Los grandes cambios urbanísticos de las últimas décadas en nuestras ciudades han modificado significativamente su respuesta hidrológica frente a un evento de lluvia. Esto se traduce en un aumento de las velocidades de circulación del agua en superficie y en mayores problemas a la hora de captar esos caudales e introducirlos en la red. Un mal funcionamiento del sistema de captación ocasiona inundaciones en la ciudad. Por ello es fundamental caracterizar la hidráulica de un sumidero y conocer mejor el flujo en sus cercanías. En este trabajo se presenta una aplicación similar al PIV (Particle Image Velocimetry) de cámaras de alta velocidad y un tratamiento de imágenes de alta resolución para obtener el campo de velocidades en las cercanías de un sumidero, lo que permite evaluar por ejemplo el caudal captado y la distribución entre caudales frontal y lateral del flujo de entrada en el sumidero.
We use an advanced version of Correlation Particle Image Velocimetry used in surface flows in order to analyze the complex fow and to relate the production and detection of vortices, some of which are advected by fast flow with cores of low pressure. These are often coincident with the core lines of strong vorticity or helicity. For example in fast flowing rivers or laboratory experiments of hydraulics or geophysical engineering.
Tellez, J-D; Gomez, M.; Russo, B.; Redondo, J. M. International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics p. 1-12 Data de presentació: 2016-07-07 Presentació treball a congrés
Surface Flow Image Velocimetry (SFIV), is a practical extension of Particle Image Velocimetry (PIV), as one of the major effective techniques in hydraulics providing velocity and vorticity fields in fast flow laboratory experiments or in field conditions. SFIV uses similar algorithms than conventional PIV, and these tools have a great deal in common with specific pattern matching used in synthetic schlieren. This paper presents an application to characterize the hydraulic behavior of a grate inlet in the area of urban drainage in order to reproduce the velocity field near the grates, as this is one of the important factors for the design of improved inlet systems and prevention of urban flooding. With a high speed camera it is possible to capture images of very high resolution and speed, which combined with the techniques SFIV for image processing, we may generate dynamic velocity and vorticity fields as well as local fluxes around the grate inlet, and combined with flow depth data, evaluate local Froude numbers. The average surface velocity measured by the imaging technique is a good approximation, especially for shallow flows, but it is also possible to extrapolate the technique to rivers, canals, or other hydraulic structures.
Tellez, J-D; Gomez, M.; Russo, B.; Redondo, J. M. International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics p. 1 Data de presentació: 2016-07-07 Presentació treball a congrés
Surface Flow Image Velocimetry (SFIV), is a practical extension of Particle Image Velocimetry (PIV), as one of the major effective techniques in hydraulics providing velocity and vorticity fields in fast flow laboratory experiments or in field conditions. SFIV uses similar algorithms than conventional PIV, and these tools have a great deal in
common with specific pattern matching used in synthetic schlieren. This paper presents an application to characterize the hydraulic behavior of a grate inlet in the area of urban drainage in order to reproduce the velocity field near the grates (Figure 1), as this is one of the important factors for the design of improved inlet systems and prevention of urban flooding. With a high speed camera it is possible to capture images of very high resolution and speed, which combined with the techniques SFIV for image processing, we may generate dynamic velocity and vorticity fields as well as local fluxes around the grate inlet, and combined with flow depth data, evaluate local Froude numbers. The average surface velocity measured by the imaging technique is a good approximation, especially for shallow flows, but it is also possible to extrapolate the technique to rivers, canals, or other hydraulic structures.
Tellez, J-D; Malik, N.; Vila, T.; Redondo, J. M. International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics p. 1 Data de presentació: 2016-07-07 Presentació treball a congrés
We present turbulence analysis and applications of Fractal analysis in Shock induced compressible flows as well as in convection in order to compare different measures of non-homogeneous use of fast reactive indicators such as Phenoftalein, provides visual indication of the complexity of shock and buoyancy driven flows. Surface Flow image
velocimetry (SFIV) allows to measure complex surface velocity fields in engineering involving 3D flow-boundary conditions and complex divergence and wave prone non uniform flows and boundary layer interactions, this may be particularly important when a single camera for PIV provides a 2D image of the real complex flows. The use of
multi-fractal analysis and improvements on Structure function calculations on standard PIV, and on several methods used in experimental fluids mechanics, calibrated towards the understanding of molecular mixing and the role of vorticity and helicity in the analysis of velocity vectors. The spectral behavior has an important role in mixing processes. A practical application is related to the Rayleigh–Taylor instability. The physical mechanism producing the instability is most easily done (Castilla and Redondo 1994) with a sudden acceleration stop of a tank in a falling frame of reference such as vertical railing. Fractal spectra of the velocity and vorticity fields show the important role of intermittency in Mixing.
Tellez, J-D; Malik, N.; Vila, T.; Redondo, J. M. International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics p. 1-11 Data de presentació: 2016-07-07 Presentació treball a congrés
New descriptors to investigate mixing in multi-scale turbulence analysis and couple PIV Laser induced applications with Fractal analysis in Shock induced flows as well as in convective driven flows are discussed. The comparison of different measures applied to complex non-homogeneous flows aid the understanding of mixing processes. We concentrate on the use of PIV and advanced multi-fractal methods in order to evaluate the “scale to scale” transfer of energy and other descriptors of great importance in mixing processes. In particular we discuss the evolution of fluxes as molecular mixing takes place, here the use of fast reactive indicators such as Phenoftalein or Rhodamine,
provides visual indication of the complexity of Rayleigh-Taylor and buoyancy driven flows. Surface Flow image velocimetry (SFIV) as discussed in this volume by (Jackson et al. 2016) also allows to measure complex surface velocity fields in engineering. These involve 3D flow-boundary conditions in divergence and wave prone nonuniform
flows and boundary layer interactions, this is particularly important when a single camera for PIV provides a 2D image of the real complex 3D flows. The use of multi-fractal analysis and improvements on Structure function calculations on standard PIV, and on other methods used in experimental fluids mechanics have to be calibrated, both in Eulerian and Lagrangian frameworks towards the understanding of molecular mixing and the role of vorticity and helicity in the analysis of velocity vectors. Energy, Enstrophy, Divergence and Vorticity- Helicity
scaling and stream function parameter spaces in stirring and mixing, seem very important. The link between Fractal spectra and energy Fourier and wavelet spectral behavior at different levels of intermittency still waits to be fully explained.
