DF - Dinàmica No Lineal de Fluids
http://hdl.handle.net/2117/1085
Wed, 25 May 2016 21:37:04 GMT2016-05-25T21:37:04ZPrecession of a rapidly rotating cylinder flow: traverse through resonance
http://hdl.handle.net/2117/86975
Precession of a rapidly rotating cylinder flow: traverse through resonance
Marqués Truyol, Francisco; López Moscat, Juan Manuel
Recent experiments using a rapidly rotating and precessing cylinder have shown that for specific values of the precession rate, aspect ratio and tilt angle, sudden catastrophic transitions to turbulence occur. Even if the precessional forcing is not too strong, there can be intermittent recurrences between a laminar state and small-scale chaotic flow. The inviscid linearized Navier Stokes equations have inertial-wave solutions called Kelvin eigenmodes. The precession forces the flow to have azimuthal wavenumber m = 1 (spin-over mode). Depending on the cylinder aspect ratio and on the ratio of the rotating and precessing frequencies, additional Kelvin modes can be in resonance with the spin-over mode. This resonant flow would grow unbounded if not for the presence of viscous and nonlinear effects. In practice, one observes a rapid transition to turbulence, and the precise nature of the transition is not entirely clear. When both the precessional forcing and viscous effects are small, weakly nonlinear models and experimental observations suggest that triadic resonance is at play. Here, we used direct numerical simulations of the full Navier Stokes equations in a narrow region of parameter space where triadic resonance has been previously predicted from a weakly nonlinear model and observed experimentally. The detailed parametric studies enabled by the numerics reveal the complex dynamics associated with weak precessional forcing, involving symmetry-breaking, hysteresis and heteroclinic cycles between states that are quasiperiodic, with two or three independent frequencies. The detailed analysis of these states leads to associations of physical mechanisms with the various time scales involved.
Wed, 11 May 2016 18:46:57 GMThttp://hdl.handle.net/2117/869752016-05-11T18:46:57ZMarqués Truyol, FranciscoLópez Moscat, Juan ManuelRecent experiments using a rapidly rotating and precessing cylinder have shown that for specific values of the precession rate, aspect ratio and tilt angle, sudden catastrophic transitions to turbulence occur. Even if the precessional forcing is not too strong, there can be intermittent recurrences between a laminar state and small-scale chaotic flow. The inviscid linearized Navier Stokes equations have inertial-wave solutions called Kelvin eigenmodes. The precession forces the flow to have azimuthal wavenumber m = 1 (spin-over mode). Depending on the cylinder aspect ratio and on the ratio of the rotating and precessing frequencies, additional Kelvin modes can be in resonance with the spin-over mode. This resonant flow would grow unbounded if not for the presence of viscous and nonlinear effects. In practice, one observes a rapid transition to turbulence, and the precise nature of the transition is not entirely clear. When both the precessional forcing and viscous effects are small, weakly nonlinear models and experimental observations suggest that triadic resonance is at play. Here, we used direct numerical simulations of the full Navier Stokes equations in a narrow region of parameter space where triadic resonance has been previously predicted from a weakly nonlinear model and observed experimentally. The detailed parametric studies enabled by the numerics reveal the complex dynamics associated with weak precessional forcing, involving symmetry-breaking, hysteresis and heteroclinic cycles between states that are quasiperiodic, with two or three independent frequencies. The detailed analysis of these states leads to associations of physical mechanisms with the various time scales involved.Continuation and stability of convective modulated rotating waves in spherical shells
http://hdl.handle.net/2117/86900
Continuation and stability of convective modulated rotating waves in spherical shells
García González, Fernando; Net Marcé, Marta; Sánchez Umbría, Juan
Modulated rotating waves (MRW), bifurcated from the thermal-Rossby waves that arise at the onset of convection of a fluid contained in a rotating spherical shell, and their stability, are studied. For this purpose, Newton-Krylov continuation techniques are applied. Nonslip boundary conditions, an Ekman number E=10-4, and a low Prandtl number fluid Pr=0.1 in a moderately thick shell of radius ratio ¿=0.35, differentially heated, are considered. The MRW are obtained as periodic orbits by rewriting the equations of motion in the rotating frame of reference where the rotating waves become steady states. Newton-Krylov continuation allows us to obtain unstable MRW that cannot be found by using only time integrations, and identify regions of multistability. For instance, unstable MRW without any azimuthal symmetry have been computed. It is shown how they become stable in a small Rayleigh-number interval, in which two branches of traveling waves are also stable. The study of the stability of the MRW helps to locate and classify the large sequence of bifurcations, which takes place in the range analyzed. In particular, tertiary Hopf bifurcations giving rise to three-frequency stable solutions are accurately determined.
