Lagrangian Random Walk Research Articles

Droplet deposition of agrochemical spraying: Comparison of results from a random‐walk model and CFD simulations

AbstractThe effectiveness of agricultural spraying processes depends considerably on the ability of the atomized droplets to reach the target site in the desired amount. In this work, two mathematical models to study the trajectories and deposition of atomized droplets are implemented and compared. On the one hand, a computational fluid dynamics (CFD) coupled with discrete phase model (DPM) is implemented to calculate the trajectories of atomized droplets and determine distances at which the droplets are deposited. The continuous phase (atmospheric air) is modelled by continuity, momentum, and energy equations. On the other hand, a Lagrangian random‐walk (LRW) model based on force and energy balances to predict the pulverization process of a nozzle is formulated and implemented in Python. Both models take into account the effects of drag, gravity, buoyancy, and evaporation on individual droplets, as well as the impact of atmospheric stability and dispersion. By tracking a large number of trajectories, meaningful estimates of dispersal statistics can be obtained. The LRW model accurately replicated the trajectories, deposition distances, and final diameters of atomized droplets for three atmospheric stability cases, compared with CFD simulation results. The results of both models agreed that 100 μm droplets were most susceptible to wind‐induced spray drift, depositing at the furthest distances from the nozzle. In addition, 50 μm droplets exhibited a significant tendency to evaporate entirely before reaching the ground. The LRW model is found to be a cost‐effective alternative for estimating spray drift compared to the computationally intensive CFD approach.

Numerical simulation research of the transportation and distribution characteristics on sea surface of the microplastic released continuously for 12 years from China's coastal cities

Based on the Lagrangian random walk particle tracking method and the global ocean reanalysis data, this study simulated the drift-diffusion process in ocean of microplastic particles (density less than seawater) discharged by coastal cities in China for 12 consecutive years. The results reveal that most of the microplastics (80.33%) essentially end up ashore or in the marginal seas around China, a small portion of microplastics (18.22%) enter the Sea of Japan and the Northwest Pacific Ocean via the Tsushima Strait and the Osumi-Kaikyo with the Kuroshio Tide, a very small portion of microplastics (1.45%) enter into the waters of Southeast Asian countries along with the west boundary current of South China Sea. The concentration distribution characteristics have obvious seasonal variation in the high concentration areas (the marginal seas around China and Sea of Japan). The mainly destination area of microplastics released in different cities is different.

Parallelized domain decomposition for multi-dimensional Lagrangian random walk mass-transfer particle tracking schemes

Abstract. Lagrangian particle tracking schemes allow a wide range of flow and transport processes to be simulated accurately, but a major challenge is numerically implementing the inter-particle interactions in an efficient manner. This article develops a multi-dimensional, parallelized domain decomposition (DDC) strategy for mass-transfer particle tracking (MTPT) methods in which particles exchange mass dynamically. We show that this can be efficiently parallelized by employing large numbers of CPU cores to accelerate run times. In order to validate the approach and our theoretical predictions we focus our efforts on a well-known benchmark problem with pure diffusion, where analytical solutions in any number of dimensions are well established. In this work, we investigate different procedures for “tiling” the domain in two and three dimensions (2-D and 3-D), as this type of formal DDC construction is currently limited to 1-D. An optimal tiling is prescribed based on physical problem parameters and the number of available CPU cores, as each tiling provides distinct results in both accuracy and run time. We further extend the most efficient technique to 3-D for comparison, leading to an analytical discussion of the effect of dimensionality on strategies for implementing DDC schemes. Increasing computational resources (cores) within the DDC method produces a trade-off between inter-node communication and on-node work. For an optimally subdivided diffusion problem, the 2-D parallelized algorithm achieves nearly perfect linear speedup in comparison with the serial run-up to around 2700 cores, reducing a 5 h simulation to 8 s, while the 3-D algorithm maintains appreciable speedup up to 1700 cores.

