Spatial model of convective solute transport in brain extracellular space does not support a “glymphatic” mechanism

Science.gov (United States)

Jin, Byung-Ju; Smith, Alex J.

2016-01-01

A “glymphatic system,” which involves convective fluid transport from para-arterial to paravenous cerebrospinal fluid through brain extracellular space (ECS), has been proposed to account for solute clearance in brain, and aquaporin-4 water channels in astrocyte endfeet may have a role in this process. Here, we investigate the major predictions of the glymphatic mechanism by modeling diffusive and convective transport in brain ECS and by solving the Navier–Stokes and convection–diffusion equations, using realistic ECS geometry for short-range transport between para-arterial and paravenous spaces. Major model parameters include para-arterial and paravenous pressures, ECS volume fraction, solute diffusion coefficient, and astrocyte foot-process water permeability. The model predicts solute accumulation and clearance from the ECS after a step change in solute concentration in para-arterial fluid. The principal and robust conclusions of the model are as follows: (a) significant convective transport requires a sustained pressure difference of several mmHg between the para-arterial and paravenous fluid and is not affected by pulsatile pressure fluctuations; (b) astrocyte endfoot water permeability does not substantially alter the rate of convective transport in ECS as the resistance to flow across endfeet is far greater than in the gaps surrounding them; and (c) diffusion (without convection) in the ECS is adequate to account for experimental transport studies in brain parenchyma. Therefore, our modeling results do not support a physiologically important role for local parenchymal convective flow in solute transport through brain ECS. PMID:27836940

Wavelength selection in traveling-wave convection in a fluid mixture

International Nuclear Information System (INIS)

Surko, C.M.; Eaton, K.D.; Baxter, G.W.; Iwata, K.

1993-01-01

The mechanisms by which a one-dimensional pattern of traveling waves changes wavelength (i.e. the Eckhaus instability) is studied in a binary fluid mixture. Propagating wavelength modulations develop when the Rayleigh number of the system is decreased below a wavelength-dependent threshold, commonly referred to as the Eckhaus boundary. These wavelength modulations increase in amplitude and narrow in spatial extent until they trigger the creation or annihilation of convection roll pairs and thereby change the average wavelength of the system. The authors find qualitatively different dynamics for wavelength-increasing events and wavelength-decreasing events; these differences are due to the strong wavelength dependence of the group velocity

Mixed convective flow of immiscible viscous fluids confined between ...

African Journals Online (AJOL)

user

International Journal of Engineering, Science and Technology ... finite difference methods to analyze the problem of natural convection boundary layer flow along a complex vertical surface ... analyzed the flow of two immiscible fluids in a parallel plate channel ... wavy and flat walls are maintained at constant temperatures w.

On triply diffusive convection in completely confined fluids

Directory of Open Access Journals (Sweden)

Prakash Jyoti

2017-01-01

Full Text Available The present paper carries forward Prakash et al. [21] analysis for triple diffusive convection problem in completely confined fluids and derives upper bounds for the complex growth rate of an arbitrary oscillatory disturbance which may be neutral or unstable through the use of some non-trivial integral estimates obtained from the coupled system of governing equations of the problem.

The Characteristics of natural convection heat transfer of Al_2O_3–water nano fluid flow in a vertical annulus pipe

International Nuclear Information System (INIS)

Reinaldy Nazar

2016-01-01

Results of several researches have shown that nano fluids have better thermal characteristics than conventional fluid (water). In this regard, ideas for using nano fluids as an alternative heat transfer fluid in the reactor coolant system have been well developed. Meanwhile the natural convection in a vertical annulus pipe is one of the important mechanisms of heat transfer and is found at the TRIGA research reactor, the new generation nuclear power plants and other energy conversion devices. On the other hand, the heat transfer characteristics of nano fluids in a vertical annulus pipe has not been known. Therefore, it is important to do research continuously to analyze the heat transfer nano fluids in a vertical annulus pipe. This study has carried out numerical analysis by using computer code of CFD (computational of fluids dynamic) on natural convection heat transfer characteristics of nano fluids flow of Al_2O_3-water 2 % volume in the vertical annulus pipe. The results showed an increase in heat transfer performance (Nusselt numbers - NU) by 20.5 % - 35 %. In natural convection mode with Rayleigh numbers 2.471 e"+"0"9 ≤ Ra ≤ 1.955 e"+"1"3 obtained empirical correlations for water is N_U = 1.065 (R_a(D_H/x))"0"."1"7"9 and empirical correlations for Al_2O_3-water nano fluids is N_U = 14.869 (R_a(D_H/x))"0"."1"1"5.(author)

On natural convection in enclosures filled with fluid-saturated porous media including viscous dissipation

Energy Technology Data Exchange (ETDEWEB)

Costa, V.A.F. [Departamento de Engenharia Mecanica, Universidade de Aveiro, Campus Universitario de Santiago, 3810-193 Aveiro (Portugal)

2006-07-15

Care needs to be taken when considering the viscous dissipation in the energy conservation formulation of the natural convection problem in fluid-saturated porous media. The unique energy formulation compatible with the First Law of Thermodynamics informs us that if the viscous dissipation term is taken into account, also the work of pressure forces term needs to be taken into account. In integral terms, the work of pressure forces must equal the energy dissipated by viscous effects, and the net energy generation in the overall domain must be zero. If only the (positive) viscous dissipation term is considered in the energy conservation equation, the domain behaves as a heat multiplier, with an heat output greater than the heat input. Only the energy formulation consistent with the First Law of Thermodynamics leads to the correct flow and temperature fields, as well as of the heat transfer parameters characterizing the involved porous device. Attention is given to the natural convection problem in a square enclosure filled with a fluid-saturated porous medium, using the Darcy Law to describe the fluid flow, but the main ideas and conclusions apply equally for any general natural or mixed convection heat transfer problem. It is also analyzed the validity of the Oberbeck-Boussinesq approximation when applied to natural convection problems in fluid-saturated porous media. (author)

Characterization of boundary layer thickness of nano fluid ZrO_2 on natural convection process

International Nuclear Information System (INIS)

V-Indriati Sri Wardhani; Henky P Rahardjo

2015-01-01

Cooling system is highly influenced by the process of convection heat transfer from the heat source to the cooling fluid. The cooling fluid usually used conventional fluid such as water. Cooling system performance can be improved by using fluids other than water such as nano fluid that is made from a mixture of water and nano-sized particles. Researchers at BATAN Bandung have made nano fluid ZrO_2 from local materials, as well as experimental equipment for studying the thermohydraulic characteristics of nano fluid as the cooling fluid. In this study, thermohydraulic characteristics of nano fluid ZrO_2 are observed through experimentation. Nano fluid ZrO_2 is made from a mixture of water with ZrO_2 nano-sized particles of 10-7-10-9 nm whose concentration is 1 g/liter. This nano fluid is used as coolant in the cooling process of natural convection. The natural convection process depends on the temperature difference between heat source and the cooling fluid, which occur in the thermal boundary layer. Therefore it is necessary to study the thermal boundary layer thickness of nano fluid ZrO_2, which is also able to determine the local velocity. Experimentations are done with several variation of the heater power and then the temperature are measured at several horizontal points to see the distribution of the temperatures. The temperature distribution measurement results can be used to determine the boundary layer thickness and flow rate. It is obtained that thermal boundary layer thickness and velocity of nano fluid ZrO_2 is not much different from the conventional fluid water. (author)

The onset of double diffusive convection in a viscoelastic fluid-saturated porous layer with non-equilibrium model.

Directory of Open Access Journals (Sweden)

Zhixin Yang

Full Text Available The onset of double diffusive convection in a viscoelastic fluid-saturated porous layer is studied when the fluid and solid phase are not in local thermal equilibrium. The modified Darcy model is used for the momentum equation and a two-field model is used for energy equation each representing the fluid and solid phases separately. The effect of thermal non-equilibrium on the onset of double diffusive convection is discussed. The critical Rayleigh number and the corresponding wave number for the exchange of stability and over-stability are obtained, and the onset criterion for stationary and oscillatory convection is derived analytically and discussed numerically.

Scrutinization of thermal radiation, viscous dissipation and Joule heating effects on Marangoni convective two-phase flow of Casson fluid with fluid-particle suspension

Science.gov (United States)

Mahanthesh, B.; Gireesha, B. J.

2018-03-01

The impact of Marangoni convection on dusty Casson fluid boundary layer flow with Joule heating and viscous dissipation aspects is addressed. The surface tension is assumed to vary linearly with temperature. Physical aspects of magnetohydrodynamics and thermal radiation are also accounted. The governing problem is modelled under boundary layer approximations for fluid phase and dust particle phase and then Runge-Kutta-Fehlberg method based numeric solutions are established. The momentum and heat transport mechanisms are focused on the result of distinct governing parameters. The Nusselt number is also calculated. It is established that the rate of heat transfer can be enhanced by suspending dust particles in the base fluid. The temperature field of fluid phase and temperature of dust phase are quite reverse for thermal dust parameter. The radiative heat, viscous dissipation and Joule heating aspects are constructive for thermal fields of fluid and dust phases. The velocity of dusty Casson fluid dominates the velocity of dusty fluid while this trend is opposite in the case of temperature. Moreover qualitative behaviour of fluid phase and dust phase temperature/velocity are similar.

Magneto thermal convection in a compressible couple-stress fluid

Energy Technology Data Exchange (ETDEWEB)

Singh, Mahinder [Lovely School of Science, Dept. of Mathematics, Lovely Professional Univ., Phagwara (India); Kumar, Pardeep [Dept. of Mathematics, ICDEOL, H.P. Univ., Shimla (India)

2010-03-15

The problem of thermal instability of compressible, electrically conducting couple-stress fluids in the presence of a uniform magnetic field is considered. Following the linearized stability theory and normal mode analysis, the dispersion relation is obtained. For stationary convection, the compressibility, couple-stress, and magnetic field postpone the onset of convection. Graphs have been plotted by giving numerical values of the parameters to depict the stability characteristics. The principle of exchange of stabilities is found to be satisfied. The magnetic field introduces oscillatory modes in the system that were non-existent in its absence. The case of overstability is also studied wherein a sufficient condition for the non-existence of overstability is obtained. (orig.)

Compressible Analysis of Bénard Convection of Magneto Rotatory Couple-Stress Fluid

Directory of Open Access Journals (Sweden)

Mehta C.B.

2018-02-01

Full Text Available Thermal Instability (Benard’s Convection in the presence of uniform rotation and uniform magnetic field (separately is studied. Using the linearized stability theory and normal mode analyses the dispersion relation is obtained in each case. In the case of rotatory Benard’s stationary convection compressibility and rotation postpone the onset of convection whereas the couple-stress have duel character onset of convection depending on rotation parameter. While in the absence of rotation couple-stress always postpones the onset of convection. On the other hand, magnetic field on thermal instability problem on couple-stress fluid for stationary convection couple-stress parameter and magnetic field postpones the onset of convection. The effect of compressibility also postpones the onset of convection in both cases as rotation and magnetic field. Graphs have been plotted by giving numerical values to the parameters to depict the stationary characteristics. Further, the magnetic field and rotation are found to introduce oscillatory modes which were non-existent in their absence and then the principle of exchange of stability is valid. The sufficient conditions for non-existence of overstability are also obtained.

Natural convective flow of a magneto-micropolar fluid along a vertical plate

Directory of Open Access Journals (Sweden)

M. Ferdows

2018-03-01

Full Text Available This paper presents a numerical study of natural convective flow of an electrically conducting viscous micropolar fluid past a vertical plate. Internal heat generation (IHG versus without IHG in the medium are discussed in the context of corresponding similarity solutions. Results are presented in terms of velocity, angular velocity, temperature, skin friction in tabular forms, local wall-coupled stress, and Nusselt number. Computations have been accomplished by parametrizing the micropolar, micro-rotation, magnetic field, suction parameters, and the Prandtl number. Several critical issues are addressed at the end of the paper with reference to a previous study by El-Hakiem. The study is relevant to high-temperature electromagnetic materials fabrication systems. Keywords: Natural convection, Thermal boundary layer, Micropolar fluid, Similarity transformation, Internal heat generation

Three-dimensional Rayleigh-Taylor convection of miscible fluids in a porous medium

Science.gov (United States)

Suekane, Tetsuya; Nakanishi, Yuji; Wang, Lei

2017-11-01

Natural convection of miscible fluids in a porous medium is relevant for fields, such as geoscience and geoengineering, and for the geological storage of CO2. In this study, we use X-ray computer tomography to visualize 3D fingering structures associated with the Rayleigh-Taylor instability between miscible fluids in a porous medium. In the early stages of the onset of the Rayleigh-Taylor instability, a fine crinkling pattern gradually appears at the interface. As the wavelength and amplitude increase, descending fingers form on the interface and extend vertically downward; moreover, ascending and highly symmetric fingers form. The adjacent fingers are cylindrical in shape and coalesce to form large fingers. Fingers appearing on the interface tend to become finer with increasing Rayleigh number, which is consistent with linear perturbation theory. If the Péclet number exceeds 10, the transverse dispersion increases the finger diameter and enhances finger coalescence, strongly impacting the decay in finger number density. When mechanical dispersion is negligible, the finger-extension velocity, the mass-transfer rate, and the onset time scale with Rayleigh number. Mechanical dispersion not only reduces the onset time but also enhances mass transport, which indicates that mechanical dispersion influences the long-term dissolution process of CO2 injected into aquifers.

Laminar flow and convective transport processes scaling principles and asymptotic analysis

CERN Document Server

Brenner, Howard

1992-01-01

Laminar Flow and Convective Transport Processes: Scaling Principles and Asymptotic Analysis presents analytic methods for the solution of fluid mechanics and convective transport processes, all in the laminar flow regime. This book brings together the results of almost 30 years of research on the use of nondimensionalization, scaling principles, and asymptotic analysis into a comprehensive form suitable for presentation in a core graduate-level course on fluid mechanics and the convective transport of heat. A considerable amount of material on viscous-dominated flows is covered.A unique feat

Effect of rotation on the onset of thermal convection in a viscoelastic fluid layer

Energy Technology Data Exchange (ETDEWEB)

Swamy, Mahantesh S [Department of Mathematics, Government College, Gulbarga 585 105 (India); Sidram, W, E-mail: mahantesh_swamy@yahoo.co.in [Department of Mathematics, Gulbarga University, Jnana Ganga, Gulbarga 585 106 (India)

2013-02-15

A rotating viscoelastic fluid layer heated from below is studied analytically using both linear and nonlinear stability analyses. The Oldroyd-B fluid model is employed to describe the rheological behaviour of the fluid. The Coriolis term is included in the momentum equation and the Oberbeck-Boussinesq approximation is invoked. The onset criterion for both stationary and oscillatory convection is derived as a function of Taylor number, Prandtl number and viscoelastic parameters. There is competition between the processes of rotation, viscous relaxation and thermal diffusion that causes the convection to set in through oscillatory rather than stationary modes. The rotation inhibits the onset of convection in both stationary and oscillatory modes. The stress relaxation parameter destabilizes the system towards the oscillatory mode, while the strain retardation parameter enhances the stability and this stabilization is reinforced by the rotation effect. The nonlinear theory is based on a truncated representation of the Fourier series method. The effect of rotation, viscoelastic parameters and also the Prandtl number on the transient heat transfer is presented graphically. (paper)

Effect of Carreau-Yasuda rheological parameters on subcritical Lapwood convection in horizontal porous cavity saturated by shear-thinning fluid

Science.gov (United States)

Khechiba, Khaled; Mamou, Mahmoud; Hachemi, Madjid; Delenda, Nassim; Rebhi, Redha

2017-06-01

The present study is focused on Lapwood convection in isotropic porous media saturated with non-Newtonian shear thinning fluid. The non-Newtonian rheological behavior of the fluid is modeled using the general viscosity model of Carreau-Yasuda. The convection configuration consists of a shallow porous cavity with a finite aspect ratio and subject to a vertical constant heat flux, whereas the vertical walls are maintained impermeable and adiabatic. An approximate analytical solution is developed on the basis of the parallel flow assumption, and numerical solutions are obtained by solving the full governing equations. The Darcy model with the Boussinesq approximation and energy transport equations are solved numerically using a finite difference method. The results are obtained in terms of the Nusselt number and the flow fields as functions of the governing parameters. A good agreement is obtained between the analytical approximation and the numerical solution of the full governing equations. The effects of the rheological parameters of the Carreau-Yasuda fluid and Rayleigh number on the onset of subcritical convection thresholds are demonstrated. Regardless of the aspect ratio of the enclosure and thermal boundary condition type, the subcritical convective flows are seen to occur below the onset of stationary convection. Correlations are proposed to estimate the subcritical Rayleigh number for the onset of finite amplitude convection as a function of the fluid rheological parameters. Linear stability of the convective motion, predicted by the parallel flow approximation, is studied, and the onset of Hopf bifurcation, from steady convective flow to oscillatory behavior, is found to depend strongly on the rheological parameters. In general, Hopf bifurcation is triggered earlier as the fluid becomes more and more shear-thinning.

Two-dimensional convection and interchange motions in fluids and magnetized plasmas

DEFF Research Database (Denmark)

Garcia, O.E.; Bian, N.H.; Naulin, V.

2006-01-01

fluids, emphasizing its relation to interchange motions of non- uniformly magnetized plasmas. This is followed by a review of the theories for the onset of convection and quasi-linear saturation in driven-dissipative systems. Non-linear numerical simulations which result in stationary convective states...... behaviour of the fluctuation level which is associated with relaxation oscillations in the kinetic energy of the azimuthally mean flows. This leads to a state of large-scale intermittency manifested by exponential tails in the single-point probability distribution function of the dependent variables...

Entropy generation in turbulent mixed convection heat transfer to highly variable property pipe flow of supercritical fluids

International Nuclear Information System (INIS)

Mohseni, Mahdi; Bazargan, Majid

2014-01-01

Highlights: • The entropy generation in supercritical fluid flows has been numerically investigated. • The mechanisms of entropy generation are different near and away from the walls. • In the near wall region, the energy dissipation is the deciding parameter. • Away from the wall, the heat transfer is the effective factor in entropy generation. • The bulk Be number is greater in the liquid-like region than in vapor-like region. - Abstract: In this study, a two dimensional CFD code has been developed to investigate entropy generation in turbulent mixed convection heat transfer flow of supercritical fluids. Since the fluid properties vary significantly under supercritical conditions, the changes of entropy generation are large. The contribution of each of the mechanisms of entropy production (heat transfer and energy dissipation) is compared in different regions of the flow. The results show that the mechanisms of entropy generation act differently in the near wall region within the viscous sub-layer and in the region away from the wall. The effects of the wall heat flux on the entropy generation are also investigated

Ignition in Convective-Diffusive Systems

National Research Council Canada - National Science Library

Law, Chung

1999-01-01

... efficiency as well as the knock and emission characteristics. The ignition event is clearly controlled by the chemical reactions of fuel oxidation and the fluid mechanics of convective and diffusive transport...

Stability analysis of natural convection in superposed fluid and porous layers

International Nuclear Information System (INIS)

Hirata, S.C.; Goyeau, B.; Gobin, D.; Cotta, R.M.

2005-01-01

A linear stability analysis of the onset of thermal natural convection in superposed fluid and porous layers is called out. The resulting eigenvalue problem is solved using a integral transformation technique. The effect of the variation of the Darcy number on the stability of the system is analyzed. (authors)

Stability analysis of natural convection in superposed fluid and porous layers

Energy Technology Data Exchange (ETDEWEB)

Hirata, S.C.; Goyeau, B.; Gobin, D. [Paris-11 Univ. - Paris-6, FAST - UMR CNRS 7608, 91 - Orsay (France); Cotta, R.M. [Rio de Janeiro Univ. (LTTC/PEM/EE/COPPE/UFRJ), RJ (Brazil)

2005-07-01

A linear stability analysis of the onset of thermal natural convection in superposed fluid and porous layers is called out. The resulting eigenvalue problem is solved using a integral transformation technique. The effect of the variation of the Darcy number on the stability of the system is analyzed. (authors)

ISS COLUMBUS laboratory experiment `GeoFlow I and II' -fluid physics research in microgravity environment to study convection phenomena inside deep Earth and mantle

Science.gov (United States)

Futterer, Birgit; Egbers, Christoph; Chossat, Pascal; Hollerbach, Rainer; Breuer, Doris; Feudel, Fred; Mutabazi, Innocent; Tuckerman, Laurette

Overall driving mechanism of flow in inner Earth is convection in its gravitational buoyancy field. A lot of effort has been involved in theoretical prediction and numerical simulation of both the geodynamo, which is maintained by convection, and mantle convection, which is the main cause for plate tectonics. Especially resolution of convective patterns and heat transfer mechanisms has been in focus to reach the real, highly turbulent conditions inside Earth. To study specific phenomena experimentally different approaches has been observed, against the background of magneto-hydrodynamic but also on the pure hydrodynamic physics of fluids. With the experiment `GeoFlow' (Geophysical Flow Simulation) instability and transition of convection in spherical shells under the influence of central-symmetry buoyancy force field are traced for a wide range of rotation regimes within the limits between non-rotating and rapid rotating spheres. The special set-up of high voltage potential between inner and outer sphere and use of a dielectric fluid as working fluid induce an electro-hydrodynamic force, which is comparable to gravitational buoyancy force inside Earth. To reduce overall gravity in a laboratory this technique requires microgravity conditions. The `GeoFlow I' experiment was accomplished on International Space Station's module COLUM-BUS inside Fluid Science Laboratory FSL und supported by EADS Astrium, Friedrichshafen, User Support und Operations Centre E-USOC in Madrid, Microgravity Advanced Research and Support Centre MARS in Naples, as well as COLUMBUS Control Center COL-CC Munich. Running from August 2008 until January 2009 it delivered 100.000 images from FSL's optical diagnostics module; here more precisely the Wollaston shearing interferometry was used. Here we present the experimental alignment with numerical prediction for the non-rotating and rapid rotation case. The non-rotating case is characterized by a co-existence of several stationary supercritical

Unsteady MHD Mixed Convection Slip Flow of Casson Fluid over Nonlinearly Stretching Sheet Embedded in a Porous Medium with Chemical Reaction, Thermal Radiation, Heat Generation/Absorption and Convective Boundary Conditions.

Science.gov (United States)

Ullah, Imran; Bhattacharyya, Krishnendu; Shafie, Sharidan; Khan, Ilyas

2016-01-01

Numerical results are presented for the effect of first order chemical reaction and thermal radiation on mixed convection flow of Casson fluid in the presence of magnetic field. The flow is generated due to unsteady nonlinearly stretching sheet placed inside a porous medium. Convective conditions on wall temperature and wall concentration are also employed in the investigation. The governing partial differential equations are converted to ordinary differential equations using suitable transformations and then solved numerically via Keller-box method. It is noticed that fluid velocity rises with increase in radiation parameter in the case of assisting flow and is opposite in the case of opposing fluid while radiation parameter has no effect on fluid velocity in the forced convection. It is also seen that fluid velocity and concentration enhances in the case of generative chemical reaction whereas both profiles reduces in the case of destructive chemical reaction. Further, increase in local unsteadiness parameter reduces fluid velocity, temperature and concentration. Over all the effects of physical parameters on fluid velocity, temperature and concentration distribution as well as on the wall shear stress, heat and mass transfer rates are discussed in detail.

Double stratification effects in chemically reactive squeezed Sutterby fluid flow with thermal radiation and mixed convection

Science.gov (United States)

Ahmad, S.; Farooq, M.; Javed, M.; Anjum, Aisha

2018-03-01

A current analysis is carried out to study theoretically the mixed convection characteristics in squeezing flow of Sutterby fluid in squeezed channel. The constitutive equation of Sutterby model is utilized to characterize the rheology of squeezing phenomenon. Flow characteristics are explored with dual stratification. In flowing fluid which contains heat and mass transport, the first order chemical reaction and radiative heat flux affect the transport phenomenon. The systems of non-linear governing equations have been modulating which then solved by mean of convergent approach (Homotopy Analysis Method). The graphs are reported and illustrated for emerging parameters. Through graphical explanations, drag force, rate of heat and mass transport are conversed for different pertinent parameters. It is found that heat and mass transport rate decays with dominant double stratified parameters and chemical reaction parameter. The present two-dimensional examination is applicable in some of the engineering processes and industrial fluid mechanics.

Numerical simulation in three space dimensions of time-dependent thermal convection in a rotating fluid

International Nuclear Information System (INIS)

Hathaway, D.H.; Somerville, R.C.J.; National Solar Observatory, Sunspot, NM; California Univ., La Jolla)

1985-01-01

Three-dimensional, time-dependent convection in a plane layer of fluid, uniformly heated from below and subject to vertical shear and to rotation about an axis tilted from the vertical, was simulated by the numerical solution of the Boussinesq equations, including all Coriolis terms. Rotation about a vertical axis produces smaller convection cells with diminished heat fluxes and considerable vorticity. When the rotation axis is tilted from the vertical to represent tropical latitudes, the convection cells become elongated in a N-S direction. Imposed flows with constant vertical shear produce convective rolls aligned with the mean flow. When the rotation vector is tilted from the vertical, the competing effects due to rotation and shear can stabilize the convective motions. 15 references

Convective heat transfer

CERN Document Server

Kakac, Sadik; Pramuanjaroenkij, Anchasa

2014-01-01

Intended for readers who have taken a basic heat transfer course and have a basic knowledge of thermodynamics, heat transfer, fluid mechanics, and differential equations, Convective Heat Transfer, Third Edition provides an overview of phenomenological convective heat transfer. This book combines applications of engineering with the basic concepts of convection. It offers a clear and balanced presentation of essential topics using both traditional and numerical methods. The text addresses emerging science and technology matters, and highlights biomedical applications and energy technologies. What’s New in the Third Edition: Includes updated chapters and two new chapters on heat transfer in microchannels and heat transfer with nanofluids Expands problem sets and introduces new correlations and solved examples Provides more coverage of numerical/computer methods The third edition details the new research areas of heat transfer in microchannels and the enhancement of convective heat transfer with nanofluids....

Numerical experiments on thermal convection of highly compressible fluids with variable viscosity and thermal conductivity: Implications for mantle convection of super-Earths

Science.gov (United States)

Kameyama, Masanori; Yamamoto, Mayumi

2018-01-01

We conduct a series of numerical experiments of thermal convection of highly compressible fluids in a two-dimensional rectangular box, in order to study the mantle convection on super-Earths. The thermal conductivity and viscosity are assumed to exponentially depend on depth and temperature, respectively, while the variations in thermodynamic properties (thermal expansivity and reference density) with depth are taken to be relevant for the super-Earths with 10 times the Earth's. From our experiments we identified a distinct regime of convecting flow patterns induced by the interplay between the adiabatic temperature change and the spatial variations in viscosity and thermal conductivity. That is, for the cases with strong temperature-dependent viscosity and depth-dependent thermal conductivity, a "deep stratosphere" of stable thermal stratification is formed at the base of the mantle, in addition to thick stagnant lids at their top surfaces. In the "deep stratosphere", the fluid motion is insignificant particularly in the vertical direction in spite of smallest viscosity owing to its strong dependence on temperature. Our finding may further imply that some of super-Earths which are lacking in mobile tectonic plates on their top surfaces may have "deep stratospheres" at the base of their mantles.

Developing natural convection in a fluid layer with localized heating and large viscosity variation

Energy Technology Data Exchange (ETDEWEB)

Hickox, C.E.; Chu, Tze Yao.

1991-01-01

Numerical simulations and laboratory experiments are used to elucidate aspects of transient natural convection in a magma chamber. The magma chamber is modeled as a horizontal fluid layer confined within an enclosure of square planform and heated from below by a strip heater centered on the lower boundary of the enclosure. The width of the strip heater and the depth of the fluid layer are one-fourth of the layer width. Corn syrup is used as the working fluid in order to approximate the large viscosity variation with temperature and the large Prandtl number typical of magma. The quiescent, uniform, fluid layer is subjected to instantaneous heating from the strip heater producing a transient flow which is dominated by two counter-rotating convective cells. Experimentally determined characteristics of the developing flow are compared with numerical simulations carried out with a finite element computer program. The results of numerical simulations are in essential agreement with experimental data. Differences between the numerical simulations and experimental measurements are conjectured to result from non-ideal effects present in the experiment which are difficult to represent accurately in a numerical simulation.

Large-scale thermal convection of viscous fluids in a faulted system: 3D test case for numerical codes

Science.gov (United States)

Magri, Fabien; Cacace, Mauro; Fischer, Thomas; Kolditz, Olaf; Wang, Wenqing; Watanabe, Norihiro

2017-04-01

In contrast to simple homogeneous 1D and 2D systems, no appropriate analytical solutions exist to test onset of thermal convection against numerical models of complex 3D systems that account for variable fluid density and viscosity as well as permeability heterogeneity (e.g. presence of faults). Owing to the importance of thermal convection for the transport of energy and minerals, the development of a benchmark test for density/viscosity driven flow is crucial to ensure that the applied numerical models accurately simulate the physical processes at hands. The presented study proposes a 3D test case for the simulation of thermal convection in a faulted system that accounts for temperature dependent fluid density and viscosity. The linear stability analysis recently developed by Malkovsky and Magri (2016) is used to estimate the critical Rayleigh number above which thermal convection of viscous fluids is triggered. The numerical simulations are carried out using the finite element technique. OpenGeoSys (Kolditz et al., 2012) and Moose (Gaston et al., 2009) results are compared to those obtained using the commercial software FEFLOW (Diersch, 2014) to test the ability of widely applied codes in matching both the critical Rayleigh number and the dynamical features of convective processes. The methodology and Rayleigh expressions given in this study can be applied to any numerical model that deals with 3D geothermal processes in faulted basins as by example the Tiberas Basin (Magri et al., 2016). References Kolditz, O., Bauer, S., Bilke, L., Böttcher, N., Delfs, J. O., Fischer, T., U. J. Görke, T. Kalbacher, G. Kosakowski, McDermott, C. I., Park, C. H., Radu, F., Rink, K., Shao, H., Shao, H.B., Sun, F., Sun, Y., Sun, A., Singh, K., Taron, J., Walther, M., Wang,W., Watanabe, N., Wu, Y., Xie, M., Xu, W., Zehner, B., 2012. OpenGeoSys: an open-source initiative for numerical simulation of thermo-hydro-mechanical/chemical (THM/C) processes in porous media. Environmental

Marangoni-buoyancy convection in binary fluids under varying noncondensable concentrations

Science.gov (United States)

Li, Yaofa; Yoda, Minami

2014-11-01

Marangoni-buoyancy convection in binary fluids in the presence of phase change is a complex and poorly understood problem. Nevertheless, this flow is of interest in evaporative cooling because solutocapillary stresses could reduce film dryout. Convection was therefore studied in methanol-water (MeOH-H2O) layers of depth h ~ 1 - 3 mm confined in a sealed rectangular cell driven by horizontal temperature differences of ~6° C applied over ~ 5 cm. Particle-image velocimetry (PIV) was used to study how varying the fraction of noncondensables (i.e., air) ca from ~ 7 mol% to ambient conditions in the vapor space affects soluto- and thermocapillary stresses in this flow. Although solutocapillary stresses can be used to drive the flow towards hot regions, solutocapillarity appears to have the greatest effect on the flow at small ca, because noncondensables suppress phase change and hence the gradient in the liquid-phase composition at the interface. Surprisingly, convection at ca ~ 50 % leads to a very weak flow and significant condensation in the central portion of the layer i.e., away from the heated and cooled walls). Supported by ONR.

Tensor viscosity method for convection in numerical fluid dynamics

International Nuclear Information System (INIS)

Dukowicz, J.K.; Ramshaw, J.D.

1979-01-01

A new method, called the tensor viscosity method, is described for differencing the convective terms in multidimensional numerical fluid dynamics. The method is the proper generalization to two or three dimensions of interpolated donor cell differencing in one dimension, and is designed to achieve numerical stability with minimal numerical damping. It is a single-step method that is distinguished by simplicity and case of implementation, even in the case of an arbitrary non-rectangular mesh. It should therefore be useful in finite-element as well as finite-difference formulations

Chaotic convection of viscoelastic fluids in porous media

Energy Technology Data Exchange (ETDEWEB)

Sheu, L.-J. [Department of Mechanical Engineering, Chung Hua University, Hsinchu, Taiwan (China)], E-mail: ljsheu@chu.edu.tw; Tam, L.-M. [Department of Electromechanical Engineering, University of Macau, Macau (China)], E-mail: fstlmt@umac.mo; Chen, J.-H. [Department of Mechanical Engineering, Chung Hua University, Hsinchu, Taiwan (China)], E-mail: chen@chu.edu.tw; Chen, H.-K. [Department of Industrial Engineering and Management, Hsiuping Institute of Technology, Taichung, Taiwan (China)], E-mail: kanechen@giga.net.tw; Lin, K.-T. [Department of Mechanical Engineering, Chung Yuan Christian University, Chung Li, Taiwan (China)], E-mail: willie@nanya.edu.tw; Kang Yuan [Department of Mechanical Engineering, Chung Yuan Christian University, Chung Li, Taiwan (China)], E-mail: yk@cycu.edu.tw

2008-07-15

Buoyancy-induced convection in a viscoelastic fluid-saturated porous medium was analyzed using an Oldroydian-type constitutive relation. An autonomous system with four differential equations was deduced by applying the truncated Galerkin expansion to the momentum and heat transfer equations. The four-dimensional system can be reduced to many systems provided in the literature such as the Lorenz system, Vadasz system, Khayat system, and Akhatov system. Depending on the flow parameters, the asymptotic behavior can be stationary, periodic, or chaotic. Generation of a four-scroll, or two-'butterfly', chaotic attractor was observed. Results also show that stress relaxation tends to precipitate the onset of chaos.

Heat transfer within hydrodissection fluids: An analysis of thermal conduction and convection using liquid and gel materials.

Science.gov (United States)

Johnson, Alexander; Brace, Christopher

2015-01-01

Interventional oncology procedures such as thermal ablation are becoming widely used for many tumours in the liver, kidney and lung. Thermal ablation refers to the focal destruction of tissue by generating cytotoxic temperatures in the treatment zone. Hydrodissection - separating tissues with fluids - protects healthy tissues adjacent to the ablation treatment zone to improve procedural safety, and facilitate more aggressive power application or applicator placement. However, fluids such as normal saline and 5% dextrose in water (D5W) can migrate into the peritoneum, reducing their protective efficacy. As an alternative, a thermo-gelable poloxamer 407 (P407) solution has been recently developed to facilitate hydrodissection procedures. We hypothesise that the P407 gel material does not provide convective heat dissipation from the ablation site, and therefore may alter the heat transfer dynamics compared to liquid materials during hydrodissection-assisted thermal ablation. The purpose of this study was to investigate the heat dissipation mechanics within D5W, liquid P407 and gel P407 hydrodissection barriers. Overall it was shown that the gel P407 dissipated heat primarily through conduction, whereas the liquid P407 and D5W dissipated heat through convection. Furthermore, the rate of temperature change within the gel P407 was greater than liquid P407 and D5W. Testing to evaluate the in vivo efficacy of the fluids with different modes of heat dissipation seems warranted for further study.

Convection of geothermal fluids in the Timanfaya volcanic area, Lanzarote, Canary Islands

Energy Technology Data Exchange (ETDEWEB)

Arana, V.; Diez, J.L.; Ortiz, R.; Yuguero, J.

1984-01-01

A mathematical model has been derived to study the superficial thermal anomalies to be found in Lanzarote (605 C at 13 m depth) in association with the convection of geothermal fluids. The model is valid for a wide range of conditions, in particular for those found beneath the Timanfaya volcano (active between 1730 and 1736). Geological and geophysical data suggest that the heat source is related to a cylindrical magma body with a radius of 200 +/- 100 m and a top temperature of 850 +/- 100 C at a depth of 4 +/- 1 km. Energy is transported through fractures by magmatic volatiles and/or by water vapor coming from a deeply located water table: in such a convection system, a fluid flow of 10 1/m/sup 2/ day, which corresponds to a thermal flux of 130 W/m/sup 2/, is sufficient to explain the temperature anomalies observed at the surface. The relationships between gas flow and the surface temperatures, as well as the thermal gradients in the conducting fracture are also discussed. 27 references.

Thermal Marangoni convection in two-phase flow of dusty Casson fluid

Science.gov (United States)

Mahanthesh, B.; Gireesha, B. J.

2018-03-01

This paper deals with the thermal Marangoni convection effects in magneto-Casson liquid flow through suspension of dust particles. The transpiration cooling aspect is accounted. The surface tension is assumed to be fluctuating linearly with temperature. The fluid and dust particle's temperature of the interface is chosen as a quadratic function of interface arc length. The governing problem is modelled by conservation laws of mass, momentum and energy for fluid and dust particle phase. Stretching transformation technique is utilized to form ordinary differential equations from the partial differential equations. Later, the numerical solutions based on Runge-Kutta-Fehlberg method are established. The momentum and heat transport distributions are focused on the outcome of distinct governing parameters. The results of Nusselt number is also presented and discussed. It is established that the heat transfer rate is higher in the case of dusty non-Newtonian fluid than dusty Newtonian fluid. The rate of heat transfer can be enhanced by suspending dust particles in a base liquid.

Mixed convection in fluid superposed porous layers

CERN Document Server

Dixon, John M

2017-01-01

This Brief describes and analyzes flow and heat transport over a liquid-saturated porous bed. The porous bed is saturated by a liquid layer and heating takes place from a section of the bottom. The effect on flow patterns of heating from the bottom is shown by calculation, and when the heating is sufficiently strong, the flow is affected through the porous and upper liquid layers. Measurements of the heat transfer rate from the heated section confirm calculations. General heat transfer laws are developed for varying porous bed depths for applications to process industry needs, environmental sciences, and materials processing. Addressing a topic of considerable interest to the research community, the brief features an up-to-date literature review of mixed convection energy transport in fluid superposed porous layers.

Double-diffusive convection in a Darcy porous medium saturated with a couple-stress fluid

International Nuclear Information System (INIS)

Malashetty, M S; Kollur, Premila; Pal, Dulal

2010-01-01

The onset of double-diffusive convection in a couple-stress fluid-saturated horizontal porous layer is studied using linear and weak nonlinear stability analyses. The modified Darcy equation that includes the time derivative term and the inertia term is used to model the momentum equation. The expressions for stationary, oscillatory and finite-amplitude Rayleigh number are obtained as a function of the governing parameters. The effect of couple-stress parameter, solute Rayleigh number, Vadasz number and diffusivity ratio on stationary, oscillatory and finite-amplitude convection is shown graphically. It is found that the couple-stress parameter and the solute Rayleigh number have a stabilizing effect on stationary, oscillatory and finite-amplitude convection. The diffusivity ratio has a destabilizing effect in the case of stationary and finite-amplitude modes, with a dual effect in the case of oscillatory convection. The Vadasz number advances the onset of oscillatory convection. The heat and mass transfer decreases with an increase in the values of couple-stress parameter and diffusivity ratio, while both increase with an increase in the value of the solute Rayleigh number.

A computational fluid dynamics model for designing heat exchangers based on natural convection

NARCIS (Netherlands)

Dirkse, M.H.; Loon, van W.K.P.; Walle, van der T.; Speetjens, S.L.; Bot, G.P.A.

2006-01-01

A computational fluid dynamics model was created for the design of a natural convection shell-and-tube heat exchanger with baffles. The flow regime proved to be turbulent and this was modelled using the k¿¿ turbulence model. The features of the complex geometry were simplified considerably resulting

On a Five-Dimensional Chaotic System Arising from Double-Diffusive Convection in a Fluid Layer

Directory of Open Access Journals (Sweden)

R. Idris

2013-01-01

Full Text Available A chaotic system arising from double-diffusive convection in a fluid layer is investigated in this paper based on the theory of dynamical systems. A five-dimensional model of chaotic system is obtained using the Galerkin truncated approximation. The results showed that the transition from steady convection to chaos via a Hopf bifurcation produced a limit cycle which may be associated with a homoclinic explosion at a slightly subcritical value of the Rayleigh number.

