Influence of Ribbon Structure Rough Wall on the Microscale Poiseuille Flow

2005 ◽  
Vol 127 (6) ◽  
pp. 1140-1145 ◽  
Author(s):  
Haoli Wang ◽  
Yuan Wang ◽  
Jiazhong Zhang
Keyword(s):  
Harmonic Functions ◽  
Wave Number ◽  
Fundamental Wave ◽  
Wall Roughness ◽  
Parallel Plates ◽  
Roughness Parameters ◽  
Regular Perturbation ◽  
Roughness Model ◽  
Ribbon Structure ◽  
Flow Resistances

The regular perturbation method is introduced to investigate the influence of two-dimensional roughness on laminar flow in microchannels between two parallel plates. By superimposing a series of harmonic functions with identical dimensional amplitude as well as the same fundamental wave number, the wall roughness functions are obtained and the relative roughness can be determined as the maximal value of the product between the normalized roughness functions and a small parameter. Through modifying the fundamental wave number, the dimensionless roughness spacing is changed. Under this roughness model, the equations with respect to the disturbance stream function are obtained and analyzed numerically. The numerical results show that flowing in microchannels are more complex than that in macrochannels; there exist apparent fluctuations with streamlines and clear vortex structures in microchannels; the flow resistances are about 5–80% higher than the theoretical value under different wall-roughness parameters. Furthermore, analysis shows that the effect of roughness on the flow pattern is distinct from that on the friction factor.

scholarly journals Investigation of Side Wall Roughness Effect on Optical Losses in a Multimode Si3N4 Waveguide Formed on a Quartz Substrate

Photonics ◽  
2020 ◽  
Vol 7 (4) ◽  
pp. 104
Author(s):  
Anastasia Yakuhina ◽  
Alexey Kadochkin ◽  
Vyacheslav Svetukhin ◽  
Dmitry Gorelov ◽  
Sergey Generalov ◽  
...  
Keyword(s):  
Optical Waveguides ◽  
Quartz Substrate ◽  
Side Wall ◽  
Wall Roughness ◽  
Roughness Parameters ◽  
Optical Losses ◽  
Waveguide Width ◽  
Integration Density ◽  
Frequency Domain Reflectometry ◽  
Multimode Operation

This article presents the results of the study of the influence of the most significant parameters of the side wall roughness of an ultra-thin silicon nitride lightguide layer of multimode integrated optical waveguides with widths of 3 and 8 microns. The choice of the waveguide width was made due to the need to provide multimode operation for telecommunication wavelengths, which is necessary to ensure high integration density. Scattering in waveguide structures was measured by optical frequency domain reflectometry (OFDR) of a backscattering reflectometer. The finite difference time domain method (FDTD) was used to study the effect of roughness parameters on optical losses in fabricated waveguides, the roughness parameters that most strongly affect optical scattering were determined, and methods of its significant reduction were specified. The prospects for implementing such structures on a quartz substrate are justified.

scholarly journals Effect of Vertical Vibrations on the Onset of Binary Convection

2013 ◽  
Vol 18 (3) ◽  
pp. 899-910 ◽  
Author(s):  
M.S. Swamy
Keyword(s):  
Rayleigh Number ◽  
Fluid Layer ◽  
Critical Rayleigh Number ◽  
Lewis Number ◽  
Wave Number ◽  
Closed Form Expression ◽  
Effective Control ◽  
Regular Perturbation ◽  
Binary Fluid ◽  
Vertical Vibrations

Abstract In the present work the linear stability analysis of double diffusive convection in a binary fluid layer is performed. The major intention of this study is to investigate the influence of time-periodic vertical vibrations on the onset threshold. A regular perturbation method is used to compute the critical Rayleigh number and wave number. A closed form expression for the shift in the critical Rayleigh number is calculated as a function of frequency of modulation, the solute Rayleigh number, Lewis number, and Prandtl number. These parameters are found to have a significant influence on the onset criterion; therefore the effective control of convection is achieved by proper tuning of these parameters. Vertical vibrations are found to enhance the stability of a binary fluid layer heated and salted from below. The results of this study are useful in the areas of crystal growth in micro-gravity conditions and also in material processing industries where vertical vibrations are involved

Measurements and Evaluation of Internal Wall Surface Roughness of Small Diameter Pipes for High Pressure Natural Gas Systems

2014 ◽  
Author(s):  
C. Hartloper ◽  
K. K. Botros ◽  
J. Geerligs ◽  
H. Golshan ◽  
K. Jensen
Keyword(s):  
Surface Roughness ◽  
Pipe Wall ◽  
Large Diameter ◽  
Roughness Parameter ◽  
Small Diameter ◽  
Wall Roughness ◽  
Roughness Parameters ◽  
Internal Wall ◽  
Effective Roughness ◽  
Pipe Size

