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Artykuły w czasopismach na temat "Parabolic Driving Forces"
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Beke, Dezső L., Z. Erdélyi i G. L. Katona. "Nonlinear Stress Effects in Diffusion". Defect and Diffusion Forum 264 (kwiecień 2007): 117–22. http://dx.doi.org/10.4028/www.scientific.net/ddf.264.117.
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According to classical Nernst-Einstein equation the diffusive flux is proportional to the driving force. However, this linear law is not valid if the driving force is very large. Attempts in the literature for the derivation of an “improved relation” till now were mostly restricted to the cases when the diffusion coefficient was independent of the composition. On the other hand, even if there are no externaldriving forces (other than related to the chemical driving force) present, deviations from the Fick I law are expected (transition from parabolic to linear growth-behaviour) on nanoscale for composition dependent diffusion coefficients. General description for the case when the driving forces and the diffusion asymmetry are large, is treated. The special case of large pressure gradients is discussed in detail and their effects on the deviation form the parabolic growth law on nanoscale will be analyzed. Effect of a pressure gradient on the crossover thickness between parabolic and linear regimes and on the interface transfer coefficient, K, is also treated.
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Wang, Dan, Yajun Yin, Jiye Wu, Xugui Wang i Zheng Zhong. "Interaction Potential between Parabolic Rotator and an Outside Particle". Journal of Nanomaterials 2014 (2014): 1–8. http://dx.doi.org/10.1155/2014/464925.
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At micro/nanoscale, the interaction potential between parabolic rotator and a particle located outside the rotator is studied on the basis of the negative exponential pair potential1/Rnbetween particles. Similar to two-dimensional curved surfaces, we confirm that the potential of the three-dimensional parabolic rotator and outside particle can also be expressed as a unified form of curvatures; that is, it can be written as the function of curvatures. Furthermore, we verify that the driving forces acting on the particle may be induced by the highly curved micro/nano-parabolic rotator. Curvatures and the gradient of curvatures are the essential elements forming the driving forces. Through the idealized numerical experiments, the accuracy of the curvature-based potential is preliminarily proved.
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Dobson, John F., Jun Wang i Hung M. Le. "Some Experimental Prospects involving Parabolic Quantum Wells". Australian Journal of Physics 53, nr 1 (2000): 119. http://dx.doi.org/10.1071/ph99048.
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We discuss two possible lines of experimental investigation based on parabolic quantum wells. In the first proposal, we note that the Generalised Kohn Theorem/Harmonic Potential Theorem forbids electron–electron damping of the Kohn mode in an electron layer gas under strictly parabolic confinement. This applies even for very strong driving. It is therefore interesting to attempt reduction of other sources of broadening in GaAlAs parabolic wells, so as to achieve a prominent narrow resonance in the far infrared. We concentrate here on phononic bandgap structures, which may be of interest for reduction of phonon effects in other systems as well. The second class of proposed experiment involves twinned parabolic wells in an attempt to observe van der Waals forces directly in GaAlAs systems. In a first approximation, the parabolic or Hooke's-law nature of the confinement allows one to use the well as a kind of spring balance to measure the weak van der Waals force. The influence of an applied magnetic field on these forces appears to be significant, and this system might provide the first measurement of such an effect.
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Kuzmina, Natalia, i Jae Hak Lee. "Driving Forces of Interleaving in the Baroclinic Front at the Equator". Journal of Physical Oceanography 35, nr 12 (1.12.2005): 2501–19. http://dx.doi.org/10.1175/jpo2828.1.