Influence of fluid-property variation on turbulent convective heat transfer in vertical annular CHANNEL FLOWS

International Nuclear Information System (INIS)

Joong Hun Bae; Jung Yul Yoo; Haecheon Choi

2005-01-01

Full text of publication follows: The influence of variable fluid property on turbulent convective heat transfer is investigated using direct numerical simulations. We consider thermally-developing flows of air and supercritical-pressure CO 2 in a vertical annular channel where the inner wall is heated with a constant heat flux and the outer wall is insulated. Turbulence statistics show that the heat and momentum transport characteristics of variable-property flows are significantly different from those of constant-property flows. The difference is mainly caused by the spatial and temporal variations of fluid density. The non-uniform density distribution causes fluid particles to be accelerated either by expansion or buoyancy force, while the temporal density fluctuations change the heat and momentum transfer via transport of turbulent mass flux, ρ'u' i . Both effects of the spatial and temporal variations of density are shown to be important in the analysis of turbulent convective heat transfer for supercritical-pressure fluids. For variable-property heated air flows, however, the effect of temporal density fluctuations can be neglected at low Mach number, which is in good accordance with the Morkovin's hypothesis. (authors)

Natural convection heat transfer of fluid with temperature-dependent specific heat

International Nuclear Information System (INIS)

Tanaka, Amane; Kubo, Shinji; Akino, Norio

1998-01-01

The present study investigates natural convection from a heated vertical plate of fluid with temperature-dependent specific heat, which is introduced as a model of microencapsulated phase change material slurries (MCPCM slurries). The temperature dependence of specific heat is represented by Gauss function with three physical parameters (peak temperature, width of phase change temperature and latent heat). Boundary layer equations are solved numerically, and the velocity and temperature fields of the flow are obtained. The relation between the heat transfer coefficients and the physical parameters of specific heat is discussed. The results show that the velocities and temperatures are smaller, and the heat transfer coefficients are larger comparing with those of the fluid with constant specific heat. (author)

Transient natural convection in an internally heated fluid layer. Topical report, June 1975--June 1976

International Nuclear Information System (INIS)

Kulacki, F.A.; Emara, A.A.

1976-06-01

An experimental study of the transient response of a horizontal fluid layer subjected to a step change in internal energy generation has been conducted to determine the time scales for the development and decay of natural convection driven solely by the internal heat release. The layer is bounded from above by a rigid, constant temperature surface and from below by a rigid, insulated surface. Two types of unsteady convection processes are considered. In the first, the layer is brought to a motionless, isothermal state, and internal energy generation is suddenly started. In the second, steady natural convection is the initial state, and internal energy generation is suddenly stopped. For both cases, the time required for the development of the final steady state is determined by measuring the temperature response of the fluid with a small thermocouple probe. The time required for the development of the maximum temperature difference in the layer with internal generation and the time required for the complete decay of the maximum temperature difference of steady convection at a given Rayleigh number when internal energy generation is suddenly stopped are correlated with the Rayleigh number in equations which will find general application in PAHR problems in nuclear power reactors and particularly in the analysis of the small-time thermal response of in-vessel and ex-vessel molten core retention devices

Conjugate Heat Transfer of Mixed Convection for Viscoelastic Fluid Past a Stretching Sheet

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Kai-Long Hsiao

2007-01-01

Full Text Available A conjugate heat transfer problem of a second-grade viscoelastic fluid past a stretching sheet has been studied. Governing equations include heat conduction equation of a stretching sheet, continuity equation, momentum equation, and energy equation of a second-grade fluid, analyzed by a combination of a series expansion method, the similarity transformation, and a second-order accurate finite-difference method. These solutions are used to iterate with the heat conduction equation of the stretching sheet to obtain distributions of the local convective heat transfer coefficient and the stretching sheet temperature. Ranges of dimensionless parameters, the Prandtl number Pr, the elastic number E and the conduction-convection coefficient Ncc are from 0.001 to 10, 0.0001 to 0.01, and 0.5 to 2.0, respectively. A parameter G, which is used to represent the dominance of the buoyant effect, is present in governing equations. Results indicated that elastic effect in the flow could increase the local heat transfer coefficient and enhance the heat transfer of a stretching sheet. In addition, same as the results from Newtonian fluid flow and conduction analysis of a stretching sheet, a better heat transfer is obtained with a larger Ncc, G, and E.

Fluid Mechanics.

Science.gov (United States)

Drazin, Philip

1987-01-01

Outlines the contents of Volume II of "Principia" by Sir Isaac Newton. Reviews the contributions of subsequent scientists to the physics of fluid dynamics. Discusses the treatment of fluid mechanics in physics curricula. Highlights a few of the problems of modern research in fluid dynamics. Shows that problems still remain. (CW)

Instabilities of convection patterns in a shear-thinning fluid between plates of finite conductivity

Science.gov (United States)

Varé, Thomas; Nouar, Chérif; Métivier, Christel

2017-10-01

Rayleigh-Bénard convection in a horizontal layer of a non-Newtonian fluid between slabs of arbitrary thickness and finite thermal conductivity is considered. The first part of the paper deals with the primary bifurcation and the relative stability of convective patterns at threshold. Weakly nonlinear analysis combined with Stuart-Landau equation is used. The competition between squares and rolls, as a function of the shear-thinning degree of the fluid, the slabs' thickness, and the ratio of the thermal conductivity of the slabs to that of the fluid is investigated. Computations of heat transfer coefficients are in agreement with the maximum heat transfer principle. The second part of the paper concerns the stability of the convective patterns toward spatial perturbations and the determination of the band width of the stable wave number in the neighborhood of the critical Rayleigh number. The approach used is based on the Ginzburg-Landau equations. The study of rolls stability shows that: (i) for low shear-thinning effects, the band of stable wave numbers is bounded by zigzag instability and cross-roll instability. Furthermore, the marginal cross-roll stability boundary enlarges with increasing shear-thinning properties; (ii) for high shear-thinning effects, Eckhaus instability becomes more dangerous than cross-roll instability. For square patterns, the wave number selection is always restricted by zigzag instability and by "rectangular Eckhaus" instability. In addition, the width of the stable wave number decreases with increasing shear-thinning effects. Numerical simulations of the planform evolution are also presented to illustrate the different instabilities considered in the paper.

Hydromagnetic slip flow of water based nano-fluids past a wedge with convective surface in the presence of heat generation (or) absorption

International Nuclear Information System (INIS)

Rahman, M.M.; Al-Lawatia, M.A.; Eltayeb, I.A.; Al-Salti, N.

2012-01-01

Heat transfer characteristics of a two-dimensional steady hydromagnetic slip flow of water based nano-fluids (TiO 2 -water, Al 2 O 3 -water, and Cu-water) over a wedge with convective surface taking into account the effects of heat generation (or absorption) has been investigated numerically. The local similarity solutions are obtained by using very robust computer algebra software MATLAB and presented graphically as well as in a tabular form. The results show that nano-fluid velocity is lower than the velocity of the base fluid and the existence of the nano-fluid leads to the thinning of the hydrodynamic boundary layer. The rate of shear stress is significantly influenced by the surface convection parameter and the slip parameter. It is higher for nano-fluids than the base fluid. The results also show that within the boundary layer the temperature of the nano-fluid is higher than the temperature of the base fluid. The rate of heat transfer is found to increase with the increase of the surface convection and the slip parameters. Addition of nano-particles to the base fluid induces the rate of heat transfer. The rate of heat transfer in the Cu-water nano-fluid is found to be higher than the rate of heat transfer in the TiO 2 -water and Al 2 O 3 -water nano-fluids. (authors)

Filtering of sound from the Navier-Stokes equations. [An approximation for describing thermal convection in a compressible fluid

Energy Technology Data Exchange (ETDEWEB)

Paolucci, S.

1982-12-01

An approximation leading to anelastic equations capable of describing thermal convection in a compressible fluid is given. These equations are more general than the Oberbeck-Boussinesq equations and different than the standard anelastic equations in that they can be used for the computation of convection in a fluid with large density gradients present. We show that the equations do not contain acoustic waves, while at the same time they can still describe the propagation of internal waves. Throughout we show that the filtering of acoustic waves, within the limits of the approximation, does not appreciably alter the description of the physics.

Natural convection flow and heat transfer between a fluid layer and a porous layer inside a rectangular enclosure

International Nuclear Information System (INIS)

Beckermann, C.; Ramadhyani, S.; Viskanta, R.

1986-01-01

A numerical and experimental study is performed to analyze the steady-state natural convection fluid flow and heat transfer in a vertical rectangular enclosure that is partially filled with a vertical layer of a fluid-saturated porous medium. The flow in the porous layer is modeled utilizing the Brinkman-Forchheimer-extended Darcy equations. The numerical model is verified by conducting a number of experiments with spherical glass beads as the porous medium and water and glycerin as the fluids in rectangular test-cells. The agreement between the flow visualization results and temperature measurements and the numerical model is, in general, good. It is found that the amount of fluid penetrating from the fluid region into the porous layer depends strongly on the Darcy (Da) and Rayleigh (Ra) numbers. For a relatively low product of Ra x Da, the flow takes place primarily in the fluid layer, and heat transfer in the porous layer is by conduction only. On the other hand, fluid penetrating into a relatively highly permeable porous layer has a significant impact on the natural convection flow patterns in the entire enclosure

Chaotic convective behavior and stability analysis of a fractional viscoelastic fluids model in porous media

KAUST Repository

N'Doye, Ibrahima

2015-05-25

In this paper, a dynamical fractional viscoelastic fluids convection model in porous media is proposed and its chaotic behavior is studied. A preformed equilibrium points analysis indicates the conditions where chaotic dynamics can be observed, and show the existence of chaos. The behavior and stability analysis of the integer-order and the fractional commensurate and non-commensurate orders of a fractional viscoelastic fluids system, which exhibits chaos, are presented as well.

Stability of Marangoni Convection in a Fluid Layer with Variable Viscosity and deformable Free Surface under Free-Slip condition

Directory of Open Access Journals (Sweden)

Nurul Hafizah Zainal Abidin

2009-01-01

Full Text Available The steady marangoni convection is investigated in ahorizontal layer of fluid with a free-slip bottom heated frombelow and cooled from above. Since the viscosity is temperaturedependentthe consequences of relaxing oberbeck-boussinesqapproximation and free surface deformability are theoreticallyexamined by means of small disturbance analysis. Prediction forthe onset of convection are obtained from the analysis bynumerical technique. The effect of variable viscosity and surfacedeformation on the onset of fluid motion is investigated in detail.It is shown that the critical values of marangoni and wavenumber depend strongly on the viscosity variation and surfacedeformation.

Computational fluid dynamics modeling of mixed convection flows in buildings enclosures

Energy Technology Data Exchange (ETDEWEB)

Kayne, Alexander; Agarwal, Ramesh K. [Department of Mechanical Engineering and Materials Science, Washington University, St. Louis, MO 63130 (United States)

2013-07-01

In recent years Computational Fluid Dynamics (CFD) simulations are increasingly used to model the air circulation and temperature environment inside the rooms of residential and office buildings to gain insight into the relative energy consumptions of various HVAC systems for cooling/heating for climate control and thermal comfort. This requires accurate simulation of turbulent flow and heat transfer for various types of ventilation systems using the Reynolds-Averaged Navier-Stokes (RANS) equations of fluid dynamics. Large Eddy Simulation (LES) or Direct Numerical Simulation (DNS) of Navier-Stokes equations is computationally intensive and expensive for simulations of this kind. As a result, vast majority of CFD simulations employ RANS equations in conjunction with a turbulence model. In order to assess the modeling requirements (mesh, numerical algorithm, turbulence model etc.) for accurate simulations, it is critical to validate the calculations against the experimental data. For this purpose, we use three well known benchmark validation cases, one for natural convection in 2D closed vertical cavity, second for forced convection in a 2D rectangular cavity and the third for mixed convection in a 2D square cavity. The simulations are performed on a number of meshes of different density using a number of turbulence models. It is found that k-epsilon two-equation turbulence model with a second-order algorithm on a reasonable mesh gives the best results. This information is then used to determine the modeling requirements (mesh, numerical algorithm, turbulence model etc.) for flows in 3D enclosures with different ventilation systems. In particular two cases are considered for which the experimental data is available. These cases are (1) air flow and heat transfer in a naturally ventilated room and (2) airflow and temperature distribution in an atrium. Good agreement with the experimental data and computations of other investigators is obtained.

Fluid mechanics in fluids at rest.

Science.gov (United States)

Brenner, Howard

2012-07-01

Using readily available experimental thermophoretic particle-velocity data it is shown, contrary to current teachings, that for the case of compressible flows independent dye- and particle-tracer velocity measurements of the local fluid velocity at a point in a flowing fluid do not generally result in the same fluid velocity measure. Rather, tracer-velocity equality holds only for incompressible flows. For compressible fluids, each type of tracer is shown to monitor a fundamentally different fluid velocity, with (i) a dye (or any other such molecular-tagging scheme) measuring the fluid's mass velocity v appearing in the continuity equation and (ii) a small, physicochemically and thermally inert, macroscopic (i.e., non-Brownian), solid particle measuring the fluid's volume velocity v(v). The term "compressibility" as used here includes not only pressure effects on density, but also temperature effects thereon. (For example, owing to a liquid's generally nonzero isobaric coefficient of thermal expansion, nonisothermal liquid flows are to be regarded as compressible despite the general perception of liquids as being incompressible.) Recognition of the fact that two independent fluid velocities, mass- and volume-based, are formally required to model continuum fluid behavior impacts on the foundations of contemporary (monovelocity) fluid mechanics. Included therein are the Navier-Stokes-Fourier equations, which are now seen to apply only to incompressible fluids (a fact well-known, empirically, to experimental gas kineticists). The findings of a difference in tracer velocities heralds the introduction into fluid mechanics of a general bipartite theory of fluid mechanics, bivelocity hydrodynamics [Brenner, Int. J. Eng. Sci. 54, 67 (2012)], differing from conventional hydrodynamics in situations entailing compressible flows and reducing to conventional hydrodynamics when the flow is incompressible, while being applicable to both liquids and gases.

Fluid and particle mechanics

CERN Document Server

Michell, S J

2013-01-01

Fluid and Particle Mechanics provides information pertinent to hydraulics or fluid mechanics. This book discusses the properties and behavior of liquids and gases in motion and at rest. Organized into nine chapters, this book begins with an overview of the science of fluid mechanics that is subdivided accordingly into two main branches, namely, fluid statics and fluid dynamics. This text then examines the flowmeter devices used for the measurement of flow of liquids and gases. Other chapters consider the principle of resistance in open channel flow, which is based on improper application of th

Stellar convection and dynamo theory

Energy Technology Data Exchange (ETDEWEB)

Jennings, R L

1989-10-01

In considering the large scale stellar convection problem the outer layers of a star are modelled as two co-rotating plane layers coupled at a fluid/fluid interface. Heating from below causes only the upper fluid to convect, although this convection can penetrate into the lower fluid. Stability analysis is then used to find the most unstable mode of convection. With parameters appropriate to the Sun the most unstable mode is steady convection in thin cells (aspect ratio {approx equal} 0.2) filling the convection zone. There is negligible vertical motion in the lower fluid, but considerable thermal penetration, and a large jump in helicity at the interface, which has implications for dynamo theory. An {alpha}{omega} dynamo is investigated in isolation from the convection problem. Complexity is included by allowing both latitudinal and time dependence in the magnetic fields. The nonlinear dynamics of the resulting partial differential equations are analysed in considerable detail. On varying the main control parameter D (the dynamo number), many transitions of behaviour are found involving many forms of time dependence, but not chaos. Further, solutions which break equatorial symmetry are common and provide a theoretical explanation of solar observations which have this symmetry. Overall the behaviour was more complicated than expected. In particular, there were multiple stable solutions at fixed D, meaning that similar stars can have very different magnetic patterns, depending upon their history. (author).

Moist Orographic Convection: Physical Mechanisms and Links to Surface-Exchange Processes

Directory of Open Access Journals (Sweden)

Daniel J. Kirshbaum

2018-02-01

Full Text Available This paper reviews the current understanding of moist orographic convection and its regulation by surface-exchange processes. Such convection tends to develop when and where moist instability coincides with sufficient terrain-induced ascent to locally overcome convective inhibition. The terrain-induced ascent can be owing to mechanical (airflow over or around an obstacle and/or thermal (differential heating over sloping terrain forcing. For the former, the location of convective initiation depends on the dynamical flow regime. In “unblocked” flows that ascend the barrier, the convection tends to initiate over the windward slopes, while in “blocked” flows that detour around the barrier, the convection tends to initiate upstream and/or downstream of the high terrain where impinging flows split and rejoin, respectively. Processes that destabilize the upstream flow for mechanically forced moist convection include large-scale moistening and ascent, positive surface sensible and latent heat fluxes, and differential advection in baroclinic zones. For thermally forced flows, convective initiation is driven by thermally direct circulations with sharp updrafts over or downwind of the mountain crest (daytime or foot (nighttime. Along with the larger-scale background flow, local evapotranspiration and transport of moisture, as well as thermodynamic heterogeneities over the complex terrain, regulate moist instability in such events. Longstanding limitations in the quantitative understanding of related processes, including both convective preconditioning and initiation, must be overcome to improve the prediction of this convection, and its collective effects, in weather and climate models.

Poly-N-acetylglucosamine matrix polysaccharide impedes fluid convection and transport of the cationic surfactant cetylpyridinium chloride through bacterial biofilms.

Science.gov (United States)

Ganeshnarayan, Krishnaraj; Shah, Suhagi M; Libera, Matthew R; Santostefano, Anthony; Kaplan, Jeffrey B

2009-03-01

Biofilms are composed of bacterial cells encased in a self-synthesized, extracellular polymeric matrix. Poly-beta(1,6)-N-acetyl-d-glucosamine (PNAG) is a major biofilm matrix component in phylogenetically diverse bacteria. In this study we investigated the physical and chemical properties of the PNAG matrix in biofilms produced in vitro by the gram-negative porcine respiratory pathogen Actinobacillus pleuropneumoniae and the gram-positive device-associated pathogen Staphylococcus epidermidis. The effect of PNAG on bulk fluid flow was determined by measuring the rate of fluid convection through biofilms cultured in centrifugal filter devices. The rate of fluid convection was significantly higher in biofilms cultured in the presence of the PNAG-degrading enzyme dispersin B than in biofilms cultured without the enzyme, indicating that PNAG decreases bulk fluid flow. PNAG also blocked transport of the quaternary ammonium compound cetylpyridinium chloride (CPC) through the biofilms. Binding of CPC to biofilms further impeded fluid convection and blocked transport of the azo dye Allura red. Bioactive CPC was efficiently eluted from biofilms by treatment with 1 M sodium chloride. Taken together, these findings suggest that CPC reacts directly with the PNAG matrix and alters its physical and chemical properties. Our results indicate that PNAG plays an important role in controlling the physiological state of biofilms and may contribute to additional biofilm-associated processes such as biocide resistance.

Chaotic Darcy-Brinkman convection in a fluid saturated porous layer subjected to gravity modulation

Directory of Open Access Journals (Sweden)

Moli Zhao

2018-06-01

Full Text Available On the basis of Darcy-Brinkman model, the chaotic convection in a couple stress fluid saturated porous media under gravity modulation is investigated using the nonlinear stability analyses. The transition from steady convection to chaos is analysed with the effect of Darcy-Brinkman couple stress parameter and the gravity modulation. The results show that the chaotic behavior is connected with the critical value of Rayleigh number which is dependent upon the oscillation frequency and the Darcy-Brinkman couple stress parameter. If the oscillation frequency Ω is not zero, the Rayleigh number value R of the chaotic behavior increases with the increase of the Darcy-Brinkman couple stress parameter. The Darcy-Brinkman couple stress parameter and the gravity modulation decrease the rate of heat transfer. Keywords: Darcy-Brinkman model, Gravity modulation, Nonlinear stability, Chaotic convection

Laminar free convection with variable fluid properties in vertical ducts having uniform wall temperature

International Nuclear Information System (INIS)

Aihara, Toshio; Maruyama, Shigenao; Choi, Jun-Seop.

1985-01-01

Recently, the research on free convection in vertical ducts has become active again concerning the problem of cooling in nuclear reactor accidents and the cooling of electronic equipment. Generally, in the convection heat transfer in ducts, when the wall temperature is high, the fluid temperature in the ducts conspicuously changes, accordingly, the temperature dependence of the properties cannot be neglected. In this study, about the laminar free convection in parallel plates and a circular pipe having uniform wall temperature, the numerical analysis taking the temperature dependence of all properties into account was carried out, thus the effect of the temperature dependence of properties exerted on free convection heat transfer was clarified, and the relation to the solution in constant properties was examined. Moreover, by introducing a new representative dimension, it was attempted to express mean heat transfer coefficient which is independent of the form of ducts in unified way. The mean Nusselt number of the constant property solution using entrance pressure condition agreed very well with the exact numerical solution. (Kako, I.)

Two-dimensional convection of an incompressible viscous fluid with the heat exchange on the free border

Directory of Open Access Journals (Sweden)

Svetlana S. Vlasova

2016-09-01

Full Text Available The exact stationary solution of the boundary-value problem that describes the convective motion of an incompressible viscous fluid in the two-dimensional layer with the square heating of a free surface in Stokes's approach is found. The linearization of the Oberbeck–Boussinesq equations allows one to describe the flow of fluid in extreme points of pressure and temperature. The condition under which the counter-current flows (two counter flows in the fluid can be observed, is introduced. If the stagnant point in the fluid exists, six non-closed whirlwinds can be observed.

Fully coupled thermal-mechanical-fluid flow model for nonliner geologic systems

International Nuclear Information System (INIS)

Hart, R.D.

1981-01-01

A single model is presented which describes fully coupled thermal-mechanical-fluid flow behavior of highly nonlinear, dynamic or quasistatic, porous geologic systems. The mathematical formulation for the model utilizes the continuum theory of mixtures to describe the multiphase nature of the system, and incremental linear constitutive theory to describe the path dependency of nonlinear material behavior. The model, incorporated in an explicit finite difference numerical procedure, was implemented in two different computer codes. A special-purpose one-dimensional code, SNEAKY, was written for initial validation of the coupling mechanisms and testing of the coupled model logic. A general purpose commercially available code, STEALTH, developed for modeling dynamic nonlinear thermomechanical processes, was modified to include fluid flow behavior and the coupling constitutive model. The fully explicit approach in the coupled calculation facilitated the inclusion of the coupling mechanisms and complex constitutive behavior. Analytical solutions pertaining to consolidation theory for soils, thermoelasticity for solids, and hydrothermal convection theory provided verification of stress and fluid flow, stress and conductive heat transfer, and heat transfer and fluid flow couplings, respectively, in the coupled model. A limited validation of the adequacy of the coupling constitutive assumptions was also performed by comparison with the physical response from two laboratory tests. Finally, the full potential of the coupled model is illustrated for geotechnical applications in energy-resource related areas. Examples in the areas of nuclear waste isolation and cut-and-fill mining are cited

Free-convective flow of fluid in a thin porous contour and geothermal anomalies

Energy Technology Data Exchange (ETDEWEB)

Magomedbekov Kh.G.; Ramazanov, M.M.; Vagabov, M.V.

1996-01-24

The problem of free convection in a thin porous contour, placed in uniform impermeable massif is considered. The approximate analitical solution of conjugate problem is obtained. The critical Rayleigh number is determined, by exceeding of which the steady fluid circulation in an annulus is established. The computations of abnormal heat flow near surface are carried out, stipulated by thermoconvection in a contour.

The onset of nonpenetrative convection in a suddenly cooled layer of fluid

Energy Technology Data Exchange (ETDEWEB)

Ihle, Christian F. [Program in Fluid Dynamics, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile, Blanco Encalada 2002 Of. 327, Santiago (Chile); Nino, Yarko [Departamento de Ingenieria Civil, Division de Recursos Hidricos y Medio Ambiente, Universidad de Chile, Av. Blanco Encalada 2002, Santiago (Chile)

2006-04-15

Conditions for the onset of nonpenetrative convection in a horizontal Boussinesq fluid layer subject to a step change in temperature are studied using propagation theory. A wide range of Prandtl numbers and two different kinematic boundary conditions are considered. It is shown that for high Rayleigh numbers, critical conditions for the onset of convective motion reproduce exactly those for the unsteady Rayleigh-Benard instability. Present results extend those of previous research and show a tendency of the rigid-rigid and free-rigid critical curves to converge for low Prandtl numbers. Comparison between present and previously reported results on critical conditions for the onset of instabilities and onset time using different methods yields good agreement on a middle to high Prandtl number range. A ratio of 10 between experimentally measured and theoretically predicted onset times is suggested for stress-free bounded systems. (author)

Heat and mass transfer of a second grade magnetohydrodynamic fluid over a convectively heated stretching sheet

Directory of Open Access Journals (Sweden)

Kalidas Das

2016-10-01

Full Text Available The present work is concerned with heat and mass transfer of an electrically conducting second grade MHD fluid past a semi-infinite stretching sheet with convective surface heat flux. The analysis accounts for thermophoresis and thermal radiation. A similarity transformations is used to reduce the governing equations into a dimensionless form. The local similarity equations are derived and solved using Nachtsheim-Swigert shooting iteration technique together with Runge–Kutta sixth order integration scheme. Results for various flow characteristics are presented through graphs and tables delineating the effect of various parameters characterizing the flow. Our analysis explores that the rate of heat transfer enhances with increasing the values of the surface convection parameter. Also the fluid velocity and temperature in the boundary layer region rise significantly for increasing the values of thermal radiation parameter.

The Impact of Convective Fluid Inertia Forces on Operation of Tilting-Pad Journal Bearings

Directory of Open Access Journals (Sweden)

Thomas Hagemann

2017-01-01

Full Text Available This paper presents a combination of experimental data, CFD analyses, and bearing code predictions on emergence of convective inertia fluid forces within the lube oil flow of tilting-pad journal bearings. Concordantly, experimental data and CFD analyses show a significant rise of local pressure at the transition between inlet and leading edge of tilting-pad, especially for high-speed applications with surface speeds up to 100 m/s. This effect can be related to convective inertia forces within fluid flow as cross-sections and flow character rapidly change at the pad entrance. An energy-based approach is implemented in the bearing code in order to provide enhanced boundary conditions for Reynolds equation considering this effect. As a result, predictions of bearing code achieved significant improved correlation with measured pressure distributions and CFD-data. Further, beside the local influence, a nonnegligible impact on characteristic parameters of bearing operation such as maximum temperature and stiffness and damping coefficients is observed. Finally, the results are critically analyzed and requirements to gain more distinct and reliable data are specified.

Modelling of large-scale structures arising under developed turbulent convection in a horizontal fluid layer (with application to the problem of tropical cyclone origination

Directory of Open Access Journals (Sweden)

G. V. Levina

2000-01-01

Full Text Available The work is concerned with the results of theoretical and laboratory modelling the processes of the large-scale structure generation under turbulent convection in the rotating-plane horizontal layer of an incompressible fluid with unstable stratification. The theoretical model describes three alternative ways of creating unstable stratification: a layer heating from below, a volumetric heating of a fluid with internal heat sources and combination of both factors. The analysis of the model equations show that under conditions of high intensity of the small-scale convection and low level of heat loss through the horizontal layer boundaries a long wave instability may arise. The condition for the existence of an instability and criterion identifying the threshold of its initiation have been determined. The principle of action of the discovered instability mechanism has been described. Theoretical predictions have been verified by a series of experiments on a laboratory model. The horizontal dimensions of the experimentally-obtained long-lived vortices are 4÷6 times larger than the thickness of the fluid layer. This work presents a description of the laboratory setup and experimental procedure. From the geophysical viewpoint the examined mechanism of the long wave instability is supposed to be adequate to allow a description of the initial step in the evolution of such large-scale vortices as tropical cyclones - a transition form the small-scale cumulus clouds to the state of the atmosphere involving cloud clusters (the stage of initial tropical perturbation.

Unsteady Mixed Convection Boundary Layer from a Circular Cylinder in a Micropolar Fluid

Directory of Open Access Journals (Sweden)

Anati Ali

2010-01-01

Full Text Available Most industrial fluids such as polymers, liquid crystals, and colloids contain suspensions of rigid particles that undergo rotation. However, the classical Navier-Stokes theory normally associated with Newtonian fluids is inadequate to describe such fluids as it does not take into account the effects of these microstructures. In this paper, the unsteady mixed convection boundary layer flow of a micropolar fluid past an isothermal horizontal circular cylinder is numerically studied, where the unsteadiness is due to an impulsive motion of the free stream. Both the assisting (heated cylinder and opposing cases (cooled cylinder are considered. Thus, both small and large time solutions as well as the occurrence of flow separation, followed by the flow reversal are studied. The flow along the entire surface of a cylinder is solved numerically using the Keller-box scheme. The obtained results are compared with the ones from the open literature, and it is shown that the agreement is very good.

Natural convection in Bingham plastic fluids from an isothermal spheroid: Effects of fluid yield stress, viscous dissipation and temperature-dependent viscosity

Science.gov (United States)

Gupta, Anoop Kumar; Gupta, Sanjay; Chhabra, Rajendra Prasad

2017-08-01

In this work, the buoyancy-induced convection from an isothermal spheroid is studied in a Bingham plastic fluid. Extensive results on the morphology of approximate yield surfaces, temperature profiles, and the local and average Nusselt numbers are reported to elucidate the effects of the pertinent dimensionless parameters: Rayleigh number, 102 ≤ Ra ≤ 106; Prandtl number, 20 ≤ Pr ≤ 100; Bingham number, 0 ≤ Bn ≤ 103, and aspect ratio, 0.2 ≤ e ≤ 5. Due to the fluid yield stress, fluid-like (yielded) and solid-like (unyielded) regions coexist in the flow domain depending upon the prevailing stress levels vis-a-vis the value of the fluid yield stress. The yielded parts progressively grow in size with the rising Rayleigh number while this tendency is countered by the increasing Bingham and Prandtl numbers. Due to these two competing effects, a limiting value of the Bingham number ( Bn max) is observed beyond which heat transfer occurs solely by conduction due to the solid-like behaviour of the fluid everywhere in the domain. Such limiting values bear a positive dependence on the Rayleigh number ( Ra) and aspect ratio ( e). In addition to this, oblate shapes ( e 1) impede it. Finally, simple predictive expressions for the maximum Bingham number and the average Nusselt number are developed which can be used to predict a priori the overall heat transfer coefficient in a new application. Also, a criterion is developed in terms of the composite parameter Bn• Gr-1/2 which predicts the onset of convection in such fluids. Similarly, another criterion is developed which delineates the conditions for the onset of settling due to buoyancy effects. The paper is concluded by presenting limited results to delineate the effects of viscous dissipation and the temperature-dependent viscosity on the Nusselt number. Both these effects are seen to be rather small in Bingham plastic fluids.

Sunspots and the physics of magnetic flux tubes. VI - Convective propulsion. VII - Heat flow in a convective downdraft

Science.gov (United States)

Parker, E. N.

1979-01-01

The effect of negative aerodynamic drag in an ideal fluid subject to convective instability is considered. It is shown that a cylinder moving in such a fluid is propelled forward in its motion by the convective forces and that the characteristic acceleration time is comparable to the onset time of convective motions in the fluid. It is suggested that convective propulsion plays an important role in the dynamics of flux tubes extending through the surface of the sun. The suppression of the upward heat flow in a Boussinesq convective cell with free upper and lower boundaries by a downdraft is then analyzed. Application to the solar convection zone indicates that downdrafts of 1 to 2 km/s at depths of 1000 to 4000 km beneath the visible surface of the sun are sufficient to reduce the upward heat flux to a small fraction of the ambient value.

On the Onset of Thermal Convection in a Layer of Oldroydian Visco-Elastic Fluid Saturated by Brinkman–Darcy Porous Medium

Directory of Open Access Journals (Sweden)

Chand Ramesh

2015-12-01

Full Text Available Thermal instability in a horizontal layer of Oldroydian visco-elastic fluid in a porous medium is investigated. For porous medium the Brinkman–Darcy model is considered. A linear stability analysis based upon perturbation method and normal mode technique is used to find solution of the fluid layer confined between two free-free boundaries. The onset criterion for stationary and oscillatory convection is derived analytically. The influence of the Brinkman–Darcy, Prandtl–Darcy number, stress relaxation parameter on the stationary and oscillatory convection is studied both analytically and graphically. The sufficient condition for the validity of PES has also been derived.

Fluid mechanics fundamentals and applications

CERN Document Server

Cengel, Yunus

2013-01-01

Cengel and Cimbala's Fluid Mechanics Fundamentals and Applications, communicates directly with tomorrow's engineers in a simple yet precise manner. The text covers the basic principles and equations of fluid mechanics in the context of numerous and diverse real-world engineering examples. The text helps students develop an intuitive understanding of fluid mechanics by emphasizing the physics, using figures, numerous photographs and visual aids to reinforce the physics. The highly visual approach enhances the learning of Fluid mechanics by students. This text distinguishes itself from others by the way the material is presented - in a progressive order from simple to more difficult, building each chapter upon foundations laid down in previous chapters. In this way, even the traditionally challenging aspects of fluid mechanics can be learned effectively. McGraw-Hill is also proud to offer ConnectPlus powered by Maple with the third edition of Cengel/Cimbabla, Fluid Mechanics. This innovative and powerful new sy...

Some problems of free convection in a macrocapillary

Energy Technology Data Exchange (ETDEWEB)

Luikov, A V; Berkovsky, B M; Kolpashchikov, V L

1971-01-01

Solution is given to a number of problems of free convection in incompressible viscous fluid in elementary macrocapillaries with nonuniform temperature distribution at the boundary. The fluid flow structure and effect of a magnetic field on convection in the case of conducting fluid has been studied in detail. The influence of macrocapillary properties on the flow structure, rate of convection, and temperature distribution has been estimated.

Convection with local thermal non-equilibrium and microfluidic effects

CERN Document Server

Straughan, Brian

2015-01-01

This book is one of the first devoted to an account of theories of thermal convection which involve local thermal non-equilibrium effects, including a concentration on microfluidic effects. The text introduces convection with local thermal non-equilibrium effects in extraordinary detail, making it easy for readers newer to the subject area to understand. This book is unique in the fact that it addresses a large number of convection theories and provides many new results which are not available elsewhere. This book will be useful to researchers from engineering, fluid mechanics, and applied mathematics, particularly those interested in microfluidics and porous media.

Understanding and controlling plasmon-induced convection

Science.gov (United States)

Roxworthy, Brian J.; Bhuiya, Abdul M.; Vanka, Surya P.; Toussaint, Kimani C.

2014-01-01

The heat generation and fluid convection induced by plasmonic nanostructures is attractive for optofluidic applications. However, previously published theoretical studies predict only nanometre per second fluid velocities that are inadequate for microscale mass transport. Here we show both theoretically and experimentally that an array of plasmonic nanoantennas coupled to an optically absorptive indium-tin-oxide (ITO) substrate can generate >micrometre per second fluid convection. Crucially, the ITO distributes thermal energy created by the nanoantennas generating an order of magnitude increase in convection velocities compared with nanoantennas on a SiO2 base layer. In addition, the plasmonic array alters absorption in the ITO, causing a deviation from Beer-Lambert absorption that results in an optimum ITO thickness for a given system. This work elucidates the role of convection in plasmonic optical trapping and particle assembly, and opens up new avenues for controlling fluid and mass transport on the micro- and nanoscale.

Fluid dynamics of the magnetic field dependent thermosolutal convection and viscosity between coaxial contracting discs

Science.gov (United States)

Khan, Aamir; Shah, Rehan Ali; Shuaib, Muhammad; Ali, Amjad

2018-06-01

The effects of magnetic field dependent (MFD) thermosolutal convection and MFD viscosity of the fluid dynamics are investigated between squeezing discs rotating with different velocities. The unsteady constitutive expressions of mass conservation, modified Navier-Stokes, Maxwell and MFD thermosolutal convection are coupled as a system of ordinary differential equations. The corresponding solutions for the transformed radial and azimuthal momentum as well as solutions for the azimuthal and axial induced magnetic field equations are determined, also the MHD pressure and torque which the fluid exerts on the upper disc is derived and discussed in details. In the case of smooth discs the self-similar equations are solved using Homotopy Analysis Method (HAM) with appropriate initial guesses and auxiliary parameters to produce an algorithm with an accelerated and assured convergence. The validity and accuracy of HAM results is proved by comparison of the HAM solutions with numerical solver package BVP4c. It has been shown that magnetic Reynolds number causes to decrease magnetic field distributions, fluid temperature, axial and tangential velocity. Also azimuthal and axial components of magnetic field have opposite behavior with increase in MFD viscosity. Applications of the study include automotive magneto-rheological shock absorbers, novel aircraft landing gear systems, heating up or cooling processes, biological sensor systems and biological prosthetic etc.

The effect of heat generation on mixed convection flow in nano fluids over a horizontal circular cylinder

Science.gov (United States)

Juliyanto, Bagus; Widodo, Basuki; Imron, Chairul

2018-04-01

The purpose of this research is to study the effect of heat generation on mixed convection flow on Nano fluids over a horizontal circular cylinder of a heated in two dimension form. A stream of fluids are steady and incompressible, a stream flowing vertically upwards for circular cylinder and the boundary layer at the stagnation point. Three different types of nanoparticles considered are Cu, Al2O3, and TiO2. Mixed convection flow in Nano fluids on the surface of a circular cylinder will cause the boundary layer. The governing boundary layer equations are transformed into a non-dimensional form, and then the non-dimensional forms are transformed into a similar boundary equations by using stream function. Furthermore, an implicit finite-difference scheme known as the Keller-box method is applied to solve numerically the resulting similar boundary layer equations. The result of the research by varying the non-dimensional parameters are mixed convection, Prandtl number, nanoparticle volume fraction, heat generation, and radius of a cylinder are as follows. First, the velocity profile increase and temperature profile decrease when mixed convection parameter increase. Second, the velocity and temperature profiles decrease when Prandtl number parameter increase. Third, the velocity profile with the variation of nanoparticle volume fraction (χ) is increased when the value of χ is 0,1 ≤ χ ≤ 0,15 and the velocity profile decreases when the value of χ is 0,19 ≤ χ ≤ 0,5 while the temperature profile is increasing when the value of χ is 0,1 ≤ χ ≤ 0,5. Fourth, the velocity and temperature profiles increase when heat generation and the radius of the cylinder increase. The last, Cu, Al 2 O 3, and TiO 2 nanoparticles produce the same velocity and temperature profiles, but the three types of nanoparticles are different at the velocity and temperature values.

Principles of fluid mechanics

International Nuclear Information System (INIS)

Kreider, J.F.

1985-01-01

This book is an introduction on fluid mechanics incorporating computer applications. Topics covered are as follows: brief history; what is a fluid; two classes of fluids: liquids and gases; the continuum model of a fluid; methods of analyzing fluid flows; important characteristics of fluids; fundamentals and equations of motion; fluid statics; dimensional analysis and the similarity principle; laminar internal flows; ideal flow; external laminar and channel flows; turbulent flow; compressible flow; fluid flow measurements

MHD axisymmetric flow of power-law fluid over an unsteady stretching sheet with convective boundary conditions

Directory of Open Access Journals (Sweden)

Jawad Ahmed

Full Text Available This paper examines the boundary layer flow and heat transfer characteristic in power law fluid model over unsteady radially stretching sheet under the influence of convective boundary conditions. A uniform magnetic field is applied transversely to the direction of the flow. The governing time dependent nonlinear boundary layer equations are reduced into nonlinear ordinary differential equations with the help of similarity transformations. The transformed coupled ordinary differential equations are then solved analytically by homotopy analysis method (HAM and numerically by shooting procedure. Effects of various governing parameters like, power law index n, magnetic parameter M, unsteadiness A, suction/injection S, Biot number γ and generalized Prandtl number Pr on velocity, temperature, local skin friction and the local Nusselt number are studied and discussed. It is found from the analysis that the magnetic parameter diminishes the velocity profile and the corresponding thermal boundary layer thickness. Keywords: Axisymmetric flow, Power law fluid, Unsteady stretching, Convective boundary conditions

Mechanisms of convective and boiling heat transfer enhancement via ultrasonic vibration

International Nuclear Information System (INIS)

Kim, Yi Gu; Kim, Ho Young; Kang, Seoung Min; Kang, Byung Ha; Lee, Jin Ho

2003-01-01

This work experimentally studies the fundamental mechanisms by which the ultrasonic vibration enhances convection and pool boiling heat transfer. A thin platinum wire is used as both a heat source and a temperature sensor. A high speed video imaging system is employed to observe the behavior of cavitation and thermal bubbles. It is found that when the liquid temperature is below its boiling point, cavitation takes place due to ultrasonic vibration while cavitation disappears when the liquid reaches the boiling point. Moreover, when the gas dissolved in liquid is removed by pre-degassing, the cavitation arises only locally. Depending on the liquid temperature, heat transfer rates in convection, subcooled boiling and saturated boiling regimes are examined. In convection heat transfer regime, fully agitated cavitation is the most efficient heat transfer enhancement mechanism. Subcooled boiling is most enhanced when the local cavitation is induced after degassing. In saturated boiling regime, acoustic pressure is shown to be a dominant heat transfer enhancement mechanism

Natural convection in a composite fluid-porous cavity by the boundary element method

International Nuclear Information System (INIS)

Jecl, R.; Skerget, L.

