Temporal Evolution of Vortical Structures in the Wall Region of Turbulent Channel Flow

Alfonsi, Giancarlo; Primavera, Leonardo

doi:10.1007/s10494-008-9189-4

Cited by 14 publications

(5 citation statements)

References 30 publications

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“…During the visualization of vortex tubes, several methods have been considered based on the second invariant (Q), discriminant (∆) or eigenvalues (λ 2 , λ ci ) of velocity gradient tensor (∇u), [51,59−61] which have been widely used in the Newtonian fluid turbulent flows, such as isotropic turbulence, [62] channel flow, [63] mixing layer, and backward-facing step flow. [64] For viscoelastic flows, Sibilla and Beretta [50] investigated the near-wall coherent structures in a turbulent channel flow using λ 2 criterion.…”

Section: Multi-scale Methods Of Identifying Vortex Structurementioning

confidence: 99%

Direct numerical simulation study of the interaction between the polymer effect and velocity gradient tensor in decaying homogeneous isotropic turbulence

蔡伟华¹,

李凤臣²,

张红娜³

2011

Chinese Phys. B

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Direct numerical simulation of decaying homogeneous isotropic turbulence (DHIT) of a polymer solution is performed. In order to understand the polymer effect on turbulence or additive-turbulence interaction, we directly investigate the influence of polymers on velocity gradient tensor including vorticity and strain. By visualizing vortex tubes and sheets, we observe a remarkable inhibition of vortex structures in an intermediate-scale field and a small-scale field but not for a large scale field in DHIT with polymers. The geometric study indicates a strong relevance among the vorticity vector, rate-of-strain tensor, and polymer conformation tensor. Joint probability density functions show that the polymer effect can increase "strain generation resistance" and "vorticity generation resistance", i.e., inhibit the generation of vortex sheets and tubes, ultimately leading to turbulence inhibition effects.

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Section: Multi-scale Methods Of Identifying Vortex Structurementioning

confidence: 99%

Direct numerical simulation study of the interaction between the polymer effect and velocity gradient tensor in decaying homogeneous isotropic turbulence

蔡伟华¹,

李凤臣²,

张红娜³

2011

Chinese Phys. B

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“…In several different flow cases (see [44][45][46] for more details), this technique has demonstrated to give very satisfactory results. As for the present work, the results of the simulations have been reported by visualizing the flow structures corresponding to a given threshold value of ( | th ) [47].…”

Section: Structures and Modesmentioning

confidence: 97%

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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“…Figure 10 shows the vortices in the impeller and the pressure distributions on the impeller for the four different blade thickness distributions given in Table 2. The equations of the Q criterion can be written as follows [19]:…”

Section: Analysis Of the Vortex Structurementioning

confidence: 99%

Numerical and Experimental Study of a Vortex Structure and Energy Loss in a Novel Self-Priming Pump

et al. 2019

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The self-priming pump as an essential energy conversion equipment is widely used in hydropower and thermal power plants. The energy losses in the internal flow passage of the pump directly affect its work efficiency. Therefore, it is important to improve the internal flow characteristic of the pump. In the present work, a novel self-priming pump which starts without water is proposed; this pump can reduce the energy consumption as well as the time needed to start its operation. The spatial structure of the vortices in the pump is investigated by employing the Q criterion with the numerical solution of the vorticity transport equation. Based on the morphology, the vortices can be separated into three categories: Trailing Edge Vortex (TEV), Leading Edge Vortex (LEV) and Gap Leakage Vortex (GLV). Generally, the morphology of the TEV is more disorderly than that of LEV and GLV, and the intensity of TEV is significantly higher than that of the other two vortices. To determine the magnitude and distribution of energy loss in the pump, entropy production analysis is employed to study the influence of blade thickness on energy characteristics of the pump. It is found that with an increase in the flow rate, the location of energy loss transfers from the trailing edge to the leading edge of the blade, and viscous entropy production (VEP) and turbulence entropy production (TEP) are the dominant factors which influence the energy conversion in the pump. More importantly, employing the blade with a thin leading edge and a thick trailing edge can not only significantly reduce the impact of incoming flow under over-load condition (flow rate higher than the design condition) but can also increase the efficiency of the pump. Thus, an increase in thickness of the blade from the leading edge to the trailing edge is beneficial for improving the pump performance. The results of this paper can be helpful in providing guidelines for reducing the energy loss and in improving the performance of a self-priming pump.

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Temporal Evolution of Vortical Structures in the Wall Region of Turbulent Channel Flow

Cited by 14 publications

References 30 publications

Direct numerical simulation study of the interaction between the polymer effect and velocity gradient tensor in decaying homogeneous isotropic turbulence

Direct numerical simulation study of the interaction between the polymer effect and velocity gradient tensor in decaying homogeneous isotropic turbulence

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

Numerical and Experimental Study of a Vortex Structure and Energy Loss in a Novel Self-Priming Pump

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