Fluid Dynamic Processes Research Articles

Acoustical observation of randomly fluctuating interior of shallow oceans

Acoustic reciprocal transmission experiments are conducted at two locations (90 m and 120 m in depth) on the outer continental shelf near New York Byte. The transmission ranges between three transceivers are 3, 4, and 5 km. The moderate‐frequency acoustic sources (5.5 kHz) are used with the source level of 192 dB re 1 mcPa at 1 m. Environmental data of fine scale currents and temperature are measured by CTD and inverted ADCP. Characteristics of hydrodynamic fluctuations are determined by transmission data and simulation by a PE code. The sound transmission data and inversion results are severely randomized by the spatial and temporal fluctuations due to fluid dynamic processes, such as turbulent flows, internal waves, and internal solitons. The vertical and temporal coherence analyses are conducted as the techniques for the waveform analyses. These techniques separate the received signals into the coherent component corresponding to the mean state of current velocity and sound speed, and the incoherent component due to fluid dynamic fluctuations. [Work supported by ONR.]

Aspects of the dynamical core of a nonhydrostatic, deep-atmosphere, unified weather and climate-prediction model

The dynamical core, which governs the evolution of resolved fluid-dynamical processes, is a critical element of any atmospheric model. Its governing equations must include all relevant dynamical terms, and the numerical formulae used to approximate them must be accurate, stable and efficient. This is particularly so in a unified modeling environment in which the same dynamical core is used for both operational weather prediction and long term climate simulations. Recent research at the Met Office on unified dynamical core issues is reviewed. Aspects covered include: properties of various equation sets; vertical coordinates; semi-Lagrangian advection and conservation; trajectory computation and dynamical equivalence; horizontal and vertical discretization; and coupling of physical parameterizations to a dynamical core.

Optimal Field Reconstruction of Distributed Process Systems from Partial Measurements

In this article, we develop a systematic approach for efficient field reconstruction in distributed process systems from a limited number of measurements. The approach generalizes previous methods for sensor placement so as to be able to handle field reconstruction problems in arbitrary spatial domains where complex nonlinear phenomena take place. Pattern formation in fluid dynamics or diffusion-reaction systems are examples exhibiting complex nonlinear distributed behaviors, especially when taking place in arbitrary 2D or 3D domains. Our approach exploits the dissipative nature of the diffusion-convection process and the underlying algebraic structure of the finite element method to efficiently construct field representations in terms of globally defined basis functions and to optimally select the placement of sensors. The results will be illustrated on a fluid dynamic process: the Rayleigh−Benard problem.

Coupling of U-Tube and Shear Layer Oscillations in an Interconnected Flow Compartment

Results of experiments conducted in a 2 m high flume at large Reynolds numbers are reported in this paper. The flume was partitioned into two compartments. Flow entered the bottom of the upstream test compartment as a wall jet, at jet Reynolds number ranging from 11,000 to 170,000. Periodic oscillations of the free surface in the two compartments resembling the oscillatory flow in a liquid-filled U-tube, and large coherent structures formed above the potential core of the wall jet were observed. Coupling of the U-tube oscillations and vortex shedding is attributed to fluid-dynamic and fluid-resonant feedback processes. For test compartment length, Lc =0.8 m , fluid-resonant feedback was found to be dominant, and the shear layer was observed to oscillate at the natural frequency of the two-compartment, U-tube system. The observed U-tube oscillations are initiated by the oscillations of the shear layer at a frequency equal to the subharmonic component for the U-tube. The flow oscillations were generally wea...

Solidification of a binary alloy: Finite-element, single-domain simulation and new benchmark solutions