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Abstract The different types of instability in the equatorial β-plane approximation are analyzed by means of a 2D linear stability problem. The double-diffusive (DD) and diffusive/baroclinic (2D baroclinic and McIntyre) instabilities are shown not to develop if contours of the mean salinity/density have a parabolic, symmetrical-relative-to-the-equator shape. Using modeling results, an illustrative scheme of Equatorial Undercurrent (EUC) regions where different types of instability can develop is presented and subsequently applied to understand the driving forces of the intrusions observed in a closed spaced CTD section, located between the equator and 1°N. Long coherence intrusions are situated within two isopycnal layers, aligned to 25 (layer 1) and 26.3 (layer 2) σT, where the vertical shear is low. It was shown from the model that the layer-1 intrusions being observed in the midlayer of the EUC where the mean horizontal gradient of salinity is approximately constant are likely generated by a combined effect of DD instability and instability due to linear horizontal shear. The layer-2 intrusions being observed in the lower part of EUC where the mean salinity contours have a parabolic shape likely arise because of linear horizontal shear only, while double diffusion can be considered as an effect that increases the growth rate of unstable modes. Special attention is focused on two different parts of the EUC in the mixing of the thermocline. It is noted that the EUC only makes the mass transfer by long coherence intrusions in certain layers where the vertical shear is small. Conversely, the EUC contributes to the growth rate of unstable modes due to the horizontal linear shear.
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Beke, Dezső L., Z. Erdélyi i B. Parditka. "Effect of Diffusion Induced Driving Forces on Interdiffusion - Stress Development/Relaxation and Kinetics of Diffusion Processes". Defect and Diffusion Forum 309-310 (marzec 2011): 113–20. http://dx.doi.org/10.4028/www.scientific.net/ddf.309-310.113.
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General description of the interplay between the Kirkendall shift (as a special way of relaxation) and diffusion induced driving forces in diffusion intermixing of binary systems is given. It is shown that, if the Kirkendall shift is negligible, a steady state Nernts-Planck regime is established with diffusion coefficient close to the slower diffusivity, independently of the type of the diffusion induced field and also independently whether this is a single field or a combination of different fields (e.g. stress field and extra chemical potential of non-equilibrium vacancies). Deviations from parabolic kinetics are expected only before or after this steady state stage. Using the results of our previous paper, on development and relaxation of diffusion induced stresses, it is illustrated that the setting of time of the Nernst-Planck regime is very short: intermixing on the scale of few tenths of nanometer is enough to reach it. It is also illustrated that this stage is realized even in the case of asymmetric interdiffusion (in one side of the diffusion zone the diffusion is orders of magnitude higher than in the other), when the stress distribution has a more complex form (having a sharp peak at the interface). Surprisingly the steady state is longer than it would be expected from the relaxation time of Newtonian flow: This is so because the composition profile is not static but changes fast in the timescale of the stress relaxation, and thus the stress re-develops continuously.
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Liu, Jie, Yi Zhao, Yongfei Yang, Qingyan Mei, Shan Yang i Chenchen Wang. "Multicomponent Shale Oil Flow in Real Kerogen Structures via Molecular Dynamic Simulation". Energies 13, nr 15 (24.07.2020): 3815. http://dx.doi.org/10.3390/en13153815.
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As an unconventional energy source, the development of shale oil plays a positive role in global energy, while shale oil is widespread in organic nanopores. Kerogen is the main organic matter component in shale and affects the flow behaviour in nanoscale-confined spaces. In this work, a molecular dynamic simulation was conducted to study the transport behaviour of shale oil within kerogen nanoslits. The segment fitting method was used to characterise the velocity and flow rate. The heterogeneous density distributions of shale oil and its different components were assessed, and the effects of different driving forces and temperatures on its flow behaviours were examined. Due to the scattering effect of the kerogen wall on high-speed fluid, the heavy components (asphaltene) increased in bulk phase regions, and the light components, such as methane, were concentrated in boundary layers. As the driving force increased, the velocity profile demonstrated plug flow in the bulk regions and a half-parabolic distribution in the boundary layers. Increasing the driving force facilitated the desorption of asphaltene on kerogen walls, but increasing the temperature had a negative impact on the flow velocity.
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KUHLMANN, H. C., i U. SCHOISSWOHL. "Flow instabilities in thermocapillary-buoyant liquid pools". Journal of Fluid Mechanics 644 (10.02.2010): 509–35. http://dx.doi.org/10.1017/s0022112009992953.
