Experimental Investigations on the Effect of a Wavy Surface on Hydrodynamic Instabilities in a Taylor-Couette System

2021 ◽  
Author(s):  
Lamia Gaied ◽  
Marc Lippert ◽  
Laurent Keirsbulck ◽  
Fethi Aloui ◽  
Emna Berrich
Keyword(s):  
Surface Roughness ◽  
Rough Surface ◽  
Outer Cylinder ◽  
Angular Speed ◽  
Experimental Investigations ◽  
Hydrodynamic Instabilities ◽  
Taylor Vortices ◽  
Surface Irregularities ◽  
Surface Nature ◽  
Effect Of Surface

Abstract In this work, we propose an experimental study of the effect of surface roughness of the internal cylinder Couette-Taylor system in order to investigate the hydrodynamic instabilities of the flow. During experiments, the inner cylinder, which presents a rough surface with u cylinder corrugations, rotates at a given angular speed and the outer cylinder, which is smooth, is kept fixed. The main objective of the study is to demonstrate the effect of geometric parameters on the flow (the shape of the roughness). Experimental results have shown that the shapes of the surface irregularities have an effect on the appearance of the first instabilities, which strongly depend on the size, shape and nature of the roughness. In fact, the nature of surface roughness not only affects the friction on the wall, but also strongly influences the transport of mass and momentum in a given flow regime. The flow therefore evokes more friction when the inner (rotating) cylinder has a rough surface. This friction, which slows the speed of the fluid particles, strongly depends on the surface nature in contact with the fluid. The movement of the particles in these irregularities will therefore, be damped as a function of the shape of the roughness. In addition, the results also showed that once Couette-Taylor vortices are present, surface roughness can promote continued flow disturbance. The resulting flow then becomes less slow in the troughs of surface irregularities; thus, leads to less friction.

scholarly journals Influence of Surface Irregularities on Hydrodynamic Instabilities in Couette-Taylor Flow

2019 ◽  
Author(s):  
Lamia Gaied ◽  
Emna Berrich ◽  
Fethi Aloui ◽  
Marc Lippert ◽  
Laurent Keirsbulck ◽  
...  
Keyword(s):  
Experimental Study ◽  
Rough Surface ◽  
Outer Cylinder ◽  
Roughness Parameter ◽  
Hydrodynamic Instabilities ◽  
Wall Roughness ◽  
Roughness Effect ◽  
Taylor Flow ◽  
Different Types ◽  
Surface Irregularities

Abstract In this work, we propose an experimental study of roughness effect on hydrodynamic instabilities’ Couette-Taylor flow. During experiments, the inner cylinder rotates at a given angular velocity and the outer cylinder is maintained fix. The main objective of the study is to highlight the geometric parameters’ effect on the flow. We mainly focused our attention on the effect of the wall roughness parameter on the appearance instabilities in the studied configuration (delay or advance in its appearance). For this purpose, a qualitative study was performed using Kalliroscope particles to visualize the instabilities. Then, we applied polarography to different types of roughness as a quantitative study. Hence, the possibility to characterize the flow regimes of the first instabilities (TVF, WVF, MWVF, and TN). The experiments have shown that surface irregularities, have an effect on the appearance of the first instabilities, which depend on the size and nature of the roughness. In fact, the surface roughness not only increases the friction on the wall, but it also greatly influences the transport of the mass and momentum in a given flow regime. The flow, therefore, undergoes more friction when the inner cylinder (in rotation) has a rough surface. This friction slows the velocity of the fluid particles; which delays the onset of instability. The movement of the particles will therefore, be dampened by the irregularities at the level of the rough surface. Moreover, the results also proved that as soon as the Couette-Taylor cells are established, the roughness is no longer a particle motion damper, but on the contrary, it promotes the continuation of the disturbance of the flow. The flow becomes then less slowdown in the hollow of the surface irregularities; which leads to less friction. For higher Taylor numbers, the study showed a faster transition from one regime to another.