A finite-element simulation of binary alloy solidification based on a single-domain formulation is presented and tested. Resolution of phase change is first checked by comparison with the analytical results of Worster [M.G. Worster, Solidification of an alloy from a cooled boundary, J. Fluid Mech. 167 (1986) 481–501] for purely diffusive solidification. Fluid dynamical processes without phase change are then tested by comparison with previous numerical studies of thermal convection in a pure fluid [G. de Vahl Davis, Natural convection of air in a square cavity: a bench mark numerical solution, Int. J. Numer. Meth. Fluids 3 (1983) 249–264; D.A. Mayne, A.S. Usmani, M. Crapper, h-adaptive finite element solution of high Rayleigh number thermally driven cavity problem, Int. J. Numer. Meth. Heat Fluid Flow 10 (2000) 598–615; D.C. Wan, B.S.V. Patnaik, G.W. Wei, A new benchmark quality solution for the buoyancy driven cavity by discrete singular convolution, Numer. Heat Transf. 40 (2001) 199–228], in a porous medium with a constant porosity [G. Lauriat, V. Prasad, Non-darcian effects on natural convection in a vertical porous enclosure, Int. J. Heat Mass Transf. 32 (1989) 2135–2148; P. Nithiarasu, K.N. Seetharamu, T. Sundararajan, Natural convective heat transfer in an enclosure filled with fluid saturated variable porosity medium, Int. J. Heat Mass Transf. 40 (1997) 3955–3967] and in a mixed liquid–porous medium with a spatially variable porosity [P. Nithiarasu, K.N. Seetharamu, T. Sundararajan, Natural convective heat transfer in an enclosure filled with fluid saturated variable porosity medium, Int. J. Heat Mass Transf. 40 (1997) 3955–3967; N. Zabaras, D. Samanta, A stabilized volume-averaging finite element method for flow in porous media and binary alloy solidification processes, Int. J. Numer. Meth. Eng. 60 (2004) 1103–1138]. Finally, new benchmark solutions for simultaneous flow through both fluid and porous domains and for convective solidification processes are presented, based on the similarity solutions in corner-flow geometries recently obtained by Le Bars and Worster [M. Le Bars, M.G. Worster, Interfacial conditions between a pure fluid and a porous medium: implications for binary alloy solidification, J. Fluid Mech. (in press)]. Good agreement is found for all tests, hence validating our physical and numerical methods. More generally, the computations presented here could now be considered as standard and reliable analytical benchmarks for numerical simulations, specifically and independently testing the different processes underlying binary alloy solidification.

PLANNING AND MANAGEMENT OF FIELD EXPERIMENTS IN ENVIRONMENTAL HYDRAULICS

Environmental Hydraulics is an applied science that deals with the problems of water environment, such as of water quality, ecosystem etc., from a view point of fluid dynamics in terms of water motion and mixing, hydraulic force, heat and mass transport and so on. Because chemical and biological processes are also essential in environmental phenomena, Environmental Hydraulics must be to some extent “interdisciplinary”, where the interaction of those processes with the process of fluid dynamics is discussed. Because Environmental Hydraulics is to offer solutions of existing environmental problems or possible measures for environmental conservation, the studies are essentially “practical”, where the description of facts and their relations existing and functioning in the field is the most concerned.For the reasons above mentioned, one of major means in researches of Environmental Hydraulics is field experiments that supply us the facts to find the mechanism of the interactive processes existing in the field. However, the experiments are not straightforward: First of all, it often includes the measurements of chemical and biological factors as well as hydraulic terms, and these measurements must be arranged properly in order to find the relation among them. In the design of experiments, you must take into account the unsteady and non-uniform aspects of the processes that are common in environmental phenomena. And finally, your plan must be practical under the condition of money, time, and manpower that you can employThis keynote lecture presents the techniques, know-how, skills, theories or principles (now, terminology is indifferent) for planning and managing field experiments. The first half is about how to enlarge the world of measurements. In a field study, you should learn “what you want to know cannot always be measurable”. Then, you must try to speculate what you want to know from what you can measure. The most fundamental and the most important tactics for the speculation is “use of correlation”. The last half is devoted to describe how to compose individual measurements to realize an effective and economic field experiment. Here, two kinds of operations called “monitoring” and “maneuver” are introduced with some examples.

Spray Pattern Analysis for Metered Dose Inhalers I: Orifice Size, Particle Size, and Droplet Motion Correlations

ABSTRACTFactors that influence spray pattern measurements of pressurized, metered-dose inhalers have been evaluated. Spray patterns were correlated with changes in actuator orifice diameter, particle size profiles, and calculated estimates of particle-size dynamics of plumes during a spray. Spray patterns, regardless of actuator orifice size, were ellipsoid in the vertical direction. Measures of elliptical ratio, major axis, and minor axis were significantly influenced by orifice size in a non-linear fashion over the range of orifice sizes investigated. Spray patterns also correlated with particle size profile and spray geometry measurements. Spray distribution asymmetry may be related to droplet evaporation and sedimentation processes. However, the spray patterns did not appear sensitive to changes in gravitational force acting on the plume. Instead, it is postulated that elliptical spray patterns may have dependence on fluid dynamic processes within the inhaler actuator. Developing an understanding of these processes may provide a basis for developing spray pattern tests with relevance to product performance.