Parallelized Domain Decomposition for Multi-Dimensional Lagrangian Random Walk, Mass-Transfer Particle Tracking Schemes

Parallelized Domain Decomposition for Multi-Dimensional Lagrangian Random Walk, Mass-Transfer Particle Tracking Schemes

Development and evaluation of a new particle tracking solver for hydrodynamic and mass transport characterization of porous media – A case study on periodic open cellular structures

The detailed understanding of local mass transport characteristics in porous catalyst supports is essential for the evaluation of their performance in reaction engineering applications. This applies particularly for the development and assessment of novel concepts such as additively manufactured periodic open cellular structures (POCS). A major drawback of the frequently used Eulerian based mass transport simulation methods is their tendency to overestimate molecular diffusion due to artificial numerical diffusion, especially in the range of high Péclet numbers (boundary-layer dispersion and pure mechanical dispersion regime) that is often encountered in industrial applications.To overcome this problem, we present a new efficient solver implementation for the OpenFOAM® simulation toolbox based on the Lagrangian Random Walk Particle Tracking method to calculate the mass transport via a deterministic convective and a stochastic diffusion term. Besides the numerical calculation of effective diffusion as well as dispersion coefficients, the new solver is also capable of analyzing residence time behavior, flow tortuosity and contact patterns with catalytically active surfaces of catalyst support structures in detail. Following a thorough validation study, we demonstrate the evaluation options provided by the results of this new solver named disTrackFoam on the example of three POCS with distinct unit cell types.

Plume dynamics and dispersion characteristics in oil horizontal release from damaged submarine pipeline

The dynamics model of plume for underwater oil spill is improved by considering the drag force of the plume. The comparisons between prediction and experiment show that the improved model is viable. The improved model combining the Lagrangian random walk method is used to simulate the entire oil transport process from release exit to water surface in underwater oil horizontal release and some new results are obtained. Firstly, the release rate, the current velocity and its direction have evident influence on plume dynamics. The plume length increases as release flow rate increases. For small oil release rate, the plume length is very short so that the plume stage can be ignored due to the small initial momentum. When the oil release in direction is the same as the current, the current will play a positive role in the plume motion and the plume will therefore extend a longer distance. In this case, the greater the current velocity is, the longer the plume extension length will be. And when the oil release in direction is opposite to the current, the plume first moves forward and then is reversed to move along the opposite direction. The position of the reversal point depends on the current velocity and the release rate. Secondly, the release rate and the current velocity also have a significant effect on oil droplet diffusion. For small oil release rate, the oil distribution area is narrow and the concentration near upper side of droplets moving path is relatively higher. As the release rate or current velocity increases, the oil droplet diffusion area expands away from the release point. Finally, the movement characteristics of oil droplets in the plume and diffusion stages will affect the time and location for oil droplets reaching the surface. In a small release rate as well as a small current velocity, the time for oil droplet reaching surface is very short and the horizontal position reaching surface is closer to release point. In this case, the time spent in the plume stage is extremely short compared to the time spent in the entire oil motion process. Therefore, the plume dynamics stage can be ignored in this case. With the increase of release rate or current velocity, the plume will be extended and the time spent in plume dynamics stage will also be longer, so the plume dynamics stage can no longer be ignored for larger release rate or current velocity. In the case of reverse current, as the plume momentum be partially consumed by the reverse current, the plume is reversed and decays quickly, the time taken in the plume dynamics stage is relatively shorter than that for positive current. Correspondingly, the total time is also somewhat shortened. The shape of the plume depends on the oil release rate, current velocity and direction.

Random Walks with negative particles for discontinuous diffusion and porosity

This study develops a new Lagrangian particle method for modeling flow and transport phenomena in complex porous media with discontinuities. For instance, diffusion processes can be modeled by Lagrangian Random Walk algorithms. However, discontinuities and heterogeneities are difficult to treat, particularly discontinuous diffusion D(x) or porosity θ(x). In the literature on particle Random Walks, previous methods used to handle this discontinuity problem can be characterized into two main classes as follows: “Interpolation techniques”, and “Partial reflection methods”. One of the main drawbacks of these methods is the small time step required in order to converge to the expected solution, particularly in the presence of many interfaces. These restrictions on the time step, lead to inefficient algorithms. The Random Walk Particle Tracking (RWPT) algorithm proposed here is, like others in the literature, discrete in time and continuous in space (gridless). We propose a novel approach to partial reflection schemes without restrictions on time step size. The new RWPT algorithm is based on an adaptive “Stop&Go” time-stepping, combined with partial reflection/refraction schemes, and extended with a new concept of negative mass particles. To test the new RWPT scheme, we develop analytical and semi-analytical solutions for diffusion in the presence of multiple interfaces (discontinuous multi-layered medium). The results show that the proposed Stop&Go RWPT scheme (with adaptive negative mass particles) fits extremely well the semi-analytical solutions, even for very high contrasts and in the neighborhood of interfaces. The scheme provides a correct diffusive solution in only a few macro-time steps, with a precision that does not depend on their size.