2005-01-01

The main purpose of this work is to present the use of the boundary element method (BEM) for analyzing the convective fluid flow and heat transfer in composite fluid-porous media domain when the fluid is compressible. In our case the flow is modeled by utilizing the Brinkman extended Darcy momentum equation (Brinkman model) which is commonly used when it is important to satisfy the no-slip boundary condition and when one wishes to compare flows in porous medium with those in pure fluids. The Brinkman equation reduce to the classical Navier Stokes equation for clear fluid when the permeability tends to infinity (porosity is equal to unity), i.e. when the solid matrix in the porous medium disappears and, when the permeability is finite the equation is valid for porous medium. Therefore it is possible to handle porous medium free fluid interface problems by changing the properties of the medium in the computational domain appropriately. Our goal is to widen the applicability of the computational model based on the boundary domain integral method (BDIM) which is an extension of the classical BEM. The governing equations are transformed by using the velocity-vorticity variables formulation and therefore the computation scheme is partitioned into kinematic and kinetic part. (authors)

Mixed convective heat transfer to Sisko fluid over a radially stretching sheet in the presence of convective boundary conditions

Energy Technology Data Exchange (ETDEWEB)

Khan, Masood; Malik, Rabia, E-mail: rabiamalik.qau@gmail.com; Munir, Asif [Department of Mathematics, Quaid-i-Azam University, Islamabad 44000 (Pakistan)

2015-08-15

In this article, the mixed convective heat transfer to Sisko fluid over a radially stretching surface in the presence of convective boundary conditions is investigated. The viscous dissipation and thermal radiation effects are also taken into account. The suitable transformations are applied to convert the governing partial differential equations into a set of nonlinear coupled ordinary differential equations. The analytical solution of the governing problem is obtained by using the homotopy analysis method (HAM). Additionally, these analytical results are compared with the numerical results obtained by the shooting technique. The obtained results for the velocity and temperature are analyzed graphically for several physical parameters for the assisting and opposing flows. It is found that the effect of buoyancy parameter is more prominent in case of the assisting flow as compared to the opposing flow. Further, in tabular form the numerical values are given for the local skin friction coefficient and local Nusselt number. A remarkable agreement is noticed by comparing the present results with the results reported in the literature as a special case.

Mixed convective heat transfer to Sisko fluid over a radially stretching sheet in the presence of convective boundary conditions

International Nuclear Information System (INIS)

Khan, Masood; Malik, Rabia; Munir, Asif

2015-01-01

In this article, the mixed convective heat transfer to Sisko fluid over a radially stretching surface in the presence of convective boundary conditions is investigated. The viscous dissipation and thermal radiation effects are also taken into account. The suitable transformations are applied to convert the governing partial differential equations into a set of nonlinear coupled ordinary differential equations. The analytical solution of the governing problem is obtained by using the homotopy analysis method (HAM). Additionally, these analytical results are compared with the numerical results obtained by the shooting technique. The obtained results for the velocity and temperature are analyzed graphically for several physical parameters for the assisting and opposing flows. It is found that the effect of buoyancy parameter is more prominent in case of the assisting flow as compared to the opposing flow. Further, in tabular form the numerical values are given for the local skin friction coefficient and local Nusselt number. A remarkable agreement is noticed by comparing the present results with the results reported in the literature as a special case

Perturbative calculations of flow patterns in free convection between coaxial cylinders. Non-linear temperature dependences of the fluid properties

International Nuclear Information System (INIS)

Navarro, J. A.; Madariaga, J. A.; Santamaria, C. M.; Saviron, J. M.

1980-01-01

10 refs. Flow pattern calculations in natural convection between two vertical coaxial cylinders are reported. It is assumed trough the paper. that fluid properties, viscosity, thermal conductivity and density, depend no-linearly on temperature and that the aspects (height/radius) ratio of the cylinders is high. Velocity profiles are calculated trough a perturbative scheme and analytic results for the three first perturbation orders are presented. We outline also an iterative method to estimate the perturbations on the flow patterns which arise when a radial composition gradient is established by external forces in a two-component fluid. This procedure, based on semiempirical basis, is applied to gaseous convection. The influence of the molecules gas properties on tho flow is also discussed. (Author) 10 refs

Fluid mechanics of heart valves.

Science.gov (United States)

Yoganathan, Ajit P; He, Zhaoming; Casey Jones, S

2004-01-01

Valvular heart disease is a life-threatening disease that afflicts millions of people worldwide and leads to approximately 250,000 valve repairs and/or replacements each year. Malfunction of a native valve impairs its efficient fluid mechanic/hemodynamic performance. Artificial heart valves have been used since 1960 to replace diseased native valves and have saved millions of lives. Unfortunately, despite four decades of use, these devices are less than ideal and lead to many complications. Many of these complications/problems are directly related to the fluid mechanics associated with the various mechanical and bioprosthetic valve designs. This review focuses on the state-of-the-art experimental and computational fluid mechanics of native and prosthetic heart valves in current clinical use. The fluid dynamic performance characteristics of caged-ball, tilting-disc, bileaflet mechanical valves and porcine and pericardial stented and nonstented bioprostheic valves are reviewed. Other issues related to heart valve performance, such as biomaterials, solid mechanics, tissue mechanics, and durability, are not addressed in this review.

Combined natural convection and radiation in a volumetrically heated fluid layer

International Nuclear Information System (INIS)

Chawla, T.C.; Chan, S.H.; Cheung, F.B.; Cho, D.H.

1980-01-01

The effect of radiation in combination with turbulent natural convection on the rates of heat transfer in volumetrically heated fluid layers characterized by high temperatures has been considered in this study. It is demonstrated that even at high Rayleigh numbers the radiation mode is as effective as the turbulent natural convection mode in removing the heat from the upper surface of the molten pools with adiabatic lower boundary. As a result of this improved heat transfer, it is shown that considerably thicker molten pools with internal heat generation can be supported without boiling inception. The total Nusselt number at a moderate but fixed value of conduction-radiation parameter, can be represented as a function of Rayleigh number in a simple power-law form. As a consequence of this relationship it is shown that maximum nonboiling pool thicknesses vary approximately inversely as the 0.9% power of internal heat generation rate. A comparison between exact analysis using the integral formulation of radiation flux and Rosseland approximation shows that the latter approximation bears out very adequately for optically thick pools with conduction-radiation parameters greater than or equal to 0.4 inspite of the fact that individual components of Nusselt number due to radiation and convection, respectively, are grossly in error. These errors in component heat fluxes are compensating due to the total heat balance constraint. However, the comparison between Rosseland approximation and exact formulation gets poorer as the value of conduction-radiation parameters decreases. This increase in error is principally incurred due to the error in estimating wall temperature differences

Combined natural convection and radiation in a volumetrically heated fluid layer

International Nuclear Information System (INIS)

Chawla, T.C.; Chan, S.H.; Cheung, F.B.; Cho, D.H.

1980-01-01

The effect of radiation in combining with turbulent natural convection on the rates of heat transfer in volumetrically heated fluid layers characterized by high temperatures has been considered in this study. It is demonstrated that even at high Rayleigh numbers the radiation mode is as effective as the turbulent natural convection mode in removing the heat from the upper surface of molten pools with adiabatic lower boundary. As a result of this improved heat transfer, it is shown that considerably thicker molten pools with internal heat generation can be supported without boiling inception. The total Nusselt number at a moderate but fixed value of conduction-radiation parameter, can be represented as a function of Rayleigh number in a simple power-law form. As a consequence of this relationship it is shown that maximum nonboiling pool thicknesses vary approximately inversely as the 0.9 power of internal heat generation rate. A comparison between exact analysis using the integral formulation of radiation flux and Rosseland approximateion shows that the latter approximation bears out very adequately for optically thick pools with conduction-radiation parameter > or approx. =0.4 inspite of the fact that individual components of Nusselt number due to radiation and convection, respectively, are grossly in error. These errors in component heat fluxes are compensating due to the total heat balance constraint. However, the comparison between Rosseland approximation and exact formulation gets poorer as the value of conduction-radiation parameter decreases. This increase in error is principally incurred due to the error in estimating wall temperature differences

Editorial Special Issue on Fluid Mechanics and Fluid Power (FMFP ...

Indian Academy of Sciences (India)

This special issue of Sadhana contains selected papers from two conferences related to fluid mechanics held in India recently, Fluid Mechanics and Fluid Power conference at NIT, Hamirpur, and an International Union of Theoretical ... A simple, well thought out, flow visualization experiment or a computation can sometimes ...

XXII Fluid Mechanics Conference (KKMP2016)

International Nuclear Information System (INIS)

2016-01-01

This Journal of Physics: Conference Series contains papers that have been presented at XXII Fluid Mechanics Conference (XXII FMC) held in Słok near Bełchatów in Poland during llth-14th September of 2016. The Conference is organized by Wrocław University of Science and Technology, Polish Academy of Sciences - Committee of Mechanics and Foun-dation for Development of Wroclaw University of Science and Technology. Let us recall some historical facts: Fluid Mechanics Conferences have been taking place every two years since 1974, which makes a total of forty-two years. The goal of this conference is to provide a forum for exposure and exchange of ideas, methods and results in fluid mechanics. We have already met in Bełchatów 10 years ago (XVII KKMP). It was a successful meeting. Since then the National Conference on Fluid Mechanics has changed title and has started to be named Fluid Mechanics Conference in the hopes that it will attract more participants from other countries. English became the Conference's first language and we started to invite world leading scientists - working in the field of fluid mechanics. At the 2006 conference we hosted for the first time prof. Keith Moffatt from the Cambridge University. In this year prof. Moffatt once again promised us to arrive to Bełchatów. The whole fluid mechanics community celebrates 9 2 anniversary of his birthday. So let us also wish happy anniversary to prof. Moffatt. In the mean time we had to pay last respects to our collages. Prof. Prosnak who is regarded as a founder of the Notational Conference on Fluid Mechanics and is well known through his books. Prof. Puzyrewski who was present at all conferences so far. He was providing via his discussions a special value to these conferences, and our colleague prof. Konrad Bajer who was intended to be the organizer and host of the present conference. Short memories to them will be given during the opening ceremony. Conference topics include, but are not limited

Hall current and Joule heating effects on peristaltic flow of viscous fluid in a rotating channel with convective boundary conditions

Directory of Open Access Journals (Sweden)

Tasawar Hayat

Full Text Available The present article has been arranged to study the Hall current and Joule heating effects on peristaltic flow of viscous fluid in a channel with flexible walls. Both fluid and channel are in a state of solid body rotation. Convective conditions for heat transfer in the formulation are adopted. Viscous dissipation in energy expression is taken into account. Resulting differential systems after invoking small Reynolds number and long wavelength considerations are numerically solved. Runge-Kutta scheme of order four is implemented for the results of axial and secondary velocities, temperature and heat transfer coefficient. Comparison with previous limiting studies is shown. Outcome of new parameters of interest is analyzed. Keywords: Rotating frame, Hall current, Joule heating, Convective conditions, Wall properties

Mathematics applied to fluid mechanics and stability; Proceedings of the Conference, Rensselaer Polytechnic Institute, Troy, NY, Sept. 9-11, 1985

International Nuclear Information System (INIS)

Drew, D.A.; Flaherty, J.E.

1986-01-01

The mathematical analysis of fluid mechanics and stability and its applications in science and engineering are examined in reviews and reports. Topics addressed include Taylor-vortex flow, isothermal fluid-film lubrication theories, the morphology of spiral galaxies, rotating-fluid problems in ballistics, coupled Lorenz oscillators, the connection between chaos and turbulence, plane-front alloy solidification versus free-surface Benard convection, and the nonlinear stability of spiral flow between rotating cylinders with a small gap. Consideration is given to resonance conditions for forced two-dimensional channel flows, the secondary bifurcation of standing surface waves in rectangular basins, instability in the flow of granular materials, and the supercritical dynamics of baroclinic disturbances

Proceedings of industrial applications of fluid mechanics

International Nuclear Information System (INIS)

Sherif, S.A.; Morrow, T.B.; Marshall, L.R.; Dalton, C.

1990-01-01

The is the fourth Forum on Industrial Applications of Fluid Mechanics sponsored by the Fluid Mechanics Committee of the ASME Fluids Engineering Division. The Forum objective is to promote the discussion and interchange of current information on developing and state-of-the-art applications of fluid mechanics technology. The program is organized as a technical forum to encourage the presentation of new ideas, especially those which may be so innovative that a conservative review process might delay their dissemination to the fluids engineering community. Four sessions and a total of 17 papers are scheduled for this program. Three of the four sessions were devoted to contributed papers, while the fourth is a panel discussion with three invited presentations. All papers were reviewed editorially to assure that they are related to the forum theme The papers were not evaluated technically, and therefore carry no endorsement from the Fluid Mechanics Committee or the Fluids Engineering Division with regard to peer evaluation. The forum presentations will focus on specific applications of fluid mechanics technology. Lively discussion of the papers is encouraged at the forum. The Fluid Mechanics Committee plans to sponsor a forum with an industrial applications theme each year at the ASME Winter Annual Meeting. In 1991, the scope of the forum will be enlarged to include the topic of textile applications of fluid mechanics, and another panel session featuring speakers with industrial experience in different areas of fluid mechanics applications. In future years, it is anticipated that the forum will solicit papers from other areas where fluid mechanics technology is applied

Convection in complex shaped vessel; Convection dans des enceintes de forme complexe

Energy Technology Data Exchange (ETDEWEB)

NONE

2000-07-01

The 8 november 2000, the SFT (Societe Francaise de Thermique) organized a technical day on the convection in complex shaped vessels. Nine papers have been presented in the domains of the heat transfers, the natural convection, the fluid distribution, the thermosyphon effect, the steam flow in a sterilization cycle and the transformers cooling. Eight papers are analyzed in ETDE and one paper dealing with the natural convection in spent fuels depository is analyzed in INIS. (A.L.B.)

Measurement of buoyancy driven convection and microaccelerations on board International Space Station with the use of convection sensor Dacon-M

Science.gov (United States)

Putin, Gennady; Belyaev, Mikhail; Babushkin, Igor; Glukhov, Alexander; Zilberman, Evgeny; Maksimova, Marina; Ivanov, Alexander; Sazonov, Viktor; Nikitin, Sergey; Zavalishin, Denis; Polezhaev, Vadim

The system for studying buoyancy driven convection and low-frequency microaccelerations aboard spacecraft is described. The system consists of: 1. facility for experimentation on a spaceship - the convection sensor and electronic equipment for apparatus control and for acquisition and processing of relevant information; 2. facility for ground-based laboratory modeling of various fluid motion mechanisms in application to orbital flight environment; 3. the system for computer simulations of convection processes in a fluid cell of a sensor using the data on microaccelerations obtained by accelerometers and another devices aboard the orbital station. The arrangement and functioning of the sensor and control hardware are expounded. The results of terrestrial experiments performed in order to determine the sensitivity of the sensor are described. The results of experiments carried out in 2008 - 2011 with the “DACON-M” apparatus in different modules of the Russian Segment of International Space Station and for various regimes of Station activity are reported. Experimental data recorded by “DACON-M” apparatus have been compared with the calculations of acceleration components based on the telemetry information about the orientation of the Station.

MHD Convective Flow of Jeffrey Fluid Due to a Curved Stretching Surface with Homogeneous-Heterogeneous Reactions.

Directory of Open Access Journals (Sweden)

Maria Imtiaz

Full Text Available This paper looks at the flow of Jeffrey fluid due to a curved stretching sheet. Effect of homogeneous-heterogeneous reactions is considered. An electrically conducting fluid in the presence of applied magnetic field is considered. Convective boundary conditions model the heat transfer analysis. Transformation method reduces the governing nonlinear partial differential equations into the ordinary differential equations. Convergence of the obtained series solutions is explicitly discussed. Characteristics of sundry parameters on the velocity, temperature and concentration profiles are analyzed by plotting graphs. Computations for pressure, skin friction coefficient and surface heat transfer rate are presented and examined. It is noted that fluid velocity and temperature through curvature parameter are enhanced. Increasing values of Biot number correspond to the enhancement in temperature and Nusselt number.

ANALYSIS OF MARANGONI CONVECTION OF NON-NEWTONIAN POWER LAW FLUIDS WITH LINEAR TEMPERATURE DISTRIBUTION

Directory of Open Access Journals (Sweden)

Yan Zhang

2011-01-01

Full Text Available The problem of steady, laminar, thermal Marangoni convection flow of non-Newtonian power law fluid along a horizontal surface with variable surface temperature is studied. The partial differential equations are transformed into ordinary differential equations by using a suitable similarity transformation and analytical approximate solutions are obtained by an efficient transformation, asymptotic expansion and Padé approximants technique. The effects of power law index and Marangoni number on velocity and temperature profiles are examined and discussed.

Simulation of forced convection in non-Newtonian fluid through sandstones

Science.gov (United States)

Gokhale, M. Y.; Fernandes, Ignatius

2017-11-01

Numerical simulation is carried out to study forced convection in non-Newtonian fluids flowing through sandstones. Simulation is carried out using lattice Boltzmann method (LBM) for both shear-thinning and shear-thickening, by varying the power law index from 0.5 to 1.5 in Carreau-Yasuda model. Parameters involved in LBM and Carreau model are identified to achieve numerical convergence. Permeability and porosity are varied in the range of 10-10-10-6 and 0.1-0.7, respectively, to match actual geometrical properties of sandstone. Numerical technology is validated by establishing Darcy's law by plotting the graph between velocity and pressure gradient. Consequently, investigation is carried out to study the influence of material properties of porous media on flow properties such as velocity profiles, temperature profiles, and Nusselt number.

Lectures on fluid mechanics

CERN Document Server

Shinbrot, Marvin

2012-01-01

Readable and user-friendly, this high-level introduction explores the derivation of the equations of fluid motion from statistical mechanics, classical theory, and a portion of the modern mathematical theory of viscous, incompressible fluids. 1973 edition.

Peristaltic flow of Johnson-Segalman fluid in asymmetric channel with convective boundary conditions

Institute of Scientific and Technical Information of China (English)

H YASMIN; T HAYAT; A ALSAEDI; HH ALSULAMI

2014-01-01

This work is concerned with the peristaltic transport of the Johnson-Segalman fluid in an asymmetric channel with convective boundary conditions. The mathematical modeling is based upon the conservation laws of mass, linear momentum, and energy. The resulting equations are solved after long wavelength and low Reynolds number are used. The results for the axial pressure gradient, velocity, and temperature profiles are obtained for small Weissenberg number. The expressions of the pressure gra-dient, velocity, and temperature are analyzed for various embedded parameters. Pumping and trapping phenomena are also explored.

Variational Multiscale error estimator for anisotropic adaptive fluid mechanic simulations: application to convection-diffusion problems

OpenAIRE

Bazile , Alban; Hachem , Elie; Larroya-Huguet , Juan-Carlos; Mesri , Youssef

2018-01-01

International audience; In this work, we present a new a posteriori error estimator based on the Variational Multiscale method for anisotropic adaptive fluid mechanics problems. The general idea is to combine the large scale error based on the solved part of the solution with the sub-mesh scale error based on the unresolved part of the solution. We compute the latter with two different methods: one using the stabilizing parameters and the other using bubble functions. We propose two different...

FOREWORD Fluid Mechanics and Fluid Power (FMFP)

Indian Academy of Sciences (India)

This section of the Special Issue carries selected articles from the Fluid Mechanics and Fluid. Power Conference held during 12–14 December 2013 at the National Institute of Technology,. Hamirpur (HP). The section includes three review articles and nine original research articles. These were selected on the basis of their ...

Free convection boundary layer flow past a horizontal flat plate embedded in porous medium filled by nano-fluid containing gyro-tactic microorganisms

Energy Technology Data Exchange (ETDEWEB)

Aziz, A. [Department of Mechanical Engineering, School of Engineering and Applied Science, Gonzaga University, Spokane, WA 99258 (United States); Khan, W.A. [Department of Engineering Sciences, National University of Sciences and Technology, Karachi 75350 (Pakistan); Pop, I. [Department of Applied Mathematics, Babes-Bolyai University, Cluj-Napoca (Romania)

2012-06-15

The steady boundary layer free convection flow past a horizontal flat plate embedded in a porous medium filled by a water-based nano-fluid containing gyro-tactic microorganisms is investigated. The Oberbeck-Boussinesq approximation is assumed in the analysis. The effects of bio-convection parameters on the dimensionless velocity, temperature, nano-particle concentration and density of motile microorganisms as well as on the local Nusselt, Sherwood and motile microorganism numbers are investigated and presented graphically. In the absence of bio-convection, the results are compared with the existing data in the open literature and found to be in good agreement. The bio-convection parameters strongly influence the heat, mass, and motile microorganism transport rates. (authors)

Mechanics of couple-stress fluid coatings

Science.gov (United States)

Waxman, A. M.

1982-01-01

The formal development of a theory of viscoelastic surface fluids with bending resistance - their kinematics, dynamics, and rheology are discussed. It is relevant to the mechanics of fluid drops and jets coated by a thin layer of immiscible fluid with rather general rheology. This approach unifies the hydrodynamics of two-dimensional fluids with the mechanics of an elastic shell in the spirit of a Cosserat continuum. There are three distinct facets to the formulation of surface continuum mechanics. Outlined are the important ideas and results associated with each: the kinematics of evolving surface geometries, the conservation laws governing the mechanics of surface continua, and the rheological equations of state governing the surface stress and moment tensors.

Non-Darcy Free Convection of Power-Law Fluids Over a Two-Dimensional Body Embedded in a Porous Medium

KAUST Repository

El-Amin, Mohamed

2010-11-27

A boundary layer analysis was presented to study the non-Darcy-free convection of a power-law fluid over a non-isothermal two-dimensional body embedded in a porous medium. The Ostwald-de Waele power-law model was used to characterize the non-Newtonian fluid behavior. Similarity solutions were obtained with variations in surface temperature or surface heat flux. In view of the fact that most of the non-Newtonian fluids have large Prandtl numbers, this study was directed toward such fluids. The effects of the porous medium parameters, k1 and k2, body shape parameter, m, and surface thermal variations parameter, p, as well as the power-law index, n, were examined. © 2010 Springer Science+Business Media B.V.

Non-Darcy Free Convection of Power-Law Fluids Over a Two-Dimensional Body Embedded in a Porous Medium

KAUST Repository

El-Amin, Mohamed; Sun, Shuyu; El-Ameen, M. A.; Jaha, Y. A.; Gorla, Rama Subba Reddy

2010-01-01

A boundary layer analysis was presented to study the non-Darcy-free convection of a power-law fluid over a non-isothermal two-dimensional body embedded in a porous medium. The Ostwald-de Waele power-law model was used to characterize the non-Newtonian fluid behavior. Similarity solutions were obtained with variations in surface temperature or surface heat flux. In view of the fact that most of the non-Newtonian fluids have large Prandtl numbers, this study was directed toward such fluids. The effects of the porous medium parameters, k1 and k2, body shape parameter, m, and surface thermal variations parameter, p, as well as the power-law index, n, were examined. © 2010 Springer Science+Business Media B.V.

A fluid-solid coupling simulation method for convection heat transfer coefficient considering the under-vehicle condition

Science.gov (United States)

Tian, C.; Weng, J.; Liu, Y.

2017-11-01

The convection heat transfer coefficient is one of the evaluation indexes of the brake disc performance. The method used in this paper to calculate the convection heat transfer coefficient is a fluid-solid coupling simulation method, because the calculation results through the empirical formula method have great differences. The model, including a brake disc, a car body, a bogie and flow field, was built, meshed and simulated in the software FLUENT. The calculation models were K-epsilon Standard model and Energy model. The working condition of the brake disc was considered. The coefficient of various parts can be obtained through the method in this paper. The simulation result shows that, under 160 km/h speed, the radiating ribs have the maximum convection heat transfer coefficient and the value is 129.6W/(m2·K), the average coefficient of the whole disc is 100.4W/(m2·K), the windward of ribs is positive-pressure area and the leeward of ribs is negative-pressure area, the maximum pressure is 2663.53Pa.

Advances in Environmental Fluid Mechanics

CERN Document Server

Mihailovic, Dragutin T

2010-01-01

Environmental fluid mechanics (EFM) is the scientific study of transport, dispersion and transformation processes in natural fluid flows on our planet Earth, from the microscale to the planetary scale. This book brings together scientists and engineers working in research institutions, universities and academia, who engage in the study of theoretical, modeling, measuring and software aspects in environmental fluid mechanics. It provides a forum for the participants, and exchanges new ideas and expertise through the presentations of up-to-date and recent overall achievements in this field.

Properties of forced convection experimental with silicon carbide based nano-fluids

Science.gov (United States)

Soanker, Abhinay

. The nano-fluid properties were tested at three different volume concentrations; 0.55%, 1% and 1.6%. Thermal conductivity was measured for the three-volume concentration as function of temperature. Thermal conductivity enhancement increased with the temperature and may be attributed to increased Brownian motion of colloidal particles at higher temperatures. Measured thermal conductivity values are compared with results obtained by theoretical model derived in this work. Effect of temperature and volume concentration on viscosity was also measured and reported. Viscosity increase and related consequences are important issues for the use of nano-fluids. Extensive measurements of heat transfer and pressure drop for forced convection in circular pipes with nano-fluids was also conducted. Parameters such as heat transfer coefficient, Nusselt number, pressure drop and a thermal hydraulic performance factor that takes into account the gains made by increase in thermal conductivity as well as penalties related to increase in pressure drop are evaluated for laminar and transition flow regimes. No significant improvement in heat transfer (Nusselt number) compared to its based fluid was observed. It is also observed that the values evaluated for the thermal-hydraulic performance factor (change in heat transfer/change in pressure drop) was under unity for many flow conditions indicating poor overall applicability of SiC based nano-fluids.

Active control of convection

Energy Technology Data Exchange (ETDEWEB)

Bau, H.H. [Univ. of Pennsylvania, Philadelphia, PA (United States)

1995-12-31

Using stability theory, numerical simulations, and in some instances experiments, it is demonstrated that the critical Rayleigh number for the bifurcation (1) from the no-motion (conduction) state to the motion state and (2) from time-independent convection to time-dependent, oscillatory convection in the thermal convection loop and Rayleigh-Benard problems can be significantly increased or decreased. This is accomplished through the use of a feedback controller effectuating small perturbations in the boundary data. The controller consists of sensors which detect deviations in the fluid`s temperature from the motionless, conductive values and then direct actuators to respond to these deviations in such a way as to suppress the naturally occurring flow instabilities. Actuators which modify the boundary`s temperature/heat flux are considered. The feedback controller can also be used to control flow patterns and generate complex dynamic behavior at relatively low Rayleigh numbers.

The Oscillatory Nature of Rotating Convection in Liquid Metal

Science.gov (United States)

Aurnou, J. M.; Bertin, V. L.; Grannan, A. M.

2016-12-01

Earth's magnetic field is assumed to be generated by fluid motions in its liquid metal core. In this fluid, the heat diffuses significantly more than momentum and thus, the ratio of these two diffusivities, the Prandtl number Pr=ν/Κ, is well below unity. The convective flow dynamics of liquid metal is very different from Pr ≈ 1 fluids like water and those used in current dynamo simulations. In order to characterize rapidly rotating thermal convection in low Pr number fluids, we have performed laboratory experiments in a cylinder using liquid gallium (Pr ≈ 0.023) as the working fluid. The Ekman number, which characterizes the effect of rotation, varies from E = 4 10-5 to 4 10-6 and the dimensionless buoyancy forcing (Rayleigh number, Ra) varies from Ra =3 105 to 2 107. Using heat transfer measurements (Nusselt number, Nu) as well as temperature measurements within the fluid, we characterize the different styles of low Pr rotating convective flow. The convection threshold is first overcome in the form of a container scale inertial oscillatory mode. At stronger forcing, wall-localized modes are identified for the first time in liquid metal laboratory experiments. These wall modes coexist with the bulk inertial oscillatory modes. When the strengh of the buoyancy increases, the bulk flow becomes turbulent while the wall modes remain. Our results imply that rotating convective flows in liquid metals do not develop in the form of quasi-steady columns, as in Pr ≈ 1 dynamo models, but in the form of oscillatory motions. Therefore, the flows that drive thermally-driven dynamo action in low Pr geophysical and astrophysical fluids can differ substantively than those occuring in current-day Pr ≈ 1 numerical models. In addition, our results suggest that relatively low wavenumber, wall-attached modes may be dynamically important in rapidly-rotating convection in liquid metals.

Solving problems in fluid mechanics. Vol. 1

International Nuclear Information System (INIS)

Douglas, J.F.

1986-01-01

Fluid mechanics is that part of applied mechanics concerned with the statics and dynamics of liquids and gases. The presentation is in a pedagogically sound question-and-answer format, which includes many worked examples preceding the exercises. This book which assumes only an elementary knowledge of mathematics and mechanics, offers a clear exposition of topics including hydrostatics, fluid pressure and the stability of floating bodies, fluid motion, flow measurement, pipelines, open channel flow, and fluid friction

Unsteady MHD free convection flow of casson fluid over an inclined vertical plate embedded in a porous media

Science.gov (United States)

Manideep, P.; Raju, R. Srinivasa; Rao, T. Siva Nageswar; Reddy, G. Jithender

2018-05-01

This paper deals, an unsteady magnetohydrodynamic heat transfer natural convection flow of non-Newtonian Casson fluid over an inclined vertical plate embedded in a porous media with the presence of boundary conditions such as oscillating velocity, constant wall temperature. The governing dimensionless boundary layer partial differential equations are reduced to simultaneous algebraic linear equation for velocity, temperature of Casson fluid through finite element method. Those equations are solved by Thomas algorithm after imposing the boundary conditions through MATLAB for analyzing the behavior of Casson fluid velocity and temperature with various physical parameters. Also analyzed the local skin-friction and rate of heat transfer. Compared the present results with earlier reported studies, the results are comprehensively authenticated and robust FEM.

Mechanics of fluid flow

CERN Document Server

Basniev, Kaplan S; Chilingar, George V 0

2012-01-01

The mechanics of fluid flow is a fundamental engineering discipline explaining both natural phenomena and human-induced processes, and a thorough understanding of it is central to the operations of the oil and gas industry.  This book, written by some of the world's best-known and respected petroleum engineers, covers the concepts, theories, and applications of the mechanics of fluid flow for the veteran engineer working in the field and the student, alike.  It is a must-have for any engineer working in the oil and gas industry.

Unsteady natural convection flow past an accelerated vertical plate in a thermally stratified fluid

Directory of Open Access Journals (Sweden)

Deka Rudra Kt.

2009-01-01

Full Text Available An exact solution to one-dimensional unsteady natural convection flow past an infinite vertical accelerated plate, immersed in a viscous thermally stratified fluid is investigated. Pressure work term and the vertical temperature advection are considered in the thermodynamic energy equation. The dimensionless governing equations are solved by Laplace Transform techniques for the Prandtl number unity. The velocity and temperature profiles as well as the skin-friction and the rate of heat transfer are presented graphically and discussed the effects of the Grashof number Gr, stratification parameter S at various times t.

Boundary-modulated Thermal Convection Model in the Mantle

Science.gov (United States)

Kurita, K.; Kumagai, I.

2008-12-01

Analog experiments have played an important role in the constructing ideas of mantle dynamics. The series of experiments by H. Ramberg is one of the successful examples. Recently, however the realm of the analog experiments seems to be overwhelmed by steady progress of computer simulations. Is there still room for the analog experiments? This might be a main and hidden subject of this session. Here we propose a working hypothesis how the convecting mantle behaves based on the analog experiments in the system of viscous fluid and particles. The essential part is the interaction of convecting flow with heterogeneities existing in the boundaries. It is proposed the preexisting topographical heterogeneity in the boundary could control the flow pattern of convecting fluid. If this kind of heterogeneity can be formed as a consequence of convective motion and mobilized by the flow, the convection also can control the heterogeneity. We can expect interactions in two ways, by which the system behaves in a self-organize fashion. To explore the mutual interactions between convection flow and heterogeneity the system of viscous fluid and particles with slightly higher density is selected as 2D Rayleigh-Benard type convection. The basic structure consists of a basal particulate layer where permeable convection transports heat and an upper viscous fluid layer. By reducing the magnitude of the density difference the convective flow can mobilize the particles and can erode the basal layer. The condition of this erosion can be identified in the phase diagram of the particle Shields"f and the Rayleigh numbers. At Ra greater than 107 the convection style drastically changed before and after the erosion. Before the erosion where the flat interface of the boundary is maintained small scaled turbulent convection pattern is dominant. After the erosion where the interface becomes bumpy the large scale convective motion is observed. The structure is coherent to that of the boundary. This

Numerical simulations of natural or mixed convection in vertical channels: comparisons of level-set numerical schemes for the modeling of immiscible incompressible fluid flows

International Nuclear Information System (INIS)

Li, R.

2012-01-01

The aim of this research dissertation is at studying natural and mixed convections of fluid flows, and to develop and validate numerical schemes for interface tracking in order to treat incompressible and immiscible fluid flows, later. In a first step, an original numerical method, based on Finite Volume discretizations, is developed for modeling low Mach number flows with large temperature gaps. Three physical applications on air flowing through vertical heated parallel plates were investigated. We showed that the optimum spacing corresponding to the peak heat flux transferred from an array of isothermal parallel plates cooled by mixed convection is smaller than those for natural or forced convections when the pressure drop at the outlet keeps constant. We also proved that mixed convection flows resulting from an imposed flow rate may exhibit unexpected physical solutions; alternative model based on prescribed total pressure at inlet and fixed pressure at outlet sections gives more realistic results. For channels heated by heat flux on one wall only, surface radiation tends to suppress the onset of re-circulations at the outlet and to unify the walls temperature. In a second step, the mathematical model coupling the incompressible Navier-Stokes equations and the Level-Set method for interface tracking is derived. Improvements in fluid volume conservation by using high order discretization (ENO-WENO) schemes for the transport equation and variants of the signed distance equation are discussed. (author)

On the fluid mechanics of fires

Energy Technology Data Exchange (ETDEWEB)

TIESZEN,SHELDON R.

2000-02-29

Fluid mechanics research related to fire is reviewed with focus on canonical flows, multiphysics coupling aspects, experimental and numerical techniques. Fire is a low-speed, chemically-reacting, flow in which buoyancy plans an important role. Fire research has focused on two canonical flows, the reacting boundary-layer and the reacting free plume. There is rich, multi-lateral, bi-directional, coupling among fluid mechanics and scalar transport, combustion, and radiation. There is only a limited experimental fluid-mechanics database for fire due to measurement difficulties in the harsh environment, and the focus within the fire community on thermal/chemical consequences. Increasingly, computational fluid dynamics techniques are being used to provide engineering guidance on thermal/chemical consequences and to study fire phenomenology.

Natural convection in nano-fluids: Are the thermophoresis and Brownian motion effects significant in nano-fluid heat transfer enhancement?

International Nuclear Information System (INIS)

Haddad, Zoubida; Abu-Nada, Eiyad; Oztop, Hakan F.; Mataoui, Amina

2012-01-01

Natural convection heat transfer and fluid flow of CuO-Water nano-fluids is studied using the Rayleigh-Benard problem. A two component non-homogenous equilibrium model is used for the nano-fluid that incorporates the effects of Brownian motion and thermophoresis. Variable thermal conductivity and variable viscosity are taken into account in this work. Finite volume method is used to solve governing equations. Results are presented by streamlines, isotherms, nano-particle distribution, local and mean Nusselt numbers and nano-particle profiles at top and bottom side. Comparison of two cases as absence of Brownian and thermophoresis effects and presence of Brownian and thermophoresis effects showed that higher heat transfer is formed with the presence of Brownian and thermophoresis effect. In general, by considering the role of thermophoresis and Brownian motion, an enhancement in heat transfer is observed at any volume fraction of nano-particles. However, the enhancement is more pronounced at low volume fraction of nano-particles and the heat transfer decreases by increasing nano-particle volume fraction. On the other hand, by neglecting the role of thermophoresis and Brownian motion, deterioration in heat transfer is observed and this deterioration elevates by increasing the volume fraction of nano-particles. (authors)

High Ra, high Pr convection with viscosity gradients

Indian Academy of Sciences (India)

First page Back Continue Last page Overview Graphics. High Ra, high Pr convection with viscosity gradients. Weak upward flow through mesh. Top fluid more viscous. Unstable layer Instability Convection.

Fluid convection, constraint and causation

Science.gov (United States)

Bishop, Robert C.

2012-01-01

Complexity—nonlinear dynamics for my purposes in this essay—is rich with metaphysical and epistemological implications but is receiving sustained philosophical analysis only recently. I will explore some of the subtleties of causation and constraint in Rayleigh–Bénard convection as an example of a complex phenomenon, and extract some lessons for further philosophical reflection on top-down constraint and causation particularly with respect to causal foundationalism. PMID:23386955

Research on the porous flow of the mechanism of viscous-elastic fluids displacing residual oil droplets in micro pores

Science.gov (United States)

Dong, Guanyu

2018-03-01

In order to analyze the microscopic stress field acting on residual oil droplets in micro pores, calculate its deformation, and explore the hydrodynamic mechanism of viscous-elastic fluids displacing oil droplets, the viscous-elastic fluid flow equations in micro pores are established by choosing the Upper Convected Maxwell constitutive equation; the numerical solutions of the flow field are obtained by volume control and Alternate Direction Implicit methods. From the above, the velocity field and microscopic stress field; the forces acting on residual oil droplets; the deformations of residual oil droplets by various viscous-elastic displacing fluids and at various Wiesenberg numbers are calculated and analyzed. The result demonstrated that both the normal stress and horizontal force acting on the residual oil droplets by viscous-elastic fluids are much larger compared to that of inelastic fluid; the distribution of normal stress changes abruptly; under the condition of the same pressure gradient in the system under investigation, the ratio of the horizontal forces acting on the residual oil droplets by different displacing fluids is about 1:8:20, which means that under the above conditions, the driving force on a oil droplet is 20 times higher for a viscous-elastic fluid compared to that of a Newtonian Fluid. The conclusions are supportive of the mechanism that viscous-elastic driving fluids can increase the Displacement Efficiency. This should be of help in designing new chemicals and selecting Enhanced Oil Recovery systems.

Experimental investigation of convective stability in a superposed fluid and porous layer when heated from below

Science.gov (United States)

Chen, Falin; Chen, C. F.

1989-01-01

Experiments have been carried out in a horizontal superposed fluid and porous layer contained in a test box 24 cm x 12 cm x 4 cm high. The porous layer consisted of 3 mm diameter glass beads, and the fluids used were water, 60 and 90 percent glycerin-water solutions, and 100 percent glycerin. The depth ratio d, which is the ratio of the thickness of the fluid layer to that of the porous layer, varied from 0 to 1.0. Fluids of increasingly higher viscosity were used for cases with larger d in order to keep the temperature difference across the tank within reasonable limits. The size of the convection cells was inferred from temperature measurements made with embedded thermocouples and from temperature distributions at the top of the layer by use of liquid crystal film. The experimental results showed: (1) a precipitous decrease in the critical Rayleigh number as the depth of the fluid layer was increased from zero, and (2) an eightfold decrease in the critical wavelength between d = 0.1 and 0.2. Both of these results were predicted by the linear stability theory reported earlier (Chen and Chen, 1988).