On the long‐term behavior of meandering rivers

In spite of notable advances in the description of river morphodynamics, the long‐term dynamics of meandering rivers is still an open question, in particular, regarding the existence of a possible statistical steady state and its scaling properties induced by the competing action of cutoffs and reach elongation. By means of extensive numerical simulations, using three fluid dynamic models of different complexity and analysis of real data from the Amazon, North America, and Russia, we show that the reach cutoffs, besides providing stability and self‐confinement to the meander belt, also act as a dynamical filter on several hydrodynamic mechanisms, selecting only those that really dominate the long‐term dynamics. The results show that the long‐term equilibrium conditions are essentially governed by only one spatial scale (proportional to the ratio of the river depth and the friction coefficient) and one temporal scale (proportional to the square of the spatial scale divided by the river width, the mean longitudinal velocity, and the erodibility coefficient) that contain the most important fluid dynamic quantities. The ensuing statistical long‐term behavior of meandering rivers proves to be universal and largely unaffected by the details of the fluid dynamic processes that govern the short‐term river behavior.

Seismic evidence for fluid escape from Mesozoic cuesta type topography in the Skagerrak

Gas and fluid dynamic processes in the Mesozoic to recent strata of the southern slope and center of the Norwegian Trench (Skagerrak) have been analyzed by high-resolution multi-channel seismic data collected with a watergun as the seismic source on board of RV Heincke in spring 2003. Three profiles across the southern slope and the center of the trench and four profiles cover the north-eastern termination of the trench. The data resolve the Quaternary succession and the subcropping Mesozoic strata. The separating unconformity shows a typical cuesta topography, caused by glacial erosion. On the slope, contourite drifts are present. Above a water depth of approximately 400 m internal reflections of the Quaternary are obscured by acoustic turbidity. Particularly, phase reversed bright reflections occurring in the entire Lower Jurassic to Upper Cretaceous succession suggest the presence of fluids therein. Sea-floor pockmarks have been observed on the southern slope and in the center of the trench. Both slope and trench pockmarks are vertically correlated with the sub-crop of fluid charged Mesozoic rocks beneath, which indicate lateral fluid escape from porous Mesozoic rocks. Fluids that migrate towards a slope pockmark are capable to wash out gas from the Quaternary, leaving gas free patches behind. Since no thermogenic gas has ever been measured in core samples from the slope and trench, freshwater seepage is a possible explanation. In this case the water outflow might represent artesian springs.

Mixing and transport in urban areas

Concern over terrorist releases of harmful material has generated interest in short-range air-borne dispersion in urban areas. Here, we review the important fluid dynamical processes that control dispersion in the first kilometre, the neighbourhood scale, when much of the material remains within the urban canopy. Dispersion is then controlled by turbulent mixing and mean flow transport through the network of streets. We consider mixing and transport in a long straight street, street intersections and then a network of streets connected by intersections. The mixing and transport in these systems are illustrated with results from recent fine-resolution numerical simulations and laboratory models, which then inform simpler scaling estimates and modelling schemes. Finally, we make some tentative steps to pull the process studies together to begin to understand results from full-scale observations. In particular, it is shown that the positions of 'shear layers' and 'dividing streamlines' largely control the patterns of mixing and transport. It is also shown that neighbourhood-scale dispersion follows one scaling in the near field and another in the far field after passage through many intersections. The challenge for the future is to bring these threads together into a coherent mathematical model.

Thermal simulation of buildings with double-skin façades

Highly glazed commercial buildings with double-skin façades may overheat during summertime due to a coincidence of high outside temperatures, solar gains and internal heat gains. To optimize thermal comfort and minimize cooling loads, the thermal behaviour of this type of building, therefore, requires careful investigation at the design stage. However, complex physical phenomena—notably optical, thermodynamic and fluid dynamic processes—are involved and as yet, no single simulation tool is able to handle all these processes while remaining an efficient design tool. This paper presents a method based on the coupling of three different types of simulation models that is economical in terms of computing time, and thereby, suitable for design purposes. These models are: spectral optical model, computational fluid dynamics model and building energy simulation model. Various tools are available at each modelling level. The method is demonstrated on a commercial building with double-skin façades and additionally, night-time ventilation.