Tue, 10 May 2016 17:55:53 GMThttp://hdl.handle.net/2117/869002016-05-10T17:55:53ZGarcía González, FernandoNet Marcé, MartaSánchez Umbría, JuanModulated rotating waves (MRW), bifurcated from the thermal-Rossby waves that arise at the onset of convection of a fluid contained in a rotating spherical shell, and their stability, are studied. For this purpose, Newton-Krylov continuation techniques are applied. Nonslip boundary conditions, an Ekman number E=10-4, and a low Prandtl number fluid Pr=0.1 in a moderately thick shell of radius ratio ¿=0.35, differentially heated, are considered. The MRW are obtained as periodic orbits by rewriting the equations of motion in the rotating frame of reference where the rotating waves become steady states. Newton-Krylov continuation allows us to obtain unstable MRW that cannot be found by using only time integrations, and identify regions of multistability. For instance, unstable MRW without any azimuthal symmetry have been computed. It is shown how they become stable in a small Rayleigh-number interval, in which two branches of traveling waves are also stable. The study of the stability of the MRW helps to locate and classify the large sequence of bifurcations, which takes place in the range analyzed. In particular, tertiary Hopf bifurcations giving rise to three-frequency stable solutions are accurately determined.Critical torsional modes of convection in rotating fluid spheres at high Taylor numbers
http://hdl.handle.net/2117/86793
Critical torsional modes of convection in rotating fluid spheres at high Taylor numbers
Sánchez Umbría, Juan; García González, Fernando; Net Marcé, Marta
A numerical study of the onset of convection in rotating internally heated self-gravitating fluid spheres is presented. The exploration of the stability of the conduction state versus the Taylor and Prandtl numbers supplies a detailed idea of the laws that fulfil the four types of solutions obtained at low Prandtl numbers. The main result found is that axisymmetric (torsional) modes of convection are preferred at high Taylor numbers in the zero-Prandtl-number limit. This instability appears at low Rayleigh numbers and gives rise to an oscillating single vortex of very high frequency.
Mon, 09 May 2016 16:44:28 GMThttp://hdl.handle.net/2117/867932016-05-09T16:44:28ZSánchez Umbría, JuanGarcía González, FernandoNet Marcé, MartaA numerical study of the onset of convection in rotating internally heated self-gravitating fluid spheres is presented. The exploration of the stability of the conduction state versus the Taylor and Prandtl numbers supplies a detailed idea of the laws that fulfil the four types of solutions obtained at low Prandtl numbers. The main result found is that axisymmetric (torsional) modes of convection are preferred at high Taylor numbers in the zero-Prandtl-number limit. This instability appears at low Rayleigh numbers and gives rise to an oscillating single vortex of very high frequency.Bone tissue properties measurement by reference point indentation in glucocorticoid-induced osteoporosis
http://hdl.handle.net/2117/86742
Bone tissue properties measurement by reference point indentation in glucocorticoid-induced osteoporosis
Mellibovsky, Leonardo; Prieto Alhambra, Daniel; Mellibovsky Elstein, Fernando; Gueerri Fernandez, Roberto; Nogues, Xavier; Randall, Connor; Hansma, Paul K.; Diez Perez, Adolfo
Glucocorticoids, widely used in inflammatory disorders, rapidly increase bone fragility and, therefore, fracture risk. However, common bone densitometry measurements are not sensitive enough to detect these changes. Moreover, densitometry only partially recognizes treatment-induced fracture reductions in osteoporosis. Here, we tested whether the reference point indentation technique could detect bone tissue property changes early after glucocorticoid treatment initiation. After initial laboratory and bone density measurements, patients were allocated into groups receiving calcium+vitamin D (Ca+D) supplements or anti-osteoporotic drugs (risedronate, denosumab, teriparatide). Reference point indentation was performed on the cortical bone layer of the tibia by a handheld device measuring bone material strength index (BMSi). Bone mineral density was measured by dual-energy X-ray absorptiometry (DXA). Although Ca+D-treated patients exhibited substantial and significant deterioration, risedronate-treated patients exhibited no significant change, and both denosumab- and teriparatide-treated participants exhibited significantly improved BMSi 7 weeks after initial treatment compared with baseline; these trends remained stable for 20 weeks. In contrast, no densitometry changes were observed during this study period. In conclusion, our study is the first to our knowledge to demonstrate that reference point indentation is sensitive enough to reflect changes in cortical bone indentation after treatment with osteoporosis therapies in patients newly exposed to glucocorticoids. (c) 2015 American Society for Bone and Mineral Research.