We discuss a taxonomy of different dynamical featuresin the ocean surface and provide some eddy
and frontstatistics, as well as describing some events detected byseveral satellites and even with additional cruise
observationsand measurements, in the North-west MediterraneanSea area between 1996 and 2012. The structureof
the flows are presented using self-similar traces thatmay be used to parametrize mixing at both limits of the Ross by
Deformation Radius scale, RL. Results showthe ability to identify different SAR signatures and at thesame time provide calibrations for the different local configurationsof vortices, spirals, Langmuir cells, oil spillsand tensioactive slicks that
eventually allow the study ofthe self-similar structure of the turbulence. Dependingon the surface wind and wave level,
and also on the fetch.the bathimetry, the spiral parameters and the resolution of vortical features change. Previous
descriptions did not includethe new wind and buoyancy features. SAR imagesalso show the turbulence structure
of the coastal area andthe Regions of Fresh Water Influence (ROFI). It is not eworthytt such complex coastal fielddependent
behavioris strongly influenced by stratification and rotation of theturbulence spectrum is observed only
in the range smallerthan the local Ross by deformation radius, RL. The measuresof diffusivity from buoy or tracer
experiments areused to calibrate the behavior of different tracers and pollutants,both natural and man-made in the NW
MediterraneanSea. Thanks to different polarization and intensitylevels in ASAR satellite imagery, these can be usedto
distinguish between natural and man-made sea surfacefeatures due to their distinct self-similar and fractal as afunction
of spill and slick parameters, environmental conditionsand history of both oil releases and weather conditions.Eddy
diffusivity map derived from SAR measurementsof the ocean surface, performing a feature spatialcorrelation of the
available images of the region are presented.Both the multi fractal discrimination of the localfeatures and the diffusivity
measurements are importantto evaluate the state of the environment. The distributionof meso-scale vortices of size,
the Ross by de for mationscale and other dominant features can be used to distinguishfeatures in the ocean surface.
Multi-fractal analysisis then very use full. The SAR images exhibited a largevariation of natural features produced
by winds, internalwaves, the bathymetric distribution, by convection, rain,etc as all of these produce variations in
the sea surfaceroughness so that the topological changes may be studiedand classified. In a similar way bathimetry
may bestudied with the methodology described here using thecoastline and the thal wegs as generators of local
Redondo, J. M.; Vila, M.; Tellez, J-D; Lopez, P.; Sánchez, M. Topical Problems of Fluid Mechanics Vol. 2016, num. 2, p. 169-176 DOI: 10.14311/TPFM.2016.023 Data de publicació: 2016-02-10 Article en revista
Turbulence affects molecular mixing in a large variety of physical processes both in the
environment, in astrophysics and in industrial situations. In some events it is interesting to
enhance the transport of mass, heat, humidity and pollutants, while sometimes it is
interesting to reduce mixing. Here we analyse some turbulent descriptors which reflect the
mixing processes in the compressible induced instabilities that take place in shocks, such as
Richtmyer-Meshkov and Rayleigh-Taylor (RM and RT). We present results related to both
instabilities and discuss their spatial and temporal variability during the advance of a
mixing front, and also their relationships with other scaling arguments. Two types of
experiments were used in this study: Mixing generated by gravitational acceleration in low
Atwood number incompressible experiments using fluids; and the full compressible shocktube
experiments using interfaces between different density gases. The role of local
turbulence has mostly relied on advanced visualization measurements through multifractal
methods. Comparisons with numerical experiments of shock driven fronts occurring at
density interfaces are also relevant. The global advance of the fronts is also measured and
fractal descriptors are calculated in both Large Eddy Simulation (LES) and Kinematic
Simulation KS models
The detailed study of the turbulence and the fluid flow in sport is an open and exciting field of research, in particular in swimming and aquatic sports there is a wealth of new techniques that may aid performance. In swimming, thanks to measurement techniques like
Particle Image Velocimetry (PIV), Particle Tracking (PT) or pattern analysis, now it is possible to measure the flow environment and not just the human movement. Numerical Computational Fluid Dynamics (CFD) is also a useful tool. We present several techniques stressing the importance of 3D effects and the dynamics of enhanced propulsion by hands and feet while the reduction in resistance need to be considered in an integrated way.
Examples of Sculling, Hand wakes, Underwater Undulatory Swimming (UUS) and Vortex Filament Analysis (VFA) are all interesting to improve swimming techniques.
Turbulent transfer is one of the most important processes in the Atmospheric Boundary Layer (ABL), showing many difficulties in stable situations (SBL): non stationary
conditions, presence of internal gravity waves, intermittency, decoupling from the surface fluxes, etc.
• The Monin-Obukhov (M-O) Theory is a suitable framework for presenting micrometeorological data, as well as for extrapolating and predicting certain micrometeorological
information where direct measurements are not available.