Testing the limits of the spatial Markov model for upscaling transport: The role of nonmonotonic effective velocity autocorrelations

The spatial Markov model is a Lagrangian random walk model, widely and successfully used for upscaling transport in heterogeneous flows across a broad range of problems. It is particularly useful at early or pre-asymptotic times when many other conventional upscaling approaches may not be valid. However, as with all upscaled models, it must have its limits. In particular, the question of what the smallest scale at which it can be legitimately applied, without violating implicit assumptions, remains. Here we address this issue by considering one of the most classical transport upscaling problems: Taylor dispersion in a bounded shear flow. We demonstrate that the smallest scale for the spatial Markov model depends on the transverse width of the domain, the variability of the flow field as quantified by a coefficient of variation, and the competition of longitudinal and transverse diffusion coefficients. We show that this scale is a factor of the Peclet number smaller than the classical Taylor dispersion scale, meaning that for advection-dominated systems where Peclet numbers are large, this model can be applied at much smaller scales than classical Taylor-Aris dispersion theories.

Incomplete mixing and reactions in laminar shear flow.

Incomplete mixing of reactive solutes is well known to slow down reaction rates relative to what would be expected from assuming perfect mixing. In purely diffusive systems, for example, it is known that small initial fluctuations in reactant concentrations can lead to reactant segregation, which in the long run can reduce global reaction rates due to poor mixing. In contrast, nonuniform flows can enhance mixing between interacting solutes. Thus, a natural question arises: Can nonuniform flows sufficiently enhance mixing to restrain incomplete mixing effects and, if so, under what conditions? We address this question by considering a specific and simple case, namely, a laminar pure shear reactive flow. Two solution approaches are developed: a Lagrangian random walk method and a semianalytical solution. The results consistently highlight that if shear effects in the system are not sufficiently strong, incomplete mixing effects initially similar to purely diffusive systems will occur, slowing down the overall reaction rate. Then, at some later time, dependent on the strength of the shear, the system will return to behaving as if it were well mixed, but represented by a reduced effective reaction rate.

Potential impact of heterogeneity on groundwater age

Groundwater age is an important water property used as an indicator of groundwater quality. There have been no sufficient data and measurements underground, and that problem has been mitigated by using direct simulation of groundwater age. This paper has been motivated by the work of Daniel J. Goode, defining a rather different approach. A numerical model has been developed, using the Lagrangian approach and random walk particle tracking method, where groundwater age is calculated as a summed-up travelling time of certain particles. Basic input of this method is flow calculation; hence, in order to get the groundwater age simulation, an upgrade has been done to the existing software. Synthetic examples have been simulated for homogeneous, layered, as well as for low and medium heterogeneous aquifer systems. A stochastic analysis of heterogeneous aquifers has been done using a Monte Carlo simulation method. The results are given as groundwater age fields. Application of such an approach lays in possible estimation of the expected groundwater age at a certain location of water intake. Therefore, the calculated probability assumptions may be used as a decision support tool in cases of groundwater pollution, estimation of the level of aquifer's auto-purification, or in events where applying certain level of water treatment prior to usage is needed.

The impact of different vertical diffusion schemes in a three-dimensional oil spill model in the Bohai Sea

Vertical transport is critical to the movement of oil spills in seawater. Breaking waves play an important role by developing a well-defined mixing layer in the upper part of the water column. A three-dimensional (3-D) Lagrangian random walk oil spill model was used here to study the influence of sea surface waves on the vertical turbulence movement of oil particles. Three vertical diffusion schemes were utilized in the model to compare their impact on oil dispersion and transportation. The first scheme calculated the vertical eddy viscosity semi-empirically. In the second scheme, the vertical diffusion coefficient was obtained directly from an Eulerian hydrodynamic model (Princeton Ocean Model, POM2k) while considering wave-caused turbulence. The third scheme was formulated by solving the Langevin equation. The trajectories, percentages of oil particles intruding into water, and the vertical distribution structures of oil particles were analyzed for a series of numerical experiments with different wind magnitudes. The results showed that the different vertical diffusion schemes could generate different horizontal trajectories and spatial distributions of oil spills on the sea surface. The vertical diffusion schemes caused different water-intruding and resurfacing oil particle behaviors, leading to different horizontal transport of oil particles at the surface and subsurface of the ocean. The vertical diffusion schemes were also applied to a realistic oil spill simulation, and these results were compared to satellite observations. All three schemes yielded acceptable results, and those of the third scheme most closely simulated the observed data.