Investigation of Crystallization in a Jet Y-Mixer by a Hybrid Computational Fluid Dynamics and Process Simulation Approach

A hybrid approach incorporating a computational fluid dynamics (CFD) package and process simulation tool was employed to simulate the steady-state crystallization of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in a Y-mixer crystallizer. Mixing effect was intensively investigated through the three-dimensional spatial distributions of velocity, supersaturation, kinetic rates, mean crystal size, coefficient of variation, and yield. The hybrid approach could predict the literature experimental data on mean crystal size, coefficient of variation, and production rate at the exit of the outlet tube reasonably by adjusting three factors (K, Ehet, and f) for nucleation and crystal growth that are difficult to determine by experiment or theory. It was found that even in a small-scale Y-mixer crystallizer a mixing effect was evident and that nuclei were generated dominantly by primary homogeneous nucleation and were grown at the rate controlled by both bulk diffusion and surface integration for the experimental supersaturation range.

Droplets and particles in sprays: tailoring particle properties within spray processes

Particle generation via atomization and spray processes is a widely applied method for powder production. By means of atomization processes, the relevant particle properties may be tailored to the powder user's need in a wide range. Understanding and control of the main subprocesses of atomization is a key feature for choosing a suitable type of spray process and operation conditions. Tailoring particle properties and extending the applications of particle production beyond the current limits is also possible in this way. This contribution highlights some features of spray processes for powder production, namely the gas- and fluid-dynamic processes involved, the materials-related subprocesses, and the formation of the multiphase flow in the spray. As an example, the production of fibre- or sphere-shaped particles from melt atomization is discussed.

Distribution and accumulation rate of ore elements in Holocene and Late Glacial Sediments of the Deryugin Basin, Sea of Okhotsk

Results of the study of contents and accumulation rates of Fe, Mn, and a number of trace elements in Upper Quaternary sediments of the Deryugin Basin are presented. Maps of the average contents and accumulation rates of excess Fe, Mn, Zn, Ba, Ni, Pb, Cu, and Mo in sediments of the first oxygen isotope stage (OIS) have been plotted. Anomalous contents and accumulation rates are confined to peripheral zones of the Deryugin sedimentary basin and large fracture zones. Different mechanisms of the influence of fluid-dynamic processes on the rate of hydrogenic and biogenic accumulation of ore elements are assumed.

Fluid Dynamics and Transfer Processes in Bended Microchannels

The understanding of the flow processes in microchannels and micromixers is essential for the design of microfluidic devices like microreactors or analytical equipment. We have performed a systematic numerical CFD-study of mixing and mass transfer in sharp 90° bends and heat transfer in T-joints to obtain a detailed insight into the flow patterns and corresponding transfer processes in a wide range of Reynolds numbers. With increasing flow velocity, the straight laminar flow starts to form symmetrical vortices in the bend, at the entrance of the mixing channel, and in T-joints. The vortices enhance the transport processes like heat and mass transfer in the channels significantly. The influence of the geometry and the flow conditions is shown by an analytical estimation of the relevant forces. The appearance of convective transport processes is used for the definition of microflows, which are controlled by viscous forces and diffusive transfer processes.

SUPG and grad‐div stabilized finite element methods for steady weakly compressible viscous flow

AbstractThe extensive application of mathematical and computational methods has become an efficient and powerful approach to the investigation and solution of many problems and processes in fluid dynamics from qualitative as well as quantitative point of view. In this work a new class of advanced numerical approximation schemes to isothermal compressible viscous flow is presented. The schemes are based on an iteration between an Oseen like problem for the velocity and a hyperbolic transport equation for the density. Such schemes seem attractive for computations because they offer a reduction to simpler problems for which highly refined numerical methods either are known or can be built from existing approximation schemes to similar equations, and because of the guidance that can be drawn from an existence theory based on them. For the generalized Oseen subproblem a Taylor–Hood finite element method is proposed that is stabilized by a reduced SUPG and grad‐div technique (cf. [1, 4]) in the convection‐dominated case. Results of theoretical investigations and numerical studies are presented. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A CFD Model for Simulating Urban Flow and Dispersion