Mon, 09 May 2016 08:05:16 GMThttp://hdl.handle.net/2117/867422016-05-09T08:05:16ZMellibovsky, LeonardoPrieto Alhambra, DanielMellibovsky Elstein, FernandoGueerri Fernandez, RobertoNogues, XavierRandall, ConnorHansma, Paul K.Diez Perez, AdolfoGlucocorticoids, widely used in inflammatory disorders, rapidly increase bone fragility and, therefore, fracture risk. However, common bone densitometry measurements are not sensitive enough to detect these changes. Moreover, densitometry only partially recognizes treatment-induced fracture reductions in osteoporosis. Here, we tested whether the reference point indentation technique could detect bone tissue property changes early after glucocorticoid treatment initiation. After initial laboratory and bone density measurements, patients were allocated into groups receiving calcium+vitamin D (Ca+D) supplements or anti-osteoporotic drugs (risedronate, denosumab, teriparatide). Reference point indentation was performed on the cortical bone layer of the tibia by a handheld device measuring bone material strength index (BMSi). Bone mineral density was measured by dual-energy X-ray absorptiometry (DXA). Although Ca+D-treated patients exhibited substantial and significant deterioration, risedronate-treated patients exhibited no significant change, and both denosumab- and teriparatide-treated participants exhibited significantly improved BMSi 7 weeks after initial treatment compared with baseline; these trends remained stable for 20 weeks. In contrast, no densitometry changes were observed during this study period. In conclusion, our study is the first to our knowledge to demonstrate that reference point indentation is sensitive enough to reflect changes in cortical bone indentation after treatment with osteoporosis therapies in patients newly exposed to glucocorticoids. (c) 2015 American Society for Bone and Mineral Research.Continuation of bifurcations of cycles in dissipative PDEs
http://hdl.handle.net/2117/86729
Continuation of bifurcations of cycles in dissipative PDEs
Sánchez Umbría, Juan; Net Marcé, Marta
A new efficient methodology for the continuation of the
codimension-one bifurcations of periodic orbits, including pitchfork bifurcations present in reflection--symmetric systems, has been developed. It is based on the combination of Newton-Krylov techniques applied to extended systems, and the integration of systems of
variational equations up to second order. The extended systems are adapted from those usually found in the literature for fixed points of maps. A deflation term is needed in some cases to remove the trivial +1 multiplier of the periodic orbits. It will be shown that to evaluate the action of the Jacobian it is only necessary to integrate
systems of ODEs of dimension at most four times that of the original system. This minimizes the computational cost.
Two main tools are required to implement the algorithms presented here, a generic continuation code, and a time integrator for the particular problem at hand including the required variational equations.
The thermal convection of a mixture of two fluids in a two-dimensional rectangular box is used as test problem. It is known that the onset of convection is oscillatory below a certain negative value of one of the parameters (the separation ratio), giving rise to a rich dynamics. A
non-trivial diagram of periodic orbits is first deployed, by varying the Rayleigh number. Some of the bifurcations found on the main branch of periodic orbits are followed by adding as second parameter the Prandtl number. Several codimension-two points are found, and a
double-Hopf bifurcation is studied in more detail. Finally the boundaries of a resonance region, found on a branch of invariant tori, are also continued.
Fri, 06 May 2016 18:06:19 GMThttp://hdl.handle.net/2117/867292016-05-06T18:06:19ZSánchez Umbría, JuanNet Marcé, MartaA new efficient methodology for the continuation of the
codimension-one bifurcations of periodic orbits, including pitchfork bifurcations present in reflection--symmetric systems, has been developed. It is based on the combination of Newton-Krylov techniques applied to extended systems, and the integration of systems of
variational equations up to second order. The extended systems are adapted from those usually found in the literature for fixed points of maps. A deflation term is needed in some cases to remove the trivial +1 multiplier of the periodic orbits. It will be shown that to evaluate the action of the Jacobian it is only necessary to integrate
systems of ODEs of dimension at most four times that of the original system. This minimizes the computational cost.
Two main tools are required to implement the algorithms presented here, a generic continuation code, and a time integrator for the particular problem at hand including the required variational equations.
