Micro-objets déformables biomimétiques sous écoulement
Dynamique des fluides et transfert en microgravité
Axe de recherche :
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Micro-objets déformables sous forçage hydrodynamique (voir les détails sur la page dédiée)
Publications scientifiques au M2P2
2024
Julian Wailliez, Paul Regazzi, Anniina Salonen, Paul G Chen, Marc Jaeger, et al.. Drop deformation in a planar elongational flow: impact of surfactant dynamics. Soft Matter, 2024, 20 (44), pp.8793-8803. ⟨10.1039/D4SM00642A⟩. ⟨hal-04740537v2⟩ Plus de détails...
Drops in extensional flow undergo a deformation, which is primarily fixed by a balance between their surface tension and the viscous stress. This deformation, predicted and measured by Taylor on millimetric drops, is expected to be affected by the presence of surfactants but has never been measured systematically. We provide a controlled experiment allowing to measure this deformation as a function of the drop size and of the shear stress for different surfactants at varying concentrations. Our observation is that the deformation predicted by Taylor is recovered at zero and high surfactant concentration, whereas it is smaller at concentrations close to the critical micellar concentration. This is in contradiction with the existing analytical models. We develop a new analytical model, taking into account the surfactant dynamics. The model predicts a transition between a deformation similar to the one of a pure liquid and a smaller one. We show that the transition is driven by a parameter K_L , which compares adsorption and desorption dynamics. Finally, the concentration C* , at which we observe this transition in the extensional flow is in good agreement with the one predicted by independent measurement of K_L .
Julian Wailliez, Paul Regazzi, Anniina Salonen, Paul G Chen, Marc Jaeger, et al.. Drop deformation in a planar elongational flow: impact of surfactant dynamics. Soft Matter, 2024, 20 (44), pp.8793-8803. ⟨10.1039/D4SM00642A⟩. ⟨hal-04740537v2⟩
V Puthumana, Paul G. Chen, M Leonetti, R Lasserre, M Jaeger. Assessment of coupled bilayer-cytoskeleton modelling strategy for red blood cell dynamics in flow. Journal of Fluid Mechanics, 2024, 979, pp.A44. ⟨10.1017/jfm.2023.1092⟩. ⟨hal-04409136⟩ Plus de détails...
The red blood cell (RBC) membrane is composed of a lipid bilayer and a cytoskeleton interconnected by protein junction complexes, allowing for potential sliding between the lipid bilayer and the cytoskeleton. Despite this biological reality, it is most often modelled as a single-layer model, a hyperelastic capsule or a fluid vesicle. Another approach involves incorporating the membrane's composite structure using double layers, where one layer represents the lipid bilayer and the other represents the cytoskeleton. In this paper, we computationally assess the various modelling strategies by analysing RBC behaviour in extensional flow and four distinct regimes that simulate RBC dynamics in shear flow. The proposed double-layer strategies, such as the vesicle--capsule and capsule--capsule models, account for the fluidity and surface incompressibility of the lipid bilayer in different ways. Our findings demonstrate that introducing sliding between the layers offers the cytoskeleton a considerable degree of freedom to alleviate its elastic stresses, resulting in a significant increase in RBC elongation. Surprisingly, our study reveals that the membrane modelling strategy for RBCs holds greater importance than the choice of the cytoskeleton's reference shape. These results highlight the inadequacy of considering mechanical properties alone and emphasise the need for careful integration of these properties. Furthermore, our findings fortuitously uncover a novel indicator for determining the appropriate stress-free shape of the cytoskeleton.
V Puthumana, Paul G. Chen, M Leonetti, R Lasserre, M Jaeger. Assessment of coupled bilayer-cytoskeleton modelling strategy for red blood cell dynamics in flow. Journal of Fluid Mechanics, 2024, 979, pp.A44. ⟨10.1017/jfm.2023.1092⟩. ⟨hal-04409136⟩
Jinming Lyu, Paul G. Chen, Alexander Farutin, Marc Jaeger, Chaouqi Misbah, et al.. Swirling of vesicles: Shapes and dynamics in Poiseuille flow as a model of RBC microcirculation. Physical Review Fluids, 2023, 8 (2), pp.L021602. ⟨10.1103/PhysRevFluids.8.L021602⟩. ⟨hal-03979358v2⟩ Plus de détails...
We report on a systematic numerical exploration of the vesicle dynamics in a channel, which is a model of red blood cells in microcirculation. We find a spontaneous transition, called swirling, from straight motion with axisymmetric shape to a motion along a helix with a stationary deformed shape that rolls on itself and spins around the flow direction. We also report on a planar oscillatory motion of the mass center, called three-dimensional snaking for which the shape deforms periodically. Both emerge from supercritical pitchfork bifurcation with the same threshold. The universality of these oscillatory dynamics emerges from Hopf bifurcations with two order parameters. These two oscillatory dynamics are put in the context of vesicle shape and dynamics in the parameter space of reduced volume v, capillary number, and confinement. Phase diagrams are established for v = 0.95, v = 0.9, and v = 0.85 showing that oscillatory dynamics appears if the vesicle is sufficiently deflated. Stationary shapes (parachute/bullet/peanut, croissant, and slipper) are fixed points, while swirling and snaking are characterized by two limit cycles.