A three-dimensional computational fluid dynamics (CFD) model is developed to simulate urban flow and dispersion, to understand fluid dynamical processes therein, and to provide practical solutions to some emerging problems of urban air pollution. The governing equations are the Reynolds-averaged equations of momentum, mass continuity, heat, and other scalar (here, passive pollutant) under the Boussinesq approximation. The Reynolds stresses and turbulent fluxes are parameterized using the eddy diffusivity approach. The turbulent diffusivities of momentum, heat, and pollutant concentration are calculated using the prognostic equations of turbulent kinetic energy and its dissipation rate. The set of governing equations is solved numerically on a staggered, nonuniform grid system using a finite-volume method with the semi-implicit method for pressure-linked equation (SIMPLE) algorithm. The CFD model is tested for three different building configurations: infinitely long canyon, long canyon of finite length, and orthogonally intersecting canyons. In each case, the CFD model is shown to simulate urban street-canyon flow and pollutant dispersion well.

Pressure changes associated with the ascent and bursting of gas slugs in liquid-filled vertical and inclined conduits

At basaltic volcanoes, the sources of long-period and very-long-period seismicity and acoustic signals are frequently described in terms of fluid dynamic processes, in particular the formation and ascent of gas slugs within the magma column and their bursting at the surface. To investigate pressure changes associated with these processes, two-phase flow experiments have been carried out in vertical and inclined pipes with both single gas slugs and a continuously supplied gas phase. The ascent of individual gas slugs is accompanied by strong dynamic pressure variations resulting from the flow of liquid around the slug. These dynamic transients generate sub-static pressures below the ascending slug in viscosity-controlled systems, and produce super-static pressures when the slug reaches the surface and motion ceases in inertia-dominated systems. Conduit inclination promotes a change of regime from bubbly to slug flow and favours an increase in size and velocity of the slugs at the expense of their frequency of occurrence during continuously supplied two-phase flow. The experimental pressure data support previous theoretical analyses of oscillatory sources in ascending slugs as the slugs approach the surface and burst. Pressure oscillations are also observed during the release of gas slugs and in their wake region.

Interfacial Rheological Properties of a Series of Bolaamphiphilic Poly(fluorooxetane)s

Interfacial rheological studies were performed on a series ofbolaamphiphilic α,ω-(diammonium disulfato)-poly(fluorooxetane)s of several perfluoroalkyl chain lengths. Similar measurements were performed on a small-molecule, anionic fluorosurfactant with a -C 8 F 1 7 perfluoroalkyl group that is known to be an effective flow and leveling aid in aqueous coatings. Dilational viscoelasticities were measured for the fluorosurfactants as a function of concentration and oscillation rate. Elasticities were found to increase with increasing perfluoroalkyl chain length. All elasticities exhibited a strain rate dependence indicative of the influence of diffusional relaxation on elasticity values. Phase angles were found to be in the range for diffusional relaxation and decreased with increasing concentration and strain rate. Using interfacial rheological data, characteristic fluid dynamics numbers were calculated for the fluorosurfactants. Among these was the Marangoni number. Calculated Marangoni numbers for the poly(fluorooxetane)s were of the same order of magnitude as that for the small-molecule, long perfluoroalkyl chain surfactant. The poly(fluorooxetane)s all have equilibrium surface tensions greater than that of the small-molecule, long perfluoroalkyl chain surfactant, yet show similar abilities to aid in flow and leveling in aqueous coatings at comparable concentrations. Rheological measurements demonstrate that equilibrium surface tension alone is not enough to explain the fluid dynamics processes occurring during flow and leveling.

Modeling of fluid dynamical processes during pulsed-laser texturing of material surfaces

Pulsed-laser texturing of material surfaces proceeds with shallow melt resulting from the absorption of laser energy. Flow processes in the fluid determine the morphological structure of the re-solidified surface. Approximations made in the literature are improved upon here to describe the fluid flow in the melt. In particular, the pressure in the melt is included in the Navier-Stokes equation and the surface boundary condition, which is shown to have significant impact on the flow processes and thus, on the final finish of the surface. The calculations for Si surface modifications are found to be in close agreement with the experimental observations, considerably improving upon the earlier descriptions.