Analyse du comportement hyperélastique d'un tuyau en EPDM : Application pour distribuer de l'eau en irrigation

International audienceDans le domaine de l'irrigation avec des eaux usées, bon nombre de travaux portent sur les aspects sanitaires. Cependant un des verrous à la diffusion de ces techniques demeure le système d'épandage. Il doit assurer une distribution homogène et durable. En s'inspirant des dispositifs agricoles, on observe que la régulation est souvent assurée par une membrane de type élastomère. Pour cela, il nous faut comprendre le comportement des matériaux de type élastomère et de définir leurs lois de comportement. La famille des élastomères est remarquable par la multiplicité de ses propriétés mécaniques. Trois d'entre eux : l'effet Mullins, l'hystérésis et l'effet visqueux, ont été mis en évidence durant les expériences en laboratoire. Dans ces travaux, nous avons cherché à nous affranchir de ces effets pour caractériser le comportement réversible de ces matériaux. Pour cela plusieurs types d'essais de traction ont été réalisés : uniaxiale, biaxiale et équibiaxiale, afin d'identifier le comportement du matériau. / In the field of the irrigation with waste water, a lot of works concern the sanitary aspects. However one of the bolts in the distribution of these techniques remains the system of manuring. It has to assure a homogeneous and sustainable distribution. Being inspired by agricultural devices, we observe that the regulation is often guaranteed by a membrane of an elastomer type. We need to understand the behaviour of the elastomer materials and the definition of their laws of behaviour. The family of elastomers is characterized by the multiplicity of its mechanical properties. Three of them: the Mullins effect, the hysteresis and the viscous effect, were noticed during the experiments in the laboratory. In these works, we tried to disengage from these effects in order to characterize the reversible behaviour of these materials. Therefore a series of tension tests were realized in order to identify the behaviour of material: uniaxial, biaxial and equibiaxial

Assessment of Airborne Transport of Potential Contaminants in a Wind Tunnel

The reuse of treated wastewater (TWW) for sprinkler irrigation could potentially diffuse pathogen-containing droplets off the application area. Wind and other unfavorable climatic factors enhance irrigation drift and bioaerosol dispersion, exposing humans to potentially severe health risks including the spread of diseases. Few studies have quantified bioaerosols during both spraying and airborne transport phases. Studies of effective sampling strategies to better qualify the dispersion process are also required. This paper presents experiments conducted in a wind tunnel for a deeper understanding of the effects of wind and temperature on pathogen or contaminant airborne dispersal and transport. It is the first time that passive collectors [polyvinyl chloride (PVC) lines] and active samplers (AGI-4 impinger) have been compared under analogous wind conditions using a fluorescent tracer. Droplet-size distribution was also investigated at 12 m from the boom with a NanoMoudi 122-NR cascade impactor in increasing wind conditions from 1 to 3 ms−1. PVC lines return a detailed evolution of the sprayed volume within a short range from the boom and for concentrated fluxes. Transport assessment of PVC lines indicates that transport and permanently airborne condition of the spray notably grow with increasing wind, resulting in a more compact and concentrated plume; mean transport increases from 0.13 to 1.18 Lh−1 m−2 at 7.7 m from the nozzle as the wind velocity increases from 1 to 3 ms−1. AGI-4 appears more suitable to assess finely aerosolized conditions because of its greater sensitivity compared to PVC lines as shown for sample values less than 1 Lh−1 m−2. The comparison between the AGI-4 and PVC lines shows higher values of recovery for the active samplers compared to the PVC lines. The total volume collected by the impingers was 2.93% of the sprayed volume, approximately twice that collected by PVC lines under analogous conditions, even though their sampling surface was only 1.54% that of PVC lines. Droplet-size distributions from the cascade impactor denote a median volume diameter from 1.1 to 2 μm, for the nozzle type used, and a relevant reduction in recovery at stronger wind velocities. An empirical relation time of flight is proposed as a first step in developing decision models that can be used to make sprinkler irrigation safe and to define standards for TWW reuse in agricultural practices (e.g., safe distance of application depending upon wind conditions and droplet-size distribution)