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The linear stability of the incompressible axisymmetric flow in a buoyant-thermocapillary liquid pool is considered which is heated from above by a heat flux with a parabolic radial profile. Buoyancy forces and radial thermocapillary stresses due to the inhomogeneous surface temperature distribution drive a toroidal vortex. In the absence of buoyancy and for low Prandtl numbers the basic flow becomes unstable typically by a stationary centrifugal instability. At moderate Prandtl numbers the rotational symmetry is broken by hydrothermal waves. In the limit of vanishing Prandtl number two other critical modes are found if the pool is very shallow. One mode is a centrifugally destabilized rotating wave with high azimuthal wavenumber. The other mode is steady and it is driven by the deceleration of the radial inward return flow as it approaches the axis. The deceleration results from an entrainment of fluid into the thin layer of rapid radial outward surface flow. The centrifugal instability of the toroidal vortex flow is assisted by buoyancy in the low-Prandtl-number limit, because the cooling from the sidewall augments the thermocapillary driving. For moderately high Prandtl numbers a stable thermal stratification suppresses the hydrothermal-wave instabilities.
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Guo, Chang Hong, Xiang Dong Liu i Shao Mei Fang. "Exact Traveling Wave Solutions to a Model for Solid-Solid Phase Transitions Driven by Configurational Forces". Advanced Materials Research 418-420 (grudzień 2011): 1694–97. http://dx.doi.org/10.4028/www.scientific.net/amr.418-420.1694.
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This paper studies the exact traveling wave solutions to a model for solid-solid phase transitions driven by configurational forces. The model consists of the partial differential equations of linear elasticity coupled to a quasilinear nonuniformly parabolic equation of second order, which describes the diffusionless phase transitions of solid materials. By using the hyperbolic tangent function expansion method and homogeneous balance method, some exact traveling wave solutions, including solitary wave solutions are obtained for the phase transitions model in one space dimension.
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Alber, Hans-Dieter, i Peicheng Zhu. "Solutions to a Model with Nonuniformly Parabolic Terms for Phase Evolution Driven by Configurational Forces". SIAM Journal on Applied Mathematics 66, nr 2 (styczeń 2005): 680–99. http://dx.doi.org/10.1137/050629951.
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Cordy, C. "A Strong, Low-Cost Mount for Parabolic Dish Solar Collectors". Journal of Solar Energy Engineering 117, nr 3 (1.08.1995): 205–9. http://dx.doi.org/10.1115/1.2847786.
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This paper presents the design of a cradle for mounting solar energy concentrator dishes. The cradle is strong and provides unobstructed space to mount a well braced dish. It will survive high winds without being driven to a stow position. The axes of rotation of the dish pass near the plane of the edge of the dish to reduce wind-induced torques in the drive system. Large radius tracks are attached to both the dish and cradle so the gear train on the drive motors can be simple and inexpensive. The cradle is a strong gimbal mount built of 12 structural members in the form of three tetrahedra. It provides a polar axis mount for the concentrator dish. All forces parallel to the polar axis are delivered to the earth at the end of the cradle closest to the equator.
Rozprawy doktorskie na temat "Parabolic Driving Forces"
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Ben, abdalah Abir. "Influence du vieillissement sur l'effet mémoire des polymères / Modélisation du mécanisme de mémoire de forme". Thesis, Paris, HESAM, 2020. http://www.theses.fr/2020HESAE046.
