On Direct Numerical Simulation of Turbulent Flows

Alfonsi, Giancarlo

doi:10.1115/1.4005282

Cited by 41 publications

(21 citation statements)

References 212 publications

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“…In the aforementioned channel-flow simulations, interesting results have been obtained, as related in particular to the evolution of the fluctuating-velocity statistical moments with the Reynolds number (see also Alfonsi [24], Marusic et al [25], Smits et al [26], Kim [27], Jiménez [28]). …”

Section: Author(s) Year Numerical Techniquementioning

confidence: 99%

Direct Numerical Simulation of Turbulent Channel Flow on High-Performance GPU Computing System

et al. 2016

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Abstract:The flow of a viscous fluid in a plane channel is simulated numerically following the DNS approach, and using a computational code for the numerical integration of the Navier-Stokes equations implemented on a hybrid CPU/GPU computing architecture (for the meaning of symbols and acronyms used, one can refer to the Nomenclature). Three turbulent-flow databases, each representing the turbulent statistically-steady state of the flow at three different values of the Reynolds number, are built up, and a number of statistical moments of the fluctuating velocity field are computed. For turbulent-flow-structure investigation, the vortex-detection technique of the imaginary part of the complex eigenvalue pair in the velocity-gradient tensor is applied to the fluctuating-velocity fields. As a result, and among other types, hairpin vortical structures are unveiled. The processes of evolution that characterize the hairpin vortices in the near-wall region of the turbulent channel are investigated, in particular at one of the three Reynolds numbers tested, with specific attention given to the relationship that exists between the dynamics of the vortical structures and the occurrence of ejection and sweep quadrant events. Interestingly, it is found that the latter events play a preminent role in the way in which the morphological evolution of a hairpin vortex develops over time, as related in particular to the establishment of symmetric and persistent hairpins. The present results have been obtained from a database that incorporates genuine DNS solutions of the Navier-Stokes equations, without superposition of any synthetic structures in the form of initial and/or boundary conditions for the simulations.

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Section: Author(s) Year Numerical Techniquementioning

confidence: 99%

Direct Numerical Simulation of Turbulent Channel Flow on High-Performance GPU Computing System

et al. 2016

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“…Hybrid Eulerian-Lagrangian methods have been utilized recently [34], but the highest Sc achieved is in the order of Sc = 50. The use of DNS for the generation of the velocity field has the advantage of providing a high fidelity representation of the flow in which mixing occurs, but has the disadvantage that the Reynolds number (Re) for the flow field is relatively small [40][41][42][43], while LES or hybrid methods can get to higher Re values but with sacrifice in fidelity.…”

Section: Introductionmentioning

confidence: 99%

Quality Measures of Mixing in Turbulent Flow and Effects of Molecular Diffusivity

Nguyen¹,

Papavassiliou²

2018

Fluids

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Abstract:Results from numerical simulations of the mixing of two puffs of scalars released in a turbulent flow channel are used to introduce a measure of mixing quality, and to investigate the effectiveness of turbulent mixing as a function of the location of the puff release and the molecular diffusivity of the puffs. The puffs are released from instantaneous line sources in the flow field with Schmidt numbers that range from 0.7 to 2400. The line sources are located at different distances from the channel wall, starting from the wall itself, the viscous wall layer, the logarithmic layer, and the channel center. The mixing effectiveness is quantified by following the trajectories of individual particles with a Lagrangian approach and carefully counting the number of particles from both puffs that arrive at different locations in the flow field as a function of time. A new measure, the mixing quality index Ø, is defined as the product of the normalized fraction of particles from the two puffs at a flow location. The mixing quality index can take values from 0, corresponding to no mixing, to 0.25, corresponding to full mixing. The mixing quality in the flow is found to depend on the Schmidt number of the puffs when the two puffs are released in the viscous wall region, while the Schmidt number is not important for the mixing of puffs released outside the logarithmic region.

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“…One of the first researches of this kind is that of Choi et al [22] who executed a study of the run-up induced by a tsunami wave around a simplified island model adopting the RANS technique coupled with an RNG closure model (see [23] for an overview of the RANS approach to the numerical integration of the Navier-Stokes equations, and refer to Nomenclature for the meaning of acronyms and symbols). Alfonsi et al [24][25][26] have faced the problem of wave diffraction caused by a circular cylinder piercing the free surface, starting from the velocity-potential approach, then the solution of the Euler equations in their velocity-pressure formulation, and finally, numerically solving the system of the Navier-Stokes equations in primitive variables, following the DNS technique. Methods for the extraction of the flow coherent structures ( [27]) and most energetic modes have also been developed and applied.…”

Section: Introductionmentioning

confidence: 99%

Recent Results from Analysis of Flow Structures and Energy Modes Induced by Viscous Wave around a Surface‐Piercing Cylinder

Alfonsi

Lauria

Primavera

2017

Mathematical Problems in Engineering

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Due to its relevance in ocean engineering, the subject of the flow field generated by water waves around a vertical circular cylinder piercing the free surface has recently started to be considered by several research groups. In particular, we studied this problem starting from the velocity-potential framework, then the implementation of the numerical solution of the Euler equations in their velocity-pressure formulation, and finally the performance of the integration of the Navier-Stokes equations in primitive variables. We also developed and applied methods of extraction of the flow coherent structures and most energetic modes. In this work, we present some new results of our research directed, in particular, toward the clarification of the main nonintuitive character of the phenomenon of interaction between a wave and a surface-piercing cylinder, namely, the fact that the wave exerts its maximum force and exhibits its maximum run-up on the cylindrical obstacle at different instants. The understanding of this phenomenon becomes of crucial importance in the perspective of governing the entity of the wave run-up on the obstacle by means of wave-flow-control techniques.

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On Direct Numerical Simulation of Turbulent Flows

Cited by 41 publications

References 212 publications

Direct Numerical Simulation of Turbulent Channel Flow on High-Performance GPU Computing System

Direct Numerical Simulation of Turbulent Channel Flow on High-Performance GPU Computing System

Quality Measures of Mixing in Turbulent Flow and Effects of Molecular Diffusivity

Recent Results from Analysis of Flow Structures and Energy Modes Induced by Viscous Wave around a Surface‐Piercing Cylinder

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