Flow characteristics and turbulence analysis of a large-scale pressure-atomized spray

International audienceA typical water round-nozzle jet for agricultural applications is presented in this study. The dispersion of a liquid for irrigation or pesticides spraying is a key subject to reduce both water consumption and air pollution. A simplified study case is constructed to tackle both scenarios, where a round dn = 1.2mm nozzle of a length Ln = 50dn is considered. The water injection bulk velocity is equal to Uj = 35m/s, aligned with gravity, placing the liquid jet in a turbulent atomization regime. Experimental and numerical approaches are considered. LDV and DTV optical techniques are used to gather statistical information from both the liquid and the gas phases of the spray. The experimental campaign is carried out from x/dn = 0 to 800. Concerning the LDV, small (∼ 1µm) olive-oil tracers are used to capture the gas phase, where a distinction between the liquid droplets and tracers is achieved by a specific setup of the laser power source and the burst Doppler setting (BP-Filter and SNR). On the dispersed zone, DTV measurements are carried out to determine velocities and sizes of droplets. Special attention to the depth-of-field (DOF) estimation is taken in order to obtain a less biased droplet's size-velocity correlation. Finally, an optical probe (OP) was also used to determine the liquid volume fraction í µí±Œ ̅ , liquid mass fraction í µí±Œ ̃ , and mixture density í µí¼Œ̅ , which are important features for such flows. These are key quantities for the determination of the mixture mean velocities and Reynolds stresses, and evaluation of the terms in their balance equations. Combining OP, LDV and DTV data allows to determine quantities such as the mixture mean density, í µí¼Œ̅ = í µí±Œ ̅ í µí¼Œ í µí°¿ + (1 − í µí±Œ ̅)í µí¼Œ í µí°º , mixture mean velocity along the i direction, í µí±¢ ̃ í µí±– = í µí±Œ ̃ í µí±¢ ̃ í µí±–,í µí°¿ + (1 − í µí±Œ ̃)í µí±¢ ̃ í µí±–,í µí°º , or mean slip velocity, í µí±¢ ̅ í µí±–,í µí±† = í µí±¢ ̅ í µí±–,í µí°¿ − í µí±¢ ̅ í µí±–,í µí°º = í µí±¢ í µí±– ′′ í µí±Œ ′′ ̃ í µí±Œ ̃ (1−í µí±Œ ̃) , where the notation '' denotes fluctuations with respect to the Favre averaged mean values. Similar relations hold for the Reynolds stresses. For such a flow, three dimensionless quantities can be constructed as a function of the forces that intervene in the atomization process. First, the nozzle Reynolds number, í µí±í µí±’ = í µí±ˆ í µí±— í µí±‘ í µí±› í µí¼ˆ í µí°¿ , allows to identify if the liquid flow inside the injector is turbulent. Then, the liquid Weber number, í µí±Ší µí±’ í µí°¿ = í µí¼Œ í µí°¿ í µí±ˆ í µí±—í µí±‘ í µí±› 2 í µí¼Ž , and the gas Weber number, í µí±Ší µí±’ í µí°º = í µí¼Œ í µí°º í µí±ˆ í µí±—í µí±‘ í µí±› 2 í µí¼Ž , which weights the importance of surface tension once the flow is in contact with the surrounding air. Finally, the Ohnesorge number, í µí±‚ ℎ = í µí¼Œ í µí°¿ í µí¼ˆ í µí°¿ √í µí¼Œ í µí°¿ í µí¼Ží µí±‘ í µí±› , characterizes the form of the liquid packets or droplets in the atomization process. Choosing Re = 41833 and Ln/dn = 50 makes the internal flow fully turbulent and ensures that the boundary layer inside the nozzle is fully developed for any upstream conditions. With WeL = 20158, WeG = 24.3 and Oh = 0.0034, the liquid phase turbulent kinetic energy should be the main responsible of the liquid-jet primary break-up, these flow conditions lying within the second wind-induced atomization regime

