Di Savino, Silvio

Ducasse, Lauris

Iovieno, Michele

Tordella, Daniela

English

PORTO Publications Open Repository TOrino

Passive scalar transport across 2D and 3D shearless mixing layers
S.Di Savino, M. Iovieno, L.Ducasse, D.Tordella,
Dipartimento di Ingegneria Aeronautica e Spaziale, Politecnico di Torino,
Corso Duca degli Abruzzi 24, 10129 Torino, Italy
We present new results concerning the passive scalar turbulent transport in two and three dimensions in a shear-less mixing
layer, see fig.1. We consider the system where one energetic turbulent isotropic field is left to convectively diffuse into a
low energy one [3, 4]. In this system the region where the two turbulent flows interact is associated to a high intermittent
thin layer that propagates into the low energy region. We have seen that the diffusion process in 2D is faster then in
3D. In 2D the time growth of the interaction width is super-diffusive, while in 3D is slightly sub-diffusive, as in the wind
tunnel experiments by Veeravalli and Warhaft (JFM 1990). In both cases the passive scalar temporal spreading follows the
spreading of corresponding kinetic energy field. The presence of the turbulent energy gradient is felt on the distribution of
statistical quantities, as the skewness, kurtosis and spectra, across the layer. In two dimension, the passive scalar spectrum
computed inside the mixing region presents an exponent in the inertial range which is half of the usually met exponent
of the velocity fluctuation spectrum, typically close to - 3. In three dimension, we instead observed a mild difference
between these two spectral exponents. The results are obtained from direct numerical simulations of the diffusion of the
passive scalar across the interface which separates the two isotropic decaying turbulent fields with different kinetic energy.
The size of the computational domain is 4pi× (2pi)2 (discretized with 1200× 6002 grid points) in the 3D simulations and
(2pi)2 (discretized with 10242 grid points) in the 2D simulations [5, 6]. For details on the numerical technique, see [3, 4].
2D
m
ix
in
g
3D
m
ix
in
g
Figure 1: Visualization of the scalar field. The high turbulent energy velocity field is on the left of each image. The three
different instants correspond from left to right to t/τ = 1, 5, 10, respectively. The 3D simulation has an initial Rλ equal
to 150 in the high energy isotropic region and 60 in the low energy region.
References
[1] Shraiman B.I., Siggia, E.D.,(2000), Scalar turbulence, Nature. 405 (6787), 639–646
[2] Warhaft, Z.,(2000), Passive scalar in turbulent flows, Ann. Rev. Fluid Mech.32, 203–240
[3] Tordella D., Iovieno M.,(2006), Numerical experiments on the intermediate asymptotis of the shear-free turbulent
transport and diffusion, Fluid Mech. 449, 429–441
[4] Tordella D., Iovieno M., Bailey P.R.,(2008), Sufficient condition for Gaussian departure in turbulence, Phys. Rev. E.
77, 016309/1-11
[5] Tordella D., Iovieno M., Ducasse L,(July 2010), Diffusion of a passive scalar across a turbulent energy step, DSFD-10,
[6] Tordella D. Iovieno, M.,Ducasse L.(September 2010), Passive scalar diffusion through a turbulent energy gradient,
EFMC-10
1


Iovieno M.,(2006), Numerical experiments on the intermediate asymptotis of the shear-free turbulent transport and diffusion,

M.,Ducasse L.(September 2010), Passive scalar diffusion through a turbulent energy gradient,

Passive scalar in turbulent ﬂows,

Siggia, E.D.,(2000), Scalar turbulence,

Sufﬁcient condition for Gaussian departure in turbulence,

Dimensionality influence of the passive scalar transport observed through experiments on the turbulence shearless mixing

DI SAVINO, SILVIO

IOVIENO, MICHELE

DUCASSE, LAURIS

TORDELLA, Daniela

PORTO@iris (Publications Open Repository TOrino - Politecnico di Torino)

