Numerical Simulation of Vortex Shedding Past a Single Cylinder Confined in a Channel
TL;DR: The vortex shedding past a circular cylinder in a two- dimensional channel of varying height is presented in the term of Strouhal number by solving continuity and momentum equations using FLUENT 6.3.
Abstract: The vortex shedding past a circular cylinder in a two- dimensional channel of varying height is presented in the term of Strouhal number by solving continuity and momentum equations using FLUENT 6.3. The computational grid structure is generated by using Gambit. In this analysis, the result is carried out with blockage ratio b=80, 0.83, 0.85, 0.88 and Reynolds number range from 50 to 300
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TL;DR: In this paper, the governing partial differential equations for momentum, energy and micro-rotation are presented and transformed into ordinary differential equations by means of similarity transformations and local skin friction co-efficient and local heat fluxes are computed analytically using optimal homotopy analysis method (OHAM) as well as numerically through mid-point integration scheme and they are found to be in excellent agreement.
Abstract: Hydromagnetic flow of a micropolar fluid between two horizontal parallel plates in a rotating system has been investigated. The governing partial differential equations for momentum, energy and micro-rotation are presented and transformed into ordinary differential equations by means of similarity transformations. The solutions for velocity, temperature and micro-rotation profiles are expressed through graphs against various emerging physical parameters such as coupling parameter, viscosity parameter, Hartman number, Reynold number, rotation parameter, porosity parameter and peclet number using optimal homotopy analysis method (OHAM). Local skin friction co-efficient and local heat fluxes are computed analytically using OHAM as well as numerically through mid-point integration scheme and they are found to be in excellent agreement. It has been observed that local skin friction is higher for the case of strong concentration compare to the case of weak concentration. Moreover, influence of strong and weak concentration on Nusselt number is also examined.
63 citations
TL;DR: The most relevant results of the work are the setup of a new method for studying the survival/resistance of yeasts to the transit into the gut based on a complex statistical analysis of results and to mark the probiotic character in Saccharomyces yeasts versus non-Saccharomycles.
Abstract: Microbial probiotic supplements are used to improve the health and wellness of people. For checking this ability (resistance to gastrointestinal conditions, auto-aggregation, cell surface hydrophobicity or biofilm formation abilities), it is crucial to evaluate some kinetics parameters. The objective of the present study was to establish an adequate method for studying the probiotic potential of Saccharomyces and non-Saccharomyces strains isolated from food ecosystems. A new protocol was designed based on kinetics parameters: lag phase (λ), generation time (G) and maximum OD (ODmax). The design was done using a step-by-step approach (up to 10 protocols), focusing on the choice of controls and the conditions to simulate the stomach and intestine. Each decision was made based on multifactorial statistical assay results. A preliminary screening indicates that protocol is adequate, quick and reproducible and that S. cerevisiae strains are more resistant than non-Saccharomyces ones. S. boulardii, (commercial control), was not one of the best yeasts evaluated. Thus, the most relevant results of the work are the setup of a new method for studying the survival/resistance of yeasts to the transit into the gut based on a complex statistical analysis of results and to mark the probiotic character in Saccharomyces yeasts versus non-Saccharomyces.
20 citations
01 Jan 2017
TL;DR: Factors affecting cucumber fermentation are discussed in this chapter since they have an impact on shelf-life, the nutritional and sensory value, flavor, digestibility, nutrient retention, and reduction of toxicity and antinutrient removal.
Abstract: Naturally fermented sour pickled cucumbers belong to the products stabilized with salt and lactic acid. Factors affecting cucumber fermentation are discussed in this chapter since they have an impact on shelf-life, the nutritional and sensory value, flavor, digestibility, nutrient retention, and reduction of toxicity and antinutrient removal. During fermentation, lactic acid bacteria (LAB) synthesize several bacteriocins and liberate antimicrobial peptides, which are inhibitory to spoilage bacteria. Fermented cucumbers are microbiologically safe, nutritious, and flavorful, have appealing sensory characteristics, and can be conveniently stored for extended periods without refrigeration. Their health benefits are associated with probiotic LAB isolated from fermented cucumbers and their ability to produce bacteriocins. Fermented cucumber is also recognized as a source of macronutrients and starter cultures with high oligosaccharide productivity.