Stereo MicroPIV measurements in an irrigation nozzle

Irrigation nozzles often feature small serpentine-shaped channels to avoid clogging. Reduced clogging improves the lifetime of the irrigation nozzle, which reduces plastic waste and thereby reduces the impact on the environment. Clogging in micro channels is often suppressed in the presence of three- dimensional (3D) flow structures called vortices. In micro scales the initiation of such 3D microstructures is normally suppressed because of the low Reynolds number inherent to micro scale flows. Passive, zig-zag shaped irrigation nozzles have the potential to induce three- dimensional rotating flow structures around sharp corners, which enhance 3D flows in the channel and thereby reduce clogging. The aim of this study is to identify and characterize such vortices using a Stereoscopic MicroPIV system

Etude expérimentale de l'atomisation d'un jet liquide

Cette étude porte sur l'atomisation d'un jet d'eau turbulent, à forts nombres de Reynolds et de Weber, dans de l'air au repos. La visualisation du jet par shadowgraphie, depuis la sortie du jet et jusqu'à une abscisse de 1000 fois le diamètre de buse, permet d'observer différents modes de rupture et différentes structures (ligaments, hélices,...). Le traitement de ces images permet de déterminer la granulométrie des gouttes en fonction des échelles turbulentes de l'écoulement amont

Elaboration d'un prototype de distributeur auto-régulé

Cette étude porte sur les interactions entre un fluide et une membrane hyperélastique ayant pour fonction de réguler un écoulement. Le comportement de la membrane contrainte par la pression a été simulé sous Abaqus. Ces résultats ont permis de modéliser l'écoulement (code CFD commercial) lorsque la membrane est déformée et de déterminer la loi débit/pression du dispositif. Ces développements numériques s'appuient sur la méthode des éléments finis et sur un algorithme de résolution itératif pour le couplage. Ces travaux participent à l'élaboration d'un prototype de distributeur régulé

MADFORWATER. WP3 Adaptation of technologies for efficient water management and treated wastewater reuse in agriculture. Task3.2 Engineering innovative irrigation technologies adapted to the target Mediterranean African Countries and to treated wastewater reuse. Subtask3.2.1 Efficient low-pressure mini-sprinkler adapted to treated wastewater

The data set consists of experimental data from lab evaluation to characterize droplet-size distribution of new sprinkler and drift/transport mechanism in controlled (i.e. wind tunnel) conditions. This works aims at obtaining an optimal water distribution from a localized irrigation micro-sprinkler. Similar data have been collected on standard irrigation sprinklers, the objective of this MADFORWATER research is to control the droplet size spectrum to minimize drift (smaller droplets carried by the wind) and compaction (bigger droplets that impact on the soil and induce crusting) risks

Simulation of Airborne Transport with a Simplified Drift-Flux Model

International audienceThe use of treated wastewater for irrigation is associated with the dispersion of fine droplets containing possibly pathogens. Their inhalation could expose workers and people in the surroundings to health problems. Wind and other atmospheric conditions may increase dispersion. The risk is difficult to assess, especially with water cannons and sprinklers, whose initial droplet conditions in airborne dispersal are not well characterized. In this study, the airborne dispersion of fine droplets (smaller than 300  μm) was investigated numerically. A simplified Eulerian drift-flux model was used to obtain airborne profiles in windy conditions (between 1 and 3  m s−1), and experiments in a wind tunnel were used for validation. The model was one-way coupled, evaporation was not taken into consideration, and droplet displacement was driven by fluid drag and gravity. Two main conclusions were drawn. First, single-diameter simulations provide a qualitative evaluation of the rapidity of sedimentation but are not exhaustive to represent the entire spray. Second, more precise predictions can be obtained by introducing an approximated size distribution, resulting from a slight improvement of the initial conditions

Etude expérimentale de la structure turbulente d’une couche limite neutre au-dessus d’une surface rugueuse

Cette étude porte sur le développement d’une couche limite neutre au-dessus d’une surface rugueuse. Des expériences en veine ont été réalisées en similitude avec la couche limite atmosphérique pour analyser la structure turbulente de tels écoulements par vélocimétrie par imagerie de particules. Ces résultats ont permis de quantifier les termes des équations d’évolution de l’énergie cinétique turbulente et des moments turbulents ainsi que de proposer une paramétrisation de la longueur de mélange