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La présente thèse a pour objectif de caractériser l’effet mémoire de forme du mélange (40%PCL/ 60%SBS) et d’étudier l’influence de l’altération de la masse molaire et des propriétés physico-chimiques sur cet EMF. Dans un premier temps, une caractérisation expérimentale a été effectuée afin de déterminer les propriétés physico-chimiques, morphologiques et mécaniques des matériaux d’études. Le mélange (PCL/SBS) présente un EMF total (EMFT) puisqu’il récupère 100% de sa forme initiale après un cycle de mémoire de forme. L’énergie emmagasinée dans la structure agit en tant que la force motrice qui pourrait être responsable de cet EMF. Donc, une méthode originale utilisant un témoin a été proposée afin d’évaluer l’évolution de la contrainte-déformation durant la recouvrance. Dans une deuxième étape, afin de changer la masse molaire du PCL dans le mélange (SBS/PCL), le vieillissement par hydrolyse enzymatique en utilisant une enzyme de type Amano Lipase de Pseudomonas fluorescens a été réalisé. L’effet du vieillissement sur les propriétés du PCL pur a été tout d’abord évalué. Ensuite, l’échantillonnage a été effectué et des mélanges (PCL/SBS) à différentes masses molaires du PCL ont été donc obtenus. Ces mélanges ont été soumis par la suite à des essais de caractérisation et à des essais de mémoire de forme afin d’étudier la relation entre la masse molaire et l’EMF. Les résultats ont montré que la diminution de la masse molaire engendre des changements morphologiques et structuraux, l’augmentation de la rigidité et la fragilisation du mélange, la diminution de la compatibilité, l’augmentation de l’hétérogénéité et la perte de l’équilibre thermodynamique des phases. Ces changements de la masse molaire et donc des propriétés du mélange ont altéré sa capacité de recouvrance. Le mélange initialement à EMFT (Rr =100%) devient à EMF partiel EMFP (Rr=50%). Dans une dernière étape, un modèle biparabolique a été employé pour la prédiction du comportement viscoélastique du mélange (40%PCL/60%SBS) avant et après son vieillissement par hydrolyse enzymatiqueThe aim of this thesis is to characterize the Shape Memory Effect (SME) of the (40% PCL/60% SBS) blend and to study the influence of the molecular weight and the physicochemical properties on this SME. Firstly, experimental characterization is performed in order to evaluate the physicochemical, morphological and mechanical properties of the used materials. The (PCL/SBS) blend exhibits a Total SME (TSME) as it recovers 100% of its original shape after one shape memory cycle. The energy stored in the structure acts as the driving force that can be responsible for this SME. Therefore, an original method using a witness is used to establish the stress-strain evolution during recovery. Secondly, to change the molecular weight of PCL in the blend, enzymatic hydrolytic degradation using an Amano Lipase from Pseudomonas fluorescens is carried out. The influence of hydrolysis on the pure PCL properties is evaluated. Then, sampling is carried out and (PCL/SBS) blends with different PCL molecular weights are obtained. Subsequently, these blends are submitted to experimental and shape memory tests to study the relationship between the molecular weight and the SME. The results show that the decrease in the molecular weight causes morphological and structural changes: the increase in stiffness and the embrittlement of the mixture, the decrease in compatibility, the increase in heterogeneity and the loss of thermo-dynamical balance of phases. These changes in the molecular weight and in the properties of blends influence its recovery capacity. The blend with the TSME is transformed to a polymer with partial SME. Finally, a bi-parabolic model is used to predict the viscoelastic behavior of the (40% PCL / 60% SBS) blend before and after its enzymatic hydrolytic aging
Streszczenia konferencji na temat "Parabolic Driving Forces"
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Bartashevich, M. V., V. V. Kuznetsov i O. A. Kabov. "Mathematical Modeling of Rivulet Flow Driven by Variable Gravity and Gas Flow in a Minichannel". W ASME 2008 6th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2008. http://dx.doi.org/10.1115/icnmm2008-62135.
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Rivulet flows are a special type of thin film flows with a bounded width. The use of rivulet flows is very perspective in various types of process equipment such as evaporators. The flow dynamics in rivulets has some peculiarities, the investigation of which allows understanding the gist of possible mechanism of enhancement of heat transfer. In the present work a mathematical model for the rivulet flow in conditions of a variable gravity has been elaborated. The liquid flow takes place in a slot between two plates and is caused by a co-current gas flow. The numerical calculations of the flow parameters depending from the gravity forces have been made. The analytical formula for connection of the main rivulet parameters (width, contact angle, liquid flow rate ...) in a linearized approach has been derived. The comparison of numerical results with experimental data obtained during 44 Parabolic Flights campaign of the European Space Agency has been carried out. Liquid film of FC-72 driven by the Nitrogen gas has been studied in experiments. Force balance is changed during a parabolic flight and due to surface tension effect the liquid film in a horizontal minichannel 40 mm width became a flattened rivulet 9 mm width at microgravity.
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Yazdi, Shahrzad, Reza Monazami i Mahmoud A. Salehi. "3D Numerical Analysis of Velocity Profiles of PD, EO and Combined PD-EO Flows Through Microchannels". W ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2006. http://dx.doi.org/10.1115/icnmm2006-96039.
