From discovery to recognition of periodic large scale vortices in rod bundles as source of natural mixing between subchannels—A review

Meyer, L.

doi:10.1016/j.nucengdes.2010.03.014

Cited by 102 publications

(20 citation statements)

References 56 publications

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“…Because of its efficient near-wall modeling the k-ω SST model of Menter (1994) is used, which blends the k-ω model near the wall with the k-model in the free stream. It is known that the k-ω SST will not predict flow features such as the large scale vortices typically encountered in rod bundles (Meyer, 2010). These flow instabilities are in this paper considered as an external excitation, and are thus not contributing to the intrinsic modal characteristics.…”

Section: Methodsmentioning

confidence: 95%

Modal characteristics of a flexible cylinder in turbulent axial flow from numerical simulations

Ridder

Degroote

Tichelen

et al. 2013

Journal of Fluids and Structures

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In this article the vibration behavior of a flexible cylinder subjected to an axial flow is investigated numerically. Therefore a methodology is constructed, which relies entirely on fluid-structure interaction calculations. Consequently, no force coefficients are necessary for the numerical simulations. Two different cases are studied. The first case is a brass cylinder vibrating in an axial water flow. This calculation is compared to experiments in literature and the results agree well. The second case is a hollow steel tube, subjected to liquid lead-bismuth flow. Different flow boundary conditions are tested on this case. Each type of boundary conditions leads to a different confinement and results in different eigenfrequencies and modal damping ratios. Wherever appropriate, a comparison has been made with an existing theory. Generally, this linear theory and the simulations in this article agree well on the frequency of a mode. With respect to damping, the agreement is highly dependent on the correlation used for the normal friction coefficients in the linear theory.

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Section: Methodsmentioning

confidence: 95%

Modal characteristics of a flexible cylinder in turbulent axial flow from numerical simulations

Ridder

Degroote

Tichelen

et al. 2013

Journal of Fluids and Structures

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“…Research on compound channels reports large-scale quasiperiodic hydrodynamic structures similar to those found in flows parallel to porous media. A comprehensive review on compound channels and flows parallel to rod bundles can be found in Meyer (2010). Recently, Merzari et al (2008) performed linear stability studies about two kinds of compound channels: annular eccentric and two rectangular channels joined through a gap.…”

Section: Introductionmentioning

confidence: 99%

Flow instabilities between two parallel planes semi-obstructed by an easily penetrable porous medium

et al. 2011

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A study of instabilities in planar flows produced by the presence of a parallel penetrable porous obstruction is presented. The case considered is a flow between parallel plates partially obstructed by a porous medium. The most unstable perturbation modes are obtained solving numerically the eigenvalue problem derived from the linear stability analysis of the two-dimensional Navier-Stokes equations applied to the geometry of interest. The analysis leads to an extended Orr-Sommerfeld equation including a porous term. It was found that the ratios of the permeability and depth of the obstruction with respect to the free flow layer depth are the relevant parameters influencing the stability margin and the structure of the most unstable modes. To validate the conclusions of the theoretical analysis, an experiment with air flowing through a channel semi-obstructed by a regular array of cylindrical wires was performed. The critical Reynolds number, which was determined by measuring the amplitude of velocity fluctuations at the interface of the porous medium, agrees with the theoretical predictions. The dominant instability mode was characterized by the cross-section profile of the root mean square of the velocity perturbations, which matches reasonable well with the eigenfunction of the most unstable eigenvalue. Also, the wavenumber was determined by correlating the velocity measurements in two sequential locations along the channel, which compares well with the theoretical value.

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“…This leads to the conclusion that the coherent structures are transported as a whole; the vortices outside of the gap region and the cross-flow inside the gap region are not moving relative to each other. No experimental (Meyer (2010); Curling and Païdoussis (1992)) evidence has indicated otherwise so far.…”

Section: Influence Of the Circumferential Coordinatementioning

confidence: 98%

Numerical investigation of large-scale vortices in an array of cylinders in axial flow

Moerloose

Aerts

Ridder

et al. 2018

Journal of Fluids and Structures

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Axial flow around an array of cylinders is commonly encountered in nuclear reactors and heat exchangers. This geometry is subject to important flow instabilities. The chaotic flow fluctuations due to turbulence are not the only source of vortex structures: large-scale vortices have also been observed, both experimentally and numerically. The periodic pressure fluctuations caused by the coherent vortex structures are possibly a source of fretting and fatigue in the aforementioned applications. In order to comprehend this phenomenon, LargeEddy Simulations are performed on a numerical domain containing a single rigid cylinder with periodic boundary conditions, representative for a cylinder in an infinite square array. The research in this paper mainly focuses on the influence of the cylinder spacing, which is analyzed by calculating the Cross Spectral Density (CSD) function of the cylinder wall pressure for different cylinder spacings. The spectral analysis shows that the amplitude of the pressure fluctuations increases up to a well-determined intercylinder gap, after which it decreases exponentially for incrementing gap size. With the weakening of the instability, the location on the cylinder circumference where the maximum pressure amplitude occurs, changes as well. Finally, it is shown that the coherent vortices are transported as a whole at a convection speed which is dependent on the cylinder spacing. An updated model for this convection speed is proposed.

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From discovery to recognition of periodic large scale vortices in rod bundles as source of natural mixing between subchannels—A review

Cited by 102 publications

References 56 publications

Modal characteristics of a flexible cylinder in turbulent axial flow from numerical simulations

Modal characteristics of a flexible cylinder in turbulent axial flow from numerical simulations

Flow instabilities between two parallel planes semi-obstructed by an easily penetrable porous medium

Numerical investigation of large-scale vortices in an array of cylinders in axial flow

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