The thermal convection of a mixture of two fluids in a two-dimensional rectangular box is used as test problem. It is known that the onset of convection is oscillatory below a certain negative value of one of the parameters (the separation ratio), giving rise to a rich dynamics. A
non-trivial diagram of periodic orbits is first deployed, by varying the Rayleigh number. Some of the bifurcations found on the main branch of periodic orbits are followed by adding as second parameter the Prandtl number. Several codimension-two points are found, and a
double-Hopf bifurcation is studied in more detail. Finally the boundaries of a resonance region, found on a branch of invariant tori, are also continued.El canvi climàtic a través dels informes de l'IPCC (1990-2014)
http://hdl.handle.net/2117/86567
El canvi climàtic a través dels informes de l'IPCC (1990-2014)
Mazón Bueso, Jordi
Des de que l’any 1990 es va publicar el primer informe del Panell Intergovernamental
del Canvi Climàtic (en anglès IPCC) quatre
més
han aparegut (els anys 1995, 2001, 2007
i 2014), els quals ens donen una visió de l’evolució en l’estat del coneixement sobre el
canvi climàtic en les diferents etapes d’aquest període 1990-2014. A partir del contingut
científic i de les conclusions més destacables recollides en aquests cinc informes, s’ha
analitzat l’evolució del coneixement sobre el canvi climàtic, les polítiques i mesures
proposades per a combatre’l. En poc més de 20 anys s’ha passat d’una exhaustiva
descripció de les bases científiques de l’efecte hivernacle i del canvi climàtic en què
es basava l’informe del 1990, amb moltes incerteses i en el què era científicament
difícil atribuir a l’ésser humà com a unic responsable d’aquest canvi de clima, al darrer
informe del 2014, el qual qualifica d’extremament probable amb un 95% de certesa de
que l’escalfaent del planeta és d’origen antròpic, el qual pot esdevenir irreversible si no
s’actua de forma urgent en la reducció de les emissions.
Wed, 04 May 2016 12:40:40 GMThttp://hdl.handle.net/2117/865672016-05-04T12:40:40ZMazón Bueso, JordiDes de que l’any 1990 es va publicar el primer informe del Panell Intergovernamental
del Canvi Climàtic (en anglès IPCC) quatre
més
han aparegut (els anys 1995, 2001, 2007
i 2014), els quals ens donen una visió de l’evolució en l’estat del coneixement sobre el
canvi climàtic en les diferents etapes d’aquest període 1990-2014. A partir del contingut
científic i de les conclusions més destacables recollides en aquests cinc informes, s’ha
analitzat l’evolució del coneixement sobre el canvi climàtic, les polítiques i mesures
proposades per a combatre’l. En poc més de 20 anys s’ha passat d’una exhaustiva
descripció de les bases científiques de l’efecte hivernacle i del canvi climàtic en què
es basava l’informe del 1990, amb moltes incerteses i en el què era científicament
difícil atribuir a l’ésser humà com a unic responsable d’aquest canvi de clima, al darrer
informe del 2014, el qual qualifica d’extremament probable amb un 95% de certesa de
que l’escalfaent del planeta és d’origen antròpic, el qual pot esdevenir irreversible si no
s’actua de forma urgent en la reducció de les emissions.Conductive and convective heat transfer in fluid flows between differentially heated and rotating cylinders
http://hdl.handle.net/2117/86416
Conductive and convective heat transfer in fluid flows between differentially heated and rotating cylinders
López, José M.; Marqués Truyol, Francisco; Avila Cañellas, Marc
The flow of fluid confined between a heated rotating cylinder and a cooled stationary cylinder is a canonical experiment for the study of heat transfer in engineering. The theoretical treatment of this system is greatly simplified if the cylinders are assumed to be of infinite length or periodic in the axial direction. In these cases heat transfer in the laminar regime occurs only through conduction as in a solid. We here investigate numerically heat transfer and the onset of turbulence in such flows by using both periodic and no-slip boundary conditions in the axial direction. The influence of the geometric parameters is comprehensively studied by varying the radius ratio (0.1 <= eta <= 0.99) and the length-to-gap aspect ratio (5 <= Gamma <= 80). Similarly, a wide range of Prandtl, Rayleigh, and Reynolds numbers is explored (0.01 <= sigma <= 100, Ra <= 30,000, and Re <= 1000, respectively). We obtain a simple criterion, Ra which determines whether the infinite-cylinder assumption can be employed. The coefficient a is well approximated by a cubic fit over the whole n-range. Noteworthy the criterion is independent of the Prandtl number and appears robust with respect to Reynolds number even beyond the laminar regime. (C) 2015 Elsevier Ltd. All rights reserved.