Lagrangian/Eulerian model of coagulation and deposition of inhaled particles in the human lung

The primary objectives of the present study were to mathematically describe particle coagulation within the human respiratory tract and to analyze its impact on local particle deposition patterns for high concentrations of inhaled cigarette smoke particles. Coagulation mechanisms simulated were thermal motion, gravitational settling, laminar shear, turbulences, electrical charges, and inertial effects at airway bifurcations. To implement concentration dependent coagulation processes, the Lagrangian random walk deposition model IDEAL, simulating the paths of an individual particle, was modified by tracking the random path of an elemental air volume containing the full size distribution, thus adding an Eulerian element to the Lagrangian random path model. In this combined Lagrangian/Eulerian deposition model, the initial size distribution is continuously modified by coagulation, hygroscopic growth and deposition. For the specific inhalation conditions and the cigarette smoke size distribution assumed in this study, thermal diffusion is by far the greatest source of coagulation, with a minor contribution of laminar shear in peripheral airway generations.Number deposition, which comprises the loss of inhaled particles not only by deposition but also by coagulation, and mass deposition fractions were computed for different puff and breath-hold scenarios as a function of lung generation numbers. The main reduction of the number of inhaled particles in the respiratory tract occurs in the mouth due to coagulation, accompanied by a significant shift of the size distribution to larger particle diameters. In the lung, particle loss is caused primarily by deposition due to diffusion with a preferential deposition of smaller particle diameters. In the size range from about 250 to 500nm, the number concentration of particles in the exhaled air is higher than that in the inhaled air, indicating that the production of particles in this size range by coagulation is greater than the loss by coagulation to larger sizes and deposition.

Adaptive time stepping algorithm for Lagrangian transport models: Theory and idealised test cases

Random walk simulations have an excellent potential in marine and oceanic modelling. This is essentially due to their relative simplicity and their ability to represent advective transport without being plagued by the deficiencies of the Eulerian methods. The physical and mathematical foundations of random walk modelling of turbulent diffusion have become solid over the years. Random walk models rest on the theory of stochastic differential equations. Unfortunately, the latter and the related numerical aspects have not attracted much attention in the oceanic modelling community. The main goal of this paper is to help bridge the gap by developing an efficient adaptive time stepping algorithm for random walk models. Its performance is examined on two idealised test cases of turbulent dispersion; (i) pycnocline crossing and (ii) non-flat isopycnal diffusion, which are inspired by shallow-sea dynamics and large-scale ocean transport processes, respectively. The numerical results of the adaptive time stepping algorithm are compared with the fixed-time increment Milstein scheme, showing that the adaptive time stepping algorithm for Lagrangian random walk models is more efficient than its fixed step-size counterpart without any loss in accuracy.

A Lagrangian particle random walk model for simulating a deep-sea hydrothermal plume with both buoyant and non-buoyant features

This paper presents a computational model of simulating a deep-sea hydrothermal plume based on a Lagrangian particle random walk algorithm. This model achieves the efficient process to calculate a numerical plume developed in a fluid-advected environment with the characteristics such as significant filament intermittency and significant plume meander due to flow variation with both time and location. Especially, this model addresses both non-buoyant and buoyant features of a deep-sea hydrothermal plume in three dimensions, which significantly challenge a strategy for tracing the deep-sea hydrothermal plume and localizing its source. This paper also systematically discusses stochastic initial and boundary conditions that are critical to generate a proper numerical plume. The developed model is a powerful tool to evaluate and optimize strategies for the tracking of a deep-sea hydrothermal plume via an autonomous underwater vehicle (AUV).