Experimental Study on the Effects of Surface Roughness on the Behaviors of Hydrodynamic Instabilities of Couette-Taylor Flow

2017 ◽  
Author(s):  
Mostafa Monfared ◽  
Lamia Gaied ◽  
Emna Berrich ◽  
Ebrahim Shirani ◽  
Maxence Bigerelle ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Vortex Flow ◽  
Outer Cylinder ◽  
Wire Mesh ◽  
Taylor Vortex ◽  
Hydrodynamic Instabilities ◽  
Taylor Flow ◽  
Taylor Vortex Flow ◽  
Concentric Cylinders ◽  
Effect Of Surface

Couette-Taylor flow is a type of fluid flow that occurs in the annulus between differentially concentric cylinders, when the outer cylinder is fixed and the inner cylinder rotates and the rotation rate exceeds a critical value. In this research we have studied the effect of surface roughness on the hydrodynamic structures of Couette-Taylor Flow. The PIV technique has been applied for flow visualization. At first, for a smooth surface, the different flow patterns include Couette flow, Taylor vortex flow, wavy vortex flow, modulated wavy vortex flow and turbulent flow. They are investigated numerically and experimentally. The transition Taylor number for every flow regime is also taken into consideration. The results showed that the numerical results correspond quite well to the experimental data. Then, the different surface conditions for inner cylinder which are studied are: a smooth one, a sandpaper-type P180, a canvas plastic with different wire-mesh roughness. They are used to study the effects of surface roughness on the flow structures and critical Taylor numbers. The experimental results showed that the roughness causes a delay in the appearance of the first instabilities.

An experimental study of Couette instability of stratified fluids

1974 ◽  
Vol 66 (4) ◽  
pp. 725-737 ◽  
Author(s):  
E. M. Withjack ◽  
C. F. Chen
Keyword(s):  
Experimental Study ◽  
Critical Speed ◽  
Outer Cylinder ◽  
Spiral Wave ◽  
Angular Speed ◽  
Wave Form ◽  
Salt Solutions ◽  
Taylor Vortices ◽  
Critical Wavelength ◽  
The Stability

The stability of Couette flow of stratified salt solutions is investigated in an apparatus with both the inner and outer cylinders rotating. The ratio of the radius of the inner cylinder to that of the outer cylinder is 0·2. The flow is visualized by means of shadowgraph and dye-trace methods. Compared with homogeneous fluids, the effect of the stabilizing density gradient is to increase the critical speed of the inner cylinder and to decrease the critical wavelength for a given angular speed of the outer cylinder. When the cylinders are rotating in the same direction, in the critical state, the instabilities appear along the inner cylinder in a spiral wave form which is itself not very stable. With counterrotating cylinders, the instabilities appear as regularly spaced vortices which, for the most part, are neither symmetric Taylor vortices nor simple spirals. In addition, these vortices rotate as a whole at a speed generally smaller than that of the inner cylinder. From shadowgraph observations, stability curves are constructed for three density gradients. The critical wavelength and the rotational periods of the vortices are also determined.

Effect of Surface Roughness on Fouling of Calcium Carbonate: An Experimental Investigation

2010 ◽  
Author(s):  
M. Izadi ◽  
D. K. Aidun ◽  
P. Marzocca ◽  
H. Lee
Keyword(s):  
Surface Roughness ◽  
Calcium Carbonate ◽  
Rough Surface ◽  
Smooth Surface ◽  
Rough Surfaces ◽  
Operating Conditions ◽  
Tubular Heat Exchanger ◽  
Analytical Microscopy ◽  
Deposit Layer ◽  
Effect Of Surface

The effect of surface roughness on the fouling behavior of calcium carbonate is experimentally investigated. The real operating conditions of a tubular heat exchanger are simulated by performing prolonged experiments with duration of 3 to 7 days. The solution used is a mixture of sodium bicarbonate and calcium chloride in de-ionized water with the concentration of 0.4 g/l of each. An on-line fouling evaluation system was developed such that the fouling resistance for a selected solution could be measured in real time. The experiments are repeated with the same procedure for 90/10 Cu/Ni tubes with different internal surface roughness. After the experiment the surface is analyzed by analytical microscopy to investigate the morphology of the deposit layer. Comparison of the experimental results of smooth and rough surfaces shows that a combination of aragonite and calcite polymorphs are formed on rough surface while only dendritic porous aragonite crystals are formed on smooth surface. Accordingly, the deposit layer formed on rough surface is denser and has a higher thermal resistance comparing to that formed on smooth surface. The fouling factor-time curves of smooth and rough surfaces obtained by the current experimental study agree with the results found by the analytical microscopy of the surface and show higher fouling resistances for rough surface. Experimental data is significantly important for the design, and formulating operating, and cleaning schedules of the equipment.