Jinming Lyu, Paul G. Chen, Alexander Farutin, Marc Jaeger, Chaouqi Misbah, et al.. Swirling of vesicles: Shapes and dynamics in Poiseuille flow as a model of RBC microcirculation. Physical Review Fluids, 2023, 8 (2), pp.L021602. ⟨10.1103/PhysRevFluids.8.L021602⟩. ⟨hal-03979358v2⟩
Sudip Das, Marc Jaeger, Marc Leonetti, Rochish M. Thaokar, Paul G. Chen. Effect of pulse width on the dynamics of a deflated vesicle in unipolar and bipolar pulsed electric fields. Physics of Fluids, 2021, 33 (8), pp.081905. ⟨10.1063/5.0057168⟩. ⟨hal-03317441⟩ Plus de détails...
Giant unilamellar vesicles subjected to pulsed direct-current (pulsed-DC) fields are promising biomimetic systems to investigate the electroporation of cells. In strong electric fields, vesicles undergo significant deformation, which strongly alters the transmembrane potential, consequently the electroporation. Previous theoretical studies investigated the electrodeformation of vesicles in DC fields (which are not pulsed). In this work, we computationally investigate the deformation of a deflated vesicle under unipolar, bipolar, and two-step unipolar pulses and show sensitive dependence of intermediate shapes on type of pulse and the pulse width. Starting with the stress-free initial shape of a deflated vesicle, which is similar to a prolate spheroid, the analysis is presented for the cases with higher and lower conductivities of the inner fluid medium relative to the outer fluid medium. For the ratio of inner to outer fluid conductivity, σ r = 10, the shape always remains prolate, including when the field is turned off. For σ r = 0.1, several complex dynamics are observed, such as the prolate-to-oblate (PO), prolate-to-oblate-to-prolate (POP) shape transitions in time depending upon the strength of the field and the pulse properties. In this case, on turning off the field, a metastable oblate equilibrium shape is seen, that seems to be a characteristics of a deflated vesicle leading to POPO transitions. When a two-step unipolar pulse (a combination of a strong and a weak subpulse) is applied, a vesicle can reach an oblate or a prolate final shape depending upon the relative durations of the two subpulses. This study suggests that the transmembrane potential can be regulated using a bipolar pulsed-DC field. It also shows that the shapes admitted in the dynamics of a vesicle depends upon whether the pulse is unipolar or bipolar. Parameters are suggested wherein, the simulation results can be demonstrated in experiments.
Sudip Das, Marc Jaeger, Marc Leonetti, Rochish M. Thaokar, Paul G. Chen. Effect of pulse width on the dynamics of a deflated vesicle in unipolar and bipolar pulsed electric fields. Physics of Fluids, 2021, 33 (8), pp.081905. ⟨10.1063/5.0057168⟩. ⟨hal-03317441⟩
J. M. Lyu, Paul G. Chen, G. Boedec, M. Leonetti, M. Jaeger, et al.. An isogeometric boundary element method for soft particles flowing in microfluidic channels. Computers and Fluids, Elsevier, 2021, 214, pp.104786. ⟨10.1016/j.compfluid.2020.104786⟩. ⟨hal-03082862⟩ Plus de détails...
Understanding the flow of deformable particles such as liquid drops, synthetic capsules and vesicles, and biological cells confined in a small channel is essential to a wide range of potential chemical and biomedical engineering applications. Computer simulations of this kind of fluid-structure (membrane) interaction in low-Reynolds-number flows raise significant challenges faced by an intricate interplay between flow stresses, complex particles' interfacial mechanical properties, and fluidic confinement. Here, we present an isogeometric computational framework by combining the finite-element method (FEM) and boundary-element method (BEM) for an accurate prediction of the deformation and motion of a single soft particle transported in microfluidic channels. The proposed numerical framework is constructed consistently with the isogeometric analysis paradigm; Loop's subdivision elements are used not only for the representation of geometry but also for the membrane mechanics solver (FEM) and the interfacial fluid dynamics solver (BEM). We validate our approach by comparison of the simulation results with highly accurate benchmark solutions to two well-known examples available in the literature, namely a liquid drop with constant surface tension in a circular tube and a capsule with a very thin hyperelastic membrane in a square channel. We show that the numerical method exhibits second-order convergence in both time and space. To further demonstrate the accuracy and long-time numerically stable simulations of the algorithm, we perform hydrodynamic computations of a lipid vesicle with bending stiffness and a red blood cell with a composite membrane in capillaries. The present work offers some possibilities to study the deformation behavior of confining soft particles, especially the particles' shape transition and dynamics and their rheological signature in channel flows.