Fri, 29 Apr 2016 10:13:31 GMThttp://hdl.handle.net/2117/864162016-04-29T10:13:31ZLópez, José M.Marqués Truyol, FranciscoAvila Cañellas, MarcThe flow of fluid confined between a heated rotating cylinder and a cooled stationary cylinder is a canonical experiment for the study of heat transfer in engineering. The theoretical treatment of this system is greatly simplified if the cylinders are assumed to be of infinite length or periodic in the axial direction. In these cases heat transfer in the laminar regime occurs only through conduction as in a solid. We here investigate numerically heat transfer and the onset of turbulence in such flows by using both periodic and no-slip boundary conditions in the axial direction. The influence of the geometric parameters is comprehensively studied by varying the radius ratio (0.1 <= eta <= 0.99) and the length-to-gap aspect ratio (5 <= Gamma <= 80). Similarly, a wide range of Prandtl, Rayleigh, and Reynolds numbers is explored (0.01 <= sigma <= 100, Ra <= 30,000, and Re <= 1000, respectively). We obtain a simple criterion, Ra which determines whether the infinite-cylinder assumption can be employed. The coefficient a is well approximated by a cubic fit over the whole n-range. Noteworthy the criterion is independent of the Prandtl number and appears robust with respect to Reynolds number even beyond the laminar regime. (C) 2015 Elsevier Ltd. All rights reserved.Filtrado transversal adaptativo de varianza constante para la ecualización de canal
http://hdl.handle.net/2117/86209
Filtrado transversal adaptativo de varianza constante para la ecualización de canal
Vázquez Grau, Gregorio; Gasull Llampallas, Antoni; Sánchez Umbría, Juan; Oliveras Vergés, Albert
This paper describes the problem of lineal filtering of noisy data under a Maximum Likelihood objective. In this sense, the paper shows that a weighted square error cost function deals and it is necessary to weight the filtering error sequence by a factor that, basically, depends the probability density function of the error sequence and on its first derivate. As it is well known, this information used to be not available and other proposals must be made. For this purpose, going around this problem, the paper discusses the design of this weighting factor for including sorne kind of data-selection mechanism for the final filter weight-vector solution design. The underlying of the proposal is the development of a recursive algorithm in such a way that for any measure or observation, its associated
Tue, 26 Apr 2016 14:37:29 GMThttp://hdl.handle.net/2117/862092016-04-26T14:37:29ZVázquez Grau, GregorioGasull Llampallas, AntoniSánchez Umbría, JuanOliveras Vergés, AlbertThis paper describes the problem of lineal filtering of noisy data under a Maximum Likelihood objective. In this sense, the paper shows that a weighted square error cost function deals and it is necessary to weight the filtering error sequence by a factor that, basically, depends the probability density function of the error sequence and on its first derivate. As it is well known, this information used to be not available and other proposals must be made. For this purpose, going around this problem, the paper discusses the design of this weighting factor for including sorne kind of data-selection mechanism for the final filter weight-vector solution design. The underlying of the proposal is the development of a recursive algorithm in such a way that for any measure or observation, its associatedTesting otter board hydrodynamic performances in wind tunnel facilities
http://hdl.handle.net/2117/85362
Testing otter board hydrodynamic performances in wind tunnel facilities
Mellibovsky Elstein, Fernando; Prat Farran, Joana d'Arc; Notti, Emilio; Sala, Antonello
The feasibility and potential advantages of wind tunnel testing of otter board designs are assessed. Traditional flume tank tests incur high operational costs and present some limitations in terms of flexibility and accuracy. Modern flume tanks, despite more flexible and accurate, are still expensive to operate or hire. Wind tunnel facilities are widespread, with a potential for low budget tests, and allow for an accurate control of velocity, angle of attack and sideslip as well as precise measurement of forces and moments in all three axes. A complete description of otter board hydrodynamics is paramount to optimising design and rigging and for the design of active control strategies that allow for stable trawling at a target speed and depth. We describe in detail the methodology of wind tunnel tests applied to general otter board designs, exemplify it with a commercial pelagic otter board and provide a comparison with existing flume tank results for the same design.