Analysis of Forced Convection Heat Transfer for Axial Annular Flow of Giesekus Viscoelastic Fluid

Energy Technology Data Exchange (ETDEWEB)

Mohseni, Mehdi Moayed; Rashidi, Fariborz; Movagar, Mohammad Reza Khorsand [Amirkabir University of Technology, Tehran (Iran, Islamic Republic of)

2015-02-15

Analytical solutions for the forced convection heat transfer of viscoelastic fluids obeying the Giesekus model are obtained in a concentric annulus under laminar flow for both thermal and hydrodynamic fully developed conditions. Boundary conditions are assumed to be (a) constant fluxes at the walls and (b) constant temperature at the walls. Temperature profiles and Nusselt numbers are derived from dimensionless energy equation. Subsequently, effects of elasticity, mobility parameter and viscous dissipation are discussed. Results show that by increasing elasticity, Nusselt number increases. However, this trend is reversed for constant wall temperature when viscous dissipation is weak. By increasing viscous dissipation, the Nusselt number decreases for the constant flux and increases for the constant wall temperature. For the wall cooling case, when the viscous dissipation exceeds a critical value, the generated heat overcomes the heat which is removed at the walls, and fluid heats up longitudinally.

Benard convection in gaps and cavities

International Nuclear Information System (INIS)

Mueller, U.

1981-04-01

The article contains two parts. In the first part a condensed review of the most striking phenomena in Benard convection in laterally confined fluid layers is given. In the second part recent experimental and theoretical work on Benard convection in gaps is presented an analysed. (orig.) [de

The charge effect on the hindrance factors for diffusion and convection of a solute in pores: II

Energy Technology Data Exchange (ETDEWEB)

Akinaga, Takeshi; O-tani, Hideyuki; Sugihara-Seki, Masako, E-mail: r091077@kansai-u.ac.jp [Department of Pure and Applied Physics, Kansai University, Yamate-cho, Suita, Osaka 564-8680 (Japan)

2012-10-15

The diffusion and convection of a solute suspended in a fluid across porous membranes are known to be reduced compared to those in a bulk solution, owing to the fluid mechanical interaction between the solute and the pore wall as well as steric restriction. If the solute and the pore wall are electrically charged, the electrostatic interaction between them could affect the hindrance to diffusion and convection. In this study, the transport of charged spherical solutes through charged circular cylindrical pores filled with an electrolyte solution containing small ions was studied numerically by using a fluid mechanical and electrostatic model. Based on a mean field theory, the electrostatic interaction energy between the solute and the pore wall was estimated from the Poisson-Boltzmann equation, and the charge effect on the solute transport was examined for the solute and pore wall of like charge. The results were compared with those obtained from the linearized form of the Poisson-Boltzmann equation, i.e. the Debye-Hueckel equation. (paper)

Recording fluid currents by holography

Science.gov (United States)

Heflinger, L. O.; Wuerker, R. F.

1980-01-01

Convection in fluids can be studied with aid of holographic apparatus that reveals three-dimensional motion of liquid. Apparatus eliminates images of fixed particles such as dust on windows and lenses, which might mask behavior of moving fluid particles. Holographic apparatus was developed for experiments on fluid convection cells under zero gravity. Principle is adaptable to study of fluid processes-for example, electrochemical plating and combustion in automotive engines.

Fluid mechanics for engineers. A graduate textbook

Energy Technology Data Exchange (ETDEWEB)

Schobeiri, Meinhard T. [Texas A and M Univ., College Station, TX (United States). Dept. of Mechanical Engineering

2010-07-01

The contents of this book covers the material required in the Fluid Mechanics Graduate Core Course (MEEN-621) and in Advanced Fluid Mechanics, a Ph.D-level elective course (MEEN-622), both of which I have been teaching at Texas A and M University for the past two decades. While there are numerous undergraduate fluid mechanics texts on the market for engineering students and instructors to choose from, there are only limited texts that comprehensively address the particular needs of graduate engineering fluid mechanics courses. To complement the lecture materials, the instructors more often recommend several texts, each of which treats special topics of fluid mechanics. This circumstance and the need to have a textbook that covers the materials needed in the above courses gave the impetus to provide the graduate engineering community with a coherent textbook that comprehensively addresses their needs for an advanced fluid mechanics text. Although this text book is primarily aimed at mechanical engineering students, it is equally suitable for aerospace engineering, civil engineering, other engineering disciplines, and especially those practicing professionals who perform CFD-simulation on a routine basis and would like to know more about the underlying physics of the commercial codes they use. Furthermore, it is suitable for self study, provided that the reader has a sufficient knowledge of calculus and differential equations. (orig.)

Fluid mechanics

International Nuclear Information System (INIS)

Granger, R.A.

1985-01-01

This text offers the most comprehensive approach available to fluid mechanics. The author takes great care to insure a physical understanding of concepts grounded in applied mathematics. The presentation of theory is followed by engineering applications, helping students develop problem-solving skills from the perspective of a professional engineer. Extensive use of detailed examples reinforces the understanding of theoretical concepts

Interaction of externally-driven acoustic waves with compressible convection

International Nuclear Information System (INIS)

Jones, P.; Merryfield, W.

1992-01-01

Two-dimensional numerical simulations are used to examine the interaction of acoustic waves with a compressible convecting fluid. Acoustic waves are forced at the lower boundary of the computational domain and propagate through a three-layer system undergoing vigorous penetrative convection. Energy exchange between the wave and the fluid is analyzed using a work integral formulation

Turbulent convection in liquid metal with and without rotation.

Science.gov (United States)

King, Eric M; Aurnou, Jonathan M

2013-04-23

The magnetic fields of Earth and other planets are generated by turbulent, rotating convection in liquid metal. Liquid metals are peculiar in that they diffuse heat more readily than momentum, quantified by their small Prandtl numbers, Pr rotating Rayleigh-Bénard convection experiments in the liquid metal gallium (Pr = 0.025) over a range of nondimensional buoyancy forcing (Ra) and rotation periods (E). Our primary diagnostic is the efficiency of convective heat transfer (Nu). In general, we find that the convective behavior of liquid metal differs substantially from that of moderate Pr fluids, such as water. In particular, a transition between rotationally constrained and weakly rotating turbulent states is identified, and this transition differs substantially from that observed in moderate Pr fluids. This difference, we hypothesize, may explain the different classes of magnetic fields observed on the Gas and Ice Giant planets, whose dynamo regions consist of Pr 1 fluids, respectively.

Analysis of stagnation point flow of an upper-convected Maxwell fluid

Directory of Open Access Journals (Sweden)

Joseph E. Paullet

2017-12-01

Full Text Available Several recent papers have investigated the two-dimensional stagnation point flow of an upper-convected Maxwell fluid by employing a similarity change of variable to reduce the governing PDEs to a nonlinear third order ODE boundary value problem (BVP. In these previous works, the BVP was studied numerically and several conjectures regarding the existence and behavior of the solutions were made. The purpose of this article is to mathematically verify these conjectures. We prove the existence of a solution to the BVP for all relevant values of the elasticity parameter. We also prove that this solution has monotonically increasing first derivative, thus verifying the conjecture that no ``overshoot'' of the boundary condition occurs. Uniqueness results are presented for a large range of parameter space and bounds on the skin friction coefficient are calculated.

Parametric numerical investigaion of natural convection in a heat-generating fluid with phase transitions

Energy Technology Data Exchange (ETDEWEB)

Aksenova, A.E.; Chudanov, V.V.; Strizhov, V.F.; Vabishchevich, P.N. [Institute of Nuclear Safety Russian Academy Science, Moscow (Russian Federation)

1995-09-01

Unsteady natural convection of a heat-generating fluid with phase transitions in the enclosures of a square section with isothermal rigid walls is investigated numerically for a wide range of dimensionless parameters. The quasisteady state solutions of conjugate heat and mass transfer problem are compared with available experimental results. Correlation relations for heat flux distributions at the domain boundaries depending on Rayleigh and Ostrogradskii numbers are obtained. It is shown that generally heat transfer is governed both by natural circulation and crust formation phenomena. Results of this paper may be used for analysis of experiments with prototypic core materials.

Oscillatory Convection in Rotating Liquid Metals

Science.gov (United States)

Bertin, Vincent; Grannan, Alex; Aurnou, Jonathan

2016-11-01

We have performed laboratory experiments in a aspect ratio Γ = 2 cylinder using liquid gallium (Pr = 0 . 023) as the working fluid. The Ekman number varies from E = 4 ×10-5 to 4 ×10-6 and the Rayleigh number varies from Ra = 3 ×105 to 2 ×107 . Using heat transfer and temperature measurements within the fluid, we characterize the different styles of low Pr rotating convective flow. The convection threshold is first overcome in the form of a container scale inertial oscillatory mode. At stronger forcing, wall-localized modes develop, coexisting with the inertial oscillatory modes in the bulk. When the strength of the buoyancy increases further, the bulk flow becomes turbulent while the wall modes remain. Our results imply that rotating convective flows in liquid metals do not develop in the form of quasi-steady columns, as in Pr = 1 planetary and stellar dynamo models, but in the form of oscillatory motions. Therefore, convection driven dynamo action in low Pr fluids can differ substantively than that occurring in typical Pr = 1 numerical models. Our results also suggest that low wavenumber, wall modes may be dynamically and observationally important in liquid metal dynamo systems. We thank the NSF Geophysics Program for support of this project.

Effects of transpiration on unsteady MHD flow of an upper convected Maxwell (UCM) fluid passing through a stretching surface in the presence of a first order chemical reaction

International Nuclear Information System (INIS)

Mukhopadhyay, Swati; Arif, M. Golam; Pk M Wazed Ali

2013-01-01

The aim of this article is to present the effects of transpiration on the unsteady two-dimensional boundary layer flow of non-Newtonian fluid passing through a stretching sheet in the presence of a first order constructive/destructive chemical reaction. The upper-convected Maxwell (UCM) model is used here to characterize the non-Newtonian behavior of the fluid. Using similarity solutions, the governing nonlinear partial differential equations are transformed into ordinary ones and are then solved numerically by the shooting method. The flow fields and mass transfer are significantly influenced by the governing parameters. The fluid velocity initially decreases as the unsteadiness parameter increases and the concentration decreases significantly due to the increase in the unsteadiness. The effect of increasing values of transpiration (suction) and the Maxwell parameter is to suppress the velocity field; however, the concentration is enhanced as transpiration (suction) and the Maxwell parameter increase. Also, it is found that the fluid velocity decreases as the magnetic parameter increases; however, the concentration increases in this case. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

Heat transfer of laminar mixed convection of liquid

CERN Document Server

Shang, De-Yi

2016-01-01

This book presents a new algorithm to calculate fluid flow and heat transfer of laminar mixed convection. It provides step-by-step tutorial help to learn quickly how to set up the theoretical and numerical models of laminar mixed convection, to consider the variable physical properties of fluids, to obtain the system of numerical solutions, to create a series of formalization equations for the convection heat transfer by using a curve-fitting approach combined with theoretical analysis and derivation. It presents the governing ordinary differential equations of laminar mixed convection, equivalently transformed by an innovative similarity transformation with the description of the related transformation process. A system of numerical calculations of the governing ordinary differential equations is presented for the water laminar mixed convection. A polynomial model is induced for convenient and reliable treatment of variable physical properties of liquids. The developed formalization equations of mixed convec...

Relativistic viscoelastic fluid mechanics

International Nuclear Information System (INIS)

Fukuma, Masafumi; Sakatani, Yuho

2011-01-01

A detailed study is carried out for the relativistic theory of viscoelasticity which was recently constructed on the basis of Onsager's linear nonequilibrium thermodynamics. After rederiving the theory using a local argument with the entropy current, we show that this theory universally reduces to the standard relativistic Navier-Stokes fluid mechanics in the long time limit. Since effects of elasticity are taken into account, the dynamics at short time scales is modified from that given by the Navier-Stokes equations, so that acausal problems intrinsic to relativistic Navier-Stokes fluids are significantly remedied. We in particular show that the wave equations for the propagation of disturbance around a hydrostatic equilibrium in Minkowski space-time become symmetric hyperbolic for some range of parameters, so that the model is free of acausality problems. This observation suggests that the relativistic viscoelastic model with such parameters can be regarded as a causal completion of relativistic Navier-Stokes fluid mechanics. By adjusting parameters to various values, this theory can treat a wide variety of materials including elastic materials, Maxwell materials, Kelvin-Voigt materials, and (a nonlinearly generalized version of) simplified Israel-Stewart fluids, and thus we expect the theory to be the most universal description of single-component relativistic continuum materials. We also show that the presence of strains and the corresponding change in temperature are naturally unified through the Tolman law in a generally covariant description of continuum mechanics.

Relativistic viscoelastic fluid mechanics.

Science.gov (United States)

Fukuma, Masafumi; Sakatani, Yuho

2011-08-01

A detailed study is carried out for the relativistic theory of viscoelasticity which was recently constructed on the basis of Onsager's linear nonequilibrium thermodynamics. After rederiving the theory using a local argument with the entropy current, we show that this theory universally reduces to the standard relativistic Navier-Stokes fluid mechanics in the long time limit. Since effects of elasticity are taken into account, the dynamics at short time scales is modified from that given by the Navier-Stokes equations, so that acausal problems intrinsic to relativistic Navier-Stokes fluids are significantly remedied. We in particular show that the wave equations for the propagation of disturbance around a hydrostatic equilibrium in Minkowski space-time become symmetric hyperbolic for some range of parameters, so that the model is free of acausality problems. This observation suggests that the relativistic viscoelastic model with such parameters can be regarded as a causal completion of relativistic Navier-Stokes fluid mechanics. By adjusting parameters to various values, this theory can treat a wide variety of materials including elastic materials, Maxwell materials, Kelvin-Voigt materials, and (a nonlinearly generalized version of) simplified Israel-Stewart fluids, and thus we expect the theory to be the most universal description of single-component relativistic continuum materials. We also show that the presence of strains and the corresponding change in temperature are naturally unified through the Tolman law in a generally covariant description of continuum mechanics.

Thermo capillary and buoyancy convection in a fluid locally heated on its free surface; Convection thermocapillaire et thermogravitaire dans un fluide chauffe localement sur sa surface libre

Energy Technology Data Exchange (ETDEWEB)

Favre, E.

1997-09-26

coupled buoyancy and thermo-capillary convection lead to a convective motion of the interface liquid/gas which drastically changes the heat and mass transfer across the liquid layer. Two experiments were considered, depending on the fluid: oil or mercury. The liquid is set in a cooled cylindrical vessel, and heated by a heat flux across the center of the free surface. The basic flow, in the case of oil, is a torus. When the heat parameter increases, a stationary flow appears as petals or rays when the aspect ratio. The lateral confinement selects the azimuthal wavelength. In the case of petals-like flow, a sub-critical Hopf bifurcation is underlined. The turbulence is found to be `weak`, even for the largest values of the Marangoni number (Ma = 1.3 10{sup 5}). In the case of mercury, the thermo-capillary effect is reduced to zero to impurities at the surface which have special trajectories we describe and compare to a simpler experiment. Only the buoyancy forces induce a unstationary, weakly turbulent flow as soon as the heating power exceeds 4W (Ra = 4.5 10{sup 3}, calculated with h = 1 mm). The past part concerns the analysis of the effect on the flow of the boundary conditions, the geometry, the Prandtl number and the buoyancy force with the help of the literature. Results concerning heat transfer, in particular the exponent of the law Nusselt number vs. heating power, were compared with available data. (author) 115 refs.

From convection rolls to finger convection in double-diffusive turbulence

NARCIS (Netherlands)

Yang, Yantao; Verzicco, Roberto; Lohse, Detlef

2015-01-01

Double-diffusive convection (DDC), which is the buoyancy-driven flow with fluid density depending on two scalar components, is ubiquitous in many natural and engineering environments. Of great interests are scalars’ transfer rate and flow structures. Here we systematically investigate DDC flow

Fluid mechanics a geometrical point of view

CERN Document Server

Rajeev, S G

2018-01-01

Fluid Mechanics: A Geometrical Point of View emphasizes general principles of physics illustrated by simple examples in fluid mechanics. Advanced mathematics (e.g., Riemannian geometry and Lie groups) commonly used in other parts of theoretical physics (e.g. General Relativity or High Energy Physics) are explained and applied to fluid mechanics. This follows on from the author's book Advanced Mechanics (Oxford University Press, 2013). After introducing the fundamental equations (Euler and Navier-Stokes), the book provides particular cases: ideal and viscous flows, shocks, boundary layers, instabilities, and transients. A restrained look at integrable systems (KdV) leads into a formulation of an ideal fluid as a hamiltonian system. Arnold's deep idea, that the instability of a fluid can be understood using the curvature of the diffeomorphism group, will be explained. Leray's work on regularity of Navier-Stokes solutions, and the modern developments arising from it, will be explained in language for physicists...

Unsteady free convection flow of a micropolar fluid with Newtonian heating: Closed form solution

Directory of Open Access Journals (Sweden)

Hussanan Abid

2017-01-01

Full Text Available This article investigates the unsteady free convection flow of a micropolar fluid over a vertical plate oscillating in its own plane with Newtonian heating condition. The problem is modelled in terms of partial differential equations with some physical conditions. Closed form solutions in terms of exponential and complementary error functions of Gauss are obtained by using the Laplace transform technique. They satisfy the governing equations and impose boundary and initial conditions. The present solution in the absence of microrotation reduces to well-known solutions of Newtonian fluid. Graphs are plotted to study the effects of various physical parameters on velocity and microrotation. Numerical results for skin friction and wall couple stress is computed in tables. Apart from the engineering point of view, the present article has strong advantage over the published literature as the exact solutions obtained here can be used as a benchmark for comparison with numerical/ approximate solutions and experimental data.

Influence of Slip Condition on Unsteady Free Convection Flow of Viscous Fluid with Ramped Wall Temperature

Directory of Open Access Journals (Sweden)

Sami Ul Haq

2015-01-01

Full Text Available The objective of this study is to explore the influence of wall slip condition on a free convection flow of an incompressible viscous fluid with heat transfer and ramped wall temperature. Exact solution of the problem is obtained by using Laplace transform technique. Graphical results to see the effects of Prandtl number Pr, time t, and slip parameter η on velocity and skin friction for the case of ramped and constant temperature of the plate are provided and discussed.

Concentration field in traveling-wave and stationary convection in fluid mixtures

International Nuclear Information System (INIS)

Eaton, K.D.; Ohlsen, D.R.; Yamamoto, S.Y.; Surko, C.M.; Barten, W.; Luecke, M.; Kamps, M.; Kolodner, P.

1991-01-01

By comparison of measurements of shadowgraph images of convection in ethanol-water mixtures with the results of recent numerical calculations, we study the role of the concentration field in traveling-wave and stationary convection. The results confirm the existence of a large concentration contrast between adjacent traveling-wave convection rolls. This concentration modulation, which decreases as the Rayleigh number is increased and the transition to stationary convection is approached, is fundamental to the translation of the pattern

Unsteady Hydromagnetic Flow of Radiating Fluid Past a Convectively Heated Vertical Plate with the Navier Slip

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O. D. Makinde

2014-01-01

Full Text Available This paper investigates the unsteady hydromagnetic-free convection of an incompressible electrical conducting Boussinesq’s radiating fluid past a moving vertical plate in an optically thin environment with the Navier slip, viscous dissipation, and Ohmic and Newtonian heating. The nonlinear partial differential equations governing the transient problem are obtained and tackled numerically using a semidiscretization finite difference method coupled with Runge-Kutta Fehlberg integration technique. Numerical data for the local skin friction coefficient and the Nusselt number have been tabulated for various values of parametric conditions. Graphical results for the fluid velocity, temperature, skin friction, and the Nusselt number are presented and discussed. The results indicate that the skin friction coefficient decreases while the heat transfer rate at the plate surface increases as the slip parameter and Newtonian heating increase.

Handbook of mathematical analysis in mechanics of viscous fluids

CERN Document Server

Novotný, Antonín

2018-01-01

Mathematics has always played a key role for researches in fluid mechanics. The purpose of this handbook is to give an overview of items that are key to handling problems in fluid mechanics. Since the field of fluid mechanics is huge, it is almost impossible to cover many topics. In this handbook, we focus on mathematical analysis on viscous Newtonian fluid. The first part is devoted to mathematical analysis on incompressible fluids while part 2 is devoted to compressible fluids.

Time-dependent convection study of the driving mechanism in the DBV white dwarfs

International Nuclear Information System (INIS)

Dupret, M A; Quirion, P O; Fontaine, G; Brassard, P; Grigahcene, A

2008-01-01

We apply for the first time time-dependent convection (TDC) models to the study of the driving mechanism of the Pulsating DB (V777 Herculis) white dwarfs. From the blue to the red edge of the instability strip of these stars, TDC appears to play a central role in the driving. Around the blue edge, the convection adapts quasi-instantaneously to the oscillations, so that TDC must be included in the models. For the first time, we show that the red edge of the DB instability strip is successfully obtained with a TDC treatment, especially thanks to the terms due to the turbulent pressure variations, while it is not reproduced with frozen convection models.

Mass transfer in nano-fluids: A review

International Nuclear Information System (INIS)

Ashrafmansouri, Seyedeh-Saba; Esfahany, Mohsen Nasr

2014-01-01

Growing attention has been recently paid to nano-fluids because of their potential for augmenting transfer processes - i.e., heat and mass transfer. Conflicting results have been reported in the literature on mass transfer in nano-fluids. The aim of this paper is to summarize the literature on mass transfer in nano-fluids stating the conflicts and possible reasons. Literature on mass transfer in nano-fluids has been reviewed in two sections. The first section concentrates on surveying mass diffusivity in nano-fluids while the second section focuses on convective mass transfer in nano-fluids. In each section, published articles, type of nano-fluids used, size and concentration range of nanoparticles, measurement methods, maximum observed enhancement, and suggested mass transport mechanisms are summarized. (authors)

Fluid Mechanics An Introduction to the Theory of Fluid Flows

CERN Document Server

Durst, Franz

2008-01-01

Advancements of fluid flow measuring techniques and of computational methods have led to new ways to treat laminar and turbulent flows. These methods are extensively used these days in research and engineering practise. This also requires new ways to teach the subject to students at higher educational institutions in an introductory manner. The book provides the knowledge to students in engineering and natural science needed to enter fluid mechanics applications in various fields. Analytical treatments are provided, based on the Navier-Stokes equations. Introductions are also given into numerical and experimental methods applied to flows. The main benefit the reader will derive from the book is a sound introduction into all aspects of fluid mechanics covering all relevant subfields.

Heat Transfer and Fluid Mechanics Institute, Meeting, 25th, University of California, Davis, Calif., June 21-23, 1976, Proceedings

Science.gov (United States)

Mckillop, A. A.; Baughn, J. W.; Dwyer, H. A.

1976-01-01

Major research advances in heat transfer and fluid dynamics are outlined, with particular reference to relevant energy problems. Of significant importance are such topics as synthetic fuels in combustion, turbulence models, combustion modeling, numerical methods for interacting boundary layers, and light-scattering diagnostics for gases. The discussion covers thermal convection, two-phase flow and boiling heat transfer, turbulent flows, combustion, and aerospace heat transfer problems. Other areas discussed include compressible flows, fluid mechanics and drag, and heat exchangers. Featured topics comprise heat and salt transfer in double-diffusive systems, limits of boiling heat transfer in a liquid-filled enclosure, investigation of buoyancy-induced flow stratification in a cylindrical plenum, and digital algorithms for dynamic analysis of a heat exchanger. Individual items are announced in this issue.

Two parameters Lie group analysis and numerical solution of unsteady free convective flow of non-Newtonian fluid

Directory of Open Access Journals (Sweden)

M.J. Uddin

2016-09-01

Full Text Available The two-dimensional unsteady laminar free convective heat and mass transfer fluid flow of a non-Newtonian fluid adjacent to a vertical plate has been analyzed numerically. The two parameters Lie group transformation method that transforms the three independent variables into a single variable is used to transform the continuity, the momentum, the energy and the concentration equations into a set of coupled similarity equations. The transformed equations have been solved by the Runge–Kutta–Fehlberg fourth-fifth order numerical method with shooting technique. Numerical calculations were carried out for the various parameters entering into the problem. The dimensionless velocity, temperature and concentration profiles were shown graphically and the skin friction, heat and mass transfer rates were given in tables. It is found that friction factor and heat transfer (mass transfer rate for methanol are higher (lower than those of hydrogen and water vapor. Friction factor decreases while heat and mass transfer rate increase as the Prandtl number increases. Friction (heat and mass transfer rate factor of Newtonian fluid is higher (lower than the dilatant fluid.

Numerical analysis of fractional MHD Maxwell fluid with the effects of convection heat transfer condition and viscous dissipation

Directory of Open Access Journals (Sweden)

Yu Bai

2017-12-01

Full Text Available This paper investigates the incompressible fractional MHD Maxwell fluid due to a power function accelerating plate with the first order slip, and the numerical analysis on the flow and heat transfer of fractional Maxwell fluid has been done. Moreover the deformation motion of fluid micelle is simply analyzed. Nonlinear velocity equation are formulated with multi-term time fractional derivatives in the boundary layer governing equations, and convective heat transfer boundary condition and viscous dissipation are both taken into consideration. A newly finite difference scheme with L1-algorithm of governing equations are constructed, whose convergence is confirmed by the comparison with analytical solution. Numerical solutions for velocity and temperature show the effects of pertinent parameters on flow and heat transfer of fractional Maxwell fluid. It reveals that the fractional derivative weakens the effects of motion and heat conduction. The larger the Nusselt number is, the greater the heat transfer capacity of fluid becomes, and the temperature gradient at the wall becomes more significantly. The lower Reynolds number enhances the viscosity of the fluid because it is the ratio of the viscous force and the inertia force, which resists the flow and heat transfer.

Numerical analysis of fractional MHD Maxwell fluid with the effects of convection heat transfer condition and viscous dissipation

Science.gov (United States)

Bai, Yu; Jiang, Yuehua; Liu, Fawang; Zhang, Yan

2017-12-01

This paper investigates the incompressible fractional MHD Maxwell fluid due to a power function accelerating plate with the first order slip, and the numerical analysis on the flow and heat transfer of fractional Maxwell fluid has been done. Moreover the deformation motion of fluid micelle is simply analyzed. Nonlinear velocity equation are formulated with multi-term time fractional derivatives in the boundary layer governing equations, and convective heat transfer boundary condition and viscous dissipation are both taken into consideration. A newly finite difference scheme with L1-algorithm of governing equations are constructed, whose convergence is confirmed by the comparison with analytical solution. Numerical solutions for velocity and temperature show the effects of pertinent parameters on flow and heat transfer of fractional Maxwell fluid. It reveals that the fractional derivative weakens the effects of motion and heat conduction. The larger the Nusselt number is, the greater the heat transfer capacity of fluid becomes, and the temperature gradient at the wall becomes more significantly. The lower Reynolds number enhances the viscosity of the fluid because it is the ratio of the viscous force and the inertia force, which resists the flow and heat transfer.

Carbon-nanotube nanofluid thermophysical properties and heat transfer by natural convection

International Nuclear Information System (INIS)

Li, Y; Inagaki, T; Suzuki, S; Yamauchi, N

2014-01-01

We measured the thermophysical properties of suspensions of carbon nanotubes in water as a type of nanofluid, and experimentally investigated their heat transfer characteristics in a horizontal, closed rectangular vessel. Using a previously constructed system for high- reliability measurement, we quantitatively determined their thermophysical properties and the temperature dependence of these properties. We also investigated the as yet unexplained mechanism of heat transport in carbon-nanotube nanofluids and their flow properties from a thermal perspective. The results indicated that these nanofluids are non-Newtonian fluids, whose high viscosity impedes convection and leads to a low heat transfer coefficient under natural convection, despite their high thermal conductivity

Stretched flow of Carreau nanofluid with convective boundary ...

Indian Academy of Sciences (India)

journal of. January 2016 physics pp. 3–17. Stretched flow of Carreau nanofluid with ... fluid over a flat plate subjected to convective surface condition. ... the steady laminar boundary layer flow over a permeable plate with a convective boundary.

NASA Ames Fluid Mechanics Laboratory research briefs

Science.gov (United States)

Davis, Sanford (Editor)

1994-01-01

The Ames Fluid Mechanics Laboratory research program is presented in a series of research briefs. Nineteen projects covering aeronautical fluid mechanics and related areas are discussed and augmented with the publication and presentation output of the Branch for the period 1990-1993.

Unsteady mixed convection flow of Casson fluid past an inclined stretching sheet in the presence of nanoparticles

Science.gov (United States)

Rawi, N. A.; Ilias, M. R.; Lim, Y. J.; Isa, Z. M.; Shafie, S.

2017-09-01

The influence of nanoparticles on the unsteady mixed convection flow of Casson fluid past an inclined stretching sheet is investigated in this paper. The effect of gravity modulation on the flow is also considered. Carboxymethyl cellulose solution (CMC) is chosen as the base fluid and copper as nanoparticles. The basic governing nonlinear partial differential equations are transformed using appropriate similarity transformation and solved numerically using an implicit finite difference scheme by means of the Keller-box method. The effect of nanoparticles volume fraction together with the effect of inclination angle and Casson parameter on the enhancement of heat transfer of Casson nanofluid is discussed in details. The velocity and temperature profiles as well as the skin friction coefficient and the Nusselt number are presented and analyzed.

Annual review of fluid mechanics. Volume 23

International Nuclear Information System (INIS)

Lumley, J.L.; Van Dyke, M.; Reed, H.L.

1991-01-01

Recent advances in theoretical, experimental, and computational fluid mechanics are discussed in a collection of annual review essays. Topics addressed include Lagrangian ocean studies, drag reduction in nature, the hydraulics of rotating strait and sill flow, analytical methods for the development of Reynolds-stress closures in turbulence, and exact solutions of the Navier-Stokes equations. Consideration is given to the theory of hurricanes, flow phenomena in CVD of thin films, particle-imaging techniques for experimental fluid mechanics, symmetry and symmetry-breaking bifurcations in fluid dynamics, turbulent mixing in stratified fluids, numerical simulation of transition in wall-bounded shear flows, fractals and multifractals in fluid turbulence, and coherent motions in the turbulent boundary layer

Turbulent thermal convection at high Rayleigh numbers for a Boussinesq fluid of constant Prandtl number

International Nuclear Information System (INIS)

Amati, G.; Koal, K.; Massaioli, F.; Sreenivasan, K.R.; Verzicco, R.

2006-12-01

The results from direct numerical simulations of turbulent Boussinesq convection are briefly presented. The flow is computed for a cylindrical cell of aspect ratio 1/2 in order to compare with the results from recent experiments. The results span eight decades of Ra from 2x10 6 to 2x10 14 and form the baseline data for a strictly Boussinesq fluid of constant Prandtl number (Pr=0.7). A conclusion is that the Nusselt number varies nearly as the 1/3 power of Ra for about four decades towards the upper end of the Ra range covered. (author)

The role of the thermal convection of fluids in the formation of unconformity-type uranium deposits: the Athabasca Basin, Canada

Science.gov (United States)

Pek, A. A.; Malkovsky, V. I.

2017-05-01

In the global production of uranium, 18% belong to the unconformity-type Canadian deposits localized in the Athabasca Basin. These deposits, which are unique in terms of their ore quality, were primarily studied by Canadian and French scientists. They have elaborated the diagenetic-hydrothermal hypothesis of ore formation, which suggests that (1) the deposits were formed within a sedimentary basin near an unconformity surface dividing the folded Archean-Proterozoic metamorphic basement and a gently dipping sedimentary cover, which is not affected by metamorphism; (2) the spatial accommodation of the deposits is controlled by the rejuvenated faults in the basement at their exit into the overlying sedimentary sequence; the ore bodies are localized above and below the unconformity surface; (3) the occurrence of graphite-bearing rocks is an important factor in controlling the local structural mineralization; (4) the ore bodies are the products of uranium precipitation on a reducing barrier. The mechanism that drives the circulation of ore-forming hydrothermal solutions has remained one of the main unclear questions in the general genetic concept. The ore was deposited above the surface of the unconformity due to the upflow discharge of the solution from the fault zones into the overlying conglomerate and sandstone. The ore formation below this surface is a result of the downflow migration of the solutions along the fault zones from sandstone into the basement rocks. A thermal convective system with the conjugated convection cells in the basement and sedimentary fill of the basin may be a possible explanation of why the hydrotherms circulate in the opposite directions. The results of our computations in the model setting of the free thermal convection of fluids are consistent with the conceptual reasoning about the conditions of the formation of unique uranium deposits in the Athabasca Basin. The calculated rates of the focused solution circulation through the fault

Quantifying near-wall coherent structures in turbulent convection

Science.gov (United States)

Gunasegarane, G. S.; A Puthenveettil, Baburaj; K Agrawal, Yogesh; Schmeling, Daniel; Bosbach, Johannes; Arakeri, Jaywant; IIT Madras-DLR-IISc Collaboration

2011-11-01

We present planforms of line plumes formed on horizontal surfaces in turbulent convection, along with the length of near- wall line plumes measured from these planforms, in a six decade range of Rayleigh numbers (105 < Ra <1011) and at three Prandtl numbers (Pr = 0 . 7 , 6 , 602). Using geometric constraints on the relations for the mean plume spacings, we obtain expressions for the total length of these near-wall plumes in turbulent convection. The plume length per unit area (Lp / A), made dimensionless by the near-wall length scale in turbulent convection (Zw) remains a constant for a given fluid. The Nusselt number is shown to be directly proportional to Lp H / A for a given fluid layer of height H. Increase in Pr has a weak influence in decreasing Lp / A . These expressions match the measurements, thereby showing that the assumption of laminar natural convection boundary layers in turbulent convection is consistent with the observed total length of line plumes. We then show that similar relationships are obtained based on the assumption that the line plumes are the outcome of the instability of laminar natural convection boundary layers on the horizontal surfaces.

Basal melting driven by turbulent thermal convection

Science.gov (United States)

Rabbanipour Esfahani, Babak; Hirata, Silvia C.; Berti, Stefano; Calzavarini, Enrico

2018-05-01

Melting and, conversely, solidification processes in the presence of convection are key to many geophysical problems. An essential question related to these phenomena concerns the estimation of the (time-evolving) melting rate, which is tightly connected to the turbulent convective dynamics in the bulk of the melt fluid and the heat transfer at the liquid-solid interface. In this work, we consider a convective-melting model, constructed as a generalization of the Rayleigh-Bénard system, accounting for the basal melting of a solid. As the change of phase proceeds, a fluid layer grows at the heated bottom of the system and eventually reaches a turbulent convection state. By means of extensive lattice-Boltzmann numerical simulations employing an enthalpy formulation of the governing equations, we explore the model dynamics in two- and three-dimensional configurations. The focus of the analysis is on the scaling of global quantities like the heat flux and the kinetic energy with the Rayleigh number, as well as on the interface morphology and the effects of space dimensionality. Independently of dimensionality, we find that the convective-melting system behavior shares strong resemblances with that of the Rayleigh-Bénard one, and that the heat flux is only weakly enhanced with respect to that case. Such similarities are understood, at least to some extent, considering the resulting slow motion of the melting front (with respect to the turbulent fluid velocity fluctuations) and its generally little roughness (compared to the height of the fluid layer). Varying the Stefan number, accounting for the thermodynamical properties of the material, also seems to have only a mild effect, which implies the possibility of extrapolating results in numerically delicate low-Stefan setups from more convenient high-Stefan ones. Finally, we discuss the implications of our findings for the geophysically relevant problem of modeling Arctic ice melt ponds.

Oscillatory magneto-convection under magnetic field modulation

Directory of Open Access Journals (Sweden)

Palle Kiran

2018-03-01

Full Text Available In this paper we investigate an oscillatory mode of nonlinear magneto-convection under time dependant magnetic field. The time dependant magnetic field consists steady and oscillatory parts. The oscillatory part of the imposed magnetic field is assumed to be of third order. An externally imposed vertical magnetic field in an electrically conducting horizontal fluid layer is considered. The finite amplitude analysis is discussed while perturbing the system. The complex Ginzburg-Landau model is used to derive an amplitude of oscillatory convection for weakly nonlinear mode. Heat transfer is quantified in terms of the Nusselt number, which is governed by the Landau equation. The variation of the modulation excitation of the magnetic field alternates heat transfer in the layer. The modulation excitation of the magnetic field is used either to enhance or diminish the heat transfer in the system. Further, it is found that, oscillatory mode of convection enhances the heat transfer and than stationary convection. The results have possible technological applications in magnetic fluid based systems involving energy transmission. Keywords: Weakly nonlinear theory, Oscillatory convection, Complex Ginzburg Landau model, Magnetic modulation

Study on turbulent characteristics and transition behavior of combined-convection boundary layer

International Nuclear Information System (INIS)

Hattori, Yasuo

2001-01-01

The stabilizing mechanism of the turbulent combined-convection boundary layer along an isothermally-heated flat plate in air aided by a weak freestream are investigated experimentally and theoretically. The turbulent statistics of the combined-convection boundary layer measured with hot- and cold wires at different Grashof numbers indicates that with an increase in the freestream velocity, a similar change in the turbulent quantities appears independently of local Grashof number. Then based on the such experimental results, it is verified that the laminarization of the boundary layer due to an increase in freestream velocity arises at Grx / Rex 6 . Then, through the experiments with a particle image velocimetry (PIV), the spatio-temporal structure of the turbulent combined-convection boundary layer is investigated. For instantaneous velocity vectors obtained with PIV, large-scale fluid motions, which play a predominant role in the generation of turbulence, are frequently observed in the outer layer, while quasi-coherent structures do not exist in the near-wall region. Thus, it is revealed that increasing freestream restricts large-scale fluid motions in the outer layer, and consequently the generation of turbulence is suppressed and the boundary layer becomes laminar. (author)

Fluid mechanics problems and solutions

CERN Document Server

Spurk, Joseph H

1997-01-01

his collection of over 200 detailed worked exercises adds to and complements the textbook Fluid Mechanics by the same author, and illustrates the teaching material through examples. In the exercises the fundamental concepts of Fluid Mechanics are applied to obtaining the solution of diverse concrete problems, and in doing this the student's skill in the mathematical modeling of practical problems is developed. In addition, 30 challenging questions without detailed solutions have been included, and while lecturers will find these questions suitable for examinations and tests, the student himself can use them to check his understanding of the subject.

Prandtl-number Effects in High-Rayleigh-number Spherical Convection

Science.gov (United States)

Orvedahl, Ryan J.; Calkins, Michael A.; Featherstone, Nicholas A.; Hindman, Bradley W.

2018-03-01

Convection is the predominant mechanism by which energy and angular momentum are transported in the outer portion of the Sun. The resulting overturning motions are also the primary energy source for the solar magnetic field. An accurate solar dynamo model therefore requires a complete description of the convective motions, but these motions remain poorly understood. Studying stellar convection numerically remains challenging; it occurs within a parameter regime that is extreme by computational standards. The fluid properties of the convection zone are characterized in part by the Prandtl number \\Pr = ν/κ, where ν is the kinematic viscosity and κ is the thermal diffusion; in stars, \\Pr is extremely low, \\Pr ≈ 10‑7. The influence of \\Pr on the convective motions at the heart of the dynamo is not well understood since most numerical studies are limited to using \\Pr ≈ 1. We systematically vary \\Pr and the degree of thermal forcing, characterized through a Rayleigh number, to explore its influence on the convective dynamics. For sufficiently large thermal driving, the simulations reach a so-called convective free-fall state where diffusion no longer plays an important role in the interior dynamics. Simulations with a lower \\Pr generate faster convective flows and broader ranges of scales for equivalent levels of thermal forcing. Characteristics of the spectral distribution of the velocity remain largely insensitive to changes in \\Pr . Importantly, we find that \\Pr plays a key role in determining when the free-fall regime is reached by controlling the thickness of the thermal boundary layer.

Numerical simulations of thermal convection in a rotating spherical fluid shell at high Taylor and Rayleigh numbers

International Nuclear Information System (INIS)

Sun, Z.; Schubert, G.