The default roughness parameter values used in industry to determine the pressure loss through small diameter pipeline systems are much higher than the values employed in typical large diameter gas transmission and lateral systems. It is uncertain whether these higher roughness values are due to higher topological roughness of the internal wall of the small diameter pipes or if they are a result of other factors. Measurements were taken on 17 small diameter pipe samples in order to evaluate the pipe-wall roughness parameter. A model to calculate the effective roughness parameter, which takes into account pressure losses due to the measured roughness as well as internal welds and scaling, has been developed. The effective roughness parameter of these samples is found to range from 20.4μm to 62.9μm, an increase of 11.0μm to 23.3μm over the measured pipe-wall roughness parameter. This range of effective roughness parameters agrees well with the default range of 35μm to 65μm used in industry, as well as the literature quoted range for clean pipe of 40μm to 100μm. The measured roughness parameter on average increases with increasing nominal pipe size, a result that may be a characteristic of the extrusion or hot-rolling processes used to manufacture small diameter pipes. Additionally, there is a large variation in the measured roughness parameters of pipe samples of the same nominal pipe size, indicating that surface roughness can vary depending on the manufacturing source of these pipes.

scholarly journals Nonlinear peristaltic flow of Walter's B fluid in an asymmetric channel with heat transfer and chemical reactions

2014 ◽  
Vol 18 (4) ◽  
pp. 1095-1107 ◽  
Author(s):  
Ullah Mehmood ◽  
Norzieha Mustapha ◽  
Sharidan Shafie
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Concentration ◽  
Flow Characteristics ◽  
Wave Number ◽  
Asymmetric Channel ◽  
Regular Perturbation ◽  
Viscoelastic Parameter ◽  
Walter’S B Fluid

In this paper, effects of heat and mass transfer on peristaltic transport of Walter's B fluid in an asymmetric channel are investigated. The governing equations are solved using regular perturbation method by taking wave number as a small parameter. Expressions for the stream function, temperature distribution, heat transfer coefficient, and mass concentration are presented in explicit form. Solutions are analyzed graphically for different values of arising parameters such as viscoelastic parameter, Prandtl, Eckert, Soret, Schmidt and Reynolds number. It has been found that these parameters considerably affect the considered flow characteristics. Results show that with an increase in Eckert and Prandtl number temperature and heat transfer coefficient increase while mass concentration decreases. Further, Mass concentration also decreases with increasing Soret and Schmidt number.

CFD simulations and evaluation of applicability of a wall roughness model applied on a NACA 63 3 ‐418 airfoil

Wind Energy ◽  
2020 ◽  
Vol 23 (11) ◽  
pp. 2056-2067
Author(s):  
Emil Krog Kruse ◽  
Niels Sørensen ◽  
Christian Bak ◽  
Mikkel Schou Nielsen
Keyword(s):  
Wall Roughness ◽  
Cfd Simulations ◽  
Roughness Model

Variable Viscosity Effects on Penetrative Convection in a Fluid Layer

2017 ◽  
Vol 13 (3) ◽  
pp. 51-65
Author(s):  
Gangadharaiah Y H
Keyword(s):  
Surface Deformation ◽  
Variable Viscosity ◽  
Fluid Layer ◽  
Perturbation Technique ◽  
Internal Heat ◽  
Internal Heat Source ◽  
Decisive Role ◽  
Wave Number ◽  
Regular Perturbation ◽  
Penetrative Convection

The effect of variable viscosity on the onset of penetrative convection simulated via internal heating in a fluid layer. The upper surface of a fluid layer is assumed to be deformably free and dependence of viscosity is assumed to be exponential. The resulting eigen value problem is solved using a regular perturbation technique with wave number a as a perturbation parameter. The viscosity parameter, surface deformation and the presence of internal heat source play a decisive role on the stability characteristics of the system.

scholarly journals INSTABILITY OF THE RAYLEIGH-BENARD CONVECTION FOR INCLINED LOWER WALL WITH TEMPERATURE VARIATION

2016 ◽  
Vol 14 (2) ◽  
pp. 179
Author(s):  
Sadoon Ayed ◽  
Gradimir Ilić ◽  
Predrag Živković ◽  
Mića Vukić ◽  
Mladen Tomić
Keyword(s):  
Temperature Variation ◽  
Wave Number ◽  
Lower Plate ◽  
Navier Stokes ◽  
Parallel Plates ◽  
Time Period ◽  
The Mean ◽  
Convective Cells ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

This paper deals with an analysis of a two-dimensional viscous fluid flow between the two parallel plates inclined with respect to the horizontal plane, where the lower plate is heated and the upper one is cooled. The temperature difference between the plates is gradually increased during a certain time period after which it is temporarily constant. The temperature distribution on the lower plate is not constant in x-direction, there is a longitudinal sinusoidal temperature variation imposed on the mean temperature. We have investigated the wave number and amplitude influence of this variation on the subcritical stability and the onset of the Rayleigh-Bénard convective cells, by direct numerical simulation of 2D Navier-Stokes and energy equation.

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