• In order to describe the surface fluxes, which is a key parameter in the atmospheric and dispersion models, the universal similarity functions fm and fh for non dimensional
wind and temperature profiles must be determined .
• Some commonly used linear universal functions can be not valid for moderate to strong stability, leading to important errors in the evaluation of surface fluxes. What is the
range of validity?
In the Edited paper, a turbulent ocean is modelled in the laboratory. The rotation of the Earth around its axis is represented by the rotation of a turntable. Similar to that in the Earth's ocean, the currents in the laboratory "ocean" are created by density effects when the water is heated or made salty. The laboratory currents are measured by a system which is not unlike the satellite altimetry system used by oceanographers to create "topographic" maps of the elevation of the water surface.
The effect of the differences between Salt and Heat agents to stratify the flow are discussed stressing the Rossby deformation scale, which marks where and when the rotation
induced Coriolis forces are in equilibrium with the effect of buoyancy. The upscale transfer of energy is inhibited at the Rossby deformation scale by baroclynic instability
at larger scales, which accounts for the dominant observed sizeof geophysical vortices.
Different regions of the parameter space based on the local versions of the Reynolds number, the Richardson number and the Rossby number should also be used to compare both laboratory observations and field data as well as the different experiments between themselves
Editor comments at Non linear Processes in Geophysics of the paper: Complex environmental ß-plane turbulence: laboratory experiments with altimetric imaging velocimetry of the Special Issue Complex Environmental and Geophysical Turbulence by
A. M. Matulka et al.
In the Edited paper, a turbulent ocean is modelled in the laboratory. The rotation of the Earth around its axis is represented by the rotation of a turntable. Similar to that in the Earth's ocean, the currents in the laboratory
Comments to PDF variation and vorticity-helicity evaluation to experiments that show new results from the spectral analyses of the flows in two experiments where turbulent flows were generated in a rotating tank with a topographic ß-effect are presented. The flows were forced either by heating water from below or supplying fresh water at the top of a saline layer. The flow was essentially barotropic in the first experiment and baroclinic in the second experiment. The gradient of the surface elevation was measured using optical altimetry (altimetric imaging velocimetry). Multiple zonal jets of alternating direction were observed in both experiments. Turbulent cascades of energy exhibit certain universal properties in spite of the different natures of flows in the experiments.
New industrial and didactic flow solutions based on new flow concepts are needed to meet the unprecedented requirements set by the dramatically increasing energy needs, the use of Thermoelectric didactive devices are neded for better environmental and industrial performance. We need improvements to existing solutions, such as better convective control with radical new developments thanks to thermoelectricity coupled with fluid dynamics descriptors such as PIV. also energy savings and reduction of adverse environmental impacts can come from multifractal concepts. The development of new flows both numerically and experimentally are important for solutions with fully resolved simulations because existing turbulence models cannot be applied indiscriminately on many untested new flow ideas.
One very recent example is the turbulent flows generated by fractal grids. Fractal grids are made from a structure, such as a square, repeated at different scales that allow higher mixing efficiencies.
We present several experimental studies on Turbulent Mixing produced by the advance of a density interface produced by brine when an oscilating grid produces zero-mean turbulence at a certain vertical distance. The older regular grid experiments have been re-calibrated and compared with fractal grids of different solidity and self-similar characteristics. Recent PIV and advanced visualizations will be compared with the initial work performed in 1993.
Pastore, N.; Cherubini, C.; Gassi, C.; Allegretti, N.; Redondo, J. M.; Tarquis Alfonso, A. Energy procedia Vol. 76, p. 273-281 DOI: 10.1016/j.egypro.2015.07.860 Data de publicació: 2015-07-01 Article en revista
Fractured rocks play an important role in transport of natural resources through subsurface systems. In recent years, interest has
grown in investigating heat transport by means of tracer tests, driven by the important current development of geothermal
applications. Many field and laboratory tracer tests in fractured media show that fracture - matrix exchange is more significant
for heat than mass tracers, thus thermal breakthrough curves are strongly controlled by matrix thermal diffusivity. In this study,
the behaviour of heat transport in a fractured network, at bench laboratory scale, has been investigated.
The UPC at the Vilanova i la Geltru Campus and UPC- CIMNE at Castelldefels will host the ERCOFTAC international summer school on Complex Environmental Turbulent Flows. This follows similar events organized in Vilanova, Madrid, Warsav, Prague, Volos and Barcelona since 1992. The main motivation for this 2015 Summer School is to study in depth Transport and diffusion in non-homogeneous, non-isotropic and non-stationary turbulence mostly affected by body forces, which is typical of Environmental Flows. Magnetic fields, Stratification and Rotation are fundamental processes afecting turbulence in industrial and environmental flows, for example to predict convective heat transport, pollutant diffusion and mixing. Reactions, solute transport in Environmental Fuid Dynamics, direct and inverse cascades in turbulence at different scales will be discussed with related topics. The experimental part of the summer school and a series of student presentations will be done at the ERCOFTAC PAN-EUROPEAN LABORATORY ON NON-HOMOGENEOUS TURBULENCE with a one day dedicated Workshop during the summer school. (2 July).
