Small flags in rectangular channels: Dynamics and mean wake characteristics

Gallegos, Ralph Kristoffer B.; Sharma, Rajnish N.

doi:10.1016/j.ijmecsci.2019.02.033

Cited by 10 publications

(10 citation statements)

References 46 publications

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“…At U d , the flag shifts back to the fixed point stability regime and the flow velocity increases as blockage effects are no longer inherent. This trend is consistent with the findings of Eloy et al (2012) and Gallegos and Sharma (2019). The values of U i and U d for each flag configuration are specified in Table 2.…”

Section: Critical Velocity Determinationsupporting

confidence: 88%

“…5(a), a distinct trend emerges for such cases. U * i increases with M * implying that it becomes easier to initiate flapping for lighter flags since the latter have a lower resistive inertial force, consistent with the observations of Lee et al (2014) and Gallegos and Sharma (2019). The inability to separate confinement ratio and aspect ratio effects and the small number of cases at a fixed mass ratio limits the analysis of this study.…”

Section: Hysteresissupporting

confidence: 79%

“…Two class 2 green lasers were aligned from either side of the test-section ( 5) and the resulting sheet was aimed at the edge of the flag along the streamwise direction. Images were recorded at a rate of 3600 Hz , sufficient to meet Nyquist criterion based on the dominant frequencies observed by Gallegos and Sharma (2019). The duration of the acquisition was limited to 6 seconds to avoid exceeding the internal memory cache of the camera.…”

Section: Methodsmentioning

confidence: 99%

“…As the freestream velocity increases, a critical point is reached where the fluctuations along the oscillation direction of the flag become orders of magnitude higher and a periodic pattern is discernible from the flag's motion. The critical velocity is defined as the velocity at which the flag starts to flap in a Reynolds number (Re) increasing flow, U * i , or stops to flap in a Reynolds number decreasing flow, U * d (Gallegos and Sharma 2019). Experiments have demonstrated that these critical velocities can be largely different, thus highlighting that under the same flow conditions, a flag can adopt more than one stable regime (Ait Abderrahmane et al 2011).…”

Section: Origin Of Hysteresismentioning

confidence: 99%

“…Specifically, we will focus on the confinement in the direction orthogonal to the flag plane, due to the separation distance between the walls and the flag's surface. Gallegos and Sharma (2019) studied the influence of this type of confinement on flag flapping dynamics. It was found that confinement in this direction strongly influences the flag dynamics and wake characteristics.…”

Section: Origin Of Hysteresismentioning

confidence: 99%

See 4 more Smart Citations

Influence of geometrical parameters on the hysteresis of flutter onset in confined configurations

Jankee

Ganapathisubramani

2022

Exp Fluids

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The interaction between a flow and a flexible structure can provide fascinating insight into the vortex shedding phenomenon and any propagation and mixing characteristics, which relate to a plethora of applications such as heat transfer, snoring, musical instruments, or propulsion mechanisms. In this investigation, the influence of confinement on the flapping behaviour of a flexible flag is explored. In particular, hysteresis, one of the least understood aspects of flapping flags, and its sensitivity on both the flexural rigidity of the flag and the confinement ratio is addressed. For the same test-section dimensions and flag material, variations in the flag thickness and flag length enable a range of mass ratios ($$M^*$$ M ∗ ) and confinement ratios ($$C^*$$ C ∗ ) to be studied. Pressure measurements and high-speed imaging allow quantification of the hysteretic behaviour. The results demonstrate that although confinement ratio does not contribute to the existence of hysteresis, the relation between the critical reduced velocities and the mass ratio is sensitive to the degree of confinement. Graphical abstract

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Section: Critical Velocity Determinationsupporting

confidence: 88%

Section: Hysteresissupporting

confidence: 79%

Section: Methodsmentioning

confidence: 99%

Section: Origin Of Hysteresismentioning

confidence: 99%

Section: Origin Of Hysteresismentioning

confidence: 99%

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Influence of geometrical parameters on the hysteresis of flutter onset in confined configurations

Jankee

Ganapathisubramani

2022

Exp Fluids

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Heat transfer enhancement in fin channels using aeroelastically fluttering reeds

Jha

Glezer

Park

et al. 2021

J Adv Manuf & Process

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Forced convection heat transfer in rectangular channels is enhanced by aeroelastically fluttering thin reeds extending over the channel span. The resulting small‐scale vortical motions substantially increase local heat transfer at the channel walls and mixing between the wall thermal boundary layers and the channel's core flow. Mechanisms associated with evolution of these small‐scale motions and their thermal effects are experimentally studied in a channel of width W, span 5W, and length 50W. Reed effects on heat transfer are characterized at Reynolds numbers (Re) of 2000, 7000, and 12,000 using embedded thermocouple arrays, and related to small‐scale motions by particle image velocimetry and hot‐wire anemometry. Reed‐induced small‐scale motions increase turbulent kinetic energy, increasing the global Nusselt number (by up to 145% at Re = 7000), with enhancement being sustained even when the base flow becomes fully turbulent (Re = 12,000). Enhancement is also demonstrated for fin arrays. Single‐reed computations show the effect of reed length on enhancement. Computations with two reeds, one downstream of the trailing edge of the other, predict heat transfer enhancement significantly greater than twice the single‐reed result, and point the way to use of a streamwise array of reeds in long channels. A techno‐economic analysis for an air‐cooled condenser suggests that fluttering reeds can be economically justified for a range of operating conditions.

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An extended and improved particle‐spectral method for analysis of unsteady inviscid incompressible flows through a channel of finite length

Говорухин

2022

Numerical Methods in Fluids

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This paper addresses the development of a method to simulate and analyze unsteady flows of incompressible and inviscid fluids in rectangular channels. Mathematically, the flow problem formulates as Euler equations in terms of the stream function and vorticity. The normal velocity and the vorticity aregiven at the inlet of the channel, and only the normal velocity is specified at the outlet. The particle-spectral method describes the vorticity field change in a Lagrangian sense by dynamics of marker particles and an Eulerian description of the velocity field using the global Galerkin approximation. The method involves the subdivision of flow domain on rectangular cells; the approximation of vorticity distribution in cells by least-squares method; Galerkin coefficients calculation using analytical integration on space variables. For time integration, the five-stage Runge-Kutta method of the third accuracy order and the sixth one of symplecticity with adaptive step size control uses. The extension of the particle-spectral approach comprises algorithms for fluid flows qualitative analysis jointly with the time simulation of unsteady flows. This includes the trajectories of marker particles calculation, computing the particle's residence time in the channel, kinetic energy dynamics, and algorithms for analyzing the dynamics and mixing of vortex patches. Test calculations based on reference solutions showed the effectiveness and good accuracy of the particle-spectral approach. Using the developed method the dynamics of one and two initial vortex patches in the channel were investigated. We found the final state of their long-time dynamics is time-periodic or quasi-periodic movements. The application of qualitative analysis algorithms demonstrates these final states produce a chaotic scattering of fluid particles in the flow-through zone of the channel. K E Y W O R D Sflowing through channel, inviscid incompressible fluid, particle-spectral method, vortex dynamics

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Small flags in rectangular channels: Dynamics and mean wake characteristics

Cited by 10 publications

References 46 publications

Influence of geometrical parameters on the hysteresis of flutter onset in confined configurations

Influence of geometrical parameters on the hysteresis of flutter onset in confined configurations

Heat transfer enhancement in fin channels using aeroelastically fluttering reeds

An extended and improved particle‐spectral method for analysis of unsteady inviscid incompressible flows through a channel of finite length

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