Velocity–vorticity correlations and the four-layer regime in turbulent channel flow of generalized Newtonian fluids

Arosemena, Arturo A.; Solsvik, Jannike

doi:10.1016/j.euromechflu.2021.08.006

Cited by 3 publications

(3 citation statements)

References 35 publications

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“…Regarding the range of length scales, also for the turbulent channel flow of GN fluids, it is known that both the fluid rheology and the Reynolds number have an influence in the velocity-vorticity correlation associated with change-of-scale-effects. 90 In this case, when comparing the Newtonian and shear-thinning fluid cases at the same N, Re is probably playing a major role over the range of length scales. From a practical point of view, it is worth commenting that the size indicator, d eq , appears to be in the range of % 1 mm to 52, 47, 53, and 49 mm for cases W600, W800, C600, and C800, respectively.…”

Section: Labelmentioning

confidence: 89%

Characterization of vortical structures in a stirred tank

2022

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Data obtained from large eddy simulations of single-phase, turbulent flow of Newtonian and shear-thinning fluids in a baffled stirred tank reactor are considered to identify and characterize vortical structures. The identification proceeds through an objectivized Eulerian method, accounting for the inhomogeneities in the flow, which palliates some shortcomings of previous implementations. The characterization focuses on turbulent vortices larger than the dissipative scales and, to a lesser extent, on trailing and macro-instability vortices. The characterization performed through different statistical analyses includes aspects such as size, number density, shape, distribution and organization in space, and correlation with the kinetic energy due to turbulence and the periodic passage of the blades. To the authors' knowledge, some of these representative aspects have been rarely investigated or have not been addressed at all for the turbulent flow in a stirred vessel. The influence of changing the rotational speed of the tank and the rheology of the working fluid are explored as well. Finally, considering one-way coupling, some potential and practical implications for liquid–liquid and gas–liquid dispersed systems are briefly discussed.

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Section: Labelmentioning

confidence: 89%

Characterization of vortical structures in a stirred tank

2022

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“…The peak negative value of the cospectra associated with up-gradient transport occurs around wavelengths (λ x , λ z ) ∼ (30y, 8y), whose ratio is indicative of sublayer streaks. These are the type of flow structures 'elongated in the stream direction' mentioned by Lighthill (1963) and whose relevance to near-wall vorticity transport has been discussed in several previous studies (Klewicki et al 1994;Brown et al 2015;Arosemena & Solsvik 2022).…”

Section: Velocity-vorticity Cospectramentioning

confidence: 81%

Vorticity cascade and turbulent drag in wall-bounded flows: plane Poiseuille flow

Kumar,

Meneveau,

Eyink

2023

J. Fluid Mech.

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Drag for wall-bounded flows is directly related to the spatial flux of spanwise vorticity outward from the wall. In turbulent flows a key contribution to this wall-normal flux arises from nonlinear advection and stretching of vorticity, interpretable as a cascade. We study this process using numerical simulation data of turbulent channel flow at friction Reynolds number $Re_\tau =1000$ . The net transfer from the wall of spanwise vorticity created by downstream pressure drop is due to two large opposing fluxes, one which is ‘down-gradient’ or outward from the wall, where most vorticity concentrates, and the other which is ‘up-gradient’ or toward the wall and acting against strong viscous diffusion in the near-wall region. We present evidence that the up-gradient/down-gradient transport occurs by a mechanism of correlated inflow/outflow and spanwise vortex stretching/contraction that was proposed by Lighthill. This mechanism is essentially Lagrangian, but we explicate its relation to the Eulerian anti-symmetric vorticity flux tensor. As evidence for the mechanism, we study (i) statistical correlations of the wall-normal velocity and of wall-normal flux of spanwise vorticity, (ii) vorticity flux cospectra identifying eddies involved in nonlinear vorticity transport in the two opposing directions and (iii) visualizations of coherent vortex structures which contribute to the transport. The ‘D-type’ vortices contributing to down-gradient transport in the log layer are found to be attached, hairpin-type vortices. However, the ‘U-type’ vortices contributing to up-gradient transport are detached, wall-parallel, pancake-shaped vortices with strong spanwise vorticity, as expected by Lighthill's mechanism. We discuss modifications to the attached eddy model and implications for turbulent drag reduction.

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“…The fluids involved in the above work are all Newtonian fluids. However, most of the solutions in industrial and biopharmaceutical applications are fluids with structural properties of non-Newtonian fluids, for instance, the long-chain molecules solutions of biological fluids with structural properties like strain force, normal shear stress, variable viscosity, hysteresis effect and memory effect [26]. Therefore, the study of electromagnetic flow of non-Newtonian fluids is of great importance in both industrial and pharmaceutical aspects.…”

Section: Introductionmentioning

confidence: 99%

Pulse electromagnetic flow of Jeffrey fluid in parallel plate microchannels

Li,

2023

Phys. Scr.

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This paper investigates the pulse electromagnetic flow of a Jeffery fluid between parallel plate microchannels, where the pulse is considered as a relatively stable and common rectangular pulse. The Laplace transform and residue theorem are employed to derive the analytical solutions for the velocity and volumetric flow rate of the pulse electromagnetic flow. Graphical representations depict the effects of several important parameters, including the Hartmann number , pulse width , relaxation time and retardation time on them. The study findings demonstrate that the Hartmann number plays a vital role in the investigation of pulse electromagnetic flow. During the first half-cycle of the pulse electric field, the magnitude of the velocity amplitude increases and then decreases with the Hartmann number . An interesting observation is that in the second half-cycle, larger Hartmann number values result in a decrease in velocity followed by a reverse increase. The profiles of velocity and volumetric flow rate exhibit oscillations over a relatively short period of time, then gradually reach a stable state with time and display periodic variation characteristics. Moreover, a larger pulse width leads to a longer variation period and more stable profiles of velocity and volumetric flow rate. For smaller Hartmann numbers , the magnitude of the volumetric flow rate amplitude grows with the relaxation time and reduces with the retardation time . However, as the Hartmann number increases, the influence of relaxation time and retardation time on the volumetric flow rate becomes significantly weakened, especially the retardation time .

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Velocity–vorticity correlations and the four-layer regime in turbulent channel flow of generalized Newtonian fluids

Cited by 3 publications

References 35 publications

Characterization of vortical structures in a stirred tank

Characterization of vortical structures in a stirred tank

Vorticity cascade and turbulent drag in wall-bounded flows: plane Poiseuille flow

Pulse electromagnetic flow of Jeffrey fluid in parallel plate microchannels

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