Design and operation of thermoelectric coolers and heaters that may be used in detailled laboratory experiments of buoyancy driven turbulence, as well as in the general fluid mechanics of convection is important, there seems to be a lack of comparison between numerical
models of turbulent flows ( Including Kinematic Simulation and DNS) and non-homogeneous experiments. We present the results of a university-industrial collaboration that developed a Fluid Dynamic Didactic Apparatus able to model steady and transient thermoelectric
driven convective models based on the control of thermal boundary conditions and also optimized to perform flow measurements inside a closed enclosure. The Thermoelectric Convection Didactic Device (TCDD) presented here is basically designed for a range of didactic uses, but a wide range of innovative research options are available,
both in the small 4x4 device shown in figure 1 and in larger and higher power equipments. We present here both the thermoelectric and the fluid flow description of the TCDD. The coupling of heat transfer and electric conduction within the semiconductor thermal assemblies
is important and takes into account the local thermoelectric effects, including Joule and Seebeck heating, Thomson effect, Peltier effect and Fourier’s heat conduction.
Mixing generated by gravitational acceleration and the role of local turbulence measured through
multifractal methods is examined in numerical experiments of Rayleigh-Taylor and Richtmyer-Meshkov driven
front occurring at density interfaces. The global advance of the fronts is compared with laboratory experiments
and Nusselt and Sherwood numbers are calculated in both large eddy simulation (LES) and kinematic simulation
KS models. In this experimental method, the mixing processes are generated by the evolution of a discrete set of forced
turbulent plumes. We describe the corresponding qualitative results and the quantitative conclusions based on measures of the
density field and of the height of the fluid layers. We present an experimental analysis to characterize the partial mixing process.
The conclusions of this analysis are related to the mixing efficiency and the height of the final mixed layer as functions
of the Atwood number, which ranges from 9.8×10-3 to 1.34×10-1
Costal Eddy Structure and Pollution Detection from SAR Spectral Analysis
Jose Manuel Redondo1,3, Juan Jose Martinez Benjamin1, Margarita Diez2,3, Pilar Lopez Gonzalez-Nieto4, Juan Jorge3, Jackson Tellez3
1ETSEB UPC Barcelona Tech, Spain; 2Ports de la Generalitat, Vilanova i la Geltru, Barcelona 08800, Spain; 3ETSECCPB, Universitat Politecnica de Catalunya, Dept. Fisica Aplicada, Barcelona, Spain; 4IPD, Univ. Complutense Madrid, Madrid, Spain.
Remote sensing by advanced radar active and passive methods provide better discrimination and higher resolution in complex geophysical flows. In the ocean, and even more so, in the coastal zone,where turbulent flow is generated in the ocear surface either by waves, wind or/and local currents. The conditions of the medium are highly non-homogeneous, and in the presence of a pollutant the SAR detects many topological features[1,2]. New techniques are used for the subsequent analysis, of more than 2000 Images provided by the ESA ERS1/2, ASAR, ENVISAT, RADARSAT and with additional cruise observations and measurements [4-9] in the North-west Mediterranean Sea area between 1996 and 2012.
Also the structure of the flows are presented using self-similar traces that may be used to parametrize mixing at both limits of the Rossby Deformation Radius scale. RL Results show the ability to identify different SAR signatures may predicting the self-similar structure of the turbulence[3,4], complex coastal field-dependent behavior is strongly influenced by stratification and rotation of the turbulence spectrum is observed only in the range smaler than local RL. The measures of diffusivity from buoy or tracer experiments are used to calibrate the behaviour of different tracers and pollutants, both natural and man-made in the NW Mediterranean Sea [4,5]. Thanks to different polarization and intensity levels in satellite imagery can be used to distinguish between natural and man-made sea surface features due to their distinct self-similar and fractal as a function of spill parameters, environmental conditions and history of both oil release and weather conditions.
Environmental factors determine [6,7] spreading. On the other hand helical and stratified turbulence is also modified by the intermittency and by the maximum fractal dimension, [5,8], which is related to the energy spectrum of the flow.
 Redondo, J.; Matulka, A.M.; Carrillo, J. (2010) Vortex decay in stratified flows. Topical Problems of Fluid Mechanics 2010. Praga, AS. pp. 127-130.
 Castilla R., Redondo J.M., Gamez P.J. and Babiano A. (2007), Non Linear Processes in Geophysics, 14, (2007) pp. 139.
 J. M. Redondo, J. H. Fernando and S. Pares (1995) Cloud entrainment by internal or
external turbulence, Mixing in geophysical flows, J. M. Redondo and O. Metais (Eds), CIMNE, Barcelona (1995) pp. 379-392.
 Platonov A., Carillo A., Matulka A., Sekula E., Grau J., Redondo J. M., Tarquis A. M. (2008) Multifractal observations of eddies, oil spills and natural slicks in the ocean surface", Il Nuovo Cimento, Vol. 31 C, N. 5-6, pp. 861-880.
 Redondo J.M. (1996) Vertical microstructure and mixing in stratified flows. Advances in Turbulence VI. Eds. S. Gavrilakis et al.(1996), pp. 605-608.
[7,8] Nicolleau, F.C.G.A.; Cambon, C.; Redondo, J.M.; Vassilicos, J.C.; Reeks, M.; Nowakowski, A.F. (Eds.)(2011) New Approaches in Modeling Multiphase Flows and Dispersion in Turbulence, Fractal Methods and Synthetic Turbulence. ERCOFTAC Serie
 Fraunie P., Berreba S. Chashechkin Yu.D., Velasco D. and Redondo J.M. (2008) Large eddy simulation and laboratory experiments on the decay of grid wakes in strongly stratified flows. Il Nuovo Cimento C 31, 909-930.
 Matulka, A., López, P., Redondo, J. M., and Tarquis, A.(2014) On the entrainment coefficient in a forced plume: quantitative effects of source parameters, Nonlin. Processes Geophys., 21, 269-278.
