Pressure Gradient Research Papers - Academia.edu (original) (raw)

The theory-based closure relations for the wall and interfacial shear stresses obtained previously for laminar stratified flow, are extended to be applicable also to turbulent flows in either or both of the phases. The closure relations are formulated in terms of the single-phase-based expressions, which are augmented by two-phase interaction factors, due to the flow of the two phases in the same channel. These closure relations, which are valid for smooth stratified flow in horizontal or inclined pipes, were used as a platform for introducing necessary empirical corrections required in the stratified wavy flow regime. Based on experimental data available from the literature, new empirical correlations for the wave effect on the interface curvature, on the interfacial shear and on the liquid wall shear were obtained. The predictions of the two-fluid model for the pressure gradient and holdup are tested against extensive data bank and some analytical solutions for stratified flows. T...

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- Engineering, Multiphase Flow, Closure, Turbulent Flow
- by James Boles
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- Geology, Geochemistry, Geophysics, Kinetics

The spatial resolution of numerical weather prediction and climate models is generally determined by their grid spacing (∆x) or spectral truncation and the numerical implementation of dynamical core and model parametrisations. For example features of the scale 2∆x and 3∆x are smoothed to avoid numerical instabilities (e.g., aliasing effects) and parameterisations in connection to advection, pressure gradient force, and subgrid-scale diffusion can only be well represented at dimensions of at least four times the grid spacing. Some parametrisations, however, generate energy at the grid-spacing scale. These multiple effects on the effective resolution of models are investigated in this study for three high resolution regional climate models (RCMs) in dependence of their grid spacing.

- by Ioannis Daglis and +1
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- Multidisciplinary, Magnetospheric Physics, Statistical Significance, Current Density

In presence of aortic stenosis, a jet is produced downstream of the aortic valve annulus during systole. The vena contracta corresponds to the location where the cross-sectional area of the flow jet is minimal. The maximal transvalvular pressure gradient (TPG(max)) is the difference between the static pressure in the left ventricle and that in the vena contracta. TPG(max) is highly time-dependent over systole and is known to depend upon the transvalvular flow rate, the effective orifice area (EOA) of the aortic valve and the cross-sectional area of the left ventricular outflow tract. However, it is still unclear how these parameters modify the TPG(max) waveform. We thus derived an explicit analytical model to describe the instantaneous TPG(max) across the aortic valve during systole. This theoretical model was validated with in vivo experiments obtained in 19 pigs with supravalvular aortic stenosis. Instantaneous TPG(max) was measured by catheter and its waveform was compared with the one determined from the derived equation. Our results showed a very good concordance between the measured and predicted instantaneous TPG(max). Total relative error and mean absolute error were on average 9.4+/-4.9% and 2.1+/-1.1 mmHg, respectively. The analytical model proposed and validated in this study provides new insight into the behaviour of the TPG(max) and thus of the aortic pressure at the level of vena contracta. Because the static pressure at the coronary inlet is similar to that at the vena contracta, the proposed equation will permit to further examine the impact of aortic stenosis on coronary blood flow.

- by Louis-gilles Durand
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- Mechanical Engineering, Biomedical Engineering, Biomechanics, Humans
- by Jalil Ouazzani
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- Statistical Mechanics, Porous Media, Heat Flux, Van Der Waals
- by Joaquim Balanzo
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- Gastroenterology, Risk, Somatostatin, Humans
- by Pierre-Yves Robin
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- Geology, Geochemistry, Silica, Stress distribution
- by Marisa Cogliati
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- Remote Sensing, Atmospheric Science, Atmospheric sciences, Air flow
- by José Luiz Gasche
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- Two Phase Flow, Pressure Drop, Flow Pattern, Flow Rate
- by Prabhata Swamee
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- Turbulent boundary layer, Boundary Layer, Pressure Gradient
- by Juan Gonzalez-Abraldes
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- Gastroenterology, Biology, Medicine, Humans
- by Clive Dorman
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- Thermodynamics, Boundary Layer Meteorology, High Pressure, Sea surface temperature