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In this paper, a three-dimensional numerical model is developed to analyze flow characteristics of pressure driven, electroosmotic and combined pressure driven-electroosmotic flows through micro-channels. The governing system of equations consists of the electric-field and flow-field equations. The solution procedure involves three steps. The net charge distribution on the cross section of the micro-channel is computed by solving two-dimensional Poisson-Boltzmann equation using the finite element method. Then, using the computed fluid’s charge distribution, the magnitude of the resulting body force due to interaction of an external electric field with the charged fluid is calculated along the micro-channel. Finally, three dimensional Navier-Stokes equations are solved by considering the presence of the electro-kinetic body forces in the flow system for electroosmotic and combined pressure driven electroosmotic flow cases. The results reveal that the flow patterns for combined PD-EO cases are significantly different from the parabolic velocity profile of the laminar pressure-driven flow. The effect of the liquid bulk ionic concentration and the external electric field strength on flow patterns through the square-shaped micro-channels is also investigated over a wide range of external electric field strengths and bulk ionic concentration.
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Castaneda, Alexander J., Nathaniel J. O’Connor i Jamal Yagoobi. "Investigation of Gravity Effects on Electrically Driven Liquid Film Flow Boiling: A Micro-Gravity Flight Campaign in Preparation of ISS Experiment". W ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-24133.
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Abstract The ongoing development of modern electronic systems leads to smaller, more powerful devices that are expected to operate in complex environments. Due to this, advanced thermal management technologies are required to meet the growing demand, especially in space where two-phase thermal systems are limited by the absence of gravity. Electrohydrodynamic (EHD) and dielectrophoretic (DEP) forces can be used to sustain stable liquid film boiling in micro-gravity, which is otherwise impractical due to the lack of a required buoyancy force to initiate bubble departure. EHD and DEP are phenomena that are represented by the interaction between electric fields and fluid flow. The DEP force especially is characterized by the unique ability to act on liquid/vapor interfaces due to a high gradient of electrical permittivity, allowing for two phase operation. This study investigates the effect of EHD conduction pumping coupled with DEP vapor extraction on liquid film flow boiling during a microgravity parabolic flight, and it characterizes the future two-phase microgravity heat transport technology prior to testing on the International Space Station (ISS). The results of this study show that EHD and DEP raise critical heat flux, lower heater surface temperature, and successfully sustain boiling in micro-gravity all at the cost of low power consumption. Additionally, the heat transfer data captured in terrestrial, microgravity, and 1.8 g conditions compare well, indicating that this technology can provide thermal enhancement independent of gravity. This study paves the way for future implementation of EHD-driven two-phase heat transport devices into space and aeronautical electronics applications.
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Sánchez, David, Miguel Rollán, Lourdes García-Rodríguez i G. S. Martínez. "Solar Desalination Based on Micro Gas Turbines Driven by Parabolic Dish Collectors". W ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-90929.
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Abstract This paper presents the preliminary design and techno-economic assessment of an innovative solar system for the simultaneous production of water and electricity at small scale, based on the combination of a solar micro gas turbine and a bottoming desalination unit. The proposed layout is such that the former system converts solar energy into electricity and rejects heat that can be used to drive a thermal desalination plant. A design model is developed in order to select the main design parameters for two different desalination technologies, phase change and membrane desalination, in order to better exploit the available electricity and waste heat from the turbine. In addition to the usual design parameters of the mGT, the impact of the size of the collector is also assessed and, for the desalination technologies, a tailored multi-effect distillation unit is analysed through the selection of the corresponding design parameters. A reverse osmosis desalination system is also designed in parallel, based on commercial software currently used by the water industry. The results show that the electricity produced by the solar micro gas turbine can be used to drive a Reverse Osmosis system effectively whereas the exhaust gases could drive a distillation unit. This would decrease the stack temperature of the plant, increasing the overall energy efficiency of the system. Nevertheless, the better thermodynamic performance of this fully integrated system does not translate into a more economical production of water. Indeed, the cost of water turns out lower when coupling the solar microturbine and Reverse Osmosis units only (between 3 and 3.5 €/m3), whilst making further use the available waste heat in a Multi Effect Distillation system rises the cost of water by 15%.
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Qazi Zade, Azad, Reza Monazami, Mehrdad T. Manzari i Vahid Bazargan. "A Novel Mechanism for Heat Transfer Enhancement Through Microchannels Using Electrokinetic Effect". W ASME 2005 Summer Heat Transfer Conference collocated with the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems. ASMEDC, 2005. http://dx.doi.org/10.1115/ht2005-72822.
