Local and nonlocal strain rate fields and vorticity alignment in turbulent flows

Hamlington, Peter E.; Schumacher, Jörg; Dahm, Werner J. A.

doi:10.1103/physreve.77.026303

Cited by 67 publications

(67 citation statements)

References 22 publications

(76 reference statements)

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“…They take the same angular space at any location but the strengths and ration of the involved terms vary. It has been established that the strain rate tensor governs the dissipation of kinetic energy, the coupling of both, strain rate tensor and rotation rate tensor, governs the process of vortex stretching and vortex compression (Tsinober 2000;Hamlington et al 2008). For a better understanding of the vortex stretching and vortex compression mechanism, the coupling of the productions of strain and rotation are discussed with respect to the characteristic evolution of turbulence at different wall-normal locations in the TBL (figure 4).…”

Section: Discussionmentioning

confidence: 99%

Evolution of the velocity gradient tensor invariant dynamics in a turbulent boundary layer

Bechlars

Sandberg

2017

J. Fluid Mech.

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(Received xx; revised xx; accepted xx)In order to improve the physical understanding of the development of turbulent structures, the compressible evolution equations for the first three invariants P ,Q and R of the velocity gradient tensor have been derived. The mean evolution of characteristic turbulent structure types were studied and compared at different wall-normal locations of a compressible turbulent boundary layer. The evolution of these structure types are fundamental to the physics that need to be captured by turbulence models. Significant variations of the mean evolution are found. The key features of the changes of the mean trajectories in the invariant phase space are highlighted and the consequences of the changes are discussed. Further, the individual elements of the overall evolution are studied separately to identify the causes that lead to the evolution varying with the distance to the wall. Significant impact of the wall-normal location on the coupling between the pressure-Hessian tensor and the velocity gradient tensor was found.

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Section: Discussionmentioning

confidence: 99%

Evolution of the velocity gradient tensor invariant dynamics in a turbulent boundary layer

Bechlars

Sandberg

2017

J. Fluid Mech.

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“…In particular, Chakraborty 18 showed that the statistical behaviour of vorticity alignment with local principal strain rates can be significantly different for the corrugated flamelets regime of combustion with Le = 1.0, and for the thin reaction zones regime of combustion with non-unity Lewis number, in comparison to earlier studies. [8][9][10][11][19][20][21][22][23][24][25][26][27][28] For example, in the corrugated flamelets regime, and for the cases with high Karlovitz number and low Le, where the most extensive principal strain rate is controlled by the local dilatation rate, 18 the vorticity vector ⃗ ω predominantly aligns with the intermediate and the most compressive principal strain rates. Such an alignment of the vorticity vector differs from the alignment observed earlier in premixed 11 and non-premixed [8][9][10] flames with unity Lewis number, or in non-reacting flows.…”

Section: Introductionmentioning

confidence: 99%

“…Such an alignment of the vorticity vector differs from the alignment observed earlier in premixed 11 and non-premixed [8][9][10] flames with unity Lewis number, or in non-reacting flows. [19][20][21][22][23][24][25][26][27][28] While each individual species j has its own Lewis number Le j , in simplified models of molecular transport, the Lewis number of the deficient reactant (fuel or oxidant) is often taken to be the characteristic global Lewis number Le 29 as was done in the aforementioned analysis by Chakraborty. 18 It is worth noting here that alternative methods of assigning a characteristic Lewis number have been proposed based on heat release measurements 30,31 and mole fractions of the mixture constituents.…”

Section: Introductionmentioning

confidence: 99%

Effects of Lewis number on vorticity and enstrophy transport in turbulent premixed flames

2016

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The effects of Lewis number Le on both vorticity and enstrophy transport within the flame brush have been analysed using direct numerical simulation data of freely propagating statistically planar turbulent premixed flames, representing the thin reaction zone regime of premixed turbulent combustion. In the simulations, Le was ranged from 0.34 to 1.2 by keeping the laminar flame speed, thermal thickness, Damköhler, Karlovitz, and Reynolds numbers unchanged. The enstrophy has been shown to decay significantly from the unburned to the burned gas side of the flame brush in the Le ≈ 1.0 flames. However, a considerable amount of enstrophy generation within the flame brush has been observed for the Le = 0.34 case and a similar qualitative behaviour has been observed in a much smaller extent for the Le = 0.6 case. The vorticity components have been shown to exhibit anisotropic behaviour within the flame brush, and the extent of anisotropy increases with decreasing Le. The baroclinic torque term has been shown to be principally responsible for this anisotropic behaviour. The vortex stretching and viscous dissipation terms have been found to be the leading order contributors to the enstrophy transport for all cases, but the baroclinic torque and the sink term due to dilatation play increasingly important role for flames with decreasing Le. Furthermore, the correlation between the fluctuations of enstrophy and dilatation rate has been shown to play an important role in determining the material derivative of enstrophy based on the mean flow in the case of a low Le.

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“…Both ω and ∇φ are known to exhibit strong preferential orientation in the S ij eigenframe, with the vorticity vector aligning along the intermediate eigenvector S 2 [19,[21][22][23][24] [ Fig. 2(a)], and the scalar gradient vector aligning with the most compressive eigenvector S 3 [19] [ Fig.…”

Section: B Alignment Of ω and ∇φ In The Eigenframementioning

confidence: 99%

Subfilter scalar-flux vector orientation in homogeneous isotropic turbulence

Verma

Blanquart

2014

Phys. Rev. E

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The geometric orientation of the subfilter-scale scalar-flux vector is examined in homogeneous isotropic turbulence. Vector orientation is determined using the eigenframe of the resolved strain-rate tensor. The Schmidt number is kept sufficiently large so as to leave the velocity field, and hence the strain-rate tensor, unaltered by filtering in the viscous-convective subrange. Strong preferential alignment is observed for the case of Gaussian and box filters, whereas the sharp-spectral filter leads to close to a random orientation. The orientation angle obtained with the Gaussian and box filters is largely independent of the filter width and the Schmidt number. It is shown that the alignment direction observed numerically using these two filters is predicted very well by the tensor-diffusivity model. Moreover, preferred alignment of the scalar gradient vector in the eigenframe is shown to mitigate any probable issues of negative diffusivity in the tensor-diffusivity model. Consequentially, the model might not suffer from solution instability when used for large eddy simulations of scalar transport in homogeneous isotropic turbulence. Further a priori tests indicate poor alignment of the Smagorinsky and stretched vortex model predictions with the exact subfilter flux. Finally, strong filter dependence of subfilter scalar-flux orientation suggests that explicit filtering may be preferable to implicit filtering in large eddy simulations.

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Local and nonlocal strain rate fields and vorticity alignment in turbulent flows

Cited by 67 publications

References 22 publications

Evolution of the velocity gradient tensor invariant dynamics in a turbulent boundary layer

Evolution of the velocity gradient tensor invariant dynamics in a turbulent boundary layer

Effects of Lewis number on vorticity and enstrophy transport in turbulent premixed flames

Subfilter scalar-flux vector orientation in homogeneous isotropic turbulence

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