Vortex Identification in Turbulent Flows: Isotropic, Sphere Wake

Volume 2: Symposia, Parts A, B, and C ◽

10.1115/fedsm2003-45082 ◽

2003 ◽

Author(s):

P. Chakraborty ◽

S. Balachandar ◽

R. J. Adrian

Keyword(s):

Turbulent Flows ◽

Spatial Coherence ◽

Strength Criterion ◽

Vortex Structures ◽

Coherent Motion ◽

Vortex Identification ◽

Coherence Measure ◽

Identification Schemes ◽

Swirling Strength ◽

Coherent Vortex

Vortices, the regions of swirling coherent motion of fluid, are of fundamental importance in understanding the dynamics of turbulent flows. Recent advances in computational and experimental resources have resulted in massive volumes of highly resolved flow field data. Identification of coherent vortex structures from these space-time discretized flow dataset is the key issue of vortex identification. We consider identification schemes based on pointwise analysis of the velocity gradient tensor. A new measure of the local spatial coherence in a vortex is introduced. Different criteria are compared for two classes of turbulent flows: isotropic and sphere wake. Remarkably similar vortex structures are observed using the Q, λ2 and swirling strength criterion. An explanation based on swirling strength and the proposed local coherence measure is offered for this observation.

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Dynamic Characterization of Vortex Structures and Their Evolution Mechanisms in a Side Channel Pump

Journal of Fluids Engineering ◽

10.1115/1.4047808 ◽

2020 ◽

Vol 142 (11) ◽

Cited By ~ 1

Author(s):

Fan Zhang ◽

Desmond Appiah ◽

Ke Chen ◽

Shouqi Yuan ◽

Kofi Asamoah Adu-Poku ◽

...

Keyword(s):

Turbulent Flows ◽

Flow Behavior ◽

Exchange Process ◽

Vortex Structures ◽

Longitudinal Vortex ◽

Side Channel ◽

Exchange Flow ◽

Vortex Identification ◽

Momentum Exchange ◽

Low Efficiency

Abstract To obtain a better insight into the unsteady flow behavior in side channel pumps by a robust vortex identification method, this study presents the efficacy of the new Ω-criterion in characterizing the evolution of vortex structures in the turbulent flows under different time steps. The flow behavior and the underlying vorticity dynamics were revealed as well. Compared to Q-criterion, the new Ω-criterion identified all vortex structures irrespective of the intensity at a universal threshold of 0.52. Three different types of vortex structures (longitudinal, axial, and radial) were identified to be responsible for the turbulent flows in the side channel pumps. The beneficial longitudinal vortex promotes the momentum exchange flow between the impeller and side channel which leads to the high hydraulic head of side channel pumps. On the other hand, the unfavorable axial and radial vortex structures restricted in the impeller passage mitigate the exchange process accounting for the low efficiency of the pumps. From this study, it can be established that the evolution of the axial vortex structures is responsible for the largest vortex distribution in the impeller compared to the total vortex evolved. The impeller outer radius contributes about 60% of the unfavorable axial structures evolved. Using the new Ω-criterion, many reported anomalous findings have been explained.

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Vortices evolution in the solar atmosphere

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038060 ◽

2020 ◽

Vol 639 ◽

pp. A118

Author(s):

José R. Canivete Cuissa ◽

Oskar Steiner

Keyword(s):

Evolution Equation ◽

Turbulent Flows ◽

Solar Atmosphere ◽

Evolution Equations ◽

Dynamical Equation ◽

Numerical Models ◽

Vortex Identification ◽

Wide Range ◽

Swirling Strength ◽

Hydrodynamical Simulations

Aims. We study vortex dynamics in the solar atmosphere by employing and deriving the analytical evolution equations of two vortex identification criteria. Methods. The two criteria used are vorticity and the swirling strength. Vorticity can be biased in the presence of shear flows, but its dynamical equation is well known; the swirling strength is a more precise criterion for the identification of vortical flows, but its evolution equation is not known yet. Therefore, we explore the possibility of deriving a dynamical equation for the swirling strength. We then apply the two equations to analyze radiative magneto-hydrodynamical simulations of the solar atmosphere produced with the CO5BOLD code. Results. We present a detailed review of the swirling strength criterion and the mathematical derivation of its evolution equation. This equation did not exist in the literature before and it constitutes a novel tool that is suitable for the analysis of a wide range of problems in (magneto-)hydrodynamics. By applying this equation to numerical models, we find that hydrodynamical and magnetic baroclinicities are the driving physical processes responsible for vortex generation in the convection zone and the photosphere. Higher up in the chromosphere, the magnetic terms alone dominate. Moreover, we find that the swirling strength is produced at small scales in a chaotic fashion, especially inside magnetic flux concentrations. Conclusions. The swirling strength represents an appropriate criterion for the identification of vortices in turbulent flows, such as those in the solar atmosphere. Moreover, its evolution equation, which is derived in this paper, is pivotal for obtaining precise information about the dynamics of these vortices and the physical mechanisms responsible for their production and evolution. Since this equation is available, the swirling strength is now the ideal quantity to study the dynamics of vortices in (magneto-)hydrodynamics.

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Investigation on the Flow Behavior of Side Channel Pumps Based on Vortex Identification

Chinese Journal of Mechanical Engineering ◽

10.1186/s10033-021-00649-1 ◽

2021 ◽

Vol 34 (1) ◽

Author(s):

Fan Zhang ◽

Desmond Appiah ◽

Ke Chen ◽

Shouqi Yuan ◽

Kofi Asamoah Adu-Poku ◽

...

Keyword(s):

Turbulent Flows ◽

Pressure Pulsation ◽

Flow Behavior ◽

Vortex Structures ◽

Longitudinal Vortex ◽

Navier Stokes ◽

Side Channel ◽

Vortex Identification ◽

Momentum Exchange ◽

Highly Turbulent Flows

AbstractThe momentum flow exchange between the impeller and side channel produces highly turbulent flows in side channel pumps. The turbulent flows feature complex patterns of vortex structures that are partly responsible for the dissipation of energy losses and unsteady pressure pulsations. The concept of turbulent flows in side channel pumps requires a reliable vortex identification criterion to capture and predict the effects of the vortex structures on the performance. For this reason, the current study presents the application of the new Ω-criterion to a side channel pump model in comparison with other traditional methods such as Q and λ2 criteria. The 3D flow fields of the pump were obtained through unsteady Reynolds-averaged Navier-Stokes (RANS) simulations. Comparative studies showed that the Ω-criterion identifies the vortex of different intensities with a standard threshold, Ω=0.52. The Q and λ2 criteria required different thresholds to capture vortex of different intensities thus leads to subjective errors. Comparing the Ω-criterion intensity on different planes with the entropy losses and pressure pulsation, the longitudinal vortex plays an important role in the momentum exchange development which increases the head performance of the pump. However, the rate of exchange is impeded by the axial and radial vortices restricted in the impeller. Therefore, the impeller generates the highest entropy loss and pressure pulsation intensities which lower the output efficiency. Finally, the findings provide a fundamental background to the morphology of the vortex structures in the turbulent flows which can be dependent upon for efficiency improvement of side channel pumps.

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