Pastore, N.; Chierubini, C.; Giassi, C.; Allegretti, N.; Redondo, J. M.; Tarquis Alfonso, A. European Geosciences Union General Assembly p. 2279- Data de presentació: 2015-04-17 Presentació treball a congrés
Fractured rocks play an important role in transport of natural resources or contaminants transport through
subsurface systems. In recent years, interest has grown in investigating heat transport by means of tracer tests,
driven by the important current development of geothermal applications. In literature different methods are
available for predicting thermal breakthrough in fractured reservoirs based on the information coming from tracer
An important achievement is the invention and development of techniques for measurement of velocities in hydraulic engineering
Knowledge of the technological advances in digital cameras with high
resolution and high speed are extremely useful to measure relevant predictive parameters in the environment. Here we present some
advances in image processing techniques, these can be used in hydraulic hazard predictions therefore, providing a tremendous potential to measure the behavior of the water surface flow.
This technique was performed at the Laboratory of Hydraulics Department of Hydraulic, Maritime and Environmental Universidad Pol
ytechnic de Catalonia, (UPC Barcelona Tech) where we used a
water flow platform with dimensions of 5.5 m long and 4 m wide allowing a zone of useful measurements of 5.5m x 3m, where the width is similar of a typical urban road. The platform allows to modify the slopes longitudinal at angles between 0% and 10% and transversal slopes of between 0% and 4%. And there is also the possibility of a range of flows. In the experiments discussed here we used flow rates up to 200 l/s
In addition, a camera high resolution 1280 x 1024 pixels with maximum speed of 488 frames per second.
A novel technique using particle image velocimetry to measure surface flow velocities has been developed and validated with the
experiments assays with the grate inlets.
In this case, the Methodology carried out can become a useful tools to understand the hydraulics behavior of the flow approaching the inlet where the traditional measuring equipment have serious problems and limitations.
We study at several non-homogeneous sites, such as the coastal Mediterranean Area (Ebro Delta, Blanes) and in
the iberian Plateau the wind intermittency as well as the fractal structure of the induced cloud and wave fronts.
Weather data from 10 and 100m hight masts are used to calculate Local Richardson number, Monin-Obukhov
length, eddy transfer coefficients, turbulent kinetic energy, turbulent intensities, friction velocities and sensible heat flux at three levels (5, 17 and 32 m) were considered. The results show how the stability at 17 and 32 minfluences the turbulent transfer near the ground.
The shear of wind or convection are the main mechanism to produce mixing in the surface, which is often detected in satellite images of nearby clouds or coastal features.
The influence of internal gravity-waves on the atmospheric boundary-layer during strong stable stratification is quantified
Redondo, J. M.; Tellez, J-D; Sotillos, L.; Lopez, P.; Furmanek, P.; Sanchez, J.; Diez, M. European Geosciences Union General Assembly p. 1-2 Data de presentació: 2015-04-14 Presentació treball a congrés
Local Diffusion and the topological structure of vorticity and velocity fields is measured in the transition from a homogeneous linearly stratified fluid to a cellular or layered structure by means of convective cooling and/or heating[1,2]. Patterns arise by setting up a convective flow generated by an array of Thermoelectric devices (Peltier/Seebeck cells) these are controlled by thermal PID generating a buoyant heat flux . The experiments described here investigate high Prandtl number mixing using brine and fresh water in order to form density interfaces and low Prandtl number mixing with temperature gradients. The set of dimensionless parameters define conditions of numeric and small scale laboratory modeling of environmental flows. Fields of velocity, density and their gradients were computed and visualized [3,4]. When convective heating and cooling takes place the combination of internal waves and buoyant turbulence is much more complicated if the Rayleigh and Reynolds numbers are high in order to study entrainment and mixing. Using ESS and selfsimilarity structures in the velocity and vorticity fieds and intermittency [3,5] that forms in the non-homogeneous flow is related to mixing and stiring. The evolution of the mixing fronts are compared and the topological characteristics of the merging of plumes and jets in different configurations presenting detailed comparison of the evolution of RM and RT, Jets and Plumes in overall mixing. The relation between structure functions, fractal analysis and spectral analysis can be very useful to determine the evolution of scales. Experimental and numerical results on the advance of a mixing or nonmixing front occurring at a density interface due to body forces and gravitational acceleration are analyzed considering the fractal and spectral structure of the fronts like in removable plate experiments for Rayleigh-Taylor flows. The evolution of the turbulent mixing layer and its complex configuration is studied taking into account the dependence on the initial modes at the early stages and its spectral, self-similar information [3,7-9]. Spectral and Fractal analysis on the images has been used in order to estimate dominant mixing structures as well as the dispersion relations of basic instabilities [4,8. Comparison of the range of entrainment values from laboratory experiments with those ocurring in nature, both in the atmosphere and ocean or in Astrophysics shows the importance of modeling correctly the integral lengthscales of the turbulence. The Entrainment may actually be related to the ratio of the flux to gradient Richardson numbers as well as the Turbulent Schmidt or Prandtl number [6,8] and their structure functions . Turbulent mixing diagnostics are based on schlieren and shadowgraph visualization, planar laser sheet, laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). We are interested by the influence of initial conditions (flux gradients of various sizes) on the transition to turbulent mixing, the influence of subsequent vortices and waves, initially in a one dimensional or plane configuration and furthermore in a two-three dimensional configuration with the interface oblique with respect to the horizontal.
Numeric modeling of a flow past vertical and horizontal strips towed in a linearly stratified tank are preformed by comparison to laboratory experiments using Schlieren visualization, density marker and probe measurements of internal wave fields. Both parts of the wave fields including upstream transient and downstream stationary waves were resolved. Analysis is here focusing on observed near wake singular components.