An integrated thermofluidic analysis of DNA hybridization, in the presence of combined electrokinetically and/or pressure-driven microchannel flows, is presented in this work. A comprehensive model is developed that combines bulk and surface transport of momentum, heat and solute with the pertinent hybridization kinetics, in a detailed manner. Results confirm that electrokinetic accumulation of DNA occurs within a few seconds or minutes, as compared to passive hybridization that could sometimes take several hours. Further, it is observed that by increasing the accumulation time, significantly higher concentration of DNA can be achieved at the capture probes. However, this eventually tends to attain a saturation state, due to a lesser probability of successful hybridization on account of a prior accumulation of target DNA molecules on the capture probe strands. While favorable pressure gradients augment DNA hybridization rates that are otherwise established by the electro-osmotic transport, adverse pressure gradients of comparable magnitude may turn out to be much less consequential in retarding the same. Such effects can be of potential significance in the designing of a microfluidic arrangement to achieve the fastest rate of DNA hybridization.

- by Siddhartha Das
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- Kinetics, Nanotechnology, DNA hybridization, Solute transport
- by Hans-Christian Hege
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- Computer Graphics, Information Visualization, Data Analysis, Time Series
- by stephen cowin and +1
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- Mechanical Engineering, Biomedical Engineering, Biomechanics, Elasticity
- by Luan Hoang
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- Mathematical Physics, Numerical Simulation, Mathematical Sciences, Porous Media
- by Panagiota Angeli and +1
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- Drag Reduction, Slug Flow, Continuous Flow, Wall Shear Stress
- by Andrea Aliverti
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- Multidisciplinary, Cardiac arrest, Humans, Blood Pressure
- by Peter H. Santschi
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- Geochemistry, Oceanography, Marine chemistry, Statistical Significance
- by Muhammad Kaurangini and +1
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- Mechanical Engineering, Applied Mathematics, Theoretical Analysis, Fluid flow

Turbulent flow over a sinusoidal solid wavy surface was investigated by a direct numerical simulation using a spectral element technique. The train of waves has an amplitude to wavelength ratio of 0.05. For the flow conditions (Re=hU b/2ν= 3460) considered, adverse pressure gradients were large enough to cause flow separation. Numerical results compare favorably with those of Hudson's (1993) measurements. Instantaneous flow fields show a large variation of the flow pattern in the spanwise direction in the separated bubble at a given time. A surprising result is the discovery of occasional velocity bursts which originate in the separated region and extend over large distances away from the wavy wall. Turbulence in this region is very different from that near a flat wall in that it is associated with a shear layer which is formed by flow separation.

- by Y'a Na
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- Applied Mathematics, Direct Numerical Simulation, Classical Physics, Shared memory
- by Xianguo Li
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- Engineering, Economics, Proton Exchange Membrane, Numerical Simulation
- by Majid Hassanizadeh
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- Chemical Engineering, Civil Engineering, Applied Mathematics, Thermodynamics
- by Vinod Jindal
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- Food Engineering, Back Propagation, Neural Network, Power Law
- by abdelsalam alsarkhi
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- Engineering, Multiphase Flow, Pergamon, Drag Reduction
- by Dennis Harry
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- Geology, Geophysics, Tectonics, North Atlantic
- by Monika Auweter-kurtz
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- Plasma Physics, Numerical Analysis, Numerical Method, Current Density

Numerical simulation of fluid flow and transport processes in the subsurface must account for the presence of wells. The pressure at a gridblock that contains a well is different from the average pressure in that block and different from the flowing bottom hole pressure for the well (17). Various finite difference well models have been developed to account for the difference. This paper presents a systematical derivation of well models for other numerical methods such as standard finite element, control volume finite element, and mixed finite element methods. Numerical results for a simple well example illustrating local grid refinement effects are given to validate these well models. The well models have particular applications to groundwater hydrology and petroleum reservoirs. Numerical simulation of fluid flow and transport processes in the subsurface must account for the presence of wells. The pressure at a gridblock that contains a well is different from the average pressure in...