1995-01-01

In this study, we carry out numerical simulations of thermal convection in a rapidly rotating spherical fluid shell at high Taylor number Ta and Rayleigh number R with a nonlinear, three-dimensional, time-dependent, spectral-transform code. The parameters used in the simulations are chosen to be in a range which allows us to study two different types of convection, i.e., single column and multi-layered types, and the transition between them. Numerical solutions feature highly time-dependent north--south open columnar convective cells. The cells occur irregularly in longitude, are quasi-layered in cylindrical radius, and maintain alternating bands of mean zonal flow. The complex convective structure and the banded mean zonal flow are results of the high Taylor and Rayleigh numbers. The transition between the two types of convection appears to occur gradually with increasing Rayleigh and Taylor numbers. At a Taylor number of 10 7 the differential rotation pattern consists of an inner cylindrical region of subrotation and an outer cylindrical shell of superrotation manifest at the outer boundary as an equatorial superrotation and a high latitude subrotation. The differential rotation pattern is similar at Ta=10 8 and low Rayleigh number. Cylindrical shells of alternately directed mean zonal flow begin to develop at Ta=10 8 and R=50R c and at Ta=10 9 and R=25R c . This pattern is seen on the outer surface as a latitudinally-banded zonal flow consisting of an equatorial superrotation, a middle and high latitude subrotation, and a polar superrotation. At Ta=10 9 and R=50R c the differential rotation appears at the surface as a broad eastward flow in the equatorial region with alternating bands of westward and eastward flow at high latitudes. copyright 1995 American Institute of Physics

Fluid mechanics as a driver of tissue-scale mechanical signaling in organogenesis.

Science.gov (United States)

Gilbert, Rachel M; Morgan, Joshua T; Marcin, Elizabeth S; Gleghorn, Jason P

2016-12-01

Organogenesis is the process during development by which cells self-assemble into complex, multi-scale tissues. Whereas significant focus and research effort has demonstrated the importance of solid mechanics in organogenesis, less attention has been given to the fluid forces that provide mechanical cues over tissue length scales. Fluid motion and pressure is capable of creating spatial gradients of forces acting on cells, thus eliciting distinct and localized signaling patterns essential for proper organ formation. Understanding the multi-scale nature of the mechanics is critically important to decipher how mechanical signals sculpt developing organs. This review outlines various mechanisms by which tissues generate, regulate, and sense fluid forces and highlights the impact of these forces and mechanisms in case studies of normal and pathological development.

Entropy generation due to double diffusive convective flow of Casson fluids over nonlinearity stretching sheets with slip conditions

Directory of Open Access Journals (Sweden)

Sameh E. Ahmed

2017-12-01

Full Text Available The present paper deals with the effects of slip boundary conditions and chemical reaction on the heat and mass transfer by mixed convective boundary layer flow of a non-Newtonian fluid over a nonlinear stretching sheet. The Casson fluid model is used to characterize the non-Newtonian fluid behavior. First order chemical reactions are considered. Similar solutions are used to convert the partial differential equations governing the problem to ordinary differential equations. The velocity, temperature and concentration profiles are obtained, numerically, using the MATLAB function bvp4c and those are used to compute the entropy generation number. The effect of increasing values of the Casson parameter is found to suppress the velocity field and temperature distribution. But the concentration is enhanced with the increasing of Casson parameter. The viscous dissipation, temperature and concentration irreversibility are determined and discussed in details.

Fluid mechanics. Vol. 2

International Nuclear Information System (INIS)

Truckenbrodt, E.

1980-01-01

The second volume contains the chapter 4 to 6. Whereas chapter 1 deals with the introduction into the mechanics of fluids and chapter 2 with the fundamental laws of fluid and thermal fluid dynamics, in chapter 3 elementary flow phenomena in fluids with constant density are treated. Chapter 4 directly continues chapter 3 and describes elementary flow phenomena in fluids with varying density. Fluid statics again is treated as a special case. If compared with the first edition the treatment of unsteady laminar flow and of pipe flow for a fluid with varying density were subject to a substantial extension. In chapter 5 rotation-free and rotating potential flows are presented together. By this means it is achieved to explain the behaviour of the multidimensional fictionless flow in closed form. A subchapter describes some related problems of potential theory like the flow along a free streamline and seepage flow through a porous medium. The boundary layer flows in chapter 6 are concerned with the flow and temperature boundary layer in laminar and turbulent flows at a fired wall. In it differential and integral methods are applied of subchapter reports on boundary layer flows without a fixed boundary, occurring e.g. in an open jet and in a wake flow. The problems of intermittence and of the Coanda effect are briefly mentioned. (orig./MH)

Fluids and the evolution of rock mechanical properties

International Nuclear Information System (INIS)

Reuschle, Thierry

1989-01-01

This research thesis reports the study of the various phenomena of fluid-solid interaction (mechanical or chemical interaction with fracturing by fluid overpressure, slow crack propagation, and pore deformation by transfer in solution) which may occur in the interaction of fluids with rocks. The author first presents the formalism of slow crack propagation based on the generalisation of the Griffith criterion. The model results are compared with experimental results obtained on four materials (glass, quartz, sandstone, and micrite) by using the double-torsion test. In the second part, the author addresses the issue of pore deformation by transfer in solution: dissolution and crystallisation under stress. The Gibbs chemical potential equation is firstly generalised to the case of a circular pore, and a formalism combining mechanics and thermodynamics is then proposed. A set of simulations highlights important parameters. In the third part, the author addresses the problem of fluid-rock mechanical interaction by studying the mechanical role of fluid pressure in crack initiation and propagation [fr

Topology Optimisation for Coupled Convection Problems

DEFF Research Database (Denmark)

Alexandersen, Joe

This thesis deals with topology optimisation for coupled convection problems. The aim is to extend and apply topology optimisation to steady-state conjugate heat transfer problems, where the heat conduction equation governs the heat transfer in a solid and is coupled to thermal transport...... in a surrounding uid, governed by a convection-diffusion equation, where the convective velocity field is found from solving the isothermal incompressible steady-state Navier-Stokes equations. Topology optimisation is also applied to steady-state natural convection problems. The modelling is done using stabilised...... finite elements, the formulation and implementation of which was done partly during a special course as prepatory work for this thesis. The formulation is extended with a Brinkman friction term in order to facilitate the topology optimisation of fluid flow and convective cooling problems. The derived...

The Status of Fluid Mechanics in Bioengineering Curricula.

Science.gov (United States)

Miller, Gerald E.; Hyman, William A.

1981-01-01

Describes the status of fluid mechanics courses in bioengineering curricula. A survey of institutions offering bioengineering degrees indicates that over half do not require fluid mechanics courses. Suggests increasing number of mechanics courses to increase the quality of bioengineering students and to prepare students for graduate work and more…

Isogeometric Analysis and Shape Optimization in Fluid Mechanics

DEFF Research Database (Denmark)

Nielsen, Peter Nørtoft

This thesis brings together the fields of fluid mechanics, as the study of fluids and flows, isogeometric analysis, as a numerical method to solve engineering problems using computers, and shape optimization, as the art of finding "best" shapes of objects based on some notion of goodness. The flow...... approximations, and for shape optimization purposes also due to its tight connection between the analysis and geometry models. The thesis is initiated by short introductions to fluid mechanics, and to the building blocks of isogeometric analysis. As the first contribution of the thesis, a detailed description...... isogeometric analysis may serve as a natural framework for shape optimization within fluid mechanics. We construct an efficient regularization measure for avoiding inappropriate parametrizations during optimization, and various numerical examples of shape optimization for fluids are considered, serving...

CONVECTIVE BURSTS AND THE COUPLING OF SATURN'S EQUATORIAL STORMS AND INTERIOR ROTATION

International Nuclear Information System (INIS)

Heimpel, Moritz; Aurnou, Jonathan M.

2012-01-01

Temporal variations of Saturn's equatorial jet and magnetic field hint at rich dynamics coupling the atmosphere and the deep interior. However, it has been assumed that rotation of the interior dynamo must be steady over tens of years of modern observations. Here we use a numerical convection model and scaling estimates to show how equatorial convective bursts can transfer angular momentum to the deeper interior. The numerical model allows angular momentum transfer between a fluid outer spherical shell and a rigid inner sphere. Convection drives a prograde equatorial jet exhibiting quasiperiodic bursts that fill the equatorial volume outside the tangent cylinder. For each burst strong changes in the equatorial surface velocity are associated with retrograde torque on the inner sphere. Our results suggest that Saturn's Great White Spot, a giant storm that was observed to fill the equatorial region in 1990, could mobilize a volume of fluid carrying roughly 15% of Saturn's moment of inertia. Conservation of angular momentum then implies that a 20% change in the equatorial jet angular velocity could change the average interior rotation rate by about 0.1%—roughly an order of magnitude less than the apparent rotation rate changes associated with Saturn's kilometric radio (SKR) signal. However, if the SKR signal originates outside the liquid metal core in a 'planetary tachocline' that separates the layer of fast zonal flow from the magnetically controlled and slowly convecting deep interior, then convective bursts can provide a possible mechanism for the observed ∼1% SKR changes.

Hydrothermal convection and uranium deposits in abnormally radioactive plutons

International Nuclear Information System (INIS)

1978-09-01

Hydrothermal uranium deposits are often closely associated with granites of abnormally high uranium content. We have studied the question whether the heat generated within such granites can cause fluid convection of sufficient magnitude to develop hydrothermal uranium deposits. Numerical models of flow through porous media were used to calculate temperatures and fluid flow in and around plutons similar to the Conway Granite, New Hampshire, i.e. with a halfwidth of 17 km, a thickness of 6.25 km, and with a uniform internal heat generation rate of 20 x 10 -13 cal/cm 3 -sec. Fluid convection was computed for plutons with permeabilities between 0.01 and 5 millidarcies (1 x10 -13 cm 2 to 5 x 10 -11 cm 2 . Flow rates and the size and location of convection cells in and around radioactive plutons like the Conway Granite were found to depend critically on the permeability distribution within the pluton and in adjacent country rocks. The depth of burial, the distribution of heat sources within the pluton, and small rates of heat generation in the country rock are only of minor importance. Topographic relief is unlikely to effect flow rates significantly, but can have a major influence on the distribution of recharge and discharge areas. Within a few million years, the mass of water transported by steady state convection through such radioactive plutons can equal the mass of water which can convect through them during initial cooling from magmatic temperatures. If the permeability in a Conway-type pluton is on the order of 0.5 millidarcies, the rate of fluid convection is probably sufficient to develop a hydrothermal ore deposit containing 10,000 tons of uranium in a period of two million years. Such a uranium deposit is most likely to develop in an area of strong upwelling or strong downwelling flow

Carbon dioxide sequestration: Modeling the diffusive and convective transport under a CO2 cap

KAUST Repository

Allen, Rebecca; Sun, Shuyu

2012-01-01

of low permeability. CO2 from this ‘capped' region diffuses into the fluid underlying it, and the resulting CO2-fluid mixture increases in density. This increase in density leads to gravity-driven convection. Accordingly, diffusive-convective transport

Syrthes thermal code and Estet or N3S fluid mechanics codes coupling; Couplage du code de thermique Syrthes et des codes de mecanique des fluides N3S et ou Estet

Energy Technology Data Exchange (ETDEWEB)

Peniguel, C [Electricite de France (EDF), 78 - Chatou (France). Direction des Etudes et Recherches; Rupp, I [SIMULOG, 78 - Guyancourt (France)

1997-06-01

EDF has developed numerical codes for modeling the conductive, radiative and convective thermal transfers and their couplings in complex industrial configurations: the convection in a fluid is solved by Estet in finite volumes or N3S in finite elements, the conduction is solved by Syrthes and the wall-to-wall thermal radiation is modelled by Syrthes with the help of a radiosity method. Syrthes controls the different heat exchanges which may occur between fluid and solid domains, using an explicit iterative method. An extension of Syrthes has been developed in order to allow the consideration of configurations where several fluid codes operate simultaneously, using ``message passing`` tools such as PVM (Parallel Virtual Machine) and the Calcium code coupler developed at EDF. Application examples are given

Finite element analysis of thermal convection in deep ocean sediments

International Nuclear Information System (INIS)

Gartling, D.K.

1980-01-01

Of obvious importance to the study and engineering of a seabed disposal is the determination of the temperature and fluid flow fields existing in the sediment layer and the perturbation of these fields due to the implantation of localized heat sources. The fluid mechanical and heat transfer process occurring in oceanic sediments may be characterized as free (or natural) convection in a porous material. In the case of an undisturbed sediment layer, the driving force for the natural circulation of pore water comes from the geothermal heat flux. Current theories for heat flow from the sea floor suggest the possibility of large scale hydrothermal circulation in the oceanic crust (see e.g., Ribando, et al. 1976) which is in turn coupled with a convection process in the overlying sediment layer (Anderson 1980, Anderson, et al. 1979). The introduction of a local heat source, such as a waste canister, into a saturated sediment layer would by itself initiate a convection process due to buoyancy forces. Since the mathematical description of natural convection in a porous medium is of sufficient complexity to preclude the use of most analytic methods of analysis, approximate numerical procedures are often employed. In the following sections, a particular type of numerical method is described that has proved useful in the solution of a variety of porous flow problems. However, rather than concentrate on the details of the numerical algorithm the main emphasis of the presentation will be on the types of problems and results that are encountered in the areas of oceanic heat flow and seabed waste disposal

Effect of Darcy, fluid Rayleigh and heat generation parameters on natural convection in a porous square enclosure: A Brinkman-extended Darcy model

International Nuclear Information System (INIS)

Das, S.; Sahoo, R.K.

1999-01-01

Analysis of flow and convective heat transfer in volumetrically heated porous layer has become a separate topic for research in the last twenty five years in view of its importance in various engineering applications, such as heat removal from nuclear fuel debris, heat transfer associated with storage of nuclear waste, exothermic reaction in packed-bed reactors, heat recovery from geothermal systems and particularly in the field of large storage systems of agricultural products. Here, a pressure-velocity solution for natural convection for fluid saturated heat generating porous medium in a square enclosure is analyzed by finite element method. The numerical solutions obtained for wide range of fluid Rayleigh number, Ra f , Darcy number, Da, and heat generating number, Q d . The justification for taking these non-dimensional parameters independently is to establish the effect of individual parameters on flow patterns. It has been observed that peak temperature occurs at the top central part and weaker velocity prevails near the vertical walls of the enclosure due to the heat generation parameter alone. On comparison, the modified Rayleigh number used by the earlier investigators, can not explain explicitly the effect of heat generation parameter on natural convection within an enclosure having differentially heated vertical walls. At higher Darcy number, the peak temperature and peak velocity are comparatively more, resulting in better enhancement of heat transfer rate

Effect of double stratification on MHD free convection in a micropolar fluid

Directory of Open Access Journals (Sweden)

D. Srinivasacharya

2013-10-01

Full Text Available This paper analyzes the flow and heat and mass transfer characteristics of the free convection on a vertical plate with variable wall temperature and concentration in a doubly stratified micropolar fluid. A uniform magnetic field is applied normal to the plate. The governing non-linear partial differential equations are transformed into a system of coupled non-linear ordinary differential equations using similarity transformations and then solved numerically using the Keller-box method. The numerical results are compared and found to be in good agreement with previously published results as special cases of the present investigation. The non-dimensional velocity, microrotation, temperature and concentration are presented graphically for various values of magnetic parameter, coupling number, thermal and solutal stratification parameters. In addition, the Nusselt number, the Sherwood number, the skin-friction coefficient, and the wall couple stress are shown in a tabular form.

Penetration of steady fluid motions into an outer stable layer excited by MHD thermal convection in rotating spherical shells

Science.gov (United States)

Takehiro, Shin-ichi; Sasaki, Youhei

2018-03-01

Penetration of steady magneto-hydrodynamic (MHD) disturbances into an upper strongly stratified stable layer excited by MHD thermal convection in rotating spherical shells is investigated. The theoretical model proposed by Takehiro (2015) is reexamined in the case of steady fluid motion below the bottom boundary. Steady disturbances penetrate into a density stratified MHD fluid existing in the semi-infinite region in the vertical direction. The axis of rotation of the system is tilted with respect to the vertical. The basic magnetic field is uniform and may be tilted with respect to the vertical and the rotation axis. Linear dispersion relation shows that the penetration distance with zero frequency depends on the amplitude of Alfvén wave speed. When Alfvén wave speed is small, viscous diffusion becomes dominant and penetration distance is similar to the horizontal scale of the disturbance at the lower boundary. In contrast, when Alfvén wave speed becomes larger, disturbance can penetrate deeper, and penetration distance becomes proportional to the Alfvén wave speed and inversely proportional to the geometric average of viscous and magnetic diffusion coefficients and to the total horizontal wavenumber. The analytic expression of penetration distance is in good agreement with the extent of penetration of mean zonal flow induced by finite amplitude convection in a rotating spherical shell with an upper stably stratified layer embedded in an axially uniform basic magnetic field. The theory expects that the stable layer suggested in the upper part of the outer core of the earth could be penetrated completely by mean zonal flows excited by thermal/compositional convection developing below the stable layer.

Mathematical models of convection

CERN Document Server

Andreev, Victor K; Goncharova, Olga N; Pukhnachev, Vladislav V

2012-01-01

Phenomena of convection are abundant in nature as well as in industry. This volume addresses the subject of convection from the point of view of both, theory and application. While the first three chapters provide a refresher on fluid dynamics and heat transfer theory, the rest of the book describes the modern developments in theory. Thus it brings the reader to the ""front"" of the modern research. This monograph provides the theoretical foundation on a topic relevant to metallurgy, ecology, meteorology, geo-and astrophysics, aerospace industry, chemistry, crystal physics, and many other fiel

Aligned Magnetic Field Effects on Flow and Heat Transfer of the Upper-Convected Maxwell Fluid over a Stretching/Shrinking Sheet

Directory of Open Access Journals (Sweden)

Waini Iskandar

2017-01-01

Full Text Available In this paper, the effect of aligned magnetic field towards the flow and heat transfer of the upper-convected Maxwell (UCM fluid over a stretching/shrinking sheet is numerically studied. The governing partial differential equations are reduced into a system of ordinary differential equations using a similarity transformation, which are then solved numerically using the shooting method. The skin friction and heat transfer coefficients, the velocity, as well as the temperature profiles of the fluid are presented and discussed. Results indicate that an increase in the aligned angle strengthens the applied magnetic field which decrease the velocity and increase the temperature profiles of the fluid. This implies that an increase in the aligned angle increases the skin friction coefficient and decreases the heat transfer coefficients.

Onset of Absolute Instability Induced by Viscous Dissipation in the Poiseuille-Darcy-Benard Convection of a Newtonian Fluid

International Nuclear Information System (INIS)

Brandão, P V; Alves, L S de B; Barletta, A

2014-01-01

The present paper investigates the transition from convective to absolute instability induced by viscous dissipation. As far as the authors are aware, this is the first time such a study is reported in the literature. Its framework is provided by the Poiseuille-Darcy-Benard convection of a Newtonian fluid. We found the same behaviour observed in the absence of viscous dissipation whenever the Gebhart number is smaller than Ge < 0.95, which is the stabilising effect of the cross flow. When 0.95 < Ge < 4.31, weak cross flows still stabilise the onset of absolute instability but stronger cross flows destabilise it. For a stronger viscous dissipation, i.e. Ge > 4.31, the cross flow always destabilises this onset. The latter two conditions create a scenario where viscous dissipation is capable of inducing a transition to absolute instability in the absence of wall heating, i.e. with a zero Rayleigh number

Fluid Mechanics of Blood Clot Formation.

Science.gov (United States)

Fogelson, Aaron L; Neeves, Keith B

2015-01-01

Intravascular blood clots form in an environment in which hydrodynamic forces dominate and in which fluid-mediated transport is the primary means of moving material. The clotting system has evolved to exploit fluid dynamic mechanisms and to overcome fluid dynamic challenges to ensure that clots that preserve vascular integrity can form over the wide range of flow conditions found in the circulation. Fluid-mediated interactions between the many large deformable red blood cells and the few small rigid platelets lead to high platelet concentrations near vessel walls where platelets contribute to clotting. Receptor-ligand pairs with diverse kinetic and mechanical characteristics work synergistically to arrest rapidly flowing cells on an injured vessel. Variations in hydrodynamic stresses switch on and off the function of key clotting polymers. Protein transport to, from, and within a developing clot determines whether and how fast it grows. We review ongoing experimental and modeling research to understand these and related phenomena.

The genesis of fluid mechanics, 1640-1780

CERN Document Server

Calero, Julián Simón

2008-01-01

Fluid Mechanics, as a scientific discipline in a modern sense, was established between the last third of the 17th century and the first half of the 18th one. This book analyses its genesis, following its evolution along two basic lines of research, which have been named the "problem of resistance" and the "problem of discharge". This approach highlights the existence of a remarkable experimental aspect in the aforementioned research lines, together with their link with problems of a practical nature, such as ballistics, hydraulics, fluid-using machines or naval theory. On the other hand, although previous studies usually present fluid mechanics from the point of view of mathematics, this is complemented here by an engineering viewpoint; gathering attempts made in the beginnings of fluid mechanics to see if the theory was capable of productive application in practical terms. This is nothing unusual in a time where the quality of knowledge and skill is measured largely by its usefulness. (c) Universidad Naciona...

Boundary layers and scaling relations in natural thermal convection

Science.gov (United States)

Shishkina, Olga; Lohse, Detlef; Grossmann, Siegfried

2017-11-01

We analyse the boundary layer (BL) equations in natural thermal convection, which includes vertical convection (VC), where the fluid is confined between two differently heated vertical walls, horizontal convection (HC), where the fluid is heated at one part of the bottom plate and cooled at some other part, and Rayleigh-Benard convection (RBC). For BL dominated regimes we derive the scaling relations of the Nusselt and Reynolds numbers (Nu, Re) with the Rayleigh and Prandtl numbers (Ra, Pr). For VC the scaling relations are obtained directly from the BL equations, while for HC they are derived by applying the Grossmann-Lohse theory to the case of VC. In particular, for RBC with large Pr we derive Nu Pr0Ra1/3 and Re Pr-1Ra2/3. The work is supported by the Deutsche Forschungsgemeinschaft (DFG) under the Grant Sh 405/4 - Heisenberg fellowship.

Bidispersive-inclined convection

Science.gov (United States)

Mulone, Giuseppe; Straughan, Brian

2016-01-01

A model is presented for thermal convection in an inclined layer of porous material when the medium has a bidispersive structure. Thus, there are the usual macropores which are full of a fluid, but there are also a system of micropores full of the same fluid. The model we employ is a modification of the one proposed by Nield & Kuznetsov (2006 Int. J. Heat Mass Transf. 49, 3068–3074. (doi:10.1016/j.ijheatmasstransfer.2006.02.008)), although we consider a single temperature field only. PMID:27616934

Proceedings of the sixth international and forty third national conference on fluid mechanics and fluid power: book of abstracts

International Nuclear Information System (INIS)

Jain, Anuj; Paul, Akshoy Ranjan

2016-01-01

Fluid Mechanics and Fluid Power (FMFP) Conference is an important meeting to promote all activities in the field of Fluid Mechanics and Fluid Power in India. FMFP-2016 offers great opportunity to scientists, researchers, engineers and business executives from all parts of the world to share the recent advancements and future trends in all aspects of fluid mechanics and fluid power- be it theoretical, experimental, applied and computational, and build network. It covers theoretical and experimental fluid dynamics, flow instability, transition, turbulence and control, fluid machinery, turbomachinery and fluid power, IC engines and gas turbines, multiphase flows, fluid-structure interaction and flow-induced noise, micro and nano fluid mechanics, bio-inspired fluid mechanics, energy and environment, specialized topics (transport phenomena in materials processing and manufacturing, MHD and EHD flows, granular flows, nuclear reactor, thermal hydraulics, defence and space engineering, sustainable habitat. Papers relevant to INIS are indexed separately

Quantification of ventilated facade efficiency by using computational fluid mechanics techniques

International Nuclear Information System (INIS)

Mora Perez, M.; Lopez Patino, G.; Bengochea Escribano, M. A.; Lopez Jimenez, P. A.

2011-01-01

In some countries, summer over-heating is a big problem in a buildings energy balance. Ventilated facades are a useful tool when applied to building design, especially in bio climatic building design. A ventilated facade is a complex, multi-layer structural solution that enables dry installation of the covering elements. The objective of this paper is to quantify the efficiency improvement in the building thermal when this sort of facade is installed. These improvements are due to convection produced in the air gap of the facade. This convection depends on the air movement inside the gap and the heat transmission in this motion. These quantities are mathematically modelled by Computational Fluid Dynamics (CFD) techniques using a commercial code: STAR CCM+. The proposed method allows an assessment of the energy potential of the ventilated facade and its capacity for cooling. (Author) 23 refs.

Stability Analysis and Internal Heating Effect on Oscillatory Convection in a Viscoelastic Fluid Saturated Porous Medium Under Gravity Modulation

Science.gov (United States)

Bhadauria, B. S.; Singh, M. K.; Singh, A.; Singh, B. K.; Kiran, P.

2016-12-01

In this paper, we investigate the combined effect of internal heating and time periodic gravity modulation in a viscoelastic fluid saturated porous medium by reducing the problem into a complex non-autonomous Ginzgburg-Landau equation. Weak nonlinear stability analysis has been performed by using power series expansion in terms of the amplitude of gravity modulation, which is assumed to be small. The Nusselt number is obtained in terms of the amplitude for oscillatory mode of convection. The influence of viscoelastic parameters on heat transfer has been discussed. Gravity modulation is found to have a destabilizing effect at low frequencies and a stabilizing effect at high frequencies. Finally, it is found that overstability advances the onset of convection, more with internal heating. The conditions for which the complex Ginzgburg-Landau equation undergoes Hopf bifurcation and the amplitude equation undergoes supercritical pitchfork bifurcation are studied.

Efficiency of Heat Transfer in Turbulent Rayleigh-Benard Convection

Czech Academy of Sciences Publication Activity Database

Urban, Pavel; Musilová, Věra; Skrbek, L.

2011-01-01

Roč. 107, č. 1 (2011), 014302:1-4 ISSN 0031-9007 R&D Projects: GA AV ČR KJB200650902 Institutional research plan: CEZ:AV0Z20650511 Keywords : natural convection * thermal convection Subject RIV: BK - Fluid Dynamics Impact factor: 7.370, year: 2011

Topological fluid mechanics of Axisymmetric Flow

DEFF Research Database (Denmark)

Brøns, Morten

1998-01-01

Topological fluid mechanics in the sense of the present paper is the study and classification of flow patterns close to a critical point. Here we discuss the topology of steady viscous incompressible axisymmetric flows in the vicinity of the axis. Following previous studies the velocity field v...... to the authors knowledge has not been used systematically to high orders in topological fluid mechanics. We compare the general results with experimental and computational results on the Vogel-Ronneberg flow. We show that the topology changes observed when recirculating bubbles on the vortex axis are created...

A Fluid Mechanics Hypercourse

Science.gov (United States)

Fay, James A.; Sonwalkar, Nishikant

1996-05-01

This CD-ROM is designed to accompany James Fay's Introduction to Fluid Mechanics. An enhanced hypermedia version of the textbook, it offers a number of ways to explore the fluid mechanics domain. These include a complete hypertext version of the original book, physical-experiment video clips, excerpts from external references, audio annotations, colored graphics, review questions, and progressive hints for solving problems. Throughout, the authors provide expert guidance in navigating the typed links so that students do not get lost in the learning process. System requirements: Macintosh with 68030 or greater processor and with at least 16 Mb of RAM. Operating System 6.0.4 or later for 680x0 processor and System 7.1.2 or later for Power-PC. CD-ROM drive with 256- color capability. Preferred display 14 inches or above (SuperVGA with 1 megabyte of VRAM). Additional system font software: Computer Modern postscript fonts (CM/PS Screen Fonts, CMBSY10, and CMTT10) and Adobe Type Manager (ATM 3.0 or later). James A. Fay is Professor Emeritus and Senior Lecturer in the Department of Mechanical Engineering at MIT.

Free convection film flows and heat transfer

CERN Document Server

Shang, Deyi

2010-01-01

Presents development of systematic studies for hydrodynamics and heat and mass transfer in laminar free convection, accelerating film boiling and condensation of Newtonian fluids, and accelerating film flow of non-Newtonian power-law fluids. This book provides a system of analysis models with a developed velocity component method.

Hydrothermal, multiphase convection of H2O-NaCl fluids from ambient to magmatic temperatures : A new numerical scheme and benchmarks for code comparison

NARCIS (Netherlands)

Weis, P.; Driesner, T.; Coumou, D.; Geiger, S.

2014-01-01

Thermohaline convection of subsurface fluids strongly influences heat and mass fluxes within the Earth's crust. The most effective hydrothermal systems develop in the vicinity of magmatic activity and can be important for geothermal energy production and ore formation. As most parts of these systems

Fluid Mechanics Can Be Fun.

Science.gov (United States)

Blanks, Robert F.

1979-01-01

A humanistic approach to teaching fluid mechanics is described which minimizes lecturing, increases professor-student interaction, uses group and individual problem solving sessions, and allows for student response. (BB)

Inhibition of ordinary and diffusive convection in the water condensation zone of the ice giants and implications for their thermal evolution

Science.gov (United States)

Friedson, A. James; Gonzales, Erica J.

2017-11-01

We explore the conditions under which ordinary and double-diffusive thermal convection may be inhibited by water condensation in the hydrogen atmospheres of the ice giants and examine the consequences. The saturation of vapor in the condensation layer induces a vertical gradient in the mean molecular weight that stabilizes the layer against convective instability when the abundance of vapor exceeds a critical value. In this instance, the layer temperature gradient can become superadiabatic and heat must be transported vertically by another mechanism. On Uranus and Neptune, water is inferred to be sufficiently abundant for inhibition of ordinary convection to take place in their respective condensation zones. We find that suppression of double-diffusive convection is sensitive to the ratio of the sedimentation time scale of the condensates to the buoyancy period in the condensation layer. In the limit of rapid sedimentation, the layer is found to be stable to diffusive convection. In the opposite limit, diffusive convection can occur. However, if the fluid remains saturated, then layered convection is generally suppressed and the motion is restricted in form to weak, homogeneous, oscillatory turbulence. This form of diffusive convection is a relatively inefficient mechanism for transporting heat, characterized by low Nusselt numbers. When both ordinary and layered convection are suppressed, the condensation zone acts effectively as a thermal insulator, with the heat flux transported across it only slightly greater than the small value that can be supported by radiative diffusion. This may allow a large superadiabatic temperature gradient to develop in the layer over time. Once the layer has formed, however, it is vulnerable to persistent erosion by entrainment of fluid into the overlying convective envelope of the cooling planet, potentially leading to its collapse. We discuss the implications of our results for thermal evolution models of the ice giants, for

Onset of Vibrational Convection in a Binary Fluid Saturated Non-Darcy Porous Layer Heated from Above

Directory of Open Access Journals (Sweden)

Saravanan S.

2012-07-01

Full Text Available A linear stability analysis is used to investigate the influence of mechanical vibration on the onset of thermosolutal convection in a horizontal porous layer heated and salted from above. Vibrations are considered with arbitrary amplitude and frequency. The Brinkman extended Darcy model is used to describe the flow and the Oberbeck-Boussinesq approximation is employed. Continued fraction method and Floquet theory are used to determine the convective instability threshold. It is found that the solutal Rayleigh number has the stabilizing effect. The existence of a closed disconnected loop of synchronous mode is predicted in the marginal curve for moderate values of solutal Rayleigh number and vibration amplitude.

Application of the principle of similarity fluid mechanics

International Nuclear Information System (INIS)

Hendricks, R.C.; Sengers, J.V.

1979-01-01

Possible applications of the principle of similarity to fluid mechanics is described and illustrated. In correlating thermophysical properties of fluids, the similarity principle transcends the traditional corresponding states principle. In fluid mechanics the similarity principle is useful in correlating flow processes that can be modeled adequately with one independent variable (i.e., one-dimensional flows). In this paper we explore the concept of transforming the conservation equations by combining similarity principles for thermophysical properties with those for fluid flow. We illustrate the usefulness of the procedure by applying such a transformation to calculate two phase critical mass flow through a nozzle

Terminal project heat convection in thin cylinders

International Nuclear Information System (INIS)

Morales Corona, J.

1992-01-01

Heat convection in thin cylinders and analysis about natural convection for straight vertical plates, and straight vertical cylinders submersed in a fluid are presented some works carry out by different authors in the field of heat transfer. In the part of conduction, deduction of the equation of heat conduction in cylindrical coordinates by means of energy balance in a control volume is presented. Enthalpy and internal energy are used for the outlining of the equation and finally the equation in its vectorial form is obtained. In the convection part development to calculate the Nusselt number for a straight vertical plate by a forces analysis, an energy balance and mass conservation over a control volume is outlined. Several empiric correlations to calculate the Nusselt number and its relations with other dimensionless numbers are presented. In the experimental part the way in which a prototype rode is assembled is presented measurements of temperatures attained in steady state and in free convection for working fluids as air and water are showed in tables. Also graphs of Nusselt numbers obtained in the experimental way through some empiric correlations are showed (Author)

Numerical simulations of convectively excited gravity waves

International Nuclear Information System (INIS)

Glatzmaier, G.A.

1983-01-01

Magneto-convection and gravity waves are numerically simulated with a nonlinear, three-dimensional, time-dependent model of a stratified, rotating, spherical fluid shell heated from below. A Solar-like reference state is specified while global velocity, magnetic field, and thermodynamic perturbations are computed from the anelastic magnetohydrodynamic equations. Convective overshooting from the upper (superadiabatic) part of the shell excites gravity waves in the lower (subadiabatic) part. Due to differential rotation and Coriolis forces, convective cell patterns propagate eastward with a latitudinally dependent phase velocity. The structure of the excited wave motions in the stable region is more time-dependent than that of the convective motions above. The magnetic field tends to be concentrated over giant-cell downdrafts in the convective zone but is affected very little by the wave motion in the stable region

Fluid mechanics

International Nuclear Information System (INIS)

Paraschivoiu, I.; Prud'homme, M.; Robillard, L.; Vasseur, P.

2003-01-01

This book constitutes at the same time theoretical and practical base relating to the phenomena associated with fluid mechanics. The concept of continuum is at the base of the approach developed in this work. The general advance proceeds of simple balances of forces as into hydrostatic to more complex situations or inertias, the internal stresses and the constraints of Reynolds are taken into account. This advance is not only theoretical but contains many applications in the form of solved problems, each chapter ending in a series of suggested problems. The major part of the applications relates to the incompressible flows

Thermo-electro-hydrodynamic convection under microgravity: a review

Energy Technology Data Exchange (ETDEWEB)

Mutabazi, Innocent; Yoshikawa, Harunori N; Fogaing, Mireille Tadie; Travnikov, Vadim; Crumeyrolle, Olivier [Laboratoire Ondes et Milieux Complexes, UMR 6294, CNRS-Université du Havre, CS 80450, F-76058 Le Havre Cedex (France); Futterer, Birgit; Egbers, Christoph, E-mail: Innocent.Mutabazi@univ-lehavre.fr [Department of Aerodynamics and Fluid Mechanics, Brandenburg University of Technology Cottbus-Senftenberg, Cottbus (Germany)

2016-12-15

Recent studies on thermo-electro-hydrodynamic (TEHD) convection are reviewed with focus on investigations motivated by the analogy with natural convection. TEHD convection originates in the action of the dielectrophoretic force generated by an alternating electric voltage applied to a dielectric fluid with a temperature gradient. This electrohydrodynamic force is analogous to Archimedean thermal buoyancy and can be regarded as a thermal buoyancy force in electric effective gravity. The review is concerned with TEHD convection in plane, cylindrical, and spherical capacitors under microgravity conditions, where the electric gravity can induce convection without any complexities arising from geometry or the buoyancy force due to the Earth’s gravity. We will highlight the convection in spherical geometry, comparing developed theories and numerical simulations with the GEOFLOW experiments performed on board the International Space Station (ISS). (paper)

Thermal convection in a closed cavity in zero-gravity space conditions with stationary magnetic forces

International Nuclear Information System (INIS)

Lyubimova, T; Mailfert, A

2013-01-01

The paper deals with the investigation of thermo-magnetic convection in a paramagnetic liquid subjected to a non-uniform magnetic field in weightlessness conditions. Indeed, in zero-g space conditions such as realized in International Space Station (ISS), or in artificial satellite, or in free-flight space vessels, the classical thermo-gravitational convection in fluid disappears. In any cases, it may be useful to restore the convective thermal exchange inside fluids such as liquid oxygen. In this paper, the restoration of heat exchange by the way of creation of magnetic convection is numerically studied.

Analytical and Numerical Study of Soret and Dufour Effects on Double Diffusive Convection in a Shallow Horizontal Binary Fluid Layer Submitted to Uniform Fluxes of Heat and Mass

Directory of Open Access Journals (Sweden)

A. Lagra

2018-01-01

Full Text Available Combined Soret and Dufour effects on thermosolutal convection induced in a horizontal layer filled with a binary fluid and subject to constant heat and mass fluxes are investigated analytically and numerically. The thresholds marking the onset of supercritical and subcritical convection are predicted analytically and explicitly versus the governing parameters. The present investigation shows that different regions exist in the N-Du plane corresponding to different parallel flow regimes. The number, the extent, and the locations of these regions depend on whether SrDu>-(1+Le2/2Le2=f(Le or SrDu<-(1+Le2/2Le2. Conjugate effects of cross-phenomena on thresholds of fluid flow and heat and mass transfer characteristics are illustrated and discussed.

Stability Analysis and Internal Heating Effect on Oscillatory Convection in a Viscoelastic Fluid Saturated Porous Medium Under Gravity Modulation

Directory of Open Access Journals (Sweden)

Bhadauria B.S.

2016-12-01

Full Text Available In this paper, we investigate the combined effect of internal heating and time periodic gravity modulation in a viscoelastic fluid saturated porous medium by reducing the problem into a complex non-autonomous Ginzgburg-Landau equation. Weak nonlinear stability analysis has been performed by using power series expansion in terms of the amplitude of gravity modulation, which is assumed to be small. The Nusselt number is obtained in terms of the amplitude for oscillatory mode of convection. The influence of viscoelastic parameters on heat transfer has been discussed. Gravity modulation is found to have a destabilizing effect at low frequencies and a stabilizing effect at high frequencies. Finally, it is found that overstability advances the onset of convection, more with internal heating. The conditions for which the complex Ginzgburg-Landau equation undergoes Hopf bifurcation and the amplitude equation undergoes supercritical pitchfork bifurcation are studied.

Combined convective heat transfer of liquid sodium flowing across tube banks

International Nuclear Information System (INIS)

Ma, Ying; Sugiyama, Ken-ichiro; Ishiguro, Ryoji

1989-01-01

In order to clarify the heat transfer characteristics of combined convection of liquid sodium, a numerical analysis is performed for liquid sodium which flows through a single horizontal row of tubes in the direction of gravity. The correlation of heat transfer characteristics between liquid sodium and ordinary fluids is also discussed. The heat transfer characteristics at large Reynolds numbers are improved when the Richardson number is increased, and the improvement rate is enlarged with increase in p/d value, since convection effect is relatively large. However heat transfer coefficients do not differ from those of forced convection at small Reynolds numbers even when the Richardson number reaches a high value because of conduction effect. A good consistence of heat transfer characteristics of combined convection between liquid sodium and air is obtained at the same Peclet number and Richardson number. This means that the fundamental heat transfer characteristics of combined convection of liquid sodium can be investigated with ordinary fluids. (author)

Thermal convection and nonlinear effects of a superfluid 3He-4He mixture in a porous medium

International Nuclear Information System (INIS)

Chien, L.C.L.

1986-01-01

The convective instability of one-component classical fluids in a porous medium confined between two unbounded slabs was studied. This system behaves like a high Prandtl number bulk fluid. It has boundary conditions similar to the stress-free boundary conditions of bulk one-component classical fluids. Both the amplitude expansion method and the Galerkin method were used to investigate the nonlinear steady convection. Two dimensional rolls are the only stable motion at the onset of convection. Beyond threshold, the steady convection rolls become unstable to formation of cross-roll and zigzag instabilities. Applying the phase-dynamics approach for the zigzag instability, the author obtained the diffusion coefficient D, which can signal the onset of instability. Also investigated was the convective instability of superfluid 3 He- 4 He mixtures in porous media. Assuming no interaction between the average superflow and the porous medium and treating the normal flow in the equation of motion like a classical fluid in a porous medium, it was found that the superfluid mixtures in a porous medium. To investigate the effects of a lateral boundary, the convective instability of classical one-component fluids in porous media inside a box was studied. The zigzag instability does not exist because of the boundary conditions at the side of the box

An introduction to the mechanics of fluids

CERN Document Server

Truesdell, C

2000-01-01

The authors have backgrounds which are ideally suited for writing this book. The late C. Truesdell is well known for his monumental treatises on continuum thermomechanics. K.R. Rajagopal has made many important contributions to the mechanics of continua in general, and to nonlinear fluids in particular. They have produced a compact, moderately general book which encompasses many fluid models of current interest…The book is written very clearly and contains a large number of exercises and their solutions. The level of mathematics is that commonly taught to undergraduates in mathematics departments. This is an excellent book which is highly recommended to students and researchers in fluid mechanics. —Mathematical Reviews The writing style is quintessential Truesdellania: purely mathematical, breathtaking, irrepressible, irreverent, uncompromising, taking no prisoners...The book is filled with historical nuggets…Its pure, exact mathematics will baptize, enlighten and exhilarate. —Applied Mechanics Review...