Experimental results in order to map the different transitions between two and three dimensional convection in an enclosure with complex driven heat flows. The size of the water tank is of 0.2 x 0.2x 0.1 m and the heat sources or sinks can be regulated both in power and sign [1-3]. The thermal convective driven flows are generated by Seebeck and Peltier effects in two opossed walls, thus generating different types of convective cells that varies strongly with the Topology of the boundary conditions as a function of Rayleigh, Peclet and Nusselt numbers,[4-6] Visualizations are performed by PIV, Particle tracking and shadowgraph.
Diffusion is measured in the transition from a homogeneous linearly stratified fluid to a cellular or layered structure by means of convective stirring. Patterns arise by setting up a convective flow generated by a buoyant heat flux . The experiments described here investigate high Prandtl number mixing using brine and fresh water in order to form density interfaces and low Prandtl number mixing with temperature gradients .
We also present a detailed comparison of the evolution of Jets and Plumes in overall mixing. The relation between fractal analysis and spectral analysis can be very useful to determine the evolution of scales. Experimental and numerical results on the convective cells are compared with Remote Sensing observations of the atmosphere, SAR images of the ocean can detect well these types of structures over the ocean[5-7].
The evolution of the turbulent mixing layer and its complex configuration is studied taking into account the dependence on the initial modes at the early stages and its spectral, self-similar information . Spectral and Fractal analysis on the images has been used in order to estimate dominant mixing structures as well as the dispersion relations of basic instabilities .
This Lecture notes are designed to complement the class notes of the course Turbulence and Mixing and Ocean Turbulence prsented at UPC, Toulon University and the Campus Universitary de la Mediterrania since 2010. It draws from Wikipedia and basic student support webs the pre-requisite knowledge on basic principles of Physics used in the Turbulence course. The main enphasis is on the use of clasical dynamics notations and thermodynamics which are not usually presented in engineering courses. It concentrates on the turbulence aspects related to energy, Entropy and scaling of the complex aspects of environmental turbulence. The use and explanation of Feynman diagrams in turbulence is also seldom presented away from quantum mechanics so the intention of these notes is also to show the synergy between different branches of physics and engineering.
A compilation of mathematical techniques and physical basic knowledge in order to prepare the post graduate students of the subjects of physical geodesy, environmental physics and the visiting students of Erasmus-Socrates projects of the Mediterranean Institute of Oceanography of Toulon and the Campus Universitari de la Mediterrania in Vilanova i la Geltru, Barcelona.
Experimental results on mixing occurring at a convective driven
or a overturning density gradient due to gravitational acceleration are
analyzed considering the velocity field of the process. We present
a thermoelectric driven heating and cooling experimental device in
order to investigate the different motions between two dimensional
convection in an enclosure and the 3 D complex flows. The size of the
enclosure is of 0.2 x 0.2 x 0.1 m and the heat sources or sinks (two
in facing walls) can be regulated both in power and sign (Redondo
1992). The thermal convective driven flows are generated by Seebeck
and Peltier effects  in 4 wall extended positions of 0.05 x 0.05 cm
each. The parameter range of convective cell array varies strongly
with the Topology of the Boundary conditions. At present side heat
fluxes are considered and estimated as a function of Rayleigh, Peclet
and Nusselt numbers, but the tilting possibilities of the BEROTZA
built experimental device also allow to heat/cool at top and bottom
at different angles
This contribution presents an experimental investigation on the behaviour of sediments
in a turbulent boundary layer flow, it compares the energy and vorticity needed to generate
a turbidity current and the zero mean flow lift off and entrainment across a stably stratified
density interface, either produced by solutes, sediment concentration or both. The
experimental parameters are used to quantify the entrainment, the mixing efficiency and
different types of dominant instability and the topological aspects of the turbulent cascade
in the environment. The experiments allow to detected both horizontally and vertically.
The local sediment and velocity fields. Grid turbulence in an enclosed two layer system
is measured with PIV as well as with sonic velocimetry. Observations of the horizontal
and vertical velocity energy spectra as well as the structure functions are used to estimate
local mixedness, entrainment and intermittency.
Turbulence affects the dynamics and the evolution of the turbulent mixing layer and its complex configuration is studied taking into account the dependence on the initial modes at the early stages and its spectral, self-similar information. Most models of the turbulent mixing evolution generated by hydrodynamics instabilities do not include any dependence on initial conditions, but in many relevant physical problems this dependence is very important, for instance, in Inertial Confinement Fusion target implosion. We discuss simple initial conditions with the aid of a numerical model developed at FIAN Lebedev which was compared with results of many simulations. The analysis of Kelvin-Helmholtz, Rayleigh-Taylor, Richtmyer-Meshkov and of accelerated instabilities is presented locally, and seen to dominate the turbulent cascade mixing zone differently under different initial conditions. Simulations and multi-fractal and neuron network analysis of Turbulent Mixing under RT and RM instabilities are presented for the different experiments and numerical simulations, further analysis on the numerical model is presented using wavelet preprocessing of the simulation results and neuron network presentation of the data. The aspect ratios of the bubble induced convective cells are seen to depend on the boundary and initial conditions applied to the front. The evolution of the Rayleigh-Taylor instability develops into a turbulent mixing front that may be investigated further using the information that the fractal dimensions or Kolmogorov Capacities give as the flow evolves in time. The basic self-similar characteristics of the flow are compared and the evolution of the multi-fractal dimensions of density, velocity and vorticity contours provides indication that most mixing takes place at the sides of the dominant convective blobs. In the context of determining the influence of structure on mixing ability and determine the regions of the front which contribute most to molecular mixing.