- by Zhi-yong Yin
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- Climate variability, Multidisciplinary, Seasonality, Evapotranspiration
- by George Voulgaris
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- Stratification, Multidisciplinary, Seasonality, Balance
- by Mathieu Dutour Sikiric
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- Oceanography, Linear Programming, Ocean modelling, Filter

Numerical simulation of an air and water two-phase flow in a micro tube is carried out. The focus is laid upon bubbly and slug flows with dry-out. An axisymmetric two-dimensional flow is assumed. The Phase-Field method is adopted to capture the interface, as well as to resolve the singularities arising at the rupture of liquid film and the consequent contact

- by Koji Fukagata
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- Mechanical Engineering, Aerospace Engineering, Two Phase Flow, Heat Transfer
- by Orhan aydın
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- Engineering, Economics, Temperature Distribution, Applied Energy
- by Faruk Civan
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- Petroleum Science and Engineering, Pressure Gradient
- by baby David
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- Humans, Water balance, Skin, Clinical Sciences
- by R. Arabjamaloei
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- Enhanced Oil Recovery, Neural Network, Compressive Strength, Pore Pressure
- by Kris Piessens and +1
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- Engineering, Earth Sciences, Climate Change, Renewable Energy
- by Andrew Orr
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- Climate Change, Multidisciplinary, Seasonality, Trajectory
- by Svetlana Poroseva
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- Turbulent Flow, Shear Stress, Shear Flow, Industrial Application
- by Oscar Rodriguez
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- Engineering, Multiphase Flow, Two Phase Flow, Pipe Flow
- by H. Flocas and +1
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- Air pollution, Atmospheric sciences, Sea Breeze, Atmospheric Circulation
- by Shahab Ayatollahi
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- Two Phase Flow, Heat Transfer, Computer Simulation, Theory and Practice
- by Francisco Valdés-parada
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- Mathematical Physics, Quantum Physics, Porous Media, Shear Stress

The present work analyzes the effects of a solid boundary and the inertial forces on flow and heat transfer in porous media. Specific attention is given to flow through a porous medium in the vicinity of an impermeable boundary. The local volume-averaging technique has been utilized to establish the governing equations, along with an indication of physical limitations and assumptions made in the course of this development. A numerical scheme for the governing equations has been developed to investigate the velocity and temperature fields inside a porous medium near an impermeable boundary, and a new concept of the momentum boundary layer central to the numerical routine is presented. The boundary and inertial effects are characterized in terms of three dimensionless groups, and these effects are shown to be more pronounced in highly permeable media, high Prandtl-number fluids, large pressure gradients, and in the region close to the leading edge of the flow boundary layer.On analyse les effets d'une frontière solide et des forces d'inertie sur l'écoulement et le transfert thermique dans les milieux poreux. Une attention particulière est portée à l'écoulement à travers un milieu poreux au voisinage d'une frontière imperméable. La technique de la moyenne locale en volume a été utilisée pour établir les équations avec une indication sur les limitations physiques et sur les hypothèses. Un schéma numérique a été développé pour déterminer les champs de vitesse et de température dans un milieu poreux près d'une frontière imperméable et un nouveau concept de couche limite placé au centre de la routine numérique est présenté. Les effets de limite et d'inertie sont caractérisés par trois groupements sans dimension et ces effets sont montrés plus prononcés dans les milieux fortement imperméables, pour des fluides à grand nombre de Prandtl, pour des forts gradients de pression et dans la région proche du bord d'attaque de la couche limite de l'écoulement.Die vorliegende Arbeit untersucht die Einflüsse einer festen Begrenzung und der Trägheitskräfte auf die Strömung und den Wärmeübergang in porösen Medien.Besondere Aufmerksamkeit wird der Strömung durch ein poröses Medium in der Nähe einer undurchlässigen Begrenzung gewidmet. Das Verfahren der örtlichen Volumen-Mittelbildung wurde bei der Aufstellung der beschreibenden Gleichungen und der Angabe der physikalischen Vereinfachungen und Näherungen verwendet, die im Verlauf der Herleitung getroffen wurden. Für die beschreibenden Gleichungen wurde ein numerisches Lösungsverfahren entwickelt, um die Geschwindigkeits- und Temperaturfelder innerhalb des porösen Mediums nahe einer undurchlässigen Begrenzung zu untersuchen. Für die Impulsgrenzschicht wird ein neues Konzept innerhalb des numerischen Verfahrens vorgestellt. Die Rand- und Trägheitseinflüsse werden durch drei dimensionslose Gruppen ausgedrückt. Diese Einflüsse erweisen sich als stärker ausgeprägt in gut durchlässigen Medien, in Fluiden mit groβer Prandtl-Zahl, bei groβen Druckgradienten und im Bereich nahe der Vorderkante der Strömungsgrenzschicht.AнAлизиpyeтcя Bлияниe тBepдoй гpAницы и cил инepции нA тeчeниe и тeплoпepeнoc B пopиcтыч cpeдAч. ocoбoe BнимAниe yдeляeтcя тeчeнию чepeз пopиcтyю cpeдy Bблизи нeпpoницAeмoй гpAницы. Для BыBoдA ocнoBныч ypABнeний иcпoльзyeтcя мeтoд лoкAльнoгo ycpeднeния пo oбъeмy. yкAзыBAeтcя нA физичecкиe oгpAничeния и пpинятыe дoпyщeния. c цeлью иccлeдoBAния пoлeй cкopocти и тeмпepAтypы Bнyтpи пopиcтoй cpeды y нeпpoницAeмoй гpAницы pAзpAбoтAнA чиcлeннAя cчeмA для peшeния ocнoBныч ypABнeний и BBeдeнo нoBoe пoнятиe пoгpAничнoгo cлoя кoличecтBA дBизeния, яBляющeгocя ocнoBным B чиcлeннoй cчeмe peшeния. Bлияниe гpAницы и cил инepции BыpAзAeтcя c пoмoщью тpeч бeзpAзмepныч кoмплeкcoB. ПoкAзAнo, чтo Bлияниe бoлee зAмeтнo B cpeдAч c Bыcoкoй пpoницAeмocтью, зидкocтяч c бoльшим чиcлoм ПpAндтля, бoльшими гpAдиeнтAми дABлeния и B oблAcти пoгpAничнoгo cлoя y пepeднeй кpoмки.