Fluid Mechanics and Homeland Security

Science.gov (United States)

Settles, Gary S.

2006-01-01

Homeland security involves many applications of fluid mechanics and offers many opportunities for research and development. This review explores a wide selection of fluids topics in counterterrorism and suggests future directions. Broad topics range from preparedness and deterrence of impending terrorist attacks to detection, response, and recovery. Specific topics include aircraft hardening, blast mitigation, sensors and sampling, explosive detection, microfluidics and labs-on-a-chip, chemical plume dispersal in urban settings, and building ventilation. Also discussed are vapor plumes and standoff detection, nonlethal weapons, airborne disease spread, personal protective equipment, and decontamination. Involvement in these applications requires fluid dynamicists to think across the traditional boundaries of the field and to work with related disciplines, especially chemistry, biology, aerosol science, and atmospheric science.

A new lattice Boltzmann equation to simulate density-driven convection of carbon dioxide

KAUST Repository

Allen, Rebecca

2013-01-01

The storage of CO2 in fluid-filled geological formations has been carried out for more than a decade in locations around the world. After CO2 has been injected into the aquifer and has moved laterally under the aquifer\\'s cap-rock, density-driven convection becomes an important transport process to model. However, the challenge lies in simulating this transport process accurately with high spatial resolution and low CPU cost. This issue can be addressed by using the lattice Boltzmann equation (LBE) to formulate a model for a similar scenario when a solute diffuses into a fluid and density differences lead to convective mixing. The LBE is a promising alternative to the traditional methods of computational fluid dynamics. Rather than discretizing the system of partial differential equations of classical continuum mechanics directly, the LBE is derived from a velocity-space truncation of the Boltzmann equation of classical kinetic theory. We propose an extension to the LBE, which can accurately predict the transport of dissolved CO2 in water, as a step towards fluid-filled porous media simulations. This is achieved by coupling two LBEs, one for the fluid flow and one for the convection and diffusion of CO2. Unlike existing lattice Boltzmann equations for porous media flow, our model is derived from a system of moment equations and a Crank-Nicolson discretization of the velocity-truncated Boltzmann equation. The forcing terms are updated locally without the need for additional central difference approximation. Therefore our model preserves all the computational advantages of the single-phase lattice Boltzmann equation and is formally second-order accurate in both space and time. Our new model also features a novel implementation of boundary conditions, which is simple to implement and does not suffer from the grid-dependent error that is present in the standard "bounce-back" condition. The significance of using the LBE in this work lies in the ability to efficiently

Convection in Slab and Spheroidal Geometries

Science.gov (United States)

Porter, David H.; Woodward, Paul R.; Jacobs, Michael L.

2000-01-01

Three-dimensional numerical simulations of compressible turbulent thermally driven convection, in both slab and spheroidal geometries, are reviewed and analyzed in terms of velocity spectra and mixing-length theory. The same ideal gas model is used in both geometries, and resulting flows are compared. The piecewise-parabolic method (PPM), with either thermal conductivity or photospheric boundary conditions, is used to solve the fluid equations of motion. Fluid motions in both geometries exhibit a Kolmogorov-like k(sup -5/3) range in their velocity spectra. The longest wavelength modes are energetically dominant in both geometries, typically leading to one convection cell dominating the flow. In spheroidal geometry, a dipolar flow dominates the largest scale convective motions. Downflows are intensely turbulent and up drafts are relatively laminar in both geometries. In slab geometry, correlations between temperature and velocity fluctuations, which lead to the enthalpy flux, are fairly independent of depth. In spheroidal geometry this same correlation increases linearly with radius over the inner 70 percent by radius, in which the local pressure scale heights are a sizable fraction of the radius. The effects from the impenetrable boundary conditions in the slab geometry models are confused with the effects from non-local convection. In spheroidal geometry nonlocal effects, due to coherent plumes, are seen as far as several pressure scale heights from the lower boundary and are clearly distinguishable from boundary effects.

Modelling of subcooled boiling and DNB-type boiling crisis in forced convection

International Nuclear Information System (INIS)

Bricard, Patrick

1995-01-01

This research thesis aims at being a contribution to the modelling of two phenomena occurring during a forced convection: the axial evolution of the vacuum rate, and the boiling crisis. Thus, the first part of this thesis addresses the prediction of the vacuum rate, and reports the development of a modelling of under-saturated convection in forced convection. The author reports the development and assessment of two-fluid one-dimensional model, the development of a finer analysis based on an averaging of local equations of right cross-sections in different areas. The second part of this thesis addresses the prediction of initiation of a boiling crisis. The author presents generalities and motivations for this study, reports a bibliographical study and a detailed analysis of mechanistic models present in this literature. A mechanism of boiling crisis is retained, and then further developed in a numerical modelling which is used to assess some underlying hypotheses [fr

Thermo-fluid-dynamics of natural convection around a heated vertical plate with a critical assessment of the standard similarity theory

Science.gov (United States)

Guha, Abhijit; Nayek, Subhajit

2017-10-01

A compulsory element of all textbooks on natural convection has been a detailed similarity analysis for laminar natural convection on a heated semi-infinite vertical plate and a routinely used boundary condition for such analysis is u = 0 at x = 0. The same boundary condition continues to be assumed in related theoretical analyses, even in recent publications. The present work examines the consequence of this long-held assumption, which appears to have never been questioned in the literature, on the fluid dynamics and heat transfer characteristics. The assessment has been made here by solving the Navier-Stokes equations numerically with two boundary conditions—one with constrained velocity at x = 0 to mimic the similarity analysis and the other with no such constraints simulating the case of a heated vertical plate in an infinite expanse of the quiescent fluid medium. It is found that the fluid flow field given by the similarity theory is drastically different from that given by the computational fluid dynamics (CFD) simulations with unconstrained velocity. This also reflects on the Nusselt number, the prediction of the CFD simulations with unconstrained velocity being quite close to the experimentally measured values at all Grashof and Prandtl numbers (this is the first time theoretically computed values of the average Nusselt number N u ¯ are found to be so close to the experimental values). The difference of the Nusselt number (Δ N u ¯ ) predicted by the similarity theory and that by the CFD simulations (as well as the measured values), both computed with a high degree of precision, can be very significant, particularly at low Grashof numbers and at Prandtl numbers far removed from unity. Computations show that within the range of investigations (104 ≤ GrL ≤ 108, 0.01 ≤ Pr ≤ 100), the maximum value of Δ N u ¯ may be of the order 50%. Thus, for quantitative predictions, the available theory (i.e., similarity analysis) can be rather inadequate. With

Fractional vector calculus and fluid mechanics

Science.gov (United States)

Lazopoulos, Konstantinos A.; Lazopoulos, Anastasios K.

2017-04-01

Basic fluid mechanics equations are studied and revised under the prism of fractional continuum mechanics (FCM), a very promising research field that satisfies both experimental and theoretical demands. The geometry of the fractional differential has been clarified corrected and the geometry of the fractional tangent spaces of a manifold has been studied in Lazopoulos and Lazopoulos (Lazopoulos KA, Lazopoulos AK. Progr. Fract. Differ. Appl. 2016, 2, 85-104), providing the bases of the missing fractional differential geometry. Therefore, a lot can be contributed to fractional hydrodynamics: the basic fractional fluid equations (Navier Stokes, Euler and Bernoulli) are derived and fractional Darcy's flow in porous media is studied.

Time-Dependent Natural Convection Couette Flow of Heat ...

African Journals Online (AJOL)

Time-Dependent Natural Convection Couette Flow of Heat Generating/Absorbing Fluid between Vertical Parallel Plates Filled With Porous Material. ... The numerical simulation conducted for some saturated liquids reveled that at t ≥ Pr the steady and unsteady state velocities (as well as the temperature of the fluid) ...

Selected topics of fluid mechanics

Science.gov (United States)

Kindsvater, Carl E.

1958-01-01

The fundamental equations of fluid mechanics are specific expressions of the principles of motion which are ascribed to Isaac Newton. Thus, the equations which form the framework of applied fluid mechanics or hydraulics are, in addition to the equation of continuity, the Newtonian equations of energy and momentum. These basic relationships are also the foundations of river hydraulics. The fundamental equations are developed in this report with sufficient rigor to support critical examinations of their applicability to most problems met by hydraulic engineers of the Water Resources Division of the United States Geological Survey. Physical concepts are emphasized, and mathematical procedures are the simplest consistent with the specific requirements of the derivations. In lieu of numerical examples, analogies, and alternative procedures, this treatment stresses a brief methodical exposition of the essential principles. An important objective of this report is to prepare the user to read the literature of the science. Thus, it begins With a basic vocabulary of technical symbols, terms, and concepts. Throughout, emphasis is placed on the language of modern fluid mechanics as it pertains to hydraulic engineering. The basic differential and integral equations of simple fluid motion are derived, and these equations are, in turn, used to describe the essential characteristics of hydrostatics and piezometry. The one-dimensional equations of continuity and motion are defined and are used to derive the general discharge equation. The flow net is described as a means of demonstrating significant characteristics of two-dimensional irrotational flow patterns. A typical flow net is examined in detail. The influence of fluid viscosity is described as an obstacle to the derivation of general, integral equations of motion. It is observed that the part played by viscosity is one which is usually dependent on experimental evaluation. It follows that the dimensionless ratios known as

Lattice BGK simulation of natural convection

International Nuclear Information System (INIS)

Chen, Yu; Ohashi, Hirotada; Akiyama, Mamoru

1995-01-01

Recently a new thermal lattice Bhatnagar-Gross-Krook fluid model was suggested by the authors. In this study, this new model was applied into the numerical simulation of natural convection, namely the Rayleigh Benard flow. The critical number for the onset of convective phenomenon was numerically measured and compared with that of theoretical prediction. A gravity dependent deviation was found in the numerical simulation, which is explained as an unavoidable consequence of the incorporation of gravity force in the lattice BGK system. (author)

Thermo-fluid analysis of water cooled research reactors in natural convection

International Nuclear Information System (INIS)

Veloso, Maria Auxiliadora Fortini

2004-01-01

The STHIRP-1 computer program, which fundamentals are described in this work, uses the principles of the subchannels analysis and has the capacity to simulate, under steady state and transient conditions, the thermal and hydraulic phenomena which occur inside the core of a water-refrigerated research reactor under a natural convection regime. The models and empirical correlations necessary to describe the flow phenomena which can not be described by theoretical relations were selected according to the characteristics of the reactor operation. Although the primary objective is the calculation of research reactors, the formulation used to describe the fluid flow and the thermal conduction in the heater elements is sufficiently generalized to extend the use of the program for applications in power reactors and other thermal systems with the same features represented by the program formulations. To demonstrate the analytical capacity of STHIRP-l, there were made comparisons between the results calculated and measured in the research reactor TRIGA IPR-R1 of CDTN/CNEN. The comparisons indicate that the program reproduces the experimental data with good precision. Nevertheless, in the future there must be used more consistent experimental data to corroborate the validation of the program. (author)

On the fluid mechanics of bilabial plosives

NARCIS (Netherlands)

Pelorson, X.; Hofmans, G.C.J.; Ranucci, M.; Bosch, R.C.M.

1997-01-01

In this paper we present a review of some fluid mechanical phenomena involved in bilabial plosive sound production. As a basis for further discussion, firstly an in vivo experimental set-up is described. The order of magnitude of some important geometrical and fluid dynamical quantities is

Crystalline heterogeneities and instabilities in thermally convecting magma chamber

Science.gov (United States)

Culha, C.; Suckale, J.; Qin, Z.

2016-12-01

A volcanic vent can supply different densities of crystals over an eruption time period. This has been seen in Hawai'i's Kilauea Iki 1959 eruption; however it is not common for all Kilauea or basaltic eruptions. We ask the question: Under what conditions can homogenous magma chamber cultivate crystalline heterogeneities? In some laboratory experiments and numerical simulations, a horizontal variation is observed. The region where crystals reside is identified as a retention zone: convection velocity balances settling velocity. Simulations and experiments that observe retention zones assume crystals do not alter the convection in the fluid. However, a comparison of experiments and simulations of convecting magma with crystals suggest that large crystal volume densities and crystal sizes alter fluid flow considerably. We introduce a computational method that fully resolves the crystalline phase. To simulate basaltic magma chambers in thermal convection, we built a numerical solver of the Navier-Stoke's equation, continuity equation, and energy equation. The modeled magma is assumed to be a viscous, incompressible fluid with a liquid and solid phase. Crystals are spherical, rigid bodies. We create Rayleigh-Taylor instability through a cool top layer and hot bottom layer and update magma density while keeping crystal temperature and size constant. Our method provides a detailed picture of magma chambers, which we compare to other models and experiments to identify when and how crystals alter magma chamber convection. Alterations include stratification, differential settling and instabilities. These characteristics are dependent on viscosity, convection vigor, crystal volume density and crystal characteristics. We reveal that a volumetric crystal density variation may occur over an eruption time period, if right conditions are met to form stratifications and instabilities in magma chambers. These conditions are realistic for Kilauea Iki's 1959 eruption.

Buoyancy and thermocapillary driven convection flow of electrically conducting fluid in an enclosure with heat generation

International Nuclear Information System (INIS)

Hossain, Md. Anwar; Rees, D.A.S.

2002-05-01

The effect of surface tension on unsteady laminar natural convection flow of a viscous incompressible fluid in a rectangle enclosure with internal heat generation and in presence of a uniform transverse magnetic field acting in the direction normal to the gravity has been investigated. The top horizontal surface of the rectangular cavity is assumed to be free and the bottom ones insulated; whereas the left vertical wall is cold and the right one is uniformly hot. The equations are non-dimensionalized and solved numerically by an upwind finite difference method together with a successive over-relaxation (SOR) technique. The effects of heat generation together with the combined effects of the magnetic field and the surface tension are presented graphically in terms of isotherms, streamlines and velocity vector plots. The effects of varying the physical parameters on the rate of heat transfer from the heated surface of the enclosure are also depicted. The fluid here has Prandtl number Pr=0.054 while the value of the Grashof number is 2x10 4 . (author)

Entropy analysis of convective MHD flow of third grade non-Newtonian fluid over a stretching sheet

Directory of Open Access Journals (Sweden)

M.M. Rashidi

2017-03-01

Full Text Available The purpose of this article is to study and analyze the convective flow of a third grade non-Newtonian fluid due to a linearly stretching sheet subject to a magnetic field. The dimensionless entropy generation equation is obtained by solving the reduced momentum and energy equations. The momentum and energy equations are reduced to a system of ordinary differential equations by a similarity method. The optimal homotopy analysis method (OHAM is used to solve the resulting system of ordinary differential equations. The effects of the magnetic field, Biot number and Prandtl number on the velocity component and temperature are studied. The results show that the thermal boundary-layer thickness gets decreased with increasing the Prandtl number. In addition, Brownian motion plays an important role to improve thermal conductivity of the fluid. The main purpose of the paper is to study the effects of Reynolds number, dimensionless temperature difference, Brinkman number, Hartmann number and other physical parameters on the entropy generation. These results are analyzed and discussed.

Evidence of nonuniqueness and oscillatory solutions in computational fluid mechanics

International Nuclear Information System (INIS)

Nunziato, J.W.; Gartling, D.K.; Kipp, M.E.

1985-01-01

We will review some of our recent experiences in computing solutions for nonlinear fluids in relatively simple, two-dimensional geometries. The purpose of this discussion will be to display by example some of the interesting but difficult questions that arise when ill-behaved solutions are obtained numerically. We will consider two examples. As the first example, we will consider a nonlinear elastic (compressible) fluid with chemical reactions and discuss solutions for detonation and detonation failure in a two-dimensional cylinder. In this case, the numerical algorithm utilizes a finite-difference method with artificial viscosity (von Neumann-Richtmyer method) and leads to two, distinctly different, stable solutions depending on the time step criterion used. The second example to be considered involves the convection of a viscous fluid in a rectangular container as a result of an exothermic polymerization reaction. A solidification front develops near the top of the container and propagates down through the fluid, changing the aspect ratio of the region ahead of the front. Using a Galerkin-based finite element method, a numerical solution of the partial differential equations is obtained which tracks the front and correctly predicts the fluid temperatures near the walls. However, the solution also exhibits oscillatory behavior with regard to the number of cells in the fluid ahead of the front and in the strength of the cells. More definitive experiments and analysis are required to determine whether this oscillatory phenomena is a numerical artifact or a physical reality. 20 refs., 14 figs

Free convective flow of a stratified fluid through a porous medium bounded by a vertical plane

Directory of Open Access Journals (Sweden)

H. K. Mondal

1994-01-01

Full Text Available Steady two-dimensional free convection flow of a thermally stratified viscous fluid through a highly porous medium bounded by a vertical plane surface of varying temperature, is considered. Analytical expressions for the velocity, temperature and the rate of heat transfer are obtained by perturbation method. Velocity distribution and rate of heat transfer for different values of parameters are shown in graphs. Velocity distribution is also obtained for certain values of the parameters by integrating the coupled differential equations by Runge-Kutta method and compared with the analytical solution. The chief concern of the paper is to study the effect of equilibrium temperature gradient on the velocity and the rate of heat transfer.

Fluid Mechanics of Fish Swimming

Indian Academy of Sciences (India)

Home; Journals; Resonance – Journal of Science Education; Volume 14; Issue 1. Fluid Mechanics of Fish Swimming - Lift-based Propulsion. Jaywant H Arakeri. General Article Volume 14 Issue 1 January 2009 pp 32-46. Fulltext. Click here to view fulltext PDF. Permanent link:

Analysis of fluid-solid interaction in MHD natural convection in a square cavity equally partitioned by a vertical flexible membrane

International Nuclear Information System (INIS)

Mehryan, S.A.M.; Ghalambaz, Mohammad; Ismael, Muneer A.; Chamkha, Ali J.

2017-01-01

This paper investigates numerically the problem of unsteady natural convection inside a square cavity partitioned by a flexible impermeable membrane. The finite element method with the arbitrary Lagrangian-Eulerian (ALE) technique has been used to model the interaction of the fluid and the membrane. The horizontal walls of the cavity are kept adiabatic while the vertical walls are kept isothermal at different temperatures. A uniform magnetic field is applied onto the cavity with different orientations. The cavity has been provided by two eyelets to compensate volume changes due the movement of the flexible membrane. A parametric study is carried out for the pertinent parameters, which are the Rayleigh number (10"5–10"8), Hartmann number (0–200) and the orientation of the magnetic field (0–180°). The change in the Hartmann number affects the shape of the membrane and the heat transfer in the cavity. The angle of the magnetic field orientation also significantly affects the shape of the membrane and the heat transfer in the cavity. - Highlights: • Magnetohydrodynamics heat transfer in a partitioned cavity is studied. • There is a flexible membrane in the cavity. • The membrane is modeled using fluid-solid structure interaction. • A moving grid formulation based on ALE is adopted. • The effect of the magnetic field on the natural convection heat transfer is examined.

Analysis of fluid-solid interaction in MHD natural convection in a square cavity equally partitioned by a vertical flexible membrane

Energy Technology Data Exchange (ETDEWEB)

Mehryan, S.A.M., E-mail: a.mansuri1366@gmail.com [Department of Mechanical Engineering, Dezful Branch, Islamic Azad University, Dezful (Iran, Islamic Republic of); Ghalambaz, Mohammad, E-mail: m.ghalambaz@iaud.ac.ir [Department of Mechanical Engineering, Dezful Branch, Islamic Azad University, Dezful (Iran, Islamic Republic of); Ismael, Muneer A., E-mail: muneerismael@yahoo.com [Mechanical Engineering Department, Engineering College, University of Basrah, Basrah (Iraq); Chamkha, Ali J., E-mail: achamkha@pmu.edu.sa [Mechanical Engineering Department, Prince Mohammad Bin Fahd University, Al-Khobar 31952 (Saudi Arabia); Prince Sultan Endowment for Energy and Environment, Prince Mohammad Bin Fahd University, Al-Khobar 31952 (Saudi Arabia)

2017-02-15

This paper investigates numerically the problem of unsteady natural convection inside a square cavity partitioned by a flexible impermeable membrane. The finite element method with the arbitrary Lagrangian-Eulerian (ALE) technique has been used to model the interaction of the fluid and the membrane. The horizontal walls of the cavity are kept adiabatic while the vertical walls are kept isothermal at different temperatures. A uniform magnetic field is applied onto the cavity with different orientations. The cavity has been provided by two eyelets to compensate volume changes due the movement of the flexible membrane. A parametric study is carried out for the pertinent parameters, which are the Rayleigh number (10{sup 5}–10{sup 8}), Hartmann number (0–200) and the orientation of the magnetic field (0–180°). The change in the Hartmann number affects the shape of the membrane and the heat transfer in the cavity. The angle of the magnetic field orientation also significantly affects the shape of the membrane and the heat transfer in the cavity. - Highlights: • Magnetohydrodynamics heat transfer in a partitioned cavity is studied. • There is a flexible membrane in the cavity. • The membrane is modeled using fluid-solid structure interaction. • A moving grid formulation based on ALE is adopted. • The effect of the magnetic field on the natural convection heat transfer is examined.

Introductory analysis of Benard-Marangoni convection

International Nuclear Information System (INIS)

Maroto, J A; Perez-Munuzuri, V; Romero-Cano, M S

2007-01-01

We describe experiments on Benard-Marangoni convection which permit a useful understanding of the main concepts involved in this phenomenon such as, for example, Benard cells, aspect ratio, Rayleigh and Marangoni numbers, Crispation number and critical conditions. In spite of the complexity of convection theory, we carry out a simple and introductory analysis which has the additional advantage of providing very suggestive experiments. As a consequence, we recommend our device for use as a laboratory experiment for undergraduate students of the thermodynamics of nonlinear and fluid physics

Introductory analysis of Benard-Marangoni convection

Energy Technology Data Exchange (ETDEWEB)

Maroto, J A [Group of Physics and Chemistry of Linares, Escuela Politecnica Superior, St Alfonso X El Sabio, 28, University of Jaen, E-23700 Linares, Jaen (Spain); Perez-Munuzuri, V [Group of Nonlinear Physics, University of Santiago de Compostela, E-15782 Santiago de Compostela (Spain); Romero-Cano, M S [Group of Complex Fluids Physics, Department of Applied Physics, University of Almeria, E-04120 Almeria (Spain)

2007-03-15

We describe experiments on Benard-Marangoni convection which permit a useful understanding of the main concepts involved in this phenomenon such as, for example, Benard cells, aspect ratio, Rayleigh and Marangoni numbers, Crispation number and critical conditions. In spite of the complexity of convection theory, we carry out a simple and introductory analysis which has the additional advantage of providing very suggestive experiments. As a consequence, we recommend our device for use as a laboratory experiment for undergraduate students of the thermodynamics of nonlinear and fluid physics.

Finite approximations in fluid mechanics

International Nuclear Information System (INIS)

Hirschel, E.H.

1986-01-01

This book contains twenty papers on work which was conducted between 1983 and 1985 in the Priority Research Program ''Finite Approximations in Fluid Mechanics'' of the German Research Society (Deutsche Forschungsgemeinschaft). Scientists from numerical mathematics, fluid mechanics, and aerodynamics present their research on boundary-element methods, factorization methods, higher-order panel methods, multigrid methods for elliptical and parabolic problems, two-step schemes for the Euler equations, etc. Applications are made to channel flows, gas dynamical problems, large eddy simulation of turbulence, non-Newtonian flow, turbomachine flow, zonal solutions for viscous flow problems, etc. The contents include: multigrid methods for problems from fluid dynamics, development of a 2D-Transonic Potential Flow Solver; a boundary element spectral method for nonstationary viscous flows in 3 dimensions; navier-stokes computations of two-dimensional laminar flows in a channel with a backward facing step; calculations and experimental investigations of the laminar unsteady flow in a pipe expansion; calculation of the flow-field caused by shock wave and deflagration interaction; a multi-level discretization and solution method for potential flow problems in three dimensions; solutions of the conservation equations with the approximate factorization method; inviscid and viscous flow through rotating meridional contours; zonal solutions for viscous flow problems

Modern fluid dynamics

CERN Document Server

Kleinstreuer, Clement

2018-01-01

Modern Fluid Dynamics, Second Edition provides up-to-date coverage of intermediate and advanced fluids topics. The text emphasizes fundamentals and applications, supported by worked examples and case studies. Scale analysis, non-Newtonian fluid flow, surface coating, convection heat transfer, lubrication, fluid-particle dynamics, microfluidics, entropy generation, and fluid-structure interactions are among the topics covered. Part A presents fluids principles, and prepares readers for the applications of fluid dynamics covered in Part B, which includes computer simulations and project writing. A review of the engineering math needed for fluid dynamics is included in an appendix.

Hydrodynamic theory of convective transport across a dynamically stabilized diffuse boundary layer

International Nuclear Information System (INIS)

Gerhauser, H.

1983-09-01

The diffuse boundary layer between miscible liquids is subject to Rayleigh-Taylor instabilities if the heavy fluid is supported by the light one. The resulting rapid interchange of the liquids can be suppressed by enforcing vertical oscillations on the whole system. This dynamic stabilization is incomplete and produces some peculiar novel transport phenomena such as decay off the density profile into several steps, periodic peeling of density sheets of the boundary layer and the appearance of steady vortex flow. The theory presented in this paper identifies the basic mechanism as formation of convective cells leading to enhanced diffusion, and explains previous experimental results with water and ZnJ 2 -solutions. A nonlinear treatment of the stationary convective flow problem gives the saturation amplitude of the ground mode and provides an upper bound for the maximum convective transport. The hydrodynamic model can be used for visualizing similar transport processes in the plasma of toroidal confinement devices such as sawtooth oscillations in soft disruptions of tokamak discharges and anomalous diffusion by excitation of convective cells. The latter process is investigated here in some detail, leading to the result that the maximum possible transport is of the order of Bohm diffusion. (orig.)

[Research advances of fluid bio-mechanics in bone].

Science.gov (United States)

Chen, Zebin; Huo, Bo

2017-04-01

It has been found for more than one century that when experiencing mechanical loading, the structure of bone will adapt to the changing mechanical environment, which is called bone remodeling. Bone remodeling is charaterized as two processes of bone formation and bone resorption. A large number of studies have confirmed that the shear stress is resulted from interstitial fluid flow within bone cavities under mechanical loading and it is the key factor of stimulating the biological responses of bone cells. This review summarizes the major research progress during the past years, including the biological response of bone cells under fluid flow, the pressure within bone cavities, the theoretical modeling, numerical simulation and experiments about fluid flow within bone, and finally analyzes and predicts the possible tendency in this field in the future.

Hall effects on free convection hydromagnetic boundary layer flow of Rivlin-Ericksen fluid past a vertical plate

International Nuclear Information System (INIS)

Jha, P.K.

1986-01-01

An attempt has been made to study the problem of free convection hydromagnetic flow of an elastico-viscous fluid past a porous vertical plate in a rotating frame of reference taking ohmic and viscous dissipations into account in the presence of Hall current. The nature of velocity profile shows the existence of multiple boundary layers. Their 'thickness' is seen to decrease with increasing values of Ekman, Hartman and Prandtl numbers and Hall parameter. The graphical study reveals that the increasing values of Hall parameter and Ekman number (for a fixed large value of Hall parameter) exert opposite influence on the flow. (author). 11 refs., 2 tables

Newtonian heating effects in three-dimensional flow of viscoelastic fluid

International Nuclear Information System (INIS)

Qayyum, A.; Hayat, T.; Alhuthali, M. S.; Malaikah, H. M.

2014-01-01

A mathematical model is constructed to investigate the three-dimensional flow of a non-Newtonian fluid. An incompressible viscoelastic fluid is used in mathematical formulation. The conjugate convective process (in which heat the transfer rate from the bounding surface with a finite capacity is proportional to the local surface temperature) in three-dimensional flow of a differential type of non-Newtonian fluid is analyzed for the first time. Series solutions for the nonlinear differential system are computed. Plots are presented for the description of emerging parameters entering into the problem. It is observed that the conjugate heating phenomenon causes an appreciable increase in the temperature at the stretching wall. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

Direct numerical simulation and statistical analysis of turbulent convection in lead-bismuth

Energy Technology Data Exchange (ETDEWEB)

Otic, I.; Grotzbach, G. [Forschungszentrum Karlsruhe GmbH, Institut fuer Kern-und Energietechnik (Germany)

2003-07-01

Improved turbulent heat flux models are required to develop and analyze the reactor concept of an lead-bismuth cooled Accelerator-Driven-System. Because of specific properties of many liquid metals we have still no sensors for accurate measurements of the high frequency velocity fluctuations. So, the development of the turbulent heat transfer models which are required in our CFD (computational fluid dynamics) tools needs also data from direct numerical simulations of turbulent flows. We use new simulation results for the model problem of Rayleigh-Benard convection to show some peculiarities of the turbulent natural convection in lead-bismuth (Pr = 0.025). Simulations for this flow at sufficiently large turbulence levels became only recently feasible because this flow requires the resolution of very small velocity scales with the need for recording long-wave structures for the slow changes in the convective temperature field. The results are analyzed regarding the principle convection and heat transfer features. They are also used to perform statistical analysis to show that the currently available modeling is indeed not adequate for these fluids. Basing on the knowledge of the details of the statistical features of turbulence in this convection type and using the two-point correlation technique, a proposal for an improved statistical turbulence model is developed which is expected to account better for the peculiarities of the heat transfer in the turbulent convection in low Prandtl number fluids. (authors)

Combined free and forced convection flow in a rotating channel with ...

African Journals Online (AJOL)

user

free and forced convection flow of a viscous incompressible electrically conducting fluid in a .... The boundary conditions (10) and (11), in dimensionless form, become ...... On hydromagnetic Flow and heat transfer in a rotating fluid past an infinite porous ... Electrically Conducting Fluid in Non-Rotating and Rotating Media”.

Gravity modulation effect on the onset of thermal buoyancy convection in a horizontal layer of the Oldroyd fluid

Energy Technology Data Exchange (ETDEWEB)

Lyubimova, Tatyana; Kovalevskaya, Kseniya, E-mail: lyubimovat@mail.ru [Institute of Continuous Media Mechanics UB RAS, Perm (Russian Federation)

2016-12-15

The effect of gravity modulation on the onset of convection in a horizontal layer of viscoelastic Oldroyd fluid heated from below is considered. The analytical solution of the problem has been obtained for the case of stress-free boundaries and rectangular modulation. It has been shown that depending on the parameter values, the modulation can produce either stabilizing or destabilizing effects. The deformation retardation always exerts a stabilizing effect, which is most pronounced in the shortwave range. The numerical results obtained by the solution of full nonlinear problems agree well with the results of linear stability analysis. (paper)

Convection flow study within a horizontal fluid layer under the action of gas flow

Directory of Open Access Journals (Sweden)

Kreta Aleksei

2016-01-01

Full Text Available Experimental investigation of convective processes within horizontal evaporating liquid layer under shear–stress of gas flow is presented. It is found the structures of the convection, which move in opposite direction relative to each other. First convective structure moves in reverse direction with the flow of gas, and the second convective structure moves towards the gas flow. Convection flow within the liquid layer is registered with help of PIV technique. Average evaporation flow rate of Ethanol liquid layer under Air gas flow is measured. Influence of the gas velocity, at a constant temperature of 20 °C, on the evaporation flow rate has been studied.

Effects of Brinkman number on thermal-driven convective spherical ...

African Journals Online (AJOL)

Michael Horsfall

KEYWORDS: Magnetic field generation, Thermal-driven convection, Brinkman number, Dynamo action, Fluid outer core ... The problem considers conducting fluid motion in a rapidly rotating spherical shell. The ... is, that the energy lost by the electric currents must be ... which are sources of free electrons and basically due.

The Pi-Theorem Applications to Fluid Mechanics and Heat and Mass Transfer

CERN Document Server

Yarin, L P

2012-01-01

This volume presents applications of the Pi-Theorem to fluid mechanics and heat and mass transfer. The Pi-theorem yields a physical motivation behind many flow processes and therefore it constitutes a valuable tool for the intelligent planning of experiments in fluids. After a short introduction to the underlying differential equations and their treatments, the author presents many novel approaches how to use the Pi-theorem to understand fluid mechanical issues. The book is a great value to the fluid mechanics community, as it cuts across many subdisciplines of experimental fluid mechanics.

Topological Fluid Mechanics with Applications to Free Surfaces and Axisymmetric Flows

DEFF Research Database (Denmark)

Brøns, Morten

1996-01-01

Topological fluid mechanics is the study of qualitative features of fluid patterns. We discuss applications to the flow beneath a stagnant surface film, and to patterns in axisymmetric flow.......Topological fluid mechanics is the study of qualitative features of fluid patterns. We discuss applications to the flow beneath a stagnant surface film, and to patterns in axisymmetric flow....

Magnetohydrodynamic flow of Carreau fluid over a convectively heated surface in the presence of non-linear radiation

Energy Technology Data Exchange (ETDEWEB)

Khan, Masood [Department of Mathematics, Quaid-i-Azam University, Islamabad 44000 (Pakistan); Hashim, E-mail: hashim_alik@yahoo.com [Department of Mathematics, Quaid-i-Azam University, Islamabad 44000 (Pakistan); Hussain, M. [Department of Sciences and Humanities, National University of Computer and Emerging Sciences, Islamabad 44000 (Pakistan); Azam, M. [Department of Mathematics, Quaid-i-Azam University, Islamabad 44000 (Pakistan)

2016-08-15

This paper presents a study of the magnetohydrodynamic (MHD) boundary layer flow of a non-Newtonian Carreau fluid over a convectively heated surface. The analysis of heat transfer is further performed in the presence of non-linear thermal radiation. The appropriate transformations are employed to bring the governing equations into dimensionless form. The numerical solutions of the partially coupled non-linear ordinary differential equations are obtained by using the Runge-Kutta Fehlberg integration scheme. The influence of non-dimensional governing parameters on the velocity, temperature, local skin friction coefficient and local Nusselt number is studied and discussed with the help of graphs and tables. Results proved that there is significant decrease in the velocity and the corresponding momentum boundary layer thickness with the growth in the magnetic parameter. However, a quite the opposite is true for the temperature and the corresponding thermal boundary layer thickness. - Highlights: • We investigated the Magnetohydrodynamic flow of Carreau constitutive fluid model. • Impact of non-linear thermal radiation is further taken into account. • Runge-Kutta Fehlberg method is employed to obtain the numerical solutions. • Fluid velocity is higher in case of hydromagnetic flow in comparison with hydrodynamic flow. • The local Nusselt number is a decreasing function of the thermal radiation parameter.

Do tropical wetland plants possess a convective gas flow mechanism?

DEFF Research Database (Denmark)

Jensen, Dennis Konnerup; Sorrell, Brian Keith; Brix, Hans

2011-01-01

Internal pressurization and convective gas flow, which can aerate wetland plants more efficiently than diffusion, are common in temperate species. Here, we present the first survey of convective flow in a range of tropical plants. The occurrence of pressurization and convective flow was determined...... in 20 common wetland plants from the Mekong Delta in Vietnam. The diel variation in pressurization in culms and the convective flow and gas composition from stubbles were examined for Eleocharis dulcis, Phragmites vallatoria and Hymenachne acutigluma, and related to light, humidity and air temperature....... Nine of the 20 species studied were able to build up a static pressure of >50Pa, and eight species had convective flow rates higher than 1mlmin-1. There was a clear diel variation, with higher pressures and flows during the day than during the night, when pressures and flows were close to zero...

Maximum Entropy Production Is Not a Steady State Attractor for 2D Fluid Convection

Directory of Open Access Journals (Sweden)

Stuart Bartlett

2016-12-01

Full Text Available Multiple authors have claimed that the natural convection of a fluid is a process that exhibits maximum entropy production (MEP. However, almost all such investigations were limited to fixed temperature boundary conditions (BCs. It was found that under those conditions, the system tends to maximize its heat flux, and hence it was concluded that the MEP state is a dynamical attractor. However, since entropy production varies with heat flux and difference of inverse temperature, it is essential that any complete investigation of entropy production allows for variations in heat flux and temperature difference. Only then can we legitimately assess whether the MEP state is the most attractive. Our previous work made use of negative feedback BCs to explore this possibility. We found that the steady state of the system was far from the MEP state. For any system, entropy production can only be maximized subject to a finite set of physical and material constraints. In the case of our previous work, it was possible that the adopted set of fluid parameters were constraining the system in such a way that it was entirely prevented from reaching the MEP state. Hence, in the present work, we used a different set of boundary parameters, such that the steady states of the system were in the local vicinity of the MEP state. If MEP was indeed an attractor, relaxing those constraints of our previous work should have caused a discrete perturbation to the surface of steady state heat flux values near the value corresponding to MEP. We found no such perturbation, and hence no discernible attraction to the MEP state. Furthermore, systems with fixed flux BCs actually minimize their entropy production (relative to the alternative stable state, that of pure diffusive heat transport. This leads us to conclude that the principle of MEP is not an accurate indicator of which stable steady state a convective system will adopt. However, for all BCs considered, the quotient of

Magnetic particle translation as a surrogate measure for synovial fluid mechanics.

Science.gov (United States)

Shah, Yash Y; Maldonado-Camargo, Lorena; Patel, Neal S; Biedrzycki, Adam H; Yarmola, Elena G; Dobson, Jon; Rinaldi, Carlos; Allen, Kyle D

2017-07-26

The mechanics of synovial fluid vary with disease progression, but are difficult to quantify quickly in a clinical setting due to small sample volumes. In this study, a novel technique to measure synovial fluid mechanics using magnetic nanoparticles is introduced. Briefly, microspheres embedded with superparamagnetic iron oxide nanoparticles, termed magnetic particles, are distributed through a 100μL synovial fluid sample. Then, a permanent magnet inside a protective sheath is inserted into the synovial fluid sample. Magnetic particles translate toward the permanent magnet and the percentage of magnetic particles collected by the magnet in a given time can be related to synovial fluid viscosity. To validate this relationship, magnetic particle translation was demonstrated in three phases. First, magnetic particle translation was assessed in glycerol solutions with known viscosities, demonstrating that as fluid viscosity increased, magnetic particle translation decreased. Next, the relationship between magnetic particle translation and synovial fluid viscosity was assessed using bovine synovial fluid that was progressively degenerated via ultrasonication. Here, particle collection in a given amount of time increased as fluid degenerated, demonstrating that the relationship between particle collection and fluid mechanics holds in non-Newtonian synovial fluid. Finally, magnetic particle translation was used to assess differences between healthy and OA affected joints in equine synovial fluid. Here, particle collection in a given time was higher in OA joints relative to healthy horses (pfluid mechanics in limited volumes of synovial fluid sample. Copyright © 2017 Elsevier Ltd. All rights reserved.

Scaling options for integral experiments for molten salt fluid mechanics and heat transfer

International Nuclear Information System (INIS)

Philippe Bardet; Per F Peterson

2005-01-01

experiments can reproduce molten salt phenomena including natural, mixed, and forced convection fluid mechanics and heat transfer, and free surface fluid mechanics, with very small scaling distortion. Weber number controlled phenomena like bubble entrainment and droplet formation are also simulated with relatively low distortion. Both molten salts and mineral oils are transparent, permitting flow visualization to be used, and the oil index of refraction nearly matches acrylic. Oils have much lower wetting angles than molten salts with typical container materials, so significant distortion of wetting-angle related phenomena, such as capillary driven flows, can be expected. Overall, scaled experiments using light mineral oils have very attractive benefits for studying molten salt fluid mechanics and heat transfer. This paper discusses scaling in detail, and presents examples from fusion chamber fluid mechanics experiments. (authors)

Topology Optimisation for Coupled Convection Problems

DEFF Research Database (Denmark)

Alexandersen, Joe; Andreasen, Casper Schousboe; Aage, Niels

stabilised finite elements implemented in a parallel multiphysics analysis and optimisation framework DFEM [1], developed and maintained in house. Focus is put on control of the temperature field within the solid structure and the problems can therefore be seen as conjugate heat transfer problems, where heat...... conduction governs in the solid parts of the design domain and couples to convection-dominated heat transfer to a surrounding fluid. Both loosely coupled and tightly coupled problems are considered. The loosely coupled problems are convection-diffusion problems, based on an advective velocity field from...