The present study compares the performances and reliabilities of the classical Mobile – Immobile Model (MIM)
and the Explicit Network Model (ENM) that takes expressly into account the network geometry for describing
tracer transport behaviour in a fractured sample at bench scale. Though ENM shows better fitting results than
MIM, the latter remains still valid as it proves to describe the observed curves quite well.
The results show that the presence of nonlinear flow plays an important role in the behaviour of solute
transport. Firstly the distribution of solute according to different pathways is not constant but it is related to the
flow rate. Secondly nonlinear flow influences advection, in that it leads to a delay in solute transport respect to the
linear flow assumption. Whereas nonlinear flow does not show to be related with dispersion. The experimental
results show that in the study case the geometrical dispersion dominates the Taylor dispersion. However the
interpretation with the ENM model shows a weak transitional regime from geometrical dispersion to Taylor
dispersion for high flow rates.
The improvements in experimental methods and high resolution image analysis are nowadays able to detect subtle
changes in the structure of the turbulence over a wide range of temporal and spatial scales, we compare the
scaling shown by different mixing fronts driven by buoyancy that form a Rayleigh-Taylor mixing front. We use
PIV and density front tracking in several experimental configurations akin to geophysical overturning . We
parametrize the role of unstable stratification by means of the Atwood number and compare both the scaling and
the multifractal and the maximum local fractal structure functions of the different markers used to visualize the
front. Both reactive and passive scalar tracers are used to investigate the mixing structure and the intermittency
of the flow. Different initial conditions are compared and the mixing efficiency of the overal turbulent processes
Matulka, A.M.; Lopez, P.; Redondo, J. M.; Tarquis Alfonso, A. Nonlinear processes in geophysics Vol. 21, num. 1, p. 269-278 DOI: 10.5194/npg-21-269-2014 Data de publicació: 2014-02-24 Article en revista
The behavior of a forced plume is mainly controlled by the source buoyancy and momentum fluxes and the efficiency of turbulent mixing between the plume and the ambient fluid (stratified or not). The interaction between the plume and the ambient fluid controls the plume dynamics and is usually represented by the entrainment coefficient aE. Commonly used one-dimensional models incorporating a constant entrainment coefficient are fundamental and very useful for predictions in geophysical flows and industrial situations. Nevertheless, if the basic geometry of the flow changes, or the type of source or the environmental fluid conditions (e.g., level of turbulence, shear, ambient stratification, presence of internal waves), new models allowing for variable entrainment are necessary. The presented paper is an experimental study based on a set of turbulent plume experiments in a calm unstratified ambient fluid under different source conditions (represented by different buoyancy and momentum fluxes). The main result is that the entrainment coefficient is not a constant and clearly varies in time within the same plume independently of the buoyancy and the source position. This paper also analyzes the influence of the source conditions on the mentioned time evolution. The measured entrainment coefficient aE has considerable variability. It ranges between 0.26 and 0.9 for variable Atwood number experiments and between 0.16 and 0.55 for variable source position experiments. As is observed, values are greater than the traditional standard value of Morton et al. (1956) for plumes and jets, which is about 0.13
We present a detailled experimental study of the thermocapillary motion of an aniline drop in an stably stratified fluid sytem driven by a laser beam. The thermocapillary motion of drops is the result of the temperature dependence of the interfacial tension. If the surface of the drop is subject to thermal gradients, then non-equilibrium surface tension effects appear, which in some cases can move the drop. We measure some of the velocity induced fields , vorticity, oscilations and intermittency of this complex flow. The source of the no uniformity of the temperature of the surface can be, as is in this experiment, the non uniform heating of the floating drop by a laser beam. In recent years, the thermocapillary movement of bubbles and drops under the influence of laser radiation has received more experimental attention thanks to the improvement in the flow visualization techniques.
We present a versatile apparatus that allows students to understand, manipulate and measure many aspects of buoyancy driven convective flows. The basic prototype presented and described in this brochure is a sturdy and simple to use laboratory or demonstration lecture equipment.
It consists of a visualization optimized Perspex enclosure of plane area 200mmx 200 mm and 100 mm thickness. Four thermoelectric Peltier effect coolers/heaters are used to generate different types of convective flows, both in steady state situations and in transients. The flow visualization patterns and techniques that are provided and may be used with ease will upgrade your student laboratory to the XXI st century.
Here we show the technical details of the experimental apparatus and show some examples of its use in several disciplines.
Tarquis Alfonso, A.; Platonov, A.; Matulka, A.M.; Grau, J.; Sekula, E.; Diez, M.; Redondo, J. M. Nonlinear processes in geophysics Vol. 21, num. 2, p. 439-450 DOI: 10.5194/npg-21-439-2014 Data de publicació: 2014-01-01 Article en revista
The use of synthetic aperture radar (SAR) to investigate the ocean surface provides a wealth of useful information that is very seldom used to its full potential. Here we will discuss the application of multifractal techniques to detect oil spills and the dynamic state of the sea regarding turbulent diffusion. We present different techniques in order to relate the shape of the multifractal spectral functions and the maximum fractal dimension to the behaviour of the ocean surface. We compare eddy and sheared dominated flows with convective driven flows and discuss the different features and observation methods. We also compare the scaling of different oil spills detected by means of SAR images. Recent spills and weathered ones are selected and compared to investigate their behaviour in different spatial and temporal ranges. We calculate the partition function based on the grey intensity value of each SAR pixel deriving several types of multifractal spectra as a function of spill residence time estimated for each image. Image manipulations are seen to reduce the speckle noise and thus distinguish much better the texture of the oil spill images. The results are used to discuss how eddy diffusivity may be estimated and used in a description of the ocean surface using a simple turbulence kinematic simulation model to predict the shape of oil spills. Differences in the multifractal spectrum among SAR images may detect the slicks due to plankton and also provide information on the age of the oil spills, on the Lagrangian turbulent structure and on ocean surface diffusivity.