scholarly journals Influence of surface roughness on fatigue life of machine elements – the development in experimental investigations and simulations

Mechanik ◽  
2019 ◽  
Vol 92 (5-6) ◽  
pp. 307-313 ◽  
Author(s):  
Wit Grzesik
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Construction Materials ◽  
Fatigue Tests ◽  
Experimental Investigations ◽  
Fundamental Information ◽  
Aerospace Alloys ◽  
Machine Elements ◽  
Effect Of Surface

In this paper fundamental information on the influence of surface roughness on fatigue life/limit stresses of machine elements made of different construction materials using different machining/manufacturing processes are presented. The rules for the assessment of surface finish influence represented by the set of microscopic notches on the real machined surfaces, which allow the determination of the stress concentration factor and the correction of a fatigue life limit, are provided. The results of fatigue tests are compared with computed data and predictions using FEM based simulations. The effect of surface discontinues resulting from surface roughness are related to machine elements made of steels, aluminium alloys, aerospace alloys – titanium and nickel based superalloys and composite reinforced by graphite fibres.

A Combined Experimental and Numerical Study of the Effect of Surface Roughness on Nanoindentation

2019 ◽  
Vol 11 (07) ◽  
pp. 1950070
Author(s):  
M. Nazemian ◽  
M. Chamani ◽  
M. Baghani
Keyword(s):  
Thin Films ◽  
Surface Roughness ◽  
Finite Element ◽  
Rough Surface ◽  
Numerical Study ◽  
Three Dimensional ◽  
Element Model ◽  
Element Analysis ◽  
Three Dimensional Finite Element ◽  
Effect Of Surface

Gold and copper thin films are widely used in microelectromechanical system (MEMS) and nanoelectromechanical system (NEMS) devices. Nanoindentation has been developed in mechanical characterization of thin films in recent years. Several researchers have examined the effect of surface roughness on nanoindentation results. It is proved that the surface roughness has great importance in nanoindentation of thin films. In this paper, the surface topography of thin films is simulated using the extracted data from the atomic force microscopy (AFM) images. Nanoindentation on a rough surface is simulated using a three-dimensional finite-element model. The results are compared with the results of finite-element analysis on a smooth surface and the experimental results. The results revealed that the surface roughness plays a key role in nanoindentation of thin films, especially at low indentation depths. There was good compatibility between the results of finite-element simulation on the rough surface and those of experiments. It is observed that on rough films, at low indentation depths, the geometry of the location where the nanoindentation is performed is of major importance.

Effect of Surface Roughness on Film Cooling Performance

1985 ◽  
Vol 107 (1) ◽  
pp. 111-116 ◽  
Author(s):  
R. J. Goldstein ◽  
E. R. G. Eckert ◽  
H. D. Chiang ◽  
E. Elovic
Keyword(s):  
Mass Transfer ◽  
Surface Roughness ◽  
Experimental Investigation ◽  
Rough Surface ◽  
Film Cooling ◽  
Free Stream ◽  
Cooling Performance ◽  
Effect Of Surface

An experimental investigation of film cooling on a rough surface has been performed using a mass transfer technique. Two injection geometries (one and two rows of holes) and six roughness patterns were used. The density of the injected gas was close to that of the free-stream air. The presence of roughness causes a decrease in the spanwise-averaged effectiveness for both injection geometries at low blowing rates, and an increase in the effectiveness for one-row injection at high blowing rates, but not for two-row injection. The results for two-row injection (with or without roughness) can be correlated by a parameter used to correlate slot-injection data. The influence of roughness pattern on the average effectiveness and on the lateral uniformity of the effectiveness is described.