Effects of variable thermal diffusivity on the structure of convection

Science.gov (United States)

Shcheritsa, O. V.; Getling, A. V.; Mazhorova, O. S.

2018-03-01

The structure of multiscale convection in a thermally stratified plane horizontal fluid layer is investigated by means of numerical simulations. The thermal diffusivity is assumed to produce a thin boundary sublayer convectively much more unstable than the bulk of the layer. The simulated flow is a superposition of cellular structures with three different characteristic scales. In contrast to the largest convection cells, the smaller ones are localised in the upper portion of the layer. The smallest cells are advected by the larger-scale convective flows. The simulated flow pattern qualitatively resembles that observed on the Sun.

Active Control of Thermal Convection in a Rectangular Loop by Changing its Spatial Orientation

Science.gov (United States)

Bratsun, Dmitry A.; Krasnyakov, Ivan V.; Zyuzgin, Alexey V.

2018-02-01

The problem of the automatic control of the fluid flow in a rectangular convective loop heated from below is studied theoretically and experimentally. The control is performed by using a feedback subsystem which changes the convection regimes by introducing small discrete changes in the spatial orientation of the loop with respect to gravity. We focus on effects that arise when the feedback controller operates with an unavoidable time delay, which is cause by the thermal inertia of the medium. The mathematical model of the phenomenon is developed. The dynamic regimes of the convection in the thermosyphon loop under control are studied. It is shown that the proposed control method can successfully stabilize not only a no-motion state of the fluid, but also time-dependent modes of convection including the irregular fluid flow at high values of the Rayleigh number. It is shown that the excessive gain of the proportional feedback can result in oscillations in the loop orientation exciting the unsteady convection modes. The comparison of the experimental data obtained for dielectric oil and dodecane with theory is given, and their good agreement is demonstrated.

Mixing in heterogeneous internally-heated convection

Science.gov (United States)

Limare, A.; Kaminski, E. C.; Jaupart, C. P.; Farnetani, C. G.; Fourel, L.; Froment, M.

2017-12-01

Past laboratory experiments of thermo chemical convection have dealt with systems involving fluids with different intrinsic densities and viscosities in a Rayleigh-Bénard setup. Although these experiments have greatly improved our understanding of the Earth's mantle dynamics, they neglect a fundamental component of planetary convection: internal heat sources. We have developed a microwave-based method in order to study convection and mixing in systems involving two layers of fluid with different densities, viscosities, and internal heat production rates. Our innovative laboratory experiments are appropriate for the early Earth, when the lowermost mantle was likely enriched in incompatible and heat producing elements and when the heat flux from the core probably accounted for a small fraction of the mantle heat budget. They are also relevant to the present-day mantle if one considers that radioactive decay and secular cooling contribute both to internal heating. Our goal is to quantify how two fluid layers mix, which is still very difficult to resolve accurately in 3-D numerical calculations. Viscosities and microwave absorptions are tuned to achieve high values of the Rayleigh-Roberts and Prandtl numbers relevant for planetary convection. We start from a stably stratified system where the lower layer has higher internal heat production and density than the upper layer. Due to mixing, the amount of enriched material gradually decreases to zero over a finite time called the lifetime. Based on more than 30 experiments, we have derived a scaling law that relates the lifetime of an enriched reservoir to the layer thickness ratio, a, to the density and viscosity contrasts between the two layers, and to their two different internal heating rates in the form of an enrichment factor beta=1+2*a*H1/H, where H1 is the heating rate of the lower fluid and H is the average heating rate. We find that the lifetime of the lower enriched reservoir varies as beta**(-7/3) in the low

Behaviors and transitions along the path to magnetostrophic convection

Science.gov (United States)

Grannan, A. M.; Vogt, T.; Horn, S.; Hawkins, E. K.; Aggarwal, A.; Aurnou, J. M.

2017-12-01

The generation of magnetic fields in planetary and stellar interiors are believed to be controlled primarily by turbulent convection constrained by Coriolis and Lorentz forces in their electrically conducting fluid layers. Yet relatively few laboratory experiments are capable of investigating the different regimes of turbulent magnetohydrodynamic convection. In this work, we perform one laboratory experiment in a cylinder at a fixed heat flux using the liquid metal gallium in order to investigate, sequentially: Rayleigh-Bènard convection without any imposed constraints, magnetoconvection with a Lorentz constraint imposed by vertical magnetic field, rotating convection with a Coriolis constraint imposed by rotation, and finally the magnetostrophic convective regime where both Coriolis and Lorentz are imposed and equal. Using an array of internal and external temperature probes, we show that each regime along the path to magnetostrophic convection is unique. The behaviors and transitions in the dominant modes of convection as well as their fundamental frequencies and wavenumbers are investigated.

Natural convection inside an irregular porous cavity

International Nuclear Information System (INIS)

Beltran, Jorge I. LLagostera; Trevisan, Osvair Vidal

1990-01-01

Natural convection flow induced by heating from below in a irregular porous cavity is investigated numerically. The influence of the modified Rayleigh number and geometric ratios on heat transfer and fluid flow is studied. Global and local Nusselt for Rayleigh numbers covering the range 0 - 1600 and for several geometric ratios. The fluid flow and the temperature field are illustrated by contour maps. (author)

Spontaneous generation and reversals of mean flows in a convectively-generated internal gravity wave field

Science.gov (United States)

Couston, Louis-Alexandre; Lecoanet, Daniel; Favier, Benjamin; Le Bars, Michael

2017-11-01

We investigate via direct numerical simulations the spontaneous generation and reversals of mean zonal flows in a stably-stratified fluid layer lying above a turbulent convective fluid. Contrary to the leading idealized theories of mean flow generation by self-interacting internal waves, the emergence of a mean flow in a convectively-generated internal gravity wave field is not always possible because nonlinear interactions of waves of different frequencies can disrupt the mean flow generation mechanism. Strong mean flows thus emerge when the divergence of the Reynolds stress resulting from the nonlinear interactions of internal waves produces a strong enough anti-diffusive acceleration for the mean flow, which, as we will demonstrate, is the case when the Prandtl number is sufficiently low, or when the energy input into the internal wavefield by the convection and density stratification are sufficiently large. Implications for mean zonal flow production as observed in the equatorial stratospheres of the Earth, Saturn and Jupiter, and possibly occurring in other geophysical systems such as planetary and stellar interiors will be briefly discussed. Funding provided by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program through Grant Agreement No. 681835-FLUDYCO-ERC-2015-CoG.

Steady, three-dimensional, internally heated convection

International Nuclear Information System (INIS)

Schubert, G.; Glatzmaier, G.A.; Travis, B.

1993-01-01

Numerical calculations have been carried out of steady, symmetric, three-dimensional modes of convection in internally heated, infinite Prandtl number, Boussinesq fluids at a Rayleigh number of 1.4x10 4 in a spherical shell with inner/outer radius of 0.55 and in a 3x3x1 rectangular box. Multiple patterns of convection occur in both geometries. In the Cartesian geometry the patterns are dominated by cylindrical cold downflows and a broad hot upwelling. In the spherical geometry the patterns consist of cylindrical cold downwellings centered either at the vertices of a tetrahedron or the centers of the faces of a cube. The cold downflow cylinders are immersed in a background of upwelling within which there are cylindrical hot concentrations (plumes) and hot halos around the downflows. The forced hot upflow return plumes of internally heated spherical convection are fundamentally different from the buoyancy-driven plumes of heated from below convection

Effects of external environment on thermocapillary convection of high prandtl number fluid

Directory of Open Access Journals (Sweden)

Liang Ruquan

2016-01-01

Full Text Available Numerical simulations have been carried out to investigate the influence of external environment on thermocapillary convection in high Prandtl number (Pr=68 liquid. The geometric model of physical problem is that the the liquid bridge surrounded by ambient air under zero or ground gravity. The interface velocity, temperature, heat flux and flow pattern in the liquid bridge are presented and discussed under different conditions by changing the external environment. The buoyancy convection produces a symmetrical vortex in the liquid bridge. The ambient air affects the distributions of the temperature velocity and heat flux on the interface by changing the thermocapillary convection.

Application of fast Fourier transform in thermo-magnetic convection analysis

International Nuclear Information System (INIS)

Pyrda, L

2014-01-01

Application of Fast Fourier Transform in thermo-magnetic convection is reported. Cubical enclosure filled with paramagnetic fluid heated from below and placed in the strong magnetic field gradients was investigated. The main aim of study was connected with identification of flow types, especially transition to turbulence. For this purpose the Fast Fourier Transform (FFT) analysis was applied. It was followed by the heat transfer characteristic for various values of magnetic induction gradient. The analysis was done at two Rayleigh numbers 7.89·10 5 and 1.86·10 6 with thermo-magnetic Rayleigh numbers up to 1.8·10 8 and 4.5·10 8 respectively. The presented results clearly indicate flow types and also demonstrate augmented heat transfer in dependence on magnetic induction gradient. Detailed analysis of flow transition to turbulent state was compared with transition line for natural convection reported in literature. The transition to turbulence in the case of thermo-magnetic convection of paramagnetic fluid was in very good agreement with transition in the case of natural convection.

Second GAMM-conference on numerical methods in fluid mechanics

International Nuclear Information System (INIS)

Hirschel, E.H.; Geller, W.

1977-01-01

Proceedings of the Second GAMM-Conference on Numerical Methods in Fluid Mechanics held at the DFVLR, Koeln, October 11 to 13, 1977. The conference was attended by approximately 100 participants from 13 European countries representing quite different fields ranging from Aerodynamics to Nuclear Energy. At the meeting 34 papers were presented, many of them concerned with basic problems in the field. It was well demonstrated that Numerical Methods in Fluid Mechanics do not only serve as means for the computation of flow fields but also as tools in the analysis of fluid mechanical phenomena, a role of large future importance if one considers the complexity especially of three-dimensional flows. (orig./RW) [de

The fluid mechanics of channel fracturing flows: experiment

Science.gov (United States)

Rashedi, Ahmadreza; Tucker, Zachery; Ovarlez, Guillaume; Hormozi, Sarah

2017-11-01

We show our preliminary experimental results on the role of fluid mechanics in channel fracturing flows, particularly yield stress fracturing fluids. Recent trends in the oil industry have included the use of cyclic pumping of a proppant slurry interspersed with a yield stress fracturing fluid, which is found to increase wells productivity, if particles disperse in a certain fashion. Our experimental study aims to investigate the physical mechanisms responsible for dispersing the particles (proppant) within a yield stress carrier fluid, and to measure the dispersion of proppant slugs in various fracturing regimes. To this end we have designed and built a unique experimental setup that resembles a fracture configuration coupled with a particle image/tracking velocimetry setup operating at micro to macro dimensions. Moreover, we have designed optically engineered suspensions of complex fluids with tunable yield stress and consistency, well controlled density match-mismatch properties and refractive indices for both X-rays and visible lights. We present our experimental system and preliminary results. NSF (Grant No. CBET-1554044- CAREER), ACS PRF (Grant No. 55661-DNI9).

Testing particle filters on convective scale dynamics

Science.gov (United States)

Haslehner, Mylene; Craig, George. C.; Janjic, Tijana

2014-05-01

fluid dynamics. - Computers and Fluids, doi:10,1016/j.compfluid.2010.11.011, 1096 2011. Würsch, M. and G. C. Craig, 2013: A simple dynamical model of cumulus convection for data assimilation research, submitted to Met. Zeitschrift.

Electrical Resistivity Imaging and Hydrodynamic Modeling of Convective Fingering in a Sabkha Aquifer

Science.gov (United States)

Van Dam, Remke; Eustice, Brian; Hyndman, David; Wood, Warren; Simmons, Craig

2014-05-01

Free convection, or fluid motion driven by density differences, is an important groundwater flow mechanism that can enhance transport and mixing of heat and solutes in the subsurface. Various issues of environmental and societal relevance are exacerbated convective mixing; it has been studied in the context of dense contaminant plumes, nuclear waste disposal, greenhouse gas sequestration, the impacts of sea level rise and saline intrusion on drinking water resources. The basic theory behind convective flow in porous media is well understood, but important questions regarding this process in natural systems remain unanswered. Most previous research on this topic has focused on theory and modeling, with only limited attention to experimental studies and field measurements. The few published studies present single snapshots, making it difficult to quantify transient changes in these systems. Non-invasive electrical methods have the potential to exploit the relation between solute concentrations and electrical conductance of a fluid, and thereby estimate fluid salinity differences in time and space. We present the results of a two-year experimental study at a shallow sabkha aquifer in the United Arab Emirates, about 50 km southwest of the city of Abu Dhabi along the coast of the Arabian Gulf, that was designed to explore the transient nature of free convection. Electrical resistivity tomography (ERT) data documented the presence of convective fingers following a significant rainfall event. One year later, the complex fingering pattern had completely disappeared. This observation is supported by analysis of the aquifer solute budget as well as hydrodynamic modeling of the system. The transient dynamics of the gravitational instabilities in the modeling results are in agreement with the timing observed in the time-lapse ERT data. Our experimental observations and modeling are consistent with the hypothesis that the instabilities arose from a dense brine that infiltrated

Development of a system code with CFD capability for analyzing turbulent mixed convection in gas-cooled reactors

International Nuclear Information System (INIS)

Kim, Hyeon Il

2010-02-01

In order to demonstrate the accuracy of predictions in a turbulent mixed convection regime in which both inertia and buoyancy force compete with each other, we found out that assessments done using a single-dimensional system code with a recently updated heat transfer package have shown that this approach cannot give a reasonable prediction of the wall temperature in a case involving strong heating, where the regime falls into turbulent mixed convection regime. It has been known that the main reason of this deficiency comes from the degraded heat transfer in turbulent mixed convection regime, which is below that of convective heat transfer during turbulent forced convection. We investigated two mechanisms that cause this deterioration in convective heat transfer influenced by buoyancy: (1) modification of turbulence, also known as the direct (structural) effect, through the buoyancy-induced production of turbulent kinetic energy: and (2) an indirect (external) effect that occurs through modification of the mean flow. We investigated the Launder-Sharma model of turbulence whether it can appropriately represent the mechanisms causing the degraded heat transfer in Computational Fluid Dynamics (CFD). We found out that this model can capture low Re effects such that a non-equilibrium turbulent boundary layer in turbulent mixed convection regime can be resolved. The model was verified and validated extensively initially with the commercial CFD code, Fluent with a user application package known as the User Defined Function (UDF). The results from this implementation were compared to a set of data that included (1) an experimental data commonly accepted as a standardized problem to verify a turbulent flow, (2) the results from a Direct Numerical Simulation (DNS) in a turbulent forced and mixed convection regime, (3) empirical correlations regarding the friction coefficient and the non-dimensional heat transfer coefficient, the Nusselt number for a turbulent forced

Canonical Models of Geophysical and Astrophysical Flows: Turbulent Convection Experiments in Liquid Metals

Directory of Open Access Journals (Sweden)

Adolfo Ribeiro

2015-03-01

Full Text Available Planets and stars are often capable of generating their own magnetic fields. This occurs through dynamo processes occurring via turbulent convective stirring of their respective molten metal-rich cores and plasma-based convection zones. Present-day numerical models of planetary and stellar dynamo action are not carried out using fluids properties that mimic the essential properties of liquid metals and plasmas (e.g., using fluids with thermal Prandtl numbers Pr < 1 and magnetic Prandtl numbers Pm ≪ 1. Metal dynamo simulations should become possible, though, within the next decade. In order then to understand the turbulent convection phenomena occurring in geophysical or astrophysical fluids and next-generation numerical models thereof, we present here canonical, end-member examples of thermally-driven convection in liquid gallium, first with no magnetic field or rotation present, then with the inclusion of a background magnetic field and then in a rotating system (without an imposed magnetic field. In doing so, we demonstrate the essential behaviors of convecting liquid metals that are necessary for building, as well as benchmarking, accurate, robust models of magnetohydrodynamic processes in Pm ≪  Pr < 1 geophysical and astrophysical systems. Our study results also show strong agreement between laboratory and numerical experiments, demonstrating that high resolution numerical simulations can be made capable of modeling the liquid metal convective turbulence needed in accurate next-generation dynamo models.

Forced convective heat transfer in boundary layer flow of Sisko fluid over a nonlinear stretching sheet.

Science.gov (United States)

Munir, Asif; Shahzad, Azeem; Khan, Masood

2014-01-01

The major focus of this article is to analyze the forced convective heat transfer in a steady boundary layer flow of Sisko fluid over a nonlinear stretching sheet. Two cases are studied, namely (i) the sheet with variable temperature (PST case) and (ii) the sheet with variable heat flux (PHF case). The heat transfer aspects are investigated for both integer and non-integer values of the power-law index. The governing partial differential equations are reduced to a system of nonlinear ordinary differential equations using appropriate similarity variables and solved numerically. The numerical results are obtained by the shooting method using adaptive Runge Kutta method with Broyden's method in the domain[Formula: see text]. The numerical results for the temperature field are found to be strongly dependent upon the power-law index, stretching parameter, wall temperature parameter, material parameter of the Sisko fluid and Prandtl number. In addition, the local Nusselt number versus wall temperature parameter is also graphed and tabulated for different values of pertaining parameters. Further, numerical results are validated by comparison with exact solutions as well as previously published results in the literature.

Similarity Solution for Combined Free-Forced Convection Past a Vertical Porous Plate in a Porous Medium with a Convective Surface Boundary Condition

Directory of Open Access Journals (Sweden)

Garg P.

2016-12-01

Full Text Available This paper studies the mathematical implications of the two dimensional viscous steady laminar combined free-forced convective flow of an incompressible fluid over a semi infinite fixed vertical porous plate embedded in a porous medium. It is assumed that the left surface of the plate is heated by convection from a hot fluid which is at a temperature higher than the temperature of the fluid on the right surface of the vertical plate. To achieve numerical consistency for the problem under consideration, the governing non linear partial differential equations are first transformed into a system of ordinary differential equations using a similarity variable and then solved numerically under conditions admitting similarity solutions. The effects of the physical parameters of both the incompressible fluid and the vertical plate on the dimensionless velocity and temperature profiles are studied and analysed and the results are depicted both graphically and in a tabular form. Finally, algebraic expressions and the numerical values are obtained for the local skin-friction coefficient and the local Nusselt number.

Modeling the natural convective flow of micropolar nanofluids

KAUST Repository

Bourantas, Georgios

2014-01-01

A micropolar model for nanofluidic suspensions is proposed in order to investigate theoretically the natural convection of nanofluids. The microrotation of the nanoparticles seems to play a significant role into flow regime and in that manner it possibly can interpret the controversial experimental data and theoretical numerical results over the natural convection of nanofluids. Natural convection of a nanofluid in a square cavity is studied and computations are performed for Rayleigh number values up to 106, for a range of solid volume fractions (0 ≤ φ ≤ 0.2) and, different types of nanoparticles (Cu, Ag, Al2O3 and TiO 2). The theoretical results show that the microrotation of the nanoparticles in suspension in general decreases overall heat transfer from the heated wall and should not therefore be neglected when computing heat and fluid flow of micropolar fluids, as nanofluids. The validity of the proposed model is depicted by comparing the numerical results obtained with available experimental and theoretical data. © 2013 Elsevier Ltd. All rights reserved.

Mechanical stimulation of bone cells using fluid flow

NARCIS (Netherlands)

Huesa, C.; Bakker, A.D.

2012-01-01

This chapter describes several methods suitable for mechanically stimulating monolayers of bone cells by fluid shear stress (FSS) in vitro. Fluid flow is generated by pumping culture medium through two parallel plates, one of which contains a monolayer of cells. Methods for measuring nitric oxide

THE EFFECT OF SOLAR RADIATION ON AUTOMOBILE ENVIRONMENT THROUGH NATURAL CONVECTION AND MIXED CONVECTION

Directory of Open Access Journals (Sweden)

MD. FAISAL KADER

2012-10-01

Full Text Available In the present paper, the effect of solar radiation on automobiles has been studied by both experimentally and numerically. The numerical solution is done by an operation friendly and fast CFD code – SC/Tetra with a full scale model of a SM3 car and turbulence is modeled by the standard k-ε equation. Numerical analysis of the three-dimensional model predicts a detailed description of fluid flow and temperature distribution in the passenger compartment during both the natural convection due to the incoming solar radiation and mixed convection due to the flow from defrost nozzle and radiation. It can be seen that solar radiation is an important parameter to raise the compartment temperature above the ambient temperature during summer. During natural convection, the rate of heat transfer is fast at the initial period. In the mixed convection analyses, it is found that the temperature drops down to a comfortable range almost linearly at the initial stage. Experimental investigations are performed to determine the temperature contour on the windshield and the local temperature at a particular point for further validation of the numerical results.

Two-dimensional turbulent convection

Science.gov (United States)

Mazzino, Andrea

2017-11-01

We present an overview of the most relevant, and sometimes contrasting, theoretical approaches to Rayleigh-Taylor and mean-gradient-forced Rayleigh-Bénard two-dimensional turbulence together with numerical and experimental evidences for their support. The main aim of this overview is to emphasize that, despite the different character of these two systems, especially in relation to their steadiness/unsteadiness, turbulent fluctuations are well described by the same scaling relationships originated from the Bolgiano balance. The latter states that inertial terms and buoyancy terms balance at small scales giving rise to an inverse kinetic energy cascade. The main difference with respect to the inverse energy cascade in hydrodynamic turbulence [R. H. Kraichnan, "Inertial ranges in two-dimensional turbulence," Phys. Fluids 10, 1417 (1967)] is that the rate of cascade of kinetic energy here is not constant along the inertial range of scales. Thanks to the absence of physical boundaries, the two systems here investigated turned out to be a natural physical realization of the Kraichnan scaling regime hitherto associated with the elusive "ultimate state of thermal convection" [R. H. Kraichnan, "Turbulent thermal convection at arbitrary Prandtl number," Phys. Fluids 5, 1374-1389 (1962)].

Modeling the overall heat conductive and convective properties of open-cell graphite foam

International Nuclear Information System (INIS)

Tee, C C; Yu, N; Li, H

2008-01-01

This work develops analytic models on the overall thermal conductivity, pressure drop and overall convective heat transfer coefficient of graphite foam. The models study the relationship between the overall heat conductive and convective properties, and foam microstructure, temperature, foam surface friction characteristics and cooling fluid properties. The predicted thermal conductivity, convective heat transfer coefficient and pressure drop agree well with experimental data

Heat transfer to MHD oscillatory dusty fluid flow in a channel filled ...

Indian Academy of Sciences (India)

The flow of fluids through porous media has become ... convection-radiation interaction with heat transfer in boundary layer flow over a flat plate sub- ... Unsteady MHD free convection flow of a compressible fluid past a moving vertical plate in.

Coupling of the SYRTHES thermal code with the ESTET or N3S fluid mechanics codes; Couplage du code de thermique SYRTHES et des codes de mecanique des fluides ESTET ou N3S

Energy Technology Data Exchange (ETDEWEB)

Peniguel, C [Electricite de France (EDF), 78 - Chatou (France). Direction des Etudes et Recherches; Rupp, I [Simulog, 78 (France)

1998-12-31

Thermal aspects take place in several industrial applications in which Electricite de France (EdF) is concerned. In most cases, several physical phenomena like conduction, radiation and convection are involved in thermal transfers. The aim of this paper is to present a numerical tool adapted to industrial configurations and which uses the coupling between fluid convection (resolved with ESTET in finite-volumes or with N3S in finite-elements) and radiant heat transfers between walls (resolved with SYRTHES using a radiosity method). SYRTHES manages the different thermal exchanges that can occur between fluid and solid domains thanks to an explicit iterative method. An extension of SYRTHES has been developed which allows to take into account simultaneously several fluid codes using `message passing` computer tools like Parallel Virtual Machine (PVM) and the code coupling software CALCIUM developed by the Direction of Studies and Researches (DER) of EdF. Various examples illustrate the interest of such a numerical tool. (J.S.) 12 refs.

Coupling of the SYRTHES thermal code with the ESTET or N3S fluid mechanics codes; Couplage du code de thermique SYRTHES et des codes de mecanique des fluides ESTET ou N3S

Energy Technology Data Exchange (ETDEWEB)

Peniguel, C. [Electricite de France (EDF), 78 - Chatou (France). Direction des Etudes et Recherches; Rupp, I. [Simulog, 78 (France)

1997-12-31

Thermal aspects take place in several industrial applications in which Electricite de France (EdF) is concerned. In most cases, several physical phenomena like conduction, radiation and convection are involved in thermal transfers. The aim of this paper is to present a numerical tool adapted to industrial configurations and which uses the coupling between fluid convection (resolved with ESTET in finite-volumes or with N3S in finite-elements) and radiant heat transfers between walls (resolved with SYRTHES using a radiosity method). SYRTHES manages the different thermal exchanges that can occur between fluid and solid domains thanks to an explicit iterative method. An extension of SYRTHES has been developed which allows to take into account simultaneously several fluid codes using `message passing` computer tools like Parallel Virtual Machine (PVM) and the code coupling software CALCIUM developed by the Direction of Studies and Researches (DER) of EdF. Various examples illustrate the interest of such a numerical tool. (J.S.) 12 refs.

Mixed convection boundary layer flow over a moving vertical flat plate in an external fluid flow with viscous dissipation effect.

Directory of Open Access Journals (Sweden)

Norfifah Bachok

Full Text Available The steady boundary layer flow of a viscous and incompressible fluid over a moving vertical flat plate in an external moving fluid with viscous dissipation is theoretically investigated. Using appropriate similarity variables, the governing system of partial differential equations is transformed into a system of ordinary (similarity differential equations, which is then solved numerically using a Maple software. Results for the skin friction or shear stress coefficient, local Nusselt number, velocity and temperature profiles are presented for different values of the governing parameters. It is found that the set of the similarity equations has unique solutions, dual solutions or no solutions, depending on the values of the mixed convection parameter, the velocity ratio parameter and the Eckert number. The Eckert number significantly affects the surface shear stress as well as the heat transfer rate at the surface.

The role of a convective surface in models of the radiative heat transfer in nanofluids

Energy Technology Data Exchange (ETDEWEB)

Rahman, M.M., E-mail: mansurdu@yahoo.com; Al-Mazroui, W.A.; Al-Hatmi, F.S.; Al-Lawatia, M.A.; Eltayeb, I.A.

2014-08-15

Highlights: • The role of a convective surface in modelling with nanofluids is investigated over a wedge. • Surface convection significantly controls the rate of heat transfer in nanofluid. • Increased volume fraction of nanoparticles to the base-fluid may not always increase the rate of heat transfer. • Effect of nanoparticles solid volume fraction depends on the types of constitutive materials. • Higher heat transfer in nanofluids is found in a moving wedge rather than in a static wedge. - Abstract: Nanotechnology becomes the core of the 21st century. Nanofluids are important class of fluids which help advancing nanotechnology in various ways. Convection in nanofluids plays a key role in enhancing the rate of heat transfer either for heating or cooling nanodevices. In this paper, we investigate theoretically the role of a convective surface on the heat transfer characteristics of water-based nanofluids over a static or moving wedge in the presence of thermal radiation. Three different types of nanoparticles, namely copper Cu, alumina Al{sub 2}O{sub 3} and titanium dioxide TiO{sub 2} are considered in preparation of nanofluids. The governing nonlinear partial differential equations are made dimensionless with the similarity transformations. Numerical simulations are carried out through the very robust computer algebra software MAPLE 13 to investigate the effects of various pertinent parameters on the flow field. The obtained results presented graphically as well as in tabular form and discussed from physical and engineering points of view. The results show that the rate of heat transfer in a nanofluid in the presence of thermal radiation significantly depends on the surface convection parameter. If the hot fluid side surface convection resistance is lower than the cold fluid side surface convection resistance, then increased volume fraction of the nanoparticles to the base fluid may reduces the heat transfer rate rather than increases from the surface of

Non-Boussinesq Dissolution-Driven Convection in Porous Media

Science.gov (United States)

Amooie, M. A.; Soltanian, M. R.; Moortgat, J.

2017-12-01

Geological carbon dioxide (CO2) sequestration in deep saline aquifers has been increasingly recognized as a feasible technology to stabilize the atmospheric carbon concentrations and subsequently mitigate the global warming. Solubility trapping is one of the most effective storage mechanisms, which is associated initially with diffusion-driven slow dissolution of gaseous CO2 into the aqueous phase, followed by density-driven convective mixing of CO2 throughout the aquifer. The convection includes both diffusion and fast advective transport of the dissolved CO2. We study the fluid dynamics of CO2 convection in the underlying single aqueous-phase region. Two modeling approaches are employed to define the system: (i) a constant-concentration condition for CO2 in aqueous phase at the top boundary, and (ii) a sufficiently low, constant injection-rate for CO2 from top boundary. The latter allows for thermodynamically consistent evolution of the CO2 composition and the aqueous phase density against the rate at which the dissolved CO2 convects. Here we accurately model the full nonlinear phase behavior of brine-CO2 mixture in a confined domain altered by dissolution and compressibility, while relaxing the common Boussinesq approximation. We discover new flow regimes and present quantitative scaling relations for global characters of spreading, mixing, and dissolution flux in two- and three-dimensional media for the both model types. We then revisit the universal Sherwood-Rayleigh scaling that is under debate for porous media convective flows. Our findings confirm the sublinear scaling for the constant-concentration case, while reconciling the classical linear scaling for the constant-injection model problem. The results provide a detailed perspective into how the available modeling strategies affect the prediction ability for the total amount of CO2 dissolved in the long term within saline aquifers of different permeabilities.

Convection in multiphase fluid flows using lattice Boltzmann methods

NARCIS (Netherlands)

Biferale, L.; Perlekar, P.; Sbragaglia, M.; Toschi, F.

2012-01-01

We present high-resolution numerical simulations of convection in multiphase flows (boiling) using a novel algorithm based on a lattice Boltzmann method. We first study the thermodynamical and kinematic properties of the algorithm. Then, we perform a series of 3D numerical simulations changing the

R-HPDC Process with Forced Convection Mixing Device for Automotive Part of A380 Aluminum Alloy

Directory of Open Access Journals (Sweden)

Bing Zhou

2014-04-01

Full Text Available The continuing quest for cost-effective and complex shaped aluminum castings with fewer defects for applications in the automotive industries has aroused the interest in rheological high pressure die casting (R-HPDC. A new machine, forced convection mixing (FCM device, based on the mechanical stirring and convection mixing theory for the preparation of semisolid slurry in convenience and functionality was proposed to produce the automotive shock absorber part by R-HPDC process. The effect of barrel temperature and rotational speed of the device on the grain size and morphology of semi-solid slurry were extensively studied. In addition, flow behavior and temperature field of the melt in the FCM process was investigated combining computational fluid dynamics simulation. The results indicate that the microstructure and pore defects at different locations of R-HPDC casting have been greatly improved. The vigorous fluid convection in FCM process has changed the temperature field and composition distribution of conventional solidification. Appropriately increasing the rotational speed can lead to a uniform temperature filed sooner. The lower barrel temperature leads to a larger uniform degree of supercooling of the melt that benefits the promotion of nucleation rate. Both of them contribute to the decrease of the grain size and the roundness of grain morphology.

MHD natural convection in open inclined square cavity with a heated circular cylinder

Science.gov (United States)

Hosain, Sheikh Anwar; Alim, M. A.; Saha, Satrajit Kumar

2017-06-01

MHD natural convection in open cavity becomes very important in many scientific and engineering problems, because of it's application in the design of electronic devices, solar thermal receivers, uncovered flat plate solar collectors having rows of vertical strips, geothermal reservoirs, etc. Several experiments and numerical investigations have been presented for describing the phenomenon of natural convection in open cavity for two decades. MHD natural convection and fluid flow in a two-dimensional open inclined square cavity with a heated circular cylinder was considered. The opposite wall to the opening side of the cavity was first kept to constant heat flux q, at the same time the surrounding fluid interacting with the aperture was maintained to an ambient temperature T∞. The top and bottom wall was kept to low and high temperature respectively. The fluid with different Prandtl numbers. The properties of the fluid are assumed to be constant. As a result a buoyancy force is created inside the cavity due to temperature difference and natural convection is formed inside the cavity. The Computational Fluid Dynamics (CFD) code are used to discretize the solution domain and represent the numerical result to graphical form.. Triangular meshes are used to obtain the solution of the problem. The streamlines and isotherms are produced, heat transfer parameter Nu are obtained. The results are presented in graphical as well as tabular form. The results show that heat flux decreases for increasing inclination of the cavity and the heat flux is a increasing function of Prandtl number Pr and decreasing function of Hartmann number Ha. It is observed that fluid moves counterclockwise around the cylinder in the cavity. Various recirculations are formed around the cylinder. The almost all isotherm lines are concentrated at the right lower corner of the cavity. The object of this work is to develop a Mathematical model regarding the effect of MHD natural convection flow around

Active Learning in Fluid Mechanics: Youtube Tube Flow and Puzzling Fluids Questions

Science.gov (United States)

Hrenya, Christine M.

2011-01-01

Active-learning exercises appropriate for a course in undergraduate fluid mechanics are presented. The first exercise involves an experiment in gravity-driven tube flow, with small groups of students partaking in a contest to predict the experimental flow rates using the mechanical energy balance. The second exercise takes the form of an…

A block-iterative nodal integral method for forced convection problems

International Nuclear Information System (INIS)

Decker, W.J.; Dorning, J.J.

1992-01-01

A new efficient iterative nodal integral method for the time-dependent two- and three-dimensional incompressible Navier-Stokes equations has been developed. Using the approach introduced by Azmy and Droning to develop nodal mehtods with high accuracy on coarse spatial grids for two-dimensional steady-state problems and extended to coarse two-dimensional space-time grids by Wilson et al. for thermal convection problems, we have developed a new iterative nodal integral method for the time-dependent Navier-Stokes equations for mechanically forced convection. A new, extremely efficient block iterative scheme is employed to invert the Jacobian within each of the Newton-Raphson iterations used to solve the final nonlinear discrete-variable equations. By taking advantage of the special structure of the Jacobian, this scheme greatly reduces memory requirements. The accuracy of the overall method is illustrated by appliying it to the time-dependent version of the classic two-dimensional driven cavity problem of computational fluid dynamics

Analysis of natural convection in volumetrically-heated melt pools

International Nuclear Information System (INIS)

Sehgal, B.R.; Dinh, T.N.; Nourgaliev, R.R.

1996-12-01

Results of series of studies on natural convection heat transfer in decay-heated core melt pools which form in a reactor lower plenum during the progression of a core meltdown accident are described. The emphasis is on modelling and prediction of turbulent heat transfer characteristics of natural convection in a liquid pool with an internal energy source. Methods of computational fluid dynamics, including direct numerical simulation, were applied for investigation

Conjugated heat transfer of natural convection in pool with internal heat sources and convection in the tube

International Nuclear Information System (INIS)

Li Longjian; Liu Hongtao; Cui Wenzhi

2007-01-01

The conjugated heat transfer of natural convection in pool with internal heat source and the forced convection in the tube was analyzed, and the corresponding three-dimensional physical and mathematical model was proposed. A control volume based finite element method was employed to solve numerically the problem. The computations were performed for different internal heat source intensity of the pool and the different flow velocity in the tube. The computed heat transfer coefficients on the inner and outer wall showed well consistency of those calculated with the empirical correlations. Compared with the measured total heat transfer coefficients between the fluids in and out of the tube, the computed ones showed also the well consistency, which implied that the numerical model proposed in this paper was reliable. The research results revealed that the total heat transfer coefficients between the fluids were strongly affected by the internal heat source intensity of the pool liquid and the flow velocity in the tube. (authors)

Reynolds number scaling in cryogenic turbulent Rayleigh-Benard convection in a cylindrical aspect ratio one cell

Czech Academy of Sciences Publication Activity Database

Musilová, Věra; Králík, Tomáš; La Mantia, M.; Macek, Michal; Urban, Pavel; Skrbek, L.

2017-01-01

Roč. 832, OCT 26 (2017), s. 721-744 ISSN 0022-1120 R&D Projects: GA ČR(CZ) GA17-03572S; GA MŠk(CZ) LO1212 Institutional support: RVO:68081731 Keywords : Benard convection * turbulent convection * turbulent flows Subject RIV: BK - Fluid Dynamics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 2.821, year: 2016

An Introduction to Computational Fluid Mechanics by Example

CERN Document Server

Biringen, Sedat

2011-01-01

This new book builds on the original classic textbook entitled: An Introduction to Computational Fluid Mechanics by C. Y. Chow which was originally published in 1979. In the decades that have passed since this book was published the field of computational fluid dynamics has seen a number of changes in both the sophistication of the algorithms used but also advances in the computer hardware and software available. This new book incorporates the latest algorithms in the solution techniques and supports this by using numerous examples of applications to a broad range of industries from mechanical

Southern Ocean Convection and tropical telleconnections

Science.gov (United States)

Marinov, I.; Cabre, A.; Gnanadesikan, A.

2014-12-01

We show that Southern Ocean (SO) temperatures in the latest generation of Earth System Models exhibit two major modes of variation, one driven by deep convection, the other by tropical variability. We perform a CMIP5 model intercomparison to understand why different climate models represent SO variability so differently in long, control simulations. We show that multiyear variability in Southern Ocean sea surface temperatures (SSTs) can in turn influence oceanic and atmospheric conditions in the tropics on short (atmospheric) time-scales. We argue that the strength and pattern of SO-tropical teleconnections depends on the intensity of SO deep convection. Periodic convection in the SO is a feature of most CMIP5 models under preindustrial forcing (deLavergne et al., 2014). Models show a wide distribution in the spatial extent, periodicity and intensity of their SO convection, with some models convecting most of the time, and some showing very little convection. In a highly convective coupled model, we find that multidecadal variability in SO and global SSTs, as well as SO heat storage are driven by Weddell Sea convective variability, with convective decades relatively warm due to the heat released from the deep southern ocean and non-convective decades cold due to the subsurface storage of heat. Furthermore, pulses of SO convection drive SST and sea ice variations, influencing absorbed shortwave and emitted longwave radiation, wind, cloud and precipitation patterns, with climatic implications for the low latitudes via fast atmospheric teleconnections. We suggest that these high-low latitude teleconnection mechanisms are relevant for understanding hiatus decades. Additionally, Southern Ocean deep convection varied significantly during past, natural climate changes such as during the last deglaciation. Weddell Sea open convection was recently weakened, likely as a consequence of anthropogenic forcing and the resulting surface freshening. Our study opens up the

Neural Control Mechanisms and Body Fluid Homeostasis

Science.gov (United States)

Johnson, Alan Kim

1998-01-01

The goal of the proposed research was to study the nature of afferent signals to the brain that reflect the status of body fluid balance and to investigate the central neural mechanisms that process this information for the activation of response systems which restore body fluid homeostasis. That is, in the face of loss of fluids from intracellular or extracellular fluid compartments, animals seek and ingest water and ionic solutions (particularly Na(+) solutions) to restore the intracellular and extracellular spaces. Over recent years, our laboratory has generated a substantial body of information indicating that: (1) a fall in systemic arterial pressure facilitates the ingestion of rehydrating solutions and (2) that the actions of brain amine systems (e.g., norepinephrine; serotonin) are critical for precise correction of fluid losses. Because both acute and chronic dehydration are associated with physiological stresses, such as exercise and sustained exposure to microgravity, the present research will aid in achieving a better understanding of how vital information is handled by the nervous system for maintenance of the body's fluid matrix which is critical for health and well-being.

Deep Learning Fluid Mechanics

Science.gov (United States)

Barati Farimani, Amir; Gomes, Joseph; Pande, Vijay

2017-11-01

We have developed a new data-driven model paradigm for the rapid inference and solution of the constitutive equations of fluid mechanic by deep learning models. Using generative adversarial networks (GAN), we train models for the direct generation of solutions to steady state heat conduction and incompressible fluid flow without knowledge of the underlying governing equations. Rather than using artificial neural networks to approximate the solution of the constitutive equations, GANs can directly generate the solutions to these equations conditional upon an arbitrary set of boundary conditions. Both models predict temperature, velocity and pressure fields with great test accuracy (>99.5%). The application of our framework for inferring and generating the solutions of partial differential equations can be applied to any physical phenomena and can be used to learn directly from experiments where the underlying physical model is complex or unknown. We also have shown that our framework can be used to couple multiple physics simultaneously, making it amenable to tackle multi-physics problems.