- by neerja mittal
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- Engineering, Heat Transfer, Heat and Mass Transfer, Mathematical Sciences

In the case of high overexpansion, the exhaust jet of the supersonic nozzle of rocket engines separates from nozzle wall because of the large adverse pressure gradient. Correspondingly, to match the pressure of the separated flow region, an oblique shock is generated which evolves through the supersonic jet starting approximately at the separation point. This shock reflects on the nozzle axis with a Mach reflection. Thus, a peculiar Mach reflection takes place whose features depend on the upstream flow conditions, which are usually not uniform. The expected features of Mach reflection may become much difficult to predict, depending on the nozzle shape and the position of the separation point along the divergent section of the nozzle.

- by Marcello Onofri
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- Shock Waves, Classical Physics, Flow Separation, Pressure Gradient

This thesis begins with a study of the origin of cosmological fluctuations with special attention to those cases in which the non-Gaussian correlation functions are large. The analysis shows that perturbations from an almost massless auxiliary field generically produce large values of the non-linear parameter f_NL. The effects of including non-Gaussian correlation functions in the statistics of cosmological structure are explored by constructing a non-Gaussian probability distribution function (PDF). Such PDF is derived for the comoving curvature perturbation from first principles in the context of quantum field theory, with n-point correlation functions as the only input. The non-Gaussian PDF is then used to explore two important problems in the physics of primordial black holes (PBHs): First, to compute non-Gaussian corrections to the number of PBHs generated from the primordial curvature fluctuations. The second application concerns new cosmological observables. The formation of PBHs is known to depend on two main physical characteristics: the strength of the gravitational field produced by the initial curvature inhomogeneity and the pressure gradient at the edge of the curvature configuration. We account for the probability of finding these configurations by using two parameters: The amplitude of the inhomogeneity and its second radial derivative, evaluated at the centre of the configuration. The implications of the derived probability for the fraction of mass in the universe in the form of PBHs are discussed.

- by Juan Hidalgo
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- Quantum Field Theory, Primordial Black Hole, Pressure Gradient, Perturbation Theory
- by Philippe Schmitz and +1
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- Engineering, Crossflow Filtration, Fluid Dynamics, Desalination