해운대 해수욕장의 이안류 발생기구 및 수치모의

At Haeundae Beach in Busan, people were swept away by the fast-moving rip current and rescued, on August 13th and 15th, 2009 & July 29th and 30th, 2010. In predicting the wave-induced current and consequent tube movement for public safety, the coastal flows and waves are calculated at each time step and grid point by means of systematic interfacing of hydrodynamic and wave models (Lee, 2001). To provide a user-friendly simulation tool for end-users, the forecasting system has been built in a software package called HAECUM. Outputs from the system are viewed as graphs of tube positions with combined current vectors for easy decision of emergency management officials. The tube-wave interaction is taken into account and the traces of swim tube are simulated by using a Lagrangian random walk (Chorin, 1978; Lee, 1994). In this study, we use the Lee`s approach (Lee, 1993) in estimating the surface onshore currents due to wave breaking.

3-d numerical simulation of particle concentration effect on a single-wire ESP performance for collecting poly-dispersed particles

In this paper a simple one stage wire-plate electrostatic precipitator is analyzed to predict particle transport and charging, and airflow patterns under the influence of EHD and external flows, assuming various particle concentrations. The investigated numerical model includes the governing equations describing the motion of ions, gas, solid particles and the effect of particle space charge. The complicated mutual interaction mechanisms between the three coexisting fields of gas flow, particle trajectories and electrostatic field, which affect an industrial ESP process, have been implemented using the User Defined Functions (UDFs) in commercial FLUENT 6.2 software. The electrostatic field and ionic space charge density due to corona discharge were computed by numerical solution of Poisson and current continuity equations using a hybrid Finite Element - Flux Corrected Transport method. The model takes into account the particle space charge density effect on the ionic charge density distribution. The airflow equations were solved inside FLUENT using the Finite Volume Method and the turbulence effect was included by using the k-e model. The Lagrangian random walk approach was used to determine particle motion, as affected by EHD flows and turbulence effects. This part was performed with the aid of Discrete Phase Model (DPM) in FLUENT. The performance of the discussed ESP in the removal of particulates and the effect of different particle concentration on the gas flow pattern and corona discharge current was evaluated numerically assuming poly-dispersed particles with lognormal particle size distribution.

Phytoplankton motility and the competition for nutrients in the thermocline

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 347:21-38 (2007) - DOI: https://doi.org/10.3354/meps06999 Phytoplankton motility and the competition for nutrients in the thermocline Oliver N. Ross1,*, Jonathan Sharples2 1Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK 2Proudman Oceanographic Laboratory, Joseph Proudman Building, 6 Brownlow Street, University of Liverpool, Liverpool L3 5DA, UK *Email: onross@essex.ac.uk ABSTRACT: Diatoms and dinoflagellates are 2 important groups of phytoplankton that co-exist in the competition for light and nutrients. Following the diatom-dominated spring bloom, the shelf sea subsurface chlorophyll maximum (SCM) is often dominated by motile species of phytoplankton, in particular dinoflagellates and sometimes coccolithophores. Turbulence in shelf seas, driven by surface winds and by tidal currents, is likely to easily counteract the typically weak swimming capabilities of phytoplankton. The thermocline marks a low turbulence region, separating the nutrient-depleted surface (wind-mixed) layer and the nutrient-replete bottom (tidally-mixed) layer, and so would seem to be an ideal environment for employing a strategy of vertical migration. However, the positioning within the thermocline is crucial, as turbulence in the adjoining boundary layers removes cells that stray too close to the edges of the thermocline and mixes them into resource-limited layers of the water column. We combined a Lagrangian random walk model, a k-ε turbulence scheme and a simple photosynthesis model to track individual phytoplankton cells in a tidally-mixed, stratified water column (e.g. a summer, temperate shelf sea). By allowing motile and non-motile species to compete, we found that an ability to use motility to balance resource requirements can offset modest physiological disadvantages compared to the non-motile phytoplankton, leading to either co-existence or even dominance of the motile species. However, more severe physiological disadvantages (e.g. combinations of growth rate, nutrient uptake capabilities, and/or respiration) cannot be compensated for by motility alone, and further adaptations (such as mixotrophy) would be required. We also show that the SCM can be a place for significant new production (values of 1 g C m–2 d–1 and f-ratios of over 0.5 are possible), which stresses its potential importance as a source of food to the pelagic throughout summer. KEY WORDS: Phytoplankton species competition · Motility · Tidal mixing · Shelf sea thermocline · Carbon export · Nitrogen flux · f-ratio · Turbulence modelling · Lagrangian modelling Full text in pdf format PreviousNextCite this article as: Ross ON, Sharples J (2007) Phytoplankton motility and the competition for nutrients in the thermocline. Mar Ecol Prog Ser 347:21-38. https://doi.org/10.3354/meps06999 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 347. Online publication date: October 11, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Swimming for survival: A role of phytoplankton motility in a stratified turbulent environment

