A DNS study of turbulent mixing of two passive scalars

1996 ◽  
Vol 8 (8) ◽  
pp. 2161-2184 ◽  
Author(s):  
A. Juneja ◽  
S. B. Pope
Keyword(s):  
Turbulent Mixing ◽  
Passive Scalars

scholarly journals Multifractal analysis of oceanic chlorophyll maps remotely sensed from space

Ocean Science ◽  
2011 ◽  
Vol 7 (2) ◽  
pp. 219-229 ◽  
Author(s):  
L. de Montera ◽  
M. Jouini ◽  
S. Verrier ◽  
S. Thiria ◽  
M. Crepon
Keyword(s):  
Turbulent Mixing ◽  
Multifractal Analysis ◽  
Numerical Models ◽  
Specific Region ◽  
Dominant Effect ◽  
Passive Scalars ◽  
Analysis Techniques ◽  
Low Cloud ◽  
Scale Range ◽  
Low Cloud Cover

Abstract. Phytoplankton patchiness has been investigated with multifractal analysis techniques. We analyzed oceanic chlorophyll maps, measured by the SeaWiFS orbiting sensor, which are considered to be good proxies for phytoplankton. The study area is the Senegalo-Mauritanian upwelling region, because it has a low cloud cover and high chlorophyll concentrations. Multifractal properties are observed, from the sub-mesoscale up to the mesoscale, and are found to be consistent with the Corssin-Obukhov scale law of passive scalars. This result indicates that, in this specific region and within this scale range, turbulent mixing would be the dominant effect leading to the observed variability of phytoplankton fields. Finally, it is shown that multifractal patchiness can be responsible for significant biases in the nonlinear source and sink terms involved in biogeochemical numerical models.

scholarly journals Multifractal analysis of oceanic chlorophyll maps remotely sensed from space

2011 ◽  
Vol 8 (1) ◽  
pp. 55-84
Author(s):  
L. de Montera ◽  
M. Jouini ◽  
S. Verrier ◽  
S. Thiria ◽  
M. Crepon
Keyword(s):  
Turbulent Mixing ◽  
Multifractal Analysis ◽  
Numerical Models ◽  
Remotely Sensed ◽  
Dominant Effect ◽  
Passive Scalars ◽  
Nonlinear Source ◽  
Analysis Techniques ◽  
Scale Range ◽  
Source And Sink

Abstract. Phytoplankton patchiness has been investigated with multifractal analysis techniques. We analyzed oceanic chlorophyll maps, measured by the SeaWiFS orbiting sensor, which are considered to be good proxies for phytoplankton. Multifractal properties are observed, from the sub-mesoscale up to the mesoscale, and are found to be consistent with the Corssin-Obukhov scale law of passive scalars. This result indicates that, within this scale range, turbulent mixing would be the dominant effect leading to the observed variability of phytoplankton fields. Finally, it is shown that multifractal patchiness can be responsible for significant biases in the nonlinear source and sink terms involved in biogeochemical numerical models.

Random-sweeping hypothesis for passive scalars in isotropic turbulence

2002 ◽  
Vol 459 ◽  
pp. 129-138 ◽  
Author(s):  
P. K. YEUNG ◽  
BRIAN L. SAWFORD
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Schmidt Number ◽  
Isotropic Turbulence ◽  
Simulation Data ◽  
Passive Scalars ◽  
Direct Numerical Simulation Data ◽  
Rates Of Change ◽  
Small Scales ◽  
Wavenumber Spectrum

The hypothesis of the small scales being passively swept along by the large-scale motions in turbulent flow is extended to passive scalars in isotropic turbulence. A theory based on strong mutual cancellation between local and advective derivatives and other assumptions is shown to capture the Reynolds and Schmidt number dependence of time scales characterizing Eulerian and Lagrangian rates of change. Agreement with direct numerical simulation data improves systematically with increasing Reynolds number. In accordance with the physics of random sweeping, the Eulerian frequency spectrum is very similar in shape to the wavenumber spectrum, but is broadened at higher frequencies compared to its Lagrangian counterpart. Overall the hypothesis appears to be even more valid for transported scalars than for the velocity field, which gives support to the use of Lagrangian approaches in the study of turbulent mixing.

scholarly journals Lagrangian views on turbulent mixing of passive scalars

2010 ◽  
Vol 368 (1916) ◽  
pp. 1561-1577 ◽  
Author(s):  
Katepalli R. Sreenivasan ◽  
Jörg Schumacher
Keyword(s):  
Data Analysis ◽  
Turbulent Mixing ◽  
Passive Scalar ◽  
Navier Stokes ◽  
Scalar Mixing ◽  
Passive Scalars ◽  
Scalar Turbulence ◽  
Kraichnan Model ◽  
Lagrangian Turbulence

The Lagrangian view of passive scalar turbulence has recently produced interesting results and interpretations. Innovations in theory, experiments, simulations and data analysis of Lagrangian turbulence are reviewed here in brief. Part of the review is closely related to the so-called Kraichnan model for the advection of the passive scalar in synthetic turbulence. Possible implications for a better understanding of the passive scalar mixing in Navier–Stokes turbulence are also discussed.

Spectrum of passive scalars of high molecular diffusivity in turbulent mixing

2013 ◽  
Vol 716 ◽  
Author(s):  
P. K. Yeung ◽  
K. R. Sreenivasan
Keyword(s):  
Reynolds Number ◽  
Turbulent Mixing ◽  
Kinematic Viscosity ◽  
Schmidt Number ◽  
Scalar Fields ◽  
Passive Scalar ◽  
Careful Examination ◽  
Passive Scalars ◽  
Molecular Diffusivity ◽  
Schmidt Numbers

AbstractWe consider the mixing of passive scalars transported in turbulent flow, with a molecular diffusivity that is large compared to the kinematic viscosity of the fluid. This particular case of mixing has not received much attention in experiment or simulation even though the first putative theory, due to Batchelor, Howells & Townsend (J. Fluid Mech., vol. 5, 1959, pp. 134–139), is now more than 50 years old. We study the problem using direct numerical simulation of decaying scalar fields in steadily sustained homogeneous turbulence as the Schmidt number (the ratio of the kinematic viscosity of the fluid to the molecular diffusivity of the scalar) is allowed to vary from $1/ 8$ to $1/ 2048$ for two values of the microscale Reynolds number, ${R}_{\lambda } \approx 140$ and $\approx $240. The simulations show that the passive scalar spectrum assumes a slope of $- 17/ 3$ in a range of scales, as predicted by the theory, when the Schmidt number is small and the Reynolds number is simultaneously large. The observed agreement between theory and simulation in the prefactor in the spectrum is not perfect. We assess the reasons for this discrepancy by a careful examination of the scalar evolution equation in the light of the assumptions of the theory, and conclude that the finite range of scales resolved in simulations is the main reason. Numerical issues specific to the regime of very low Schmidt numbers are also addressed briefly.

Sign in / Sign up

Export Citation Format

Share Document