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TL;DR: In this paper, the quasi-steady translational motion of an incompressible couple stress fluid confined between two eccentric spherical surfaces is investigated and the boundary collocation technique is utilized numerically to satisfy the boundary conditions on the spherical surfaces.
Abstract: The quasi-steady translational motion of an incompressible couple stress fluid confined between two eccentric spherical surfaces is investigated. It is assumed that the motion is generated by allowing the internal sphere to translate with a constant velocity. The Stokesian assumption of low Reynolds numbers is considered so that the nonlinear terms of the equation of motion are neglected. The superposition principle is employed to construct the general solution of the governing equations in the presence of spherical surfaces using two spherical systems of coordinates relative to the centers of the two spherical surfaces. The no-slip boundary conditions on the spherical boundaries are applied. In addition, the conditions of vanishing couple stresses on the bounding surfaces are imposed. The boundary collocation technique is utilized numerically to satisfy the boundary conditions on the spherical surfaces. The drag force experienced by the fluid flow on the spherical particle is obtained and represented numerically through table and graphs. The numerical results show that the values of the drag force increases monotonically with the increase in the radii ratio. It increases also with the increase of the couple stress viscosity parameter. The obtained results are consistence with the results available in the literature for viscous fluids.
6 citations
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TL;DR: In this article, the authors measured the mean pressure around a circular cylinder placed at various heights above a plane boundary and found that the turbulent boundary layer on the plate at the cylinder position, but with it removed from the tunnel, was equal to 0·8 of the cylinder diameter.
Abstract: The flow around a circular cylinder placed at various heights above a plane boundary has been investigated experimentally. The cylinder spanned the test section of a wind tunnel and was aligned with its axis parallel to a long plate and normal to the free stream. It was placed 36 diameters downstream of the leading edge of the plate and its height above the plate was varied from zero, the cylinder lying on the surface, to 3·5 cylinder diameters. The thickness of the turbulent boundary layer on the plate at the cylinder position, but with it removed from the tunnel, was equal to 0·8 of the cylinder diameter. Distributions of mean pressure around the cylinder and along the plate were measured at a Reynolds number, based on cylinder diameter, of 4·5 × 104. Spectral analysis of hot-wire signals demonstrated that regular vortex shedding was suppressed for all gaps less than about 0·3 cylinder diameters. For gaps greater than 0·3 the Strouhal number was found to be remarkably constant and the only influence of the plate on vortex shedding was to make it a more highly tuned process as the gap was reduced. Flow-visualization experiments in a smoke tunnel revealed the wake structure at various gap-to-diameter ratios.
484 citations
TL;DR: In this article, a finite volume method based on a velocity-only formulation is used to solve the flow field around a confined circular cylinder in a channel in order to investigate lateral wall proximity effects on stability, Strouhal number, hydrodynamic forces and wake structure behind the cylinder for a wide range of blockage ratios (0.1<β⩽0.9) and Reynolds numbers (0
Abstract: A finite volume method based on a velocity-only formulation is used to solve the flow field around a confined circular cylinder in a channel in order to investigate lateral wall proximity effects on stability, Strouhal number, hydrodynamic forces and wake structure behind the cylinder for a wide range of blockage ratios (0.1<β⩽0.9) and Reynolds numbers (0
221 citations
"Numerical Simulation of Vortex Shed..." refers background in this paper
...Sahin and Owens [9] have presented a parameter for study the transition from steady two-dimensional flow to periodic vortex shedding across a range of blockage ratio....
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TL;DR: In this article, the case of a circular cylinder placed between two parallel walls is studied numerically with a finite element method based on the vorticity{stream function formulation for values of the Reynolds number consistent with a two-dimensional assumption.