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In this paper a three-dimensional numerical model is developed in order to study the heat transfer enhancement in rectangular microchannels due to electrokinetic effect. The electrokinetic body force on fluid elements gives some superior convective transport properties to the flow relative to pure pressure driven flow in microchannels. Unlike the conventional parabolic velocity profile of pressure driven laminar flow, the electrokinetic body force transforms the velocity profile to a slug-like flow. Due to sharp velocity gradient near the wall, the convective heat transfer properties of the flow are improved dramatically. Net charge distribution across the channel is obtained by solving the 2D Poisson-Boltzmann equation. The incompressible laminar Navier-Stokes equations are then solved numerically by considering the presence of electrokinetic body force using the finite element method. Finally to obtain the temperature field through the channel, three-dimensional energy equation is solved for constant wall temperature condition. The analysis provides a unique fundamental insight into the complex flow and heat transfer pattern established in the channel due to combined pressure driven-electroosmotic pumping mechanism. The results are compared with the pressure driven flow in same channel. The comparison reveals significant change in flow pattern and heat transfer characteristics of single phase flow through microchannel by adding electroosmotic pumping mechanism to pressure driven flow.
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Lee, Ho-Hoon. "Control Design of a Mobile Robot in the Environment of Obstacles Based on a Rounded V-Shape Lyapunov Function". W ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-10989.
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Abstract This paper proposes a V-shape Lyapunov function method with application to the design of a control scheme for a mobile robot navigating through multiple obstacles. The proposed design method solves the serious problem of input saturation due to big position errors in the beginning of the control associated with the conventional parabolic Lyapunov function method. The resulting control consists of a trajectory generation scheme and a motion control scheme. The trajectory generation scheme computes the translational and rotational reference velocities in real time that drive the robot to a given goal position while avoiding multiple obstacles. The motion control scheme computes the driving force and rotational torque to track the reference velocities. The nonholonomic constraints of the mobile robot are used in the design of the kinematic trajectory generation scheme, where a repulsive potential function is used for obstacle avoidance. The dynamic model of the robot is used in the design of the motion control scheme. Under certain conditions, the proposed control guarantees asymptotic stability while keeping all internal signals bounded. The effectiveness of the proposed control method has been shown with realistic computer simulations.
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Kabov, Oleg A. "Interfacial Thermal Fluid Phenomena in Thin Liquid Films". W 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22959.
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Films are ubiquitous in nature and play an important role in our daily life. The paper focuses on the recent progress that has been achieved in the interfacial thermal fluid phenomena in thin liquid films and rivulets through conducting experiments and theory. Phase shift schlieren technique, fluorescence method and infrared thermography have been used. A spanwise regular structures formation was discovered for films falling down an inclined plate with a built-in local rectangular heater. If the heating is low enough, a stable 2D flow with a bump at the front edge of the heater is observed. For lager heat flux this primary flow becomes unstable, and the instability leads to another steady 3D flow, which looks like a regular structure with a periodically bent leading bump and an array of longitudinal rolls or rivulets descending from it downstream. The heat flux needed for the onset of instability grows almost linearly with the increase of Re number. Strong surface temperature gradients up to 10–15 K/mm, both in the streamwise and spanwise directions have been measured. For a wavy film it was found that heating may increase the wave amplitude because thermocapillary forces are directed from the valley to the crest of the wave. Thin and very thin (less than 10 μm) liquid films driven by a forced gas/vapor flow (stratified or annular flows), i.e. shear-driven liquid films in a narrow channel are a promising candidate for the thermal management of advanced semiconductor devices in earth and space applications. Development of such technology requires significant advances in fundamental research, since the stability of joint flow of locally heated liquid film and gas is a rather complex problem. Experiments with water and FC-72 in flat channels (height 0.2–2 mm) have been conducted. Maps of flow regimes were plotted. It was found that stratified flow exists and stable in the channels with 0.2 mm height and 40 mm width. The critical heat flux for a shear driven film may be up to 10 times higher than that for a falling liquid film, and reaches 400 W/cm2 in experiments with water at atmospheric pressure. Some experiments have been done during parabolic flight campaigns of the European Space Agency under microgravity conditions. It was found that decreasing of gravity leads to a flow destabilization.