J. M. Lyu, Paul G. Chen, G. Boedec, M. Leonetti, M. Jaeger, et al.. An isogeometric boundary element method for soft particles flowing in microfluidic channels. Computers and Fluids, Elsevier, 2021, 214, pp.104786. ⟨10.1016/j.compfluid.2020.104786⟩. ⟨hal-03082862⟩
Jinming Lyu, Paul G. Chen, G. Boedec, M. Leonetti, Marc Jaeger. An isogeometric boundary element method for soft particles flowing in microfluidic channels. Computers and Fluids, 2021, 214, pp.104786. ⟨10.1016/j.compfluid.2020.104786⟩. ⟨hal-02476945v2⟩ Plus de détails...
Understanding the flow of deformable particles such as liquid drops, synthetic capsules and vesicles, and biological cells confined in a small channel is essential to a wide range of potential chemical and biomedical engineering applications. Computer simulations of this kind of fluid-structure (mem-brane) interaction in low-Reynolds-number flows raise significant challenges faced by an intricate interplay between flow stresses, complex particles' in-terfacial mechanical properties, and fluidic confinement. Here, we present an isogeometric computational framework by combining the finite-element method (FEM) and boundary-element method (BEM) for an accurate prediction of the deformation and motion of a single soft particle transported in microfluidic channels. The proposed numerical framework is constructed consistently with the isogeometric analysis paradigm; Loop's subdivision elements are used not only for the representation of geometry but also for the membrane mechanics solver (FEM) and the interfacial fluid dynamics solver (BEM). We validate our approach by comparison of the simulation results with highly accurate benchmark solutions to two well-known examples available in the literature, namely a liquid drop with constant surface tension in a circular tube and a capsule with a very thin hyperelastic membrane in a square channel. We show that the numerical method exhibits second-order convergence in both time and space. To further demonstrate the accuracy and long-time numerically stable simulations of the algorithm, we perform hydrodynamic computations of a lipid vesicle with bending stiffness and a red blood cell with a composite membrane in capillaries. The present work offers some possibilities to study the deformation behavior of confining soft particles, especially the particles' shape transition and dynamics and their rheological signature in channel flows.
Jinming Lyu, Paul G. Chen, G. Boedec, M. Leonetti, Marc Jaeger. An isogeometric boundary element method for soft particles flowing in microfluidic channels. Computers and Fluids, 2021, 214, pp.104786. ⟨10.1016/j.compfluid.2020.104786⟩. ⟨hal-02476945v2⟩
Paul G. Chen, J M Lyu, M Jaeger, M. Leonetti. Shape transition and hydrodynamics of vesicles in tube flow. Physical Review Fluids, 2020, 5 (4), pp.043602. ⟨10.1103/PhysRevFluids.5.043602⟩. ⟨hal-02415320v2⟩ Plus de détails...
The steady motion and deformation of a lipid-bilayer vesicle translating through a circular tube in low Reynolds number pressure-driven flow are investigated numerically using an axisymmetric boundary element method. This fluid-structure interaction problem is determined by three dimen-sionless parameters: reduced volume (a measure of the vesicle asphericity), geometric confinement (the ratio of the vesicle effective radius to the tube radius), and capillary number (the ratio of viscous to bending forces). The physical constraints of a vesicle--fixed surface area and enclosed volume when it is confined in a tube--determine critical confinement beyond which it cannot pass through without rupturing its membrane. The simulated results are presented in a wide range of reduced volumes [0.6, 0.98] for different degrees of confinement; the reduced volume of 0.6 mimics red blood cells. We draw a phase diagram of vesicle shapes and propose a shape transition line separating the parachutelike shape region from the bulletlike one in the reduced volume versus confinement phase space. We show that the shape transition marks a change in the behavior of vesicle mobility, especially for highly deflated vesicles. Most importantly, high-resolution simulations make it possible for us to examine the hydrodynamic interaction between the wall boundary and the vesicle surface at conditions of very high confinement, thus providing the limiting behavior of several quantities of interest, such as the thickness of lubrication film, vesicle mobility and its length, and the extra pressure drop due to the presence of the vesicle. This extra pressure drop holds implications for the rheology of dilute vesicle suspensions. Furthermore, we present various correlations and discuss a number of practical applications. The results of this work may serve as a benchmark for future studies and help devise tube-flow experiments.
Paul G. Chen, J M Lyu, M Jaeger, M. Leonetti. Shape transition and hydrodynamics of vesicles in tube flow. Physical Review Fluids, 2020, 5 (4), pp.043602. ⟨10.1103/PhysRevFluids.5.043602⟩. ⟨hal-02415320v2⟩
Wenjun Liu, Paul G. Chen, Jalil Ouazzani, Qiusheng Liu. Thermocapillary flow transition in an evaporating liquid layer in a heated cylindrical cell. International Journal of Heat and Mass Transfer, 2020, 153, pp.119587. ⟨10.1016/j.ijheatmasstransfer.2020.119587⟩. ⟨hal-02488876⟩ Plus de détails...
