying Chen ◽  
Nanrong Zhao
Keyword(s):  
Langevin Dynamics ◽  
Dynamics Simulation ◽  
Biological Processes ◽  
Two Dimensional ◽  
Complex Environments ◽  
Polymer Translocation ◽  
Langevin Dynamics Simulation

Polymer translocation in complex environments is crucially important to many biological processes in life. In the present work, we adopted two-dimensional Langevin dynamics simulation to study the forced and unbiased...

scholarly journals Investigation of Two-Dimensional Ultrasonic Surface Burnishing Process on 7075-T6 Aluminum

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Zhenyu Zhou ◽  
Qiuyang Zheng ◽  
Cong Ding ◽  
Guanglei Yu ◽  
Guangjian Peng ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Parameter Optimization ◽  
Wear Mechanism ◽  
Feed Rate ◽  
Sample Surface ◽  
Original Sample ◽  
Two Dimensional ◽  
Delamination Wear ◽  
Treated Sample ◽  
Burnishing Process

AbstractA novel two-dimensional ultrasonic surface burnishing process (2D-USBP) is proposed. 7075-T6 aluminum samples are processed by a custom-designed 2D-USBP setup. Parameter optimization of 2D-USBP is conducted to determine the best processing strategy of 7075-T6 aluminum. A uniform design method is utilized to optimize the 2D-USBP process. U13(133) and U7(72) tables are established to conduct parameter optimization. Burnishing depth, spindle speed, and feed rate are taken as the control parameters. The surface roughness and Vickers hardness are taken as the evaluation indicators. It establishes the active control models for surface quality. Dry wear tests are conducted to compare the wear-resistance of the 2D-USBP treated sample and the original sample. Results show that the machining quality of 2D-USBP is best under 0.24 mm burnishing depth, 5000 r/min spindle speed, and 25 mm/min feed rate. The surface roughness Sa of the sample is reduced from 2517.758 to 50.878 nm, and the hardness of the sample surface is improved from 167 to 252 HV. Under the lower load, the wear mechanism of the 2D-USBP treated sample is mainly abrasive wear accompanied by delamination wear, while the wear mechanism of the original sample is mainly delamination wear. Under the higher load, the accumulation of frictional heat on the sample surface transforms the wear mechanisms of the original and the 2D-USBP treated samples into thermal wear.

scholarly journals Modeling of Drag Finishing—Influence of Abrasive Media Shape

2021 ◽  
Vol 5 (2) ◽  
pp. 41
Author(s):  
Irati Malkorra ◽  
Hanène Souli ◽  
Ferdinando Salvatore ◽  
Pedro Arrazola ◽  
Joel Rech ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Material Removal ◽  
Direct Shear Test ◽  
Shear Test ◽  
Shear Resistance ◽  
Arbitrary Lagrangian Eulerian ◽  
Eulerian Model ◽  
Drag Forces ◽  
Drag Finishing ◽  
Surrounding Liquid

Drag finishing is a widely used superfinishing technique in the industry to polish parts under the action of abrasive media combined with an active surrounding liquid. However, the understanding of this process is not complete. It is known that pyramidal abrasive media are more prone to rapidly improving the surface roughness compared to spherical ones. Thus, this paper aims to model how the shape of abrasive media (spherical vs. pyramidal) influences the material removal mechanisms at the interface. An Arbitrary Lagrangian–Eulerian model of drag finishing is proposed with the purpose of estimating the mechanical loadings (normal stress, shear stress) induced by both abrasive media at the interface. The rheological behavior of both abrasive slurries (media and liquid) has been characterized by means of a Casagrande direct shear test. In parallel, experimental drag finishing tests were carried out with both media to quantify the drag forces. The correlation between the numerical and experimental drag forces highlights that the abrasive media with a pyramidal shape exhibits a higher shear resistance, and this is responsible for inducing higher mechanical loadings on the surfaces and, through this, for a faster decrease of the surface roughness.