We investigate a role for vertical migration in stratified coastal water, where the swimming speed is generally significantly less than the typical turbulent fluctuations in a tidally-mixed bottom layer. In our modelling approach we use a k- ɛ turbulence model to describe the physical forcing, a Lagrangian random walk model to describe the vertical displacement of individual cells in response to turbulence and due to cell motility, and a phytoplankton growth model to direct the swimming behaviour of the phytoplankton according to their light and nutrient requirements. The model results show how the cells form a stable subsurface chlorophyll maximum (SCM) at the base of the thermocline where episodic tidal turbulence causes erosion of part of the SCM biomass into the bottom mixed layer (BML). We then focus on the question of whether an ability to swim (weakly, compared to typical bottom layer turbulent intensities) provides any advantage by allowing return to the SCM. Our results show that tidal turbulence in the BML helps both motile and neutrally-buoyant cells by periodically pushing them into the base of the thermocline. Motile cells then have the advantage that they can swim further into the thermocline towards higher light which also reduces the likelihood of being re-mixed back into the BML.

Reactive hydrocarbon flux footprints during canopy senescence

A coupled Lagrangian random walk and atmospheric turbulence model was employed to investigate the magnitude of isoprene source distribution within a mixed deciduous forest canopy undergoing defoliation. Modeled source distributions were studied to understand how the flux footprint evolved as the total amount and vertical distribution of foliage changed during the leaf senescing and abscission period. The modeled ensemble air parcel residence times inside the forest canopy were also studied to quantify the fraction of isoprene destroyed inside forest canopies due to rapid chemical reactions. Defoliation in the canopy affected the footprint by vertically redistributing the flux sources, and by reducing the leaf drag area encountered by flows within the canopy. For air parcel releases in the upper canopy, the increased in-canopy turbulence associated with defoliation shifted the footprint peak probability closer to the measurement point. However, when integrated through the depth of the canopy, the net effect of defoliation was to increase the upwind source areas farther from the flux measurement point. Defoliation also impacted air parcel residence times within the canopy. Under fully foliated conditions, air parcels remained within the canopy for periods ranging from 2 to 50 min, depending on levels of atmospheric turbulence and air parcel release height. Under 25–75% defoliated conditions, air parcels remained in the forest canopy for periods lasting less than 10 min. The estimated air parcel residence times inside the fully leafed canopy resulted in significant isoprene chemical processing. Based on Lagrangian footprint simulations with active chemistry, the integrated rates of isoprene destruction from reactions with ozone, hydroxyl, and nitrate radicals ranged from 12% for air parcels released in the upper canopy to 40% for air parcels released from the lower canopy. We conclude that active scalar flux estimates, often based only on the footprint transfer function and source strength distribution, can be substantially improved by incorporating an active chemistry term.

Modelling Fluxes and Concentrations of CO 2 , H 2 O and Sensible Heat Within and Above a Mountain Meadow Canopy: A Comparison of Three Lagrangian Models and Three Parameterisation Options for the Lagrangian Time Scale

Two simple analytical Lagrangian and a Lagrangian random walk model,together with three options for the parameterisation of the Lagrangian timescale, are compared in their ability to predict fluxes and scalar concentrationsof CO2, H2O and sensible heat within and above a mountain meadowin the eastern Alps. Results indicate that both scalar concentrations and ecosystemfluxes exhibit little sensitivity to the differences between the investigated modelsand may be predicted satisfactorily by one of the simpler models so long as thesource/sink strength is parameterised correctly. Model results also show littlesensitivity to the parameterisation of the vertical variation of the Lagrangiantime scale, yet the increase of the Lagrangian time scale towards the groundpredicted by one of the three investigated parameterisation options resulted inless agreement with measurements as compared to the other two, which assumedthe Lagrangian time scale to be either constant with height or to decay towardszero at the ground surface. Correspondence between simulated and measuredfluxes and scalar concentrations of CO2, H2O and sensible heat weregenerally satisfactory, except for shortly after the meadow was cut, when thesignificant increase of respiratory carbon losses could not be captured by themodel.