Motived by recent ground-based and microgravity experiments investigating the interfacial dynamics of a volatile liquid (FC-72, P r = 12.34) contained in a heated cylindrical cell, we numerically study the thermocapillary-driven flow in such an evaporating liquid layer. Particular attention is given to the prediction of the transition of the axisymmetric flow to fully three-dimensional patterns when the applied temperature increases. The numerical simulations rely on an improved one-sided model of evaporation by including heat and mass transfer through the gas phase via the heat transfer Biot number and the evaporative Biot number. We present the axisymmetric flow characteristics, show the variation of the transition points with these Biot numbers, and more importantly elucidate the twofold role of the latent heat of evaporation in the stability; evaporation not only destabilizes the flow but also stabilizes it, depending upon the place where the evaporation-induced thermal gradients come into play. We also show that buoyancy in the liquid layer has a stabilizing effect, though its effect is insignificant. At high Marangoni numbers, the numerical simulations revealed smaller-scale thermal patterns formed on the surface of a thinner evaporating layer, in qualitative agreement with experimental observations. The present work helps to gain a better understanding of the role of a phase change in the thermocapillary instability of an evaporating liquid layer.
Wenjun Liu, Paul G. Chen, Jalil Ouazzani, Qiusheng Liu. Thermocapillary flow transition in an evaporating liquid layer in a heated cylindrical cell. International Journal of Heat and Mass Transfer, 2020, 153, pp.119587. ⟨10.1016/j.ijheatmasstransfer.2020.119587⟩. ⟨hal-02488876⟩
Journal: International Journal of Heat and Mass Transfer
Xue Chen, Xun Wang, Paul G. Chen, Qiusheng Liu. Determination of Diffusion Coefficient in Droplet Evaporation Experiment Using Response Surface Method. Microgravity Science and Technology, 2018, 30, pp.675-682. ⟨10.1007/s12217-018-9645-2⟩. ⟨hal-02112826⟩ Plus de détails...
Evaporation of a liquid droplet resting on a heated substrate is a complex free-surface advection-diffusion problem, in which the main driving force of the evaporation is the vapor concentration gradient across the droplet surface. Given the uncertainty associated with the diffusion coefficient of the vapor in the atmosphere during space evaporation experiments due to the environmental conditions, a simple and accurate determination of its value is of paramount importance for a better understanding of the evaporation process. Here we present a novel approach combining numerical simulations and experimental results to address this issue. Specifically, we construct a continuous function of output using a Kriging-based response surface method, which allows to use the numerical results as a black-box with a limited number of inputs and outputs. Relevant values of the diffusion coefficient can then be determined by solving an inverse problem which is based on accessible experimental data and the proposed response surface. In addition, on the basis of our numerical simulation results, we revisit a widely used formula for the prediction of the evaporation rate in the literature and propose a refined expression for the droplets evaporating on a heated substrate.
Xue Chen, Xun Wang, Paul G. Chen, Qiusheng Liu. Determination of Diffusion Coefficient in Droplet Evaporation Experiment Using Response Surface Method. Microgravity Science and Technology, 2018, 30, pp.675-682. ⟨10.1007/s12217-018-9645-2⟩. ⟨hal-02112826⟩
Jinming Lyu, Paul G. Chen, Gwenn Boedec, Marc Leonetti, Marc Jaeger. Hybrid continuum–coarse-grained modeling of erythrocytes. Comptes Rendus Mécanique, 2018, 346, pp.439-448. ⟨10.1016/j.crme.2018.04.015⟩. ⟨hal-01785429⟩ Plus de détails...
The red blood cell (RBC) membrane is a composite structure, consisting of a phospholipid bilayer and an underlying membrane-associated cytoskeleton. Both continuum and particle-based coarse-grained RBC models make use of a set of vertices connected by edges to represent the RBC membrane, which can be seen as a triangular surface mesh for the former and a spring network for the latter. Here, we present a modeling approach combining an existing continuum vesicle model with a coarse-grained model for the cytoskeleton. Compared to other two-component approaches, our method relies on only one mesh, representing the cytoskeleton, whose velocity in the tangential direction of the membrane may be different from that of the lipid bilayer. The finitely extensible nonlinear elastic (FENE) spring force law in combination with a repulsive force defined as a power function (POW), called FENE-POW, is used to describe the elastic properties of the RBC membrane. The mechanical interaction between the lipid bilayer and the cytoskeleton is explicitly computed and incorporated into the vesicle model. Our model includes the fundamental mechanical properties of the RBC membrane, namely fluidity and bending rigidity of the lipid bilayer, and shear elasticity of the cytoskeleton while maintaining surface-area and volume conservation constraint. We present three simulation examples to demonstrate the effectiveness of this hybrid continuum--coarse-grained model for the study of RBCs in fluid flows.