Abstract: The flow about a body placed inside a channel diers from its unbounded counterpart because of the eects of wall connement, shear in the incoming velocity prole, and separation of vorticity from the channel walls. The case of a circular cylinder placed between two parallel walls is here studied numerically with a nite element method based on the vorticity{streamfunction formulation for values of the Reynolds number consistent with a two-dimensional assumption. The transition from steady flow to a periodic vortex shedding regime has been analysed: transition is delayed as the body approaches one wall because the interaction between the cylinder wake and the wall boundary layer vorticity constrains the separating shear layer, reducing its oscillations. The results conrm previous observations of the inhibition of vortex shedding for a body placed near one wall. The unsteady vortex shedding regime changes, from a pattern similar to the von K arm an street (with some dierences) when the body is in about the centre of the channel, to a single row of same-sign vortices as the body approaches one wall. The separated vortex dynamics leading to this topological modication is presented. The mean drag coecients, once they have been normalized properly, are comparable when the cylinder is placed at dierent distances from one wall, down to gaps less than one cylinder diameter. At smaller gaps the body behaves similarly to a surface-mounted obstacle. The lift force is given by a repulsive component plus an attractive one. The former, well known from literature, is given by the deviation of the wake behind the body. Evidence of the latter, which is a consequence of the shear in front of the body, is given.
190 citations
"Numerical Simulation of Vortex Shed..." refers methods in this paper
...The effect of varying gap between the cylinder and the channel walls was analysed by Zovatto and Pedrizzetti [8]....
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...The effect of varying gap between the cylinder and the channel walls was analysed by Zovatto and Pedrizzetti [8]....
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TL;DR: In this paper, the formation of the steady vortex pair behind the cylinder was investigated and it was determined that the first appearance of the vortices is not associated with a bifurcation of the full dynamical problem but instead it is probably associated with the bifurbation of a restricted kinematical problem.
Abstract: Numerical experiments are described to ascertain how the steady flow past a circular cylinder loses stability as the Reynolds number is increased. A novel feature of the present study is that the cylinder is confined between parallel planes, allowing a more definitive specification of the flow, both experimentally and computationally, than is possible for the unbounded case. Since the structure of the bifurcation is unclear from the extant literature, with the experimental and computational evidence not in good agreement, a critical appraisal of both sets of evidence is presented.A study has been made of the formation of the steady vortex pair behind the cylinder, and it has been determined that the first appearance of the vortices is not associated with a bifurcation of the full dynamical problem but instead it is probably associated with a bifurcation of a restricted kinematical problem.A set of numerical experiments has been made in which the steady flow past the cylinder was perturbed slightly and the ensuing time-dependent motions were computed. These experiments revealed that, for a given blockage ratio, the perturbation would die away at small Reynolds numbers but that, above a critical Reynolds number, the disturbance would be amplified and the flow would eventually settle down to a new state comprising a time-periodic motion.Experiments were also carried out to determine the bifurcation point numerically by considering an eigenvalue problem based on a linearization about the computed steady flow past the cylinder. The calculations showed that stability is lost through a symmetry-breaking Hopf bifurcation and that, for a given blockage ratio, the critical Reynolds number was in very good agreement with that estimated from the time-dependent computations.
156 citations
"Numerical Simulation of Vortex Shed..." refers background in this paper
...[7] gave the numerically simulated a centrally placed cylinder with a focus on the nature and occurrence of the bifurcation from steady symmetric flow to the periodic shedding regime....
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TL;DR: In this article, a circular cylinder placed close to a horizontal plane wall was investigated experimentally and the fluctuating fluid forces acting on the cylinder sharply increased, and the regular vortex shedding, i.e. Karman vortex streets, started to form beyond a critical gap height.
Abstract: The flow around a circular cylinder placed close to a horizontal plane wall was investigated experimentally. Fluctuations of lift and drag of the cylinder and wall interference effects were studied in terms of the gap height between the cylinder and wall and the thickness of the turbulent wall boundary layer. The fluctuating fluid forces acting on the cylinder sharply increased, and the regular vortex shedding, i.e. Karman vortex streets, started to form beyond a critical gap height. The formation of Karman vortex streets was abruptly interrupted when the bottom of the cylinder came in contact with the outer layer of the boundary layer developed on the wall. This critical gap height correlated well with the thickness of the boundary layer.
122 citations