04 August 2020POLITECNICO DI TORINORepository ISTITUZIONALEDimensionality influence of the passive scalar transport observed through experiments on the turbulence shearlessmixing / S. Di Savino; M. Iovieno; L. Ducasse; D. Tordella. - STAMPA. - 5(2011), pp. 105-105. ((Intervento presentato alconvegno 5th European Postgraduate Fluid Dynamics Conference tenutosi a Gottingen, Germany nel August, 9-12,2011.OriginalDimensionality influence of the passive scalar transport observed through experiments on the turbulenceshearless mixingPublisher:PublishedDOI:Terms of use:openAccessPublisher copyright(Article begins on next page)This article is made available under terms and conditions as specified in the  corresponding bibliographic description inthe repositoryAvailability:This version is available at: 11583/2447777 since:DLR Institute of Aerodyamics and Flow TechnologyPassive scalar transport across 2D and 3D shearless mixing layersS.Di Savino, M. Iovieno, L.Ducasse, D.Tordella,Dipartimento di Ingegneria Aeronautica e Spaziale, Politecnico di Torino,Corso Duca degli Abruzzi 24, 10129 Torino, ItalyWe present new results concerning the passive scalar turbulent transport in two and three dimensions in a shear-less mixinglayer, see fig.1. We consider the system where one energetic turbulent isotropic field is left to convectively diffuse into alow energy one [3, 4]. In this system the region where the two turbulent flows interact is associated to a high intermittentthin layer that propagates into the low energy region. We have seen that the diffusion process in 2D is faster then in3D. In 2D the time growth of the interaction width is super-diffusive, while in 3D is slightly sub-diffusive, as in the windtunnel experiments by Veeravalli and Warhaft (JFM 1990). In both cases the passive scalar temporal spreading follows thespreading of corresponding kinetic energy field. The presence of the turbulent energy gradient is felt on the distribution ofstatistical quantities, as the skewness, kurtosis and spectra, across the layer. In two dimension, the passive scalar spectrumcomputed inside the mixing region presents an exponent in the inertial range which is half of the usually met exponentof the velocity fluctuation spectrum, typically close to - 3. In three dimension, we instead observed a mild differencebetween these two spectral exponents. The results are obtained from direct numerical simulations of the diffusion of thepassive scalar across the interface which separates the two isotropic decaying turbulent fields with different kinetic energy.The size of the computational domain is 4pi× (2pi)2 (discretized with 1200× 6002 grid points) in the 3D simulations and(2pi)2 (discretized with 10242 grid points) in the 2D simulations [5, 6]. For details on the numerical technique, see [3, 4].2Dmixing3DmixingFigure 1: Visualization of the scalar field. The high turbulent energy velocity field is on the left of each image. The threedifferent instants correspond from left to right to t/τ = 1, 5, 10, respectively. The 3D simulation has an initial Rλ equalto 150 in the high energy isotropic region and 60 in the low energy region.References[1] Shraiman B.I., Siggia, E.D.,(2000), Scalar turbulence, Nature. 405 (6787), 639–646[2] Warhaft, Z.,(2000), Passive scalar in turbulent flows, Ann. Rev. Fluid Mech.32, 203–240[3] Tordella D., Iovieno M.,(2006), Numerical experiments on the intermediate asymptotis of the shear-free turbulenttransport and diffusion, Fluid Mech. 449, 429–441[4] Tordella D., Iovieno M., Bailey P.R.,(2008), Sufficient condition for Gaussian departure in turbulence, Phys. Rev. E.77, 016309/1-11[5] Tordella D., Iovieno M., Ducasse L,(July 2010), Diffusion of a passive scalar across a turbulent energy step, DSFD-10,[6] Tordella D. Iovieno, M.,Ducasse L.(September 2010), Passive scalar diffusion through a turbulent energy gradient,EFMC-101

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Dimensionality influence of the passive scalar transport observed through experiments on the turbulence shearless mixing

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