Jinming Lyu, Paul G. Chen, Gwenn Boedec, Marc Leonetti, Marc Jaeger. Hybrid continuum–coarse-grained modeling of erythrocytes. Comptes Rendus Mécanique, 2018, 346, pp.439-448. ⟨10.1016/j.crme.2018.04.015⟩. ⟨hal-01785429⟩
Xue Chen, Xun Wang, Paul G. Chen, Qiusheng Liu. Thermal effects of substrate on Marangoni flow in droplet evaporation: Response surface and sensitivity analysis. International Journal of Heat and Mass Transfer, 2017, 113, pp.354 - 365. ⟨10.1016/j.ijheatmasstransfer.2017.05.076⟩. ⟨hal-01532757⟩ Plus de détails...
In this paper, the evaporation of sessile droplets resting on a substrate with different thermal properties is numerically investigated. Computations are based on a transient axisymmetric numerical model. Special attention is paid to evaluate thermal effects of substrate on the structure of bulk fluid flow in the course of evaporation. Numerical results reveal that Marangoni convection induced by non-uniform distribution of temperature along the interface exhibits three distinctly different behaviours: inward flow, multicellular flow and outward flow, consequently resulting in different particle depositions. It is highlighted that three factors (i.e. relative thermal conductivity, relative substrate thickness and relative substrate temperature) strongly affect the flow pattern. In order to further investigate the coupling effects of different influential factors, a Kriging-based response surface method is introduced. We model the flow behaviour as a function of continuous influential factors using a limited number of computations corresponding to discrete values of the inputs. The sensitivities of the Marangoni flow are also analysed using Sobol’ index to study the coupling mechanisms of influential factors. The proposed method can be used to forecast the flow patterns for any input parameter without additional sophisticated computer simulation, and allows to confidently estimate an unknown environmental parameter.
Xue Chen, Xun Wang, Paul G. Chen, Qiusheng Liu. Thermal effects of substrate on Marangoni flow in droplet evaporation: Response surface and sensitivity analysis. International Journal of Heat and Mass Transfer, 2017, 113, pp.354 - 365. ⟨10.1016/j.ijheatmasstransfer.2017.05.076⟩. ⟨hal-01532757⟩
Journal: International Journal of Heat and Mass Transfer
Xue Chen, Paul G. Chen, Jalil Ouazzani, Qiusheng Liu. Numerical simulations of sessile droplet evaporating on heated substrate. The European Physical Journal. Special Topics, 2017, 226 (6), pp.1325-1335. ⟨10.1140/epjst/e2016-60203-y⟩. ⟨hal-01509843⟩ Plus de détails...
Motivated by the space project EFILE, a 2D axisymmetric numerical model in the framework of ALE method is developed to investigate the coupled physical mechanism during the evaporation of a pinned drop that partially wets on a heated substrate. The model accounts for mass transport in surrounding air, Marangoni convection inside the drop and heat conduction in the substrate as well as moving interface. Numerical results predict simple scaling laws for the evaporation rate which scales linearly with drop radius but follows a power-law with substrate temperature. It is highlighted that thermal effect of the substrate has a great impact on the temperature profile at the drop surface, which leads to a multicellular thermocapillary flow pattern. In particular, the structure of the multicellular flow behavior induced within a heated drop is mainly controlled by a geometric parameter (aspect ratio). A relationship between the number of thermal cells and the aspect ratio is proposed。
Xue Chen, Paul G. Chen, Jalil Ouazzani, Qiusheng Liu. Numerical simulations of sessile droplet evaporating on heated substrate. The European Physical Journal. Special Topics, 2017, 226 (6), pp.1325-1335. ⟨10.1140/epjst/e2016-60203-y⟩. ⟨hal-01509843⟩
Journal: The European Physical Journal. Special Topics
E Alekseenko, B Roux, D Fougere, Paul G. Chen. The effect of wind induced bottom shear stress and salinity on Zostera noltii replanting in a Mediterranean coastal lagoon. Estuarine, Coastal and Shelf Science, 2017, 187, pp.293-305. ⟨10.1016/j.ecss.2017.01.010⟩. ⟨hal-01453377⟩ Plus de détails...