Convection in Porous Media

CERN Document Server

Nield, Donald A

2013-01-01

Convection in Porous Media, 4th Edition, provides a user-friendly introduction to the subject, covering a wide range of topics, such as fibrous insulation, geological strata, and catalytic reactors. The presentation is self-contained, requiring only routine mathematics and the basic elements of fluid mechanics and heat transfer. The book will be of use not only to researchers and practicing engineers as a review and reference, but also to graduate students and others entering the field. The new edition features approximately 1,750 new references and covers current research in nanofluids, cellular porous materials, strong heterogeneity, pulsating flow, and more. Recognized as the standard reference in the field Includes a comprehensive, 250-page reference list Cited over 2300 times to date in its various editions Serves as an introduction for those entering the field and as a comprehensive reference for experienced researchers Features new sections on nanofluids, carbon dioxide sequestration, and applications...

Convection in porous media

CERN Document Server

Nield, Donald A

1992-01-01

This book provides a user-friendly introduction to the topic of convection in porous media The authors as- sume that the reader is familiar with the basic elements of fluid mechanics and heat transfer, but otherwise the book is self-contained The book will be useful both as a review (for reference) and as a tutorial work, suitable as a textbook in a graduate course or seminar The book brings into perspective the voluminous research that has been performed during the last two decades The field has recently exploded because of worldwide concern with issues such as energy self-sufficiency and pollution of the environment Areas of application include the insulation of buildings and equipment, energy storage and recovery, geothermal reservoirs, nuclear waste disposal, chemical reactor engineering, and the storage of heat-generating materials such as grain and coal Geophysical applications range from the flow of groundwater around hot intrusions to the stability of snow against avalanches

Time-dependent mixed convection heat transfer from a sphere in a micro-gravity environment

International Nuclear Information System (INIS)

Hommel, M.J.

1987-01-01

A fundamental problem of interest for crystal growth in micro-gravity applications involves the mixed convection heat transfer from a sphere in a uniform flow of fluid at a differing temperature. Under the combined influence of the imposed free stream as well as an induced buoyancy force due to thermal expansion of the fluid, the heat transfer from the sphere will be different from that of either the pure forced convection flow or the pure free convection flow. For the present study, the method of matched asymptotic expansions is applied to the laminar flow problem of an impulsively heated, impulsively started sphere in an originally quiescent fluid. Time series expansions are developed for the dependent variables by acknowledging the existence of two district regions: one, an inner region, near the sphere, in which viscous effects are significant; and two, an outer region in which the fluid may be treated as inviscid. The time series expansions are developed in terms of the Reynolds number and Richardson number (Buoyancy Parameter), and the relevant heat transfer and drag coefficients are calculated and plotted

A meshless method for modeling convective heat transfer

Energy Technology Data Exchange (ETDEWEB)

Carrington, David B [Los Alamos National Laboratory

2010-01-01

A meshless method is used in a projection-based approach to solve the primitive equations for fluid flow with heat transfer. The method is easy to implement in a MATLAB format. Radial basis functions are used to solve two benchmark test cases: natural convection in a square enclosure and flow with forced convection over a backward facing step. The results are compared with two popular and widely used commercial codes: COMSOL, a finite element model, and FLUENT, a finite volume-based model.

Natural convection and wall radiation in tall cavities

Energy Technology Data Exchange (ETDEWEB)

Balaji, C [Regional Engineering College, Tiruchirapalli (India). Dept. of Mechanical Engineering; Venkateshan, S P [Indian Inst. of Tech., Madras (India). Dept. of Mechanical Engineering

1996-12-01

The problem of combined natural convection and wall radiation in tall cavities has been taken up for a detailed numerical investigation. The governing equations for fluid flow have been solved by a finite volume method and the radiation has been treated by the radiosity-irradiation method. The analysis has been specifically made for the case where the emissivity of the hot left wall is different from that of the cold right wall. For this case it was found that decoupling radiation from free convection can lead to considerable error. Correlations have been suggested for predicting both the convective as well as the radiative heat transfer rates across the cavity. (author). 7 refs., 3 figs., 3 tabs.

Natural convection and wall radiation in tall cavities

International Nuclear Information System (INIS)

Balaji, C.; Venkateshan, S.P.

1996-01-01

The problem of combined natural convection and wall radiation in tall cavities has been taken up for a detailed numerical investigation. The governing equations for fluid flow have been solved by a finite volume method and the radiation has been treated by the radiosity-irradiation method. The analysis has been specifically made for the case where the emissivity of the hot left wall is different from that of the cold right wall. For this case it was found that decoupling radiation from free convection can lead to considerable error. Correlations have been suggested for predicting both the convective as well as the radiative heat transfer rates across the cavity. (author). 7 refs., 3 figs., 3 tabs

Turbulent convection in liquid metal with and without rotation

OpenAIRE

King, Eric M.; Aurnou, Jonathan M.

2013-01-01

The magnetic fields of Earth and other planets are generated by turbulent, rotating convection in liquid metal. Liquid metals are peculiar in that they diffuse heat more readily than momentum, quantified by their small Prandtl numbers, . Most analog models of planetary dynamos, however, use moderate fluids, and the systematic influence of reducing is not well understood. We perform rotating Rayleigh–Bénard convection experiments in the liquid metal gallium over a range of nondimensional bu...

Analysis of natural convection in volumetrically-heated melt pools

Energy Technology Data Exchange (ETDEWEB)

Sehgal, B.R.; Dinh, T.N.; Nourgaliev, R.R. [Royal Inst. of Tech., Stockholm (Sweden). Div. of Nuclear Power Safety

1996-12-01

Results of series of studies on natural convection heat transfer in decay-heated core melt pools which form in a reactor lower plenum during the progression of a core meltdown accident are described. The emphasis is on modelling and prediction of turbulent heat transfer characteristics of natural convection in a liquid pool with an internal energy source. Methods of computational fluid dynamics, including direct numerical simulation, were applied for investigation. Refs, figs, tabs.

Rotating fluid models in classical and quantum mechanics

International Nuclear Information System (INIS)

Arvieu, R.; Troudet, T.

1979-01-01

To describe the behavior of high-spin nuclei it is necessary to refer back to the classical mechanics of fluids in rotation where some results are general enough to apply to the rotational nuclear fluid. It is then shown that the quantum model of rotational oscillator gives a simple classification of rotating configurations [fr

Convection and crystal settling in sills

Science.gov (United States)

Gibb, Fergus G. F.; Henderson, C. Michael B.

1992-02-01

It has been advocated that convective and crystal settling processes play significant, and perhaps crucial, roles in magmatic differentiation. The fluid dynamics of magma chambers have been extensively studied in recent years, both theoretically and experimentally, but there is disagreement over the nature and scale of the convection, over its bearing on fractionation and possibly over whether it occurs at all. The differential distribution of modal olivine with height in differentiated alkaline basic sills provides critical evidence to resolve this controversy, at least for small to medium-large magma chambers. Our own and others' published data for such sills show that, irrespective of overall olivine content, modal olivine contents tend to increase in a roughly symmetrical manner inwards from the upper and lower margins of the sill, i.e. the distribution patterns are more often approximately D-shaped rather than the classic S-shape generally ascribed to gravity settling. We concur with the majority of other authors that this is an original feature of the filling process which has survived more or less unchanged since emplacement. We therefore conclude that the magmas have not undergone turbulent convection and that gravity settling has usually played only a minor modifying role since the intrusion of these sills. We offer a possible explanation for the apparent contradiction between fluid dynamical theory and the petrological evidence by suggesting that such sills rarely fill by the rapid injection of a single pulse of magma. Rather, they form from a series of pulses or a continuous pulsed influx over a protracted interval during which marginal cooling severely limits the potential for thermal convection.

Computational fluid mechanics and heat transfer

CERN Document Server

Pletcher, Richard H; Anderson, Dale

2012-01-01

""I have always considered this book the best gift from one generation to the next in computational fluid dynamics. I earnestly recommend this book to graduate students and practicing engineers for the pleasure of learning and a handy reference. The description of the basic concepts and fundamentals is thorough and is crystal clear for understanding. And since 1984, two newer editions have kept abreast to the new, relevant, and fully verified advancements in CFD.""-Joseph J.S. Shang, Wright State University""Computational Fluid Mechanics and Heat Transfer is very well written to be used as a t

Apparatus for real-time acoustic imaging of Rayleigh-Bénard convection

Energy Technology Data Exchange (ETDEWEB)

Kuehn, Kerry, K.

2008-10-28

We have successfully designed, built and tested an experimental apparatus which is capable of providing the first real-time ultrasound images of Rayleigh-B\\'{e}nard convection in optically opaque fluids confined to large aspect ratio experimental cells. The apparatus employs a modified version of a commercially available ultrasound camera to capture images (30 frames per second) of flow patterns in a fluid undergoing Rayleigh Bénard convection. The apparatus was validated by observing convection rolls in 5cSt polydimethylsiloxane (PDMS) polymer fluid. Our first objective, after having built the apparatus, was to use it to study the sequence of transitions from diffusive to time--dependent heat transport in liquid mercury. The aim was to provide important information on pattern formation in the largely unexplored regime of very low Prandtl number fluids. Based on the theoretical stability diagram for liquid mercury, we anticipated that straight rolls should be stable over a range of Rayleigh numbers, between 1708 and approximately 1900. Though some of our power spectral densities were suggestive of the existence of weak convection, we have been unable to unambiguously visualize stable convection rolls above the theoretical onset of convection in liquid mercury. Currently, we are seeking ways to increase the sensitivity of our apparatus, such as (i) improving the acoustic impedance matching between our materials in the ultrasound path and (ii) reducing the noise level in our acoustic images due to turbulence and cavitation in the cooling fluids circulating above and below our experimental cell. If we are able to convincingly improve the sensitivity of our apparatus, and we still do not observe stable convection rolls in liquid mercury, then it may be the case that the theoretical stability diagram requires revision. In that case, either (i) straight rolls are not stable in a large aspect ratio cell at the Prandtl numbers associated with liquid mercury, or (ii

Towards the ultimate variance-conserving convection scheme

International Nuclear Information System (INIS)

Os, J.J.A.M. van; Uittenbogaard, R.E.

2004-01-01

In the past various arguments have been used for applying kinetic energy-conserving advection schemes in numerical simulations of incompressible fluid flows. One argument is obeying the programmed dissipation by viscous stresses or by sub-grid stresses in Direct Numerical Simulation and Large Eddy Simulation, see e.g. [Phys. Fluids A 3 (7) (1991) 1766]. Another argument is that, according to e.g. [J. Comput. Phys. 6 (1970) 392; 1 (1966) 119], energy-conserving convection schemes are more stable i.e. by prohibiting a spurious blow-up of volume-integrated energy in a closed volume without external energy sources. In the above-mentioned references it is stated that nonlinear instability is due to spatial truncation rather than to time truncation and therefore these papers are mainly concerned with the spatial integration. In this paper we demonstrate that discretized temporal integration of a spatially variance-conserving convection scheme can induce non-energy conserving solutions. In this paper the conservation of the variance of a scalar property is taken as a simple model for the conservation of kinetic energy. In addition, the derivation and testing of a variance-conserving scheme allows for a clear definition of kinetic energy-conserving advection schemes for solving the Navier-Stokes equations. Consequently, we first derive and test a strictly variance-conserving space-time discretization for the convection term in the convection-diffusion equation. Our starting point is the variance-conserving spatial discretization of the convection operator presented by Piacsek and Williams [J. Comput. Phys. 6 (1970) 392]. In terms of its conservation properties, our variance-conserving scheme is compared to other spatially variance-conserving schemes as well as with the non-variance-conserving schemes applied in our shallow-water solver, see e.g. [Direct and Large-eddy Simulation Workshop IV, ERCOFTAC Series, Kluwer Academic Publishers, 2001, pp. 409-287

Molecular mechanics and structure of the fluid-solid interface in simple fluids

Science.gov (United States)

Wang, Gerald J.; Hadjiconstantinou, Nicolas G.

2017-09-01

Near a fluid-solid interface, the fluid spatial density profile is highly nonuniform at the molecular scale. This nonuniformity can have profound effects on the dynamical behavior of the fluid and has been shown to play an especially important role when modeling a wide variety of nanoscale heat and momentum transfer phenomena. We use molecular-mechanics arguments and molecular-dynamics (MD) simulations to develop a better understanding of the structure of the first fluid layer directly adjacent to the solid in the layering regime, as delineated by a nondimensional number that compares the effects of wall-fluid interaction to thermal energy. Using asymptotic analysis of the Nernst-Planck equation, we show that features of the fluid density profile close to the wall, such as the areal density of the first layer ΣFL (defined as the number of atoms in this layer per unit of fluid-solid interfacial area), can be expressed as polynomial functions of the fluid average density ρave. This is found to be in agreement with MD simulations, which also show that the width of the first layer hFL is a linear function of the average density and only a weak function of the temperature T . These results can be combined to show that, for system average densities corresponding to a dense fluid (ρave≥0.7 ), the ratio C ≡ΣFLρavehFL, representing a density enhancement with respect to the bulk fluid, depends only weakly on temperature and is essentially independent of density. Further MD simulations suggest that the above results, nominally valid for large systems (solid in contact with semi-infinite fluid), also describe fluid-solid interfaces under considerable nanoconfinement, provided ρave is appropriately defined.

Convective heat transfer enhancement by diamond shaped micro-protruded patterns for heat sinks: Thermal fluid dynamic investigation and novel optimization methodology

International Nuclear Information System (INIS)

Ventola, Luigi; Dialameh, Masoud; Fasano, Matteo; Chiavazzo, Eliodoro; Asinari, Pietro

2016-01-01

Highlights: • A novel methodology for optimal design of patterned heat sink surfaces is proposed. • Heat transfer enhancement by patterned surfaces is measured experimentally. • Role of fluid dynamics and geometrical scales on heat transfer is clarified. - Abstract: In the present work, micro-protruded patterns on flush mounted heat sinks for convective heat transfer enhancement are investigated and a novel methodology for thermal optimization is proposed. Patterned heat sinks are experimentally characterized in fully turbulent regime, and the role played by geometrical parameters and fluid dynamic scales is discussed. A methodology specifically suited for micro-protruded pattern optimization is designed, leading to 73% enhancement in thermal performance respect to commercially available heat sinks, at fixed costs. This work is expected to introduce a new methodological approach for a more systematic and efficient development of solutions for electronics cooling.

Statistical mechanics of fluids under internal constraints: Rigorous results for the one-dimensional hard rod fluid

International Nuclear Information System (INIS)

Corti, D.S.; Debenedetti, P.G.

1998-01-01

The rigorous statistical mechanics of metastability requires the imposition of internal constraints that prevent access to regions of phase space corresponding to inhomogeneous states. We derive exactly the Helmholtz energy and equation of state of the one-dimensional hard rod fluid under the influence of an internal constraint that places an upper bound on the distance between nearest-neighbor rods. This type of constraint is relevant to the suppression of boiling in a superheated liquid. We determine the effects of this constraint upon the thermophysical properties and internal structure of the hard rod fluid. By adding an infinitely weak and infinitely long-ranged attractive potential to the hard core, the fluid exhibits a first-order vapor-liquid transition. We determine exactly the equation of state of the one-dimensional superheated liquid and show that it exhibits metastable phase equilibrium. We also derive statistical mechanical relations for the equation of state of a fluid under the action of arbitrary constraints, and show the connection between the statistical mechanics of constrained and unconstrained ensembles. copyright 1998 The American Physical Society

Isogeometric shape optimization in fluid mechanics

DEFF Research Database (Denmark)

Nørtoft, Peter; Gravesen, Jens

2013-01-01

The subject of this work is numerical shape optimization in fluid mechanics, based on isogeometric analysis. The generic goal is to design the shape of a 2-dimensional flow domain to minimize some prescribed objective while satisfying given geometric constraints. As part of the design problem...

EVIDENCE OF ACTIVE MHD INSTABILITY IN EULAG-MHD SIMULATIONS OF SOLAR CONVECTION

Energy Technology Data Exchange (ETDEWEB)

Lawson, Nicolas; Strugarek, Antoine; Charbonneau, Paul, E-mail: nicolas.laws@gmail.ca, E-mail: strugarek@astro.umontreal.ca, E-mail: paulchar@astro.umontreal.ca [Département de Physique, Université de Montréal, C.P. 6128 Succ. Centre-ville, Montréal, Qc H3C 3J7 (Canada)

2015-11-10

We investigate the possible development of magnetohydrodynamical instabilities in the EULAG-MHD “millennium simulation” of Passos and Charbonneau. This simulation sustains a large-scale magnetic cycle characterized by solar-like polarity reversals taking place on a regular multidecadal cadence, and in which zonally oriented bands of strong magnetic fields accumulate below the convective layers, in response to turbulent pumping from above in successive magnetic half-cycles. Key aspects of this simulation include low numerical dissipation and a strongly sub-adiabatic fluid layer underlying the convectively unstable layers corresponding to the modeled solar convection zone. These properties are conducive to the growth and development of two-dimensional instabilities that are otherwise suppressed by stronger dissipation. We find evidence for the action of a non-axisymmetric magnetoshear instability operating in the upper portions of the stably stratified fluid layers. We also investigate the possibility that the Tayler instability may be contributing to the destabilization of the large-scale axisymmetric magnetic component at high latitudes. On the basis of our analyses, we propose a global dynamo scenario whereby the magnetic cycle is driven primarily by turbulent dynamo action in the convecting layers, but MHD instabilities accelerate the dissipation of the magnetic field pumped down into the overshoot and stable layers, thus perhaps significantly influencing the magnetic cycle period. Support for this scenario is found in the distinct global dynamo behaviors observed in an otherwise identical EULAG-MHD simulations, using a different degree of sub-adiabaticity in the stable fluid layers underlying the convection zone.

Sensitivity study of CFD turbulent models for natural convection analysis

International Nuclear Information System (INIS)

Yu sun, Park

2007-01-01

The buoyancy driven convective flow fields are steady circulatory flows which were made between surfaces maintained at two fixed temperatures. They are ubiquitous in nature and play an important role in many engineering applications. Application of a natural convection can reduce the costs and efforts remarkably. This paper focuses on the sensitivity study of turbulence analysis using CFD (Computational Fluid Dynamics) for a natural convection in a closed rectangular cavity. Using commercial CFD code, FLUENT and various turbulent models were applied to the turbulent flow. Results from each CFD model will be compared each other in the viewpoints of grid resolution and flow characteristics. It has been showed that: -) obtaining general flow characteristics is possible with relatively coarse grid; -) there is no significant difference between results from finer grid resolutions than grid with y + + is defined as y + = ρ*u*y/μ, u being the wall friction velocity, y being the normal distance from the center of the cell to the wall, ρ and μ being respectively the fluid density and the fluid viscosity; -) the K-ε models show a different flow characteristic from K-ω models or from the Reynolds Stress Model (RSM); and -) the y + parameter is crucial for the selection of the appropriate turbulence model to apply within the simulation

A statistical mechanics approach to mixing in stratified fluids

OpenAIRE

Venaille , Antoine; Gostiaux , Louis; Sommeria , Joël

2016-01-01

Accepted for the Journal of Fluid Mechanics; Predicting how much mixing occurs when a given amount of energy is injected into a Boussinesq fluid is a longstanding problem in stratified turbulence. The huge number of degrees of freedom involved in these processes renders extremely difficult a deterministic approach to the problem. Here we present a statistical mechanics approach yielding a prediction for a cumulative, global mixing efficiency as a function of a global Richard-son number and th...

The influence of magma viscosity on convection within a magma chamber

Science.gov (United States)

Schubert, M.; Driesner, T.; Ulmer, P.

2012-12-01

Magmatic-hydrothermal ore deposits are the most important sources of metals like Cu, Mo, W and Sn and a major resource for Au. It is well accepted that they are formed by the release of magmatic fluids from a batholith-sized magma body. Traditionally, it has been assumed that crystallization-induced volatile saturation (called "second boiling") is the main mechanism for fluid release, typically operating over thousands to tens of thousands of years (Candela, 1991). From an analysis of alteration halo geometries caused by magmatic fluids, Cathles and Shannon (2007) suggested much shorter timescales in the order of hundreds of years. Such rapid release of fluids cannot be explained by second boiling as the rate of solidification scales with the slow conduction of heat away from the system. However, rapid fluid release is possible if convection is assumed within the magma chamber. The magma would degas in the upper part of the magma chamber and volatile poor magma would sink down again. Such, the rates of degassing can be much higher than due to cooling only. We developed a convection model using Navier-Stokes equations provided by the computational fluid dynamics platform OpenFOAM that gives the possibility to use externally derived meshes with complex (natural) geometries. We implemented a temperature, pressure, composition and crystal fraction dependent viscosity (Ardia et al., 2008; Giordano et al., 2008; Moore et al., 1998) and a temperature, pressure, composition dependent density (Lange1994). We found that the new viscosity and density models strongly affect convection within the magma chamber. The dependence of viscosity on crystal fraction has a particularly strong effect as the steep viscosity increase at the critical crystal fraction leads to steep decrease of convection velocity. As the magma chamber is cooling from outside to inside a purely conductive layer is developing along the edges of the magma chamber. Convection continues in the inner part of the

A fractal model for heat transfer of nanofluids by convection in a pool

Energy Technology Data Exchange (ETDEWEB)

Xiao Boqi, E-mail: xiaoboqi2006@126.co [Department of Physics and Electromechanical Engineering, Sanming University, 25 Jingdong Road, Sanming 365004 (China); Yu Boming [School of Physics, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074 (China); Wang Zongchi; Chen Lingxia [Department of Physics and Electromechanical Engineering, Sanming University, 25 Jingdong Road, Sanming 365004 (China)

2009-11-02

Based on the fractal distribution of nanoparticles, a fractal model for heat transfer of nanofluids is presented in the Letter. Considering heat convection between nanoparticles and liquids due to the Brownian motion of nanoparticles in fluids, the formula of calculating heat flux of nanofluids by convection is given. The proposed model is expressed as a function of the average size of nanoparticle, concentration of nanoparticle, fractal dimension of nanoparticle, temperature and properties of fluids. It is shown that the fractal model is effectual according to a good agreement between the model predictions and experimental data.

A fractal model for heat transfer of nanofluids by convection in a pool

International Nuclear Information System (INIS)

Xiao Boqi; Yu Boming; Wang Zongchi; Chen Lingxia

2009-01-01

Based on the fractal distribution of nanoparticles, a fractal model for heat transfer of nanofluids is presented in the Letter. Considering heat convection between nanoparticles and liquids due to the Brownian motion of nanoparticles in fluids, the formula of calculating heat flux of nanofluids by convection is given. The proposed model is expressed as a function of the average size of nanoparticle, concentration of nanoparticle, fractal dimension of nanoparticle, temperature and properties of fluids. It is shown that the fractal model is effectual according to a good agreement between the model predictions and experimental data.

Dynamics of a secondary instability in Benard-Marangoni convection with unidimensional heating

International Nuclear Information System (INIS)

Burguete, J.; Mancini, H.L.; Perez-Garcia, C.

1993-01-01

The dynamics of Benard-Marangoni convection with unidimensional heating in a pure fluid is studied experimentally. Convection begins with rolls parallel to the heater. The characteristics of these primary rolls have been determined. When the temperature difference across the liquid layer is increased beyond a critical value a secondary instability appears. Motions transverse to the heater with a definite wavelength can be seen. Moreover, for small angles between the heater and the fluid surface, the pattern drifts along the heater with a velocity that depends almost linearly on the inclination. A phenomenological phase equation is proposed to interpret this observation. (orig.)

The structure of sidewall boundary layers in conned rotating Rayleigh-Bénard convection

NARCIS (Netherlands)

Kunnen, R.P.J.; Clercx, H.J.H.; van Heijst, G.J.F.

2013-01-01

Turbulent rotating convection is usually studied in a cylindrical geometry, as this is its most convenient experimental realization. In our previous work (Kunnen et al., J. Fluid Mech., vol. 688, 2011, pp. 422–442) we studied turbulent rotating convection in a cylinder with the emphasis on the

Induced convection cylindrical probe conductivity measurements on permeable media

International Nuclear Information System (INIS)

Fodemesi, S.P.; Beck, A.E.

1983-01-01

This chapter presents results from a program of investigation using the transient needle probe thermal conductivity technique on fluid saturated permeable media with a glass bead matrix. Uses eight additional radially located sensors in order to correlate the convection effects on the temperature sensor in the heater probe with convection behavior in the medium; all were scanned frequently with a data acquisition system, from the start of the experiment through a few hours of experimental time. Points out that with typical conditions encountered in oceanic heat flow work, induced convection may commence as early as 60 s from the start of the experiment. Finds that the convection effects are worse when the needle probe is oriented horizontally than when it is oriented vertically (gradients orthogonal to the gravitational field), and a correlation is made between permeability and the time of onset and the extent of convective effects. Indicates errors in conductivity as large as 40%. Suggests empirical techniques for detecting and correcting for thermal convection using probe sensor data alone

The Interplay Between Saline Fluid Flow and Dynamic Permeability in Magmatic-Hydrothermal Systems

Science.gov (United States)

Weis, P.

2014-12-01

Magmatic-hydrothermal ore deposits document the interplay between saline fluid flow and rock permeability. Numerical simulations of multi-phase flow of variably miscible, compressible H20-NaCl fluids in concert with a dynamic permeability model can reproduce characteristics of porphyry copper and epithermal gold systems. This dynamic permeability model incorporates depth-dependent permeability profiles characteristic for tectonically active crust as well as pressure- and temperature-dependent relationships describing hydraulic fracturing and the transition from brittle to ductile rock behavior. In response to focused expulsion of magmatic fluids from a crystallizing upper crustal magma chamber, the hydrothermal system self-organizes into a hydrological divide, separating an inner part dominated by ascending magmatic fluids under near-lithostatic pressures from a surrounding outer part dominated by convection of colder meteoric fluids under near-hydrostatic pressures. This hydrological divide also provides a mechanism to transport magmatic salt through the crust, and prevents the hydrothermal system to become "clogged" by precipitation of solid halite due to depressurization of saline, high-temperature magmatic fluids. The same physical processes at similar permeability ranges, crustal depths and flow rates are relevant for a number of active systems, including geothermal resources and excess degassing at volcanos. The simulations further suggest that the described mechanism can separate the base of free convection in high-enthalpy geothermal systems from the magma chamber as a driving heat source by several kilometers in the vertical direction in tectonic settings with hydrous magmatism. This hydrology would be in contrast to settings with anhydrous magmatism, where the base of the geothermal systems may be closer to the magma chamber.

Convective Performance of Nanofluids in Commercial Electronics Cooling Systems

International Nuclear Information System (INIS)

Roberts, N.A.; Walker, D.G.

2010-01-01

Nanofluids are stable engineered colloidal suspensions of a small fraction of nanoparticles in a base fluid. Nanofluids have shown great promise as heat transfer fluids over typically used base fluids and fluids with micron sized particles. Suspensions with micron sized particles are known to settle rapidly and cause clogging and damage to the surfaces of pumping and flow equipment. These problems are dramatically reduced in nanofluids. In the current work we investigate the performance of different volume loadings of water-based alumina nanofluids in a commercially available electronics cooling system. The commercially available system is a water block used for liquid cooling of a computational processing unit. The size of the nanoparticles in the study is 20-30 nm. Results show an enhancement in convective heat transfer due to the addition of nanoparticles in the commercial cooling system with volume loadings of nanoparticles up to 1.5% by volume. The enhancement in the convective performance observed is similar to what has been reported in well controlled and understood systems and is commensurate with bulk models. The current nanoparticle suspensions showed visible signs of settling which varied from hours to weeks depending on the size of the particles used.

Fluid transportation mechanisms by a coupled system of elastic membranes and magnetic fluids

International Nuclear Information System (INIS)

Ido, Y.; Tanaka, K.; Sugiura, Y.

2002-01-01

The basic properties of the fluid transportation mechanism that is produced by the coupled waves propagating along a thin elastic membrane covering a magnetic fluid layer in a shallow and long rectangular vessel are investigated. It is shown that the progressive magnetic field induced by the rectangular pulses generates sinusoidal vibration of the displacement of elastic membrane and makes the system work more efficiently than the magnetic field induced by the pulse-width-modulation method

A 'backward' free-convective boundary layer

NARCIS (Netherlands)

Kuiken, H.K.

1981-01-01

In this paper the cooling of a low-heat-resistance sheet that moves downwards is considered. The free-convective velocities are assumed to be much larger than the velocity of the sheet. As a result the motion of the fluid is mainly towards the point where the sheet enters the system and a ‘backward’

Cumulus convection and the terrestrial water-vapor distribution

Science.gov (United States)

Donner, Leo J.

1988-01-01

Cumulus convection plays a significant role in determining the structure of the terrestrial water vapor field. Cumulus convection acts directly on the moisture field by condensing and precipitating water vapor and by redistributing water vapor through cumulus induced eddy circulations. The mechanisms by which cumulus convection influences the terrestrial water vapor distribution is outlined. Calculations using a theory due to Kuo is used to illustrate the mechanisms by which cumulus convection works. Understanding of these processes greatly aids the ability of researchers to interpret the seasonal and spatial distribution of atmospheric water vapor by providing information on the nature of sources and sinks and the global circulation.

Estimation of the effect of thermal convection and casing on the temperature regime of boreholes: a review

International Nuclear Information System (INIS)

Eppelbaum, L V; Kutasov, I M

2011-01-01

In a vertical borehole, free heat convection arises when the temperature gradient equals or exceeds the so-called critical gradient. The critical temperature gradient is expressed through the critical Rayleigh number and depends on two parameters: (a) the ratio of formation (casings) to fluid (gas) conductivities (λ f /λ) and (b) the convective parameter of the fluid. Both these parameters depend on the temperature (depth). An empirical equation for the critical Rayleigh number as a function of the ratio λ f /λ is suggested. For the 0–100 °C range, empirical equations for convective parameters of water and air are proposed. The analysis of the published results of field investigations in deep boreholes and modelling shows that the temperature disturbances caused by thermal convection do not exceed 0.01–0.05 °C. Thus, in deep wells the temperature deviations due to thermal convection are usually within the accuracy of the temperature surveys. However, due to convection cells the geothermal gradient cannot be determined with sufficient accuracy for short well sections. In shallow boreholes the effect of thermal convection is more essential (up to 3–5 °C). To reduce the effect of convection on the temperature regime in shallow observational wells, it is necessary to reduce the diameter of the wellbores and use well fillers (fluids and gases) with low values of the convective parameters. The field observations and numerical calculations indicate that the distorting effect due to casing pipes is small and its influence is localized to the ends of the pipes, and this effect is independent of time. (topical review)

Mechanism of chain formation in nanofluid based MR fluids

International Nuclear Information System (INIS)

Patel, Rajesh

2011-01-01

Mechanism of structure formation in bidispersed colloids is important for its physical and optical properties. It is microscopically observed that the mechanism of chain formation in magnetic nanofluid based magnetorheological (MR) fluid is quite different from that in the conventional MR fluid. Under the application of magnetic field the magnetic nanoparticles are filled inside the structural microcavities formed due to the association of large magnetic particles, and some of the magnetic nanoparticles are attached at the end of the chains formed by the large particles. The dipolar energy of the large particles in a magnetic nanofluid matrix becomes effective magnetic permeability (μ eff ) times smaller than that of the neutral medium. Inclusion of magnetic nanoparticles (∼10 nm) with large magnetic particles (∼3-5 μm) restricts the aggregation of large particles, which causes the field induced phase separation in MR fluids. Hence, nanofluid based MR fluids are more stable than conventional MR fluids, which subsequently increase their application potentiality. - Research highlights: → In bidispersed magnetic colloids nanoparticles are attached at the end of the chains formed by the large particles. → Inclusion of magnetic nanoparticles (∼10 nm) with large magnetic particles (∼3-5 m) restricts the aggregation of large particles. → Nanofluid based MR fluids are more stable than conventional MR fluids.

Measurement of the temperature of density maximum of water solutions using a convective flow technique

OpenAIRE

Cawley, M.F.; McGlynn, D.; Mooney, P.A.

2006-01-01

A technique is described which yields an accurate measurement of the temperature of density maximum of fluids which exhibit such anomalous behaviour. The method relies on the detection of changes in convective flow in a rectangular cavity containing the test fluid.The normal single-cell convection which occurs in the presence of a horizontal temperature gradient changes to a double cell configuration in the vicinity of the density maximum, and this transition manifests itself in changes in th...

Advances in cardiovascular fluid mechanics: bench to bedside.

Science.gov (United States)

Dasi, Lakshmi P; Sucosky, Philippe; de Zelicourt, Diane; Sundareswaran, Kartik; Jimenez, Jorge; Yoganathan, Ajit P

2009-04-01

This paper presents recent advances in cardiovascular fluid mechanics that define the current state of the art. These studies include complex multimodal investigations with advanced measurement and simulation techniques. We first discuss the complex flows within the total cavopulmonary connection in Fontan patients. We emphasize the quantification of energy losses by studying the importance of caval offsets as well as the differences among various Fontan surgical protocols. In our studies of the fluid mechanics of prosthetic heart valves, we reveal for the first time the full three-dimensional complexity of flow fields in the vicinity of bileaflet and trileaflet valves and the microscopic hinge flow dynamics. We also present results of these valves functioning in a patient-specific native aorta geometry. Our in vitro mitral valve studies show the complex mechanism of the native mitral valve apparatus. We demonstrate that the different components of the mitral valve have independent and synergistically complex functions that allow the valve to operate efficiently. We also show how valve mechanics change under pathological and repair conditions associated with enlarged ventricles. Finally, our ex vivo studies on the interactions between the aortic valve and its surrounding hemodynamic environment are aimed at providing insights into normal valve function and valve pathology. We describe the development of organ- and tissue-culture systems and the biological response of the tissue subjected to their respective simulated mechanical environment. The studies noted above have enhanced our understanding of the complex fluid mechanics associated with the cardiovascular system and have led to new translational technologies.

Instabilities in vertically vibrated fluid-grain systems.

Science.gov (United States)

King, P J; Lopez-Alcaraz, P; Pacheco-Martinez, H A; Clement, C P; Smith, A J; Swift, M R

2007-03-01

When a bed of fluid-immersed fine grains is exposed to vertical vibration a wealth of phenomena may be observed. At low frequencies a horizontal bed geometry is generally unstable and the bed breaks spatial symmetry, acquiring a tilt. At the same time it undergoes asymmetric granular convection. Fine binary mixtures may separate completely into layers or patterns of stripes. The separated regions may exhibit instabilities in which they undergo wave-like motion or exhibit quasi-periodic oscillations. We briefly review these and a number of related behaviours, identifying the physical mechanisms behind each. Finally, we discuss the magneto-vibratory separation of binary mixtures which results from exposing each component to a different effective gravity and describe the influence of a background fluid on this process.

Peculiarities of natural convective heat removal from complex pools

International Nuclear Information System (INIS)

Groetzbach, Guenther

2002-01-01

Considerable sensitivities are investigated in using natural convection for cooling large pools. Such a flow occurred in a sump cooling concept for a water cooled reactor. The related SUCOS model experiments were analyzed by means of the FLUTAN code. The numerical interpretations show, the natural convection in large pools is strongly influenced by local thermal disturbances, either due to structures in the fluid domain, or by bounding structures interacting thermally with the fluid. These experiment specific disturbances must be recorded in the numerical model in order to achieve adequate simulations of the heat transport. Some geometric imperfections of horizontal coolers or heaters could also have tremendous influences. As a consequence, not only the numerical model has to record all relevant phenomena as realistic as possible, but also the model experiment. (author)

Streaks to rings to vortex grids: generic patterns in transient convective spin up of an evaporating fluid.

Science.gov (United States)

Zhong, J-Q; Patterson, M D; Wettlaufer, J S

2010-07-23

We observe the transient formation of a ringed pattern state during spin up of an evaporating fluid on a time scale of order a few Ekman spin up times. The ringed state is probed using infrared thermometry and particle image velocimetry and it is demonstrated to be a consequence of the transient balance between Coriolis and viscous forces which dominate inertia, each of which are extracted from the measured velocity field. The breakdown of the ringed state is quantified in terms of the antiphasing of these force components which drives a Kelvin-Helmholtz instability and we show that the resulting vortex grid spacing scales with the ring wavelength. This is the fundamental route to quasi-two-dimensional turbulent vortex flow and thus may have implications in astrophysics and geophysics wherein rotating convection is ubiquitous.

AFDM: An Advanced Fluid-Dynamics Model

International Nuclear Information System (INIS)

Wilhelm, D.

1990-09-01

This volume describes the Advanced Fluid-Dynamics Model (AFDM) for topologies, flow regimes, and interfacial areas. The objective of these models is to provide values for the interfacial areas between all components existing in a computational cell. The interfacial areas are then used to evaluate the mass, energy, and momentum transfer between the components. A new approach has been undertaken in the development of a model to convect the interfacial areas of the discontinuous velocity fields in the three-velocity-field environment of AFDM. These interfacial areas are called convectible surface areas. The continuous and discontinuous components are chosen using volume fraction and levitation criteria. This establishes so-called topologies for which the convectible surface areas can be determined. These areas are functions of space and time. Solid particulates that are limited to being discontinuous within the bulk fluid are assumed to have a constant size. The convectible surface areas are subdivided to model contacts between two discontinuous components or discontinuous components and the structure. The models have been written for the flow inside of large pools. Therefore, the structure is tracked only as a boundary to the fluid volume without having a direct influence on velocity or volume fraction distribution by means of flow regimes or boundary layer models. 17 refs., 7 tabs., 18 figs

Categorization of Brazil nut effect and its reverse under less-convective conditions for microgravity geology

Science.gov (United States)

Chujo, Toshihiro; Mori, Osamu; Kawaguchi, Junichiro; Yano, Hajime

2018-03-01

Due to its important role in the sorting of particles on microgravity bodies by size, Brazil nut effect (BNE) is a major subject of study for understanding the evolution of planetesimals. Recent studies have revealed that the mechanism for the BNE on microgravity bodies is the percolation of particles or void-filling, rather than granular convection. This study also considers the mechanism for the BNE under `less-convective' conditions and introduces three categories of behaviour for particles that mainly depend on the dimensionless acceleration of vibration Γ (ratio of maximum acceleration to gravitational acceleration), using a simplified analytical model. The conditions for Γ proposed by the model for each category are verified by both numerical simulations and laboratory experiments. `Less-convective' conditions are realized by reducing the friction force between particles and the wall. We found three distinct behaviours of the particles when Γ > 1: the (i) `slow BNE', (ii) `fast BNE', and (iii) `fluid motion' (the reverse BNE may be induced), and the thresholds for Γ correspond well with those proposed by the simple model. We also applied this categorization to low-gravity environments and found that the categorization scales with gravity level. These results imply that laboratory experiments can provide knowledge of granular mobility on the surface of microgravity bodies.

A Course in Fluid Mechanics of Suspensions.

Science.gov (United States)

Davis, Robert H.

1989-01-01

Discusses a course focusing on fluid mechanics and physical chemistry of suspensions. Describes the main themes of the lectures and includes a list of course outlines. Possible textbooks and many journal articles are listed. (YP)

Penetrative convection at high Rayleigh numbers

Science.gov (United States)

Toppaladoddi, Srikanth; Wettlaufer, John S.

2018-04-01

We study penetrative convection of a fluid confined between two horizontal plates, the temperatures of which are such that a temperature of maximum density lies between them. The range of Rayleigh numbers studied is Ra=[0.01 ,4 ]106,108 and the Prandtl numbers are Pr=1 and 11.6. An evolution equation for the growth of the convecting region is obtained through an integral energy balance. We identify a new nondimensional parameter, Λ , which is the ratio of temperature difference between the stable and unstable regions of the flow; larger values of Λ denote increased stability of the upper stable layer. We study the effects of Λ on the flow field using well-resolved lattice Boltzmann simulations and show that the characteristics of the flow depend sensitively upon it. For the range Λ = , we find that for a fixed Ra the Nusselt number, Nu, increases with decreasing Λ . We also investigate the effects of Λ on the vertical variation of convective heat flux