On the Effect of Surface Roughness on the Vapor Flow Under Leidenfrost-Levitated Droplets

1995 ◽  
Vol 117 (3) ◽  
pp. 519-525 ◽  
Author(s):  
M. Prat ◽  
P. Schmitz ◽  
D. Poulikakos
Keyword(s):  
Surface Roughness ◽  
Rough Surface ◽  
Relative Size ◽  
Vapor Flow ◽  
Roughness Elements ◽  
Levitated Droplets ◽  
Macroscopic Approach ◽  
Semi Empirical ◽  
Hot Surface ◽  
Effect Of Surface

In this paper a theoretical investigation is reported on the effect of surface roughness on the phenomenon of Leidenfrost-levitation of droplets above a hot surface. The problem is solved first approximately using a macroscopic approach in which the roughness is replaced by a semi-empirical slip condition of the Beavers-Joseph type. Next, a microscopic model which determines the vapor flow in the close vicinity of the rough surface is solved numerically. Three basic periodic roughnesses are examined: triangular, rectangular and semi-cylindrical. The effect of the relative size of the droplet and the roughness elements on the vapor flow is investigated in the course of the study.

Effect of Surface Roughness on Elastohydrodynamic Line Contact

1982 ◽  
Vol 104 (3) ◽  
pp. 401-407 ◽  
Author(s):  
B. C. Majumdar ◽  
B. J. Hamrock
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Strain Analysis ◽  
Elastohydrodynamic Lubrication ◽  
Asperity Contact ◽  
Pressure Dependent Viscosity ◽  
Surface Irregularities ◽  
Dependent Viscosity ◽  
Contact Pressures ◽  
Effect Of Surface

A numerical solution of an elastohydrodynamic lubrication (EHL) contact between two long, rough surface cylinders is obtained. A theoretical solution of pressure distribution, elastohydrodynamic load, and film thickness for given speeds and for lubricants with pressure-dependent viscosity, material properties of cylinders, and surface roughness parameters is made by simultaneous solution of an elasticity equation and the Reynolds equation for two partially lubricated rough surfaces. The pressure due to asperity contact is calculated by assuming a Gaussian distribution of surface irregularities. The elastic deformation is found from hydrodynamic and contact pressures by using plane strain analysis. The effect of surface roughness on EHL loads, speeds, and central film thicknesses is studied. The results indicate that for a constant central film thickness (1) increasing the surface roughness decreases the EHL load and (2) there is little variation in minimum film thickness as the surface roughness is increased.

Thermohydraulic Behavior of Minichannel Surface Simulated With Gaussian Function and Actual Roughness Data Generated Using Three-Dimensional Optical Surface Profilometer

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Indrasis Mitra ◽  
Indranil Ghosh
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Nusselt Number ◽  
Rough Surface ◽  
Gaussian Function ◽  
Three Dimensional ◽  
Optical Surface ◽  
Flow Perturbation ◽  
Smooth Channel ◽  
Effect Of Surface

Abstract The effect of surface roughness on the thermohydraulics in minichannels has been studied numerically. Fluid flow (at low Reynolds number) through a typical three-dimensional (3D) channel subjected to constant heat flux (at the bottom) is analyzed incorporating surface roughness on the solid–fluid interfaces characterized by its true random and nonperiodic nature. Two different approaches are adopted to model the rough channel surfaces. Topographic measurements have been performed on a stainless steel minichannel using an optical surface profilometer (OSP) to generate digital replica of the rough surface. Alternatively, the Gaussian function defined by two statistical parameters, namely average roughness (Ra) and correlation length (Cl), are employed to imitate the random nature of rough interface. At the outset, conjugate heat transfer simulations have been performed on the rough channel models and the results are validated against the experimental data. Finally, the effect of surface roughness on both local and global nondimensional performance parameters is analyzed and compared with findings from simulations performed on a similar smooth channel. The outcomes reveal an enhanced friction factor for flow over a rough surface, attributable to the near wall shear rate fluctuations experienced by the flow. Unlike smooth channels, the local Nusselt number (Nuy) exhibits continuous fluctuations along the channel axial length. The fully developed (Nufd) and the average (Nu¯) counterparts of the Nusselt number show enhanced magnitudes when compared to the theoretical predictions of the same in a smooth surface channel. This amplification can be attributed to two simultaneously acting factors: augmentation in heat transfer area and chaotic mixing due to flow perturbation. The magnitude of enhancement in terms of fully developed Nusselt number (Nufd) is roughly 1.3 times of its corresponding value in a smooth channel and the factor remains invariant of the supplied heat.

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