The paper concerns the wind influence on bottom shear stress and salinity levels in a Mediterranean semi-enclosed coastal lagoon (Etang de Berre), with respect to a replanting program of Zostera noltii . The MARS3D numerical model is used to analyze the 3D current, salinity and temperature distribution induced by three meteorological, oceanic and anthropogenic forcings in this lagoon. The numerical model has been carefully validated by comparison with daily observations of the vertical salinity and temperature profiles at three mooring stations, for one year. Then, two modelling scenarios are considered. The first scenario (scen.## 1), starting with an homogeneous salinity of S = 20 PSU and without wind forcing, studies a stratification process under the influence of a periodic seawater inflow and a strong freshwater inflow from an hydropower plant (250 m3/s). Then, in the second scenario (scen.## 2), we study how a strong wind of 80 km/h can mix the haline stratification obtained at the end of scen.## 1. The most interesting results concern four nearshore replanting areas; two are situated on the eastern side of EB and two on the western side. The results of scen.## 2 show that all these areas are subject to a downwind coastal jet. Concerning bottom salinity, the destratification process is very beneficial; it always remains greater than 12 PSU for a N-NW wind of 80 km/h and an hydropower runoff of 250 m3/s. Special attention is devoted to the bottom shear stress (BSS) for different values of the bottom roughness parameter (for gravels, sands and silts), and to the bottom salinity. Concerning BSS, it presents a maximum near the shoreline and decreases along transects perpendicular to the shoreline. There exists a zone, parallel to the shoreline, where BSS presents a minimum (close to zero). When comparing the BSS value at the four replanting areas with the critical value, BSScr, at which the sediment mobility would occur, we see that for the smaller roughness values (ranging from z0 = 3.5 × 10-4 mm, to 3.5 × 10-2 mm) BSS largely surpasses this critical value. For a N-NW wind speed of 40 km/h (which is blowing for around 100 days per year), BSS still largely surpasses BSScr - at least for the silt sediments (ranging from z0 = 3.5 × 10-4 mm, to 3.5 × 10-3 mm). This confirms the possibility that the coastal jet could generate sediment mobility which could have a negative impact for SAV replanting.
E Alekseenko, B Roux, D Fougere, Paul G. Chen. The effect of wind induced bottom shear stress and salinity on Zostera noltii replanting in a Mediterranean coastal lagoon. Estuarine, Coastal and Shelf Science, 2017, 187, pp.293-305. ⟨10.1016/j.ecss.2017.01.010⟩. ⟨hal-01453377⟩
Achim Guckenberger, Marcel P. Schrame, Paul G. Chen, Marc Leonetti, Stephan Gekle. On the bending algorithms for soft objects in flows. Computer Physics Communications, 2016, 207, pp.1-23. ⟨10.1016/j.cpc.2016.04.018⟩. ⟨hal-01314722⟩ Plus de détails...
One of the most challenging aspects in the accurate simulation of three-dimensional soft objects such as vesicles or biological cells is the computation of membrane bending forces. The origin of this difficulty stems from the need to numerically evaluate a fourth order derivative on the discretized surface geometry. Here we investigate six different algorithms to compute membrane bending forces, including regularly used methods as well as novel ones. All are based on the same physical model (due to Canham and Helfrich) and start from a surface discretization with flat triangles. At the same time, they differ substantially in their numerical approach. We start by comparing the numerically obtained mean curvature, the Laplace-Beltrami operator of the mean curvature and finally the surface force density to analytical results for the discocyte resting shape of a red blood cell. We find that none of the considered algorithms converges to zero error at all nodes and that for some algorithms the error even diverges. There is furthermore a pronounced influence of the mesh structure: Discretizations with more irregular triangles and node connectivity present serious difficulties for most investigated methods. To assess the behavior of the algorithms in a realistic physical application, we investigate the deformation of an initially spherical capsule in a linear shear flow at small Reynolds numbers. To exclude any influence of the flow solver, two conceptually very different solvers are employed: the Lattice-Boltzmann and the Boundary Integral Method. Despite the largely different quality of the bending algorithms when applied to the static red blood cell, we find that in the actual flow situation most algorithms give consistent results for both hydrodynamic solvers. Even so, a short review of earlier works reveals a wide scattering of reported results for, e.g., the Taylor deformation parameter. Besides the presented application to biofluidic systems, the investigated algorithms are also of high relevance to the computer graphics and numerical mathematics communities.
Achim Guckenberger, Marcel P. Schrame, Paul G. Chen, Marc Leonetti, Stephan Gekle. On the bending algorithms for soft objects in flows. Computer Physics Communications, 2016, 207, pp.1-23. ⟨10.1016/j.cpc.2016.04.018⟩. ⟨hal-01314722⟩
Jian-Kang Zhang, Bo Xun, Paul G. Chen. A Continuation Method Applied to the Study of Thermocapillary Instabilities in Liquid Bridges. Microgravity Science & Technology, 2009, 21 (Suppl 1), pp.111-117. ⟨10.1007/s12217-009-9111-2⟩. ⟨hal-01307220⟩ Plus de détails...
A continuation method is applied to investigate the linear stability of the steady, axisymmetric thermocapillary flows in liquid bridges. The method is based upon an appropriate extended system of perturbation equations depending on the nature of transition of the basic flow. The dependence of the critical Reynolds number and corresponding azimuthal wavenumber on serval parameters is presented for both cylindrical and non-cylindrical liquid bridges.