Thu, 07 Apr 2016 14:06:46 GMThttp://hdl.handle.net/2117/853622016-04-07T14:06:46ZMellibovsky Elstein, FernandoPrat Farran, Joana d'ArcNotti, EmilioSala, AntonelloThe feasibility and potential advantages of wind tunnel testing of otter board designs are assessed. Traditional flume tank tests incur high operational costs and present some limitations in terms of flexibility and accuracy. Modern flume tanks, despite more flexible and accurate, are still expensive to operate or hire. Wind tunnel facilities are widespread, with a potential for low budget tests, and allow for an accurate control of velocity, angle of attack and sideslip as well as precise measurement of forces and moments in all three axes. A complete description of otter board hydrodynamics is paramount to optimising design and rigging and for the design of active control strategies that allow for stable trawling at a target speed and depth. We describe in detail the methodology of wind tunnel tests applied to general otter board designs, exemplify it with a commercial pelagic otter board and provide a comparison with existing flume tank results for the same design.Numerical simulation of the genesis of superhighway convection in a slightly inclined layer of a binary liquid mixture
http://hdl.handle.net/2117/84854
Numerical simulation of the genesis of superhighway convection in a slightly inclined layer of a binary liquid mixture
Alonso Maleta, María Aránzazu; Mercader Calvo, María Isabel; Batiste Boleda, Oriol
Convection in a fluid layer is affected by its orientation with
respect to the gravitational field. In the present work, we
investigate numerically pattern selection in a vertical cylindrical
cell heated from below for positive Soret coefficient mixtures and
analyse the effect of marginal inclinations of gravity in pattern
formation.
The dynamics of mixtures with a positive value of the Soret
coefficient without inclination has essentially been studied in
laboratory experiments, and numerical simulations reduce to periodic
domains. According to these studies, close to convective onset, the
motion is dominated by the solute gradient, and a stationary square
pattern with negligible change in heat transport is reached (Soret regime).
Far from threshold, convection selects the usual roll structure observed
in pure fluid convection, where a strong change in heat transport takes
place. In the crossover region, a cross roll regime is observed and the
competition between square and roll patterns leads to oscillations.
Interestingly, positive Soret coefficient mixtures have been used in
the recent experimental work of Croccolo et al. to investigate the effect
of inclination of the layer on the long-term stability. At small Rayleigh
numbers, the mass transfer is dominated by the induced large scale shear flow,
while at larger Rayleigh numbers, it is dominated by solutal convection.
Unexpected results are reported at the transition: drifting columnar flows moving
in opposite directions along parallel lanes in a superhighway configuration have
been observed.
We will present simulations corresponding to both non-inclined and
inclined cells. In particular, we have been able to obtain numerically
superhighway convection (SHC). The numerical analysis should shed
some light on the origin of these fast drifting columnar flows
observed in experiments.
Wed, 30 Mar 2016 10:37:42 GMThttp://hdl.handle.net/2117/848542016-03-30T10:37:42ZAlonso Maleta, María AránzazuMercader Calvo, María IsabelBatiste Boleda, OriolConvection in a fluid layer is affected by its orientation with
respect to the gravitational field. In the present work, we
investigate numerically pattern selection in a vertical cylindrical
cell heated from below for positive Soret coefficient mixtures and
analyse the effect of marginal inclinations of gravity in pattern
formation.
The dynamics of mixtures with a positive value of the Soret
coefficient without inclination has essentially been studied in
laboratory experiments, and numerical simulations reduce to periodic
domains. According to these studies, close to convective onset, the
motion is dominated by the solute gradient, and a stationary square
pattern with negligible change in heat transport is reached (Soret regime).
Far from threshold, convection selects the usual roll structure observed
in pure fluid convection, where a strong change in heat transport takes
place. In the crossover region, a cross roll regime is observed and the
competition between square and roll patterns leads to oscillations.
Interestingly, positive Soret coefficient mixtures have been used in
the recent experimental work of Croccolo et al. to investigate the effect
of inclination of the layer on the long-term stability. At small Rayleigh
numbers, the mass transfer is dominated by the induced large scale shear flow,
while at larger Rayleigh numbers, it is dominated by solutal convection.
Unexpected results are reported at the transition: drifting columnar flows moving
in opposite directions along parallel lanes in a superhighway configuration have
been observed.
We will present simulations corresponding to both non-inclined and
inclined cells. In particular, we have been able to obtain numerically
superhighway convection (SHC). The numerical analysis should shed
some light on the origin of these fast drifting columnar flows
observed in experiments.