The study of particle diffusion and of turbulent sedimentation is of great importance in many geophysical fields, such as in Environmental Science or Oceanography as well as in Bio-environmental and industrial processes. For a long time, the study of diffusion was numerically computed with random free paths, which gives Brownian behavior.
These stochastics methods have the objection that do not take into account the flow profile. On the other hand, there are many ways to simulate a fluid flow, but when this is turbulent our aim is to simulate the behaviour of neutral or heavy and inertial particles of biological or geological nature in a turbulent flow, in a simple way with a kinematically simulated model and to validate the results. We use the Kinematic Simulation (KS) model, also known as Synthetic Turbulence to model several environmental situations, both in the Atmosphere and the Ocean.
We calculate diffusion and scaling of the velocity and vorticity in a thermoelectric driven heating and cooling experimental device in order to map the different transitions between two and three dimensional convection in an
enclosure and complex driven flows. The size of the water tank is of 0.2 x 0.2 x 0.1 m and the heat sources or sinks can be regulated both in power and sign. The thermal convective driven flows are generated by Seebeck
and Peltier effects in 4 wall extended positions of 0.05 x 0.05 cm each. The parameter range of convective cell array varies strongly with the Topology of the boundary conditions. At present side heat fluxes are considered
and estimated as a function of Rayleigh, Peclet and Nusselt numbers, Visualizations are performed by PIV, Particle tracking and shadowgraph using the DigiFlow fluid visualization programme.
We present a description and some applications of the basic relationships that may affect the figure of merit in complex multiscale thermoelectric materials.
The success of Onsager’s Linear relationships between Fluxes and Forces in explaining the reversible Thermoelectric effects and in deriving Kelvin’s relationships (Onsager 1931) has been extended to include Magneto-Thermo- Electrical effects. Nerst or Nerst-Ettinghausen Effects, among others provide further examples of possible applications in thermal technologies.
The way in which the material structure is built with a controllable multifractal aspect, alternating at many different scales the grains which, either due to intrinsic cristaline anisotropy or due to a selective doping produce power relationships between the interfacial line lengths and the areas in 2D, or beween the area of the surface separating subsets of different material properties and the volumes of the respective grains in 3D. The application of these fractal aspects in order to describe fluxes that may be very different when measured at different scales may also be stated in terms of the relationships between fluxes and forces or between fluxes per unit area and gradients perpendicular to that same area.
When basic physical properties that are defined in a very different geometrical way, such as masic properties or surface properties, the need of integrating over all possible scales arises in order to avoid singularities in the theory. The effect of minimum and maximum grain size clusters and their geometrical self similarity is studied in terms of non-linear relationships and of higher order cumulants for several of the Magneto-Thermo-Electric (Devies 1952) and Thermo-electric Effects
In this Chapter we report on an experimental study of the thermocapillary motion of an aniline drop in an stably stratified fluid system and driven by a laser beam. The thermocapillary motion of drops is the result of the temperature dependence of the interfacial tension. If the surface of the drop is not isothermal gradients of the surface tension appear, which in some cases can move the drop. The source of the no uniformity of the temperature of the surface can be, in particular, the heating of the drop by a laser beam. In the last years, the thermocapillary movement of bubbles and drops under the influence of laser radiation was studied theoretically and experimentally. However, in the literature there is no data on observation of the movement of a single drop in a laser beam. In this paper an experimental methodology is proposed to study such a motion of a drop.
We present scaling applications of coastal SAR images in the NW Mediterranean Sea. The distribution of meso-scale vortices of size, related to the Talwegs, to the local Rossby deformation scale and other dominant features can be used to distinguish dinamical features in the ocean surface. Multi-fractal analysis is then very usefull. The SAR images exhibited a large variation of natural features produced by winds, internal waves, the bathymetric distribution, by convection, rain, etc as all of these produce variations in the sea surface roughness so that the topological changes may be studied and classified. An additional unique value that characterizes the overall
spatial fractal dimension of the system is to integrate the multifractal functions for different intensities. Several types of SAR images exhibit also their different structure functions. The flatness or Kurthosis is a statistic parameter which indicates the shape of the pdfs of the SAR intensity, and seems to be a very good indicator of the degree of existing structure; when flatness changes with scale following a potencial law, intermittency is present. Both the multifractal spectra and the distribution of the Flatness function F are found to be useful tools to measure intermittency, when it is applied to the correlations between the different SAR polarizations and to different physical features. Comparisons with the standard multi-fractal formalism also may reveal the importance of anisotropy and non-locality.
Series of flow percolation experiments under gravity were performed in different glass model and real karstic media
samples. We present a multifractal characterization of the experiments in several parametric non-dimensional
flow descriptors. Using the maximum local multifractal dimension as an additional flow indicator. Also experiments
Non laminar flow and transport conditions in fractured and karstified media were performed at Bari.
The investigation on hypothesis of non linear flow and non fickian transport in fractured aquifers led to a
distinction on the different role of channels and microchannels and of the presence of vortices and eddy trapping. The dominance of the elongated channels produced early arrival times, with the solute traveling along the high velocity channel network. On the other hand in a lumped structured karstic media, the percolation flow produced long tails with local Eddy mixing, entrapment in eddies, and slow flow out of the eddies.