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Fukui, Tomohiro, Misa Kawaguchi i Koji Morinishi. "Relationship Between Macroscopic Rheological Properties and Microstructure of a Dilute Suspension by a Two-Way Coupling Numerical Scheme". W ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-5449.
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Abstract The rheological properties of a suspension depend on particle shape, spatial arrangement of the particles and hydrodynamic interactions as well as the concentration of the particles. So far, we proposed a two-way coupling numerical scheme to evaluate the effects of particle rotation on the rheological properties. This particle rotation decreases the fluid resistance. However, these studies were conducted on the condition that suspended particles were homogeneously distributed. Therefore, the particles in this study are randomly scattered in a suspension for better practical applications. Pressure-driven suspension flow simulations were conducted to consider the effects of inertia on the relationship between spatial arrangement of the particles and the rheological properties of a suspension. The channel width and axial length were set 400 μm and 1620 μm, respectively, and periodic boundary conditions were applied in the flow direction. The rigid spherical particles whose diameter was 20 μm were randomly scattered in the channel as an initial condition. The concentration of the suspension was set 1.02% for dilute assumption, and the suspension flows with the Reynolds number from 2 to 128 were reproduced in order to investigate the inertial effects of the suspended particles on the rheological properties. The rheological properties of the suspension were evaluated in terms of power-law index (non-Newtonian index). The velocity profile of a suspension for low Reynolds number conditions exhibited almost parabolic. This indicates the suspension behaves as a Newtonian fluid. For higher Reynolds number conditions, on the other hand, the lift force on the particles increased and they migrated toward the equilibrium y-axis position, where the lift force is zero. These changes in the y-axis position of the particles caused a change in microstructure of the suspension, which were followed by a change in macroscopic rheological properties. Owing to these microstructure changes, the non-Newtonian (thixotropic) properties were enhanced as the Reynolds number increased.
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Shan, Hua, Shawn Aram i Yu-Tai Lee. "Application of an Integrated Flow and DBD Plasma Actuation Model to a High-Lift Airfoil: Part I — RANS". W ASME/JSME/KSME 2015 Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ajkfluids2015-14213.
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An integrated numerical simulation tool that couples the Reynolds averaged Navier-Stokes (RANS) or the large eddy simulation (LES) solver for incompressible flows with the dielectric barrier discharge (DBD) electro-hydrodynamic (EHD) body force model has been developed. The EHD body force model is based on solving the electrostatic equations for the electric potential due to applied voltage and the net charge density due to ionized air. The boundary condition for the charge density on the dielectric surface is obtained from a Space-Time Lumped-Element (STLE) circuit model that accounts for the time and space dependence of air ionization on the input voltage amplitude, frequency, electrode geometry, and dielectric properties. The development of the numerical simulation tool is based on the framework of NavyFOAM using a multi-domain approach. The electric potential equation, the net charge density equation, and the flow equations are solved in separate computational domains. All equations are discretized in space using the cell-centered finite volume method. Parallel computation is implemented using domain-decomposition and message passing interface (MPI). Due to a large disparity in time scales between the electric discharge and the flow, a multiple sub-cycle technique is used in coupling the plasma solver and the flow solver. This paper focuses on its application to numerical simulation of flow separation and control over a high-lift flapped airfoil at a Reynolds number of 240,000. The 2-D unsteady RANS simulation utilized the Wilcox k-ω, the SST k-ω, and the k-kl-ω turbulence models. For the baseline case, in comparison with the measurement, the k-kl-ω model captures the feature of the unsteadiness of flow field associated with flow separation and shedding of vortices, better than the Wilcox k-ω and SST k-ω models. In the RANS simulations for flow separation control with DBD plasma actuation, the actuator is driven by voltage signals of a continuous or an amplitude-modulated sine waveform with a range of voltage amplitudes. The numerical results indicate that the modulated forcing is more effective than the continuous forcing for a certain range of applied voltages. The electrical power consumption calculated by the plasma model fits to a parabolic curve as a function of the root-mean-square of applied voltage.