Jian-Kang Zhang, Bo Xun, Paul G. Chen. A Continuation Method Applied to the Study of Thermocapillary Instabilities in Liquid Bridges. Microgravity Science & Technology, 2009, 21 (Suppl 1), pp.111-117. ⟨10.1007/s12217-009-9111-2⟩. ⟨hal-01307220⟩
Bo Xun, Kai Li, Paul G. Chen, Wen-Rui Hu. Effect of interfacial heat transfer on the onset of oscillatory convection in liquid bridge. International Journal of Heat and Mass Transfer, 2009, 52 (19-20), pp.4211-4220. ⟨10.1016/j.ijheatmasstransfer.2009.04.008⟩. ⟨hal-01307193⟩ Plus de détails...
In present study, effect of interfacial heat transfer with ambient gas on the onset of oscillatory convection in a liquid bridge of large Prandtl number on the ground is systematically investigated by the method of linear stability analyses. With both the constant and linear ambient air temperature distributions, the numerical results show that the interfacial heat transfer modifies the free-surface temperature distribution directly and then induces a steeper temperature gradient on the middle part of the free surface, which may destabilize the convection. On the other hand, the interfacial heat transfer restrains the temperature disturbances on the free surface, which may stabilize the convection. The two coupling effects result in a complex dependence of the stability property on the Biot number. Effects of melt free-surface deformation on the critical conditions of the oscillatory convection were also investigated. Moreover, to better understand the mechanism of the instabilities, rates of kinetic energy change and ''thermal " energy change of the critical disturbances were investigated
Bo Xun, Kai Li, Paul G. Chen, Wen-Rui Hu. Effect of interfacial heat transfer on the onset of oscillatory convection in liquid bridge. International Journal of Heat and Mass Transfer, 2009, 52 (19-20), pp.4211-4220. ⟨10.1016/j.ijheatmasstransfer.2009.04.008⟩. ⟨hal-01307193⟩
Journal: International Journal of Heat and Mass Transfer
B Xun, Paul G. Chen, K Li, Z Yin, W.R. Hu. A linear stability analysis of large-Prandtl-number thermocapillary liquid bridges. Advances in Space Research, 2008, 41 (12), pp.2094-2100. ⟨10.1016/j.asr.2007.07.016⟩. ⟨hal-01307161⟩ Plus de détails...
A linear stability analysis is applied to determine the onset of oscillatory thermocapillary convection in cylindrical liquid bridges of large Prandtl numbers (4 ⩽ Pr ⩽ 50). We focus on the relationships between the critical Reynolds number Re c , the azimuthal wave number m, the aspect ratio C and the Prandtl number Pr. A detailed Re c–Pr stability diagram is given for liquid bridges with various C. In the region of Pr > 1, which has been less studied previously and where Re c has been usually believed to decrease with the increase of Pr, we found Re c exhibits an early increase for liquid bridges with C around one. From the computed surface temperature gradient, it is concluded that the boundary layers developed at both solid ends of liquid bridges strengthen the stability of basic axisymmetric thermocap-illary convection at large Prandtl number, and that the stability property of the basic flow is determined by the ''effective'' part of liquid bridge.
B Xun, Paul G. Chen, K Li, Z Yin, W.R. Hu. A linear stability analysis of large-Prandtl-number thermocapillary liquid bridges. Advances in Space Research, 2008, 41 (12), pp.2094-2100. ⟨10.1016/j.asr.2007.07.016⟩. ⟨hal-01307161⟩
D.V. Lyubimov, T. P. Lyubimova, R.V. Skuridin, G. Chen, B. Roux. Numerical investigation of meniscus deformation and flow in an isothermal liquid bridge subject to high-frequency vibrations under zero gravity conditions. Computers and Fluids, 2002, 31, pp.663-682. ⟨10.1016/S0045-7930(01)00078-0⟩. ⟨hal-01307320⟩ Plus de détails...
This paper deals with meniscus deformation and flow in an isothermal liquid bridge maintained between two circular rods, when one rod is subject to axial monochromatic vibrations. It concerns a fundamental aspect of the problem of crystal growth from melt by the floating-zone technique which is often considered in weightlessness conditions. In the absence of vibrations the bridge is cylindrical; but due to vibration the mean shape of the meniscus is no more cylindrical and the meniscus oscillates around this mean shape. Two models are developed. First, we take into account the pulsating deformations of the meniscus (free surface), but we assume that the mean shape of meniscus remains cylindrical (i.e., we neglect the influence of vibration on this mean shape). For this simple case, a solution of the problem for the pulsating meniscus deformations and the pulsating velocity field is found in explicit form. For the mean flow, the problem is solved numerically by a finite-difference method. The calculations demonstrate the contribution of two basic mechanisms of mean flow generation due to vibrations, related to the generation of mean vorticity in the viscous boundary layer near the rigid boundaries and surface-wave propagation at a free surface. The intensity of the mean flow induced by surface waves is found to be sharply increasing when the vibration frequency approaches the resonance values that are determined from the explicit form of the solution of pulsation problem. In the second model, we take into account both pulsating and mean deformations of the meniscus. The governing equations for the potential of pulsating velocity and mean velocity, and for the pressure, are solved by using a finite-difference method and a boundary-fitted curvilinear coordinate system fitting the free surface.
D.V. Lyubimov, T. P. Lyubimova, R.V. Skuridin, G. Chen, B. Roux. Numerical investigation of meniscus deformation and flow in an isothermal liquid bridge subject to high-frequency vibrations under zero gravity conditions. Computers and Fluids, 2002, 31, pp.663-682. ⟨10.1016/S0045-7930(01)00078-0⟩. ⟨hal-01307320⟩
Eric Serre, Sandrine Hugues, Emilia Crespo del Arco, Anthony Randriamampianina, Patrick Bontoux. Axisymmetric and three-dimensional instabilities in an Ekman boundary layer flow. International Journal of Heat and Fluid Flow, 2001, 22 (1), pp.82-93. ⟨hal-01023080⟩ Plus de détails...
Eric Serre, Sandrine Hugues, Emilia Crespo del Arco, Anthony Randriamampianina, Patrick Bontoux. Axisymmetric and three-dimensional instabilities in an Ekman boundary layer flow. International Journal of Heat and Fluid Flow, 2001, 22 (1), pp.82-93. ⟨hal-01023080⟩
Journal: International Journal of Heat and Fluid Flow
Gang Chen, Stephan E. Belcher. Effects of Long Waves on Wind-Generated Waves. Journal of Physical Oceanography, 2000, 30 (9), pp.2246-2256. ⟨10.1175/1520-0485(2000)0302.0.CO;2⟩. ⟨hal-01307127⟩ Plus de détails...
A model is developed to explain the observation made in several laboratory experiments that short wind-generated waves are suppressed by a train of long, mechanically generated waves. A sheltering mechanism is responsible for generation of the short wind waves, by which wave growth is proportional to the local turbulent wind stress. Hence, if the turbulent wind stress near the surface is reduced by the long wave, then the short wind wave amplitude, and hence also the energy in the short waves at a given fetch, is lower than in the absence of long wave. A quantitative model of this process is formulated to examine the ratios of the growth rate and the total energy density of wind waves with and without a long wave, which is shown to agree reasonably well with the laboratory experiments. The model also explains why this suppression of wind waves by a very long swell is not observed in the ocean where the effects of swell on wind waves are extremely difficult to detect. In the model, the reduction in the turbulent wind stress by the long wave is largest for small values of C L /u * (where C L is the phase speed of the long wave and u * is the friction velocity of the wind). When this ratio is larger than about 25 (typical of ocean swell), both the reduction of the turbulent wind stress by the long wave and, consequently, the reduction in the total energy density of the wind waves are very small, which explains why this phenomenon has not yet been observed on the ocean.
Gang Chen, Stephan E. Belcher. Effects of Long Waves on Wind-Generated Waves. Journal of Physical Oceanography, 2000, 30 (9), pp.2246-2256. ⟨10.1175/1520-0485(2000)0302.0.CO;2⟩. ⟨hal-01307127⟩
Gang Chen, Christian Kharif, Stéphane Zaleski, Jie Li. Two-dimensional Navier–Stokes simulation of breaking waves. Physics of Fluids, 1999, 11 (1), pp.121-133. ⟨10.1063/1.869907⟩. ⟨hal-01307123⟩ Plus de détails...
Numerical simulations describing plunging breakers including the splash-up phenomenon are presented. The motion is governed by the classical, incompressible, two-dimensional Navier–Stokes equation. The numerical modeling of this two-phase flow is based on a piecewise linear version of the volume of fluid method. Capillary effects are taken into account such as a nonisotropic stress tensor concentrated near the interface. Results concerning the time evolution of liquid–gas interface and velocity field are given for short waves, showing how an initial steep wave undergoes breaking and successive splash-up cycles. Breaking processes including overturning, splash-up and gas entrainment, and breaking induced vortex-like motion beneath the surface and energy dissipation, are presented and discussed. It is found that strong vorticities are generated during the breaking process, and that more than 80% of the total pre-breaking wave energy is dissipated within three wave periods. The numerical results are compared with some laboratory measurements, and a favorable agreement is found.
Gang Chen, Christian Kharif, Stéphane Zaleski, Jie Li. Two-dimensional Navier–Stokes simulation of breaking waves. Physics of Fluids, 1999, 11 (1), pp.121-133. ⟨10.1063/1.869907⟩. ⟨hal-01307123⟩