Acoustic receptivity and evolution of two-dimensional and oblique disturbances in a Blasius boundary layer

2001 ◽  
Vol 432 ◽  
pp. 69-90 ◽  
Author(s):  
RUDOLPH A. KING ◽  
KENNETH S. BREUER
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Acoustic Wave ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Surface Waviness ◽  
S Wave ◽  
Boundary Layer Instability ◽  
Blasius Boundary Layer ◽  
Tollmien Schlichting

An experimental investigation was conducted to examine acoustic receptivity and subsequent boundary-layer instability evolution for a Blasius boundary layer formed on a flat plate in the presence of two-dimensional and oblique (three-dimensional) surface waviness. The effect of the non-localized surface roughness geometry and acoustic wave amplitude on the receptivity process was explored. The surface roughness had a well-defined wavenumber spectrum with fundamental wavenumber kw. A planar downstream-travelling acoustic wave was created to temporally excite the flow near the resonance frequency of an unstable eigenmode corresponding to kts = kw. The range of acoustic forcing levels, ε, and roughness heights, Δh, examined resulted in a linear dependence of receptivity coefficients; however, the larger values of the forcing combination εΔh resulted in subsequent nonlinear development of the Tollmien–Schlichting (T–S) wave. This study provides the first experimental evidence of a marked increase in the receptivity coefficient with increasing obliqueness of the surface waviness in excellent agreement with theory. Detuning of the two-dimensional and oblique disturbances was investigated by varying the streamwise wall-roughness wavenumber αw and measuring the T–S response. For the configuration where laminar-to-turbulent breakdown occurred, the breakdown process was found to be dominated by energy at the fundamental and harmonic frequencies, indicative of K-type breakdown.

The effect of a footprint on perceived surface roughness

1986 ◽  
Vol 405 (1829) ◽  
pp. 303-327 ◽  
Keyword(s):  
Surface Roughness ◽  
Weighting Function ◽  
Sampling Interval ◽  
Asymptotic Convergence ◽  
Reference Surface ◽  
Two Dimensional ◽  
Random Surface ◽  
Spectral Density Functions ◽  
Continuous Theory ◽  
Discrete Theory

A two-dimensional homogeneous random surface { y ( X )} is generated from another such surface { z ( X )} by a process of smoothing represented by y ( X ) = ∫ ∞ d u w ( u – X ) z ( u ), where w ( X ) is a deterministic weighting function satisfying certain conditions. The two-dimensional autocorrelation and spectral density functions of the smoothed surface { y ( X )} are calculated in terms of the corresponding functions of the reference surface { z ( X )} and the properties of the ‘footprint’ of the contact w ( X ). When the surfaces are Gaussian, the statistical properties of their peaks and summits are given by the continuous theory of surface roughness. If only sampled values of the surface height are available, there is a corresponding discrete theory. Provided that the discrete sampling interval is small enough, profile statistics calculated by the discrete theory should approach asymptotically those calculated by the continuous theory, but it is known that such asymptotic convergence may not occur in practice. For a smoothed surface { y ( X )} which is generated from a reference surface { z ( X )} by a ‘good’ footprint of finite area, it is shown in this paper that the expected asymptotic convergence does occur always, even if the reference surface is ideally white. For a footprint to be a good footprint, w ( X ) must be continuous and smooth enough that it can be differentiated twice everywhere, including at its edges. Sample calculations for three footprints, two of which are good footprints, illustrate the theory.

An Evaluation of the Average Flow Model [1] for Surface Roughness Effects in Lubrication

1980 ◽  
Vol 102 (3) ◽  
pp. 360-366 ◽  
Author(s):  
J. L. Teale ◽  
A. O. Lebeck
Keyword(s):  
Surface Roughness ◽  
Flow Model ◽  
Two Dimensional ◽  
Roughness Effects ◽  
Important Conclusion ◽  
Average Flow ◽  
One Dimensional ◽  
Dimensional Flow ◽  
Two Dimensional Flow ◽  
Average Flow Model

The average flow model presented by Patir and Cheng [1] is evaluated. First, it is shown that the choice of grid used in the average flow model influences the results. The results presented are different from those given by Patir and Cheng. Second, it is shown that the introduction of two-dimensional flow greatly reduces the effect of roughness on flow. Results based on one-dimensional flow cannot be relied upon for two-dimensional problems. Finally, some average flow factors are given for truncated rough surfaces. These can be applied to partially worn surfaces. The most important conclusion reached is that an even closer examination of the average flow concept is needed before the results can be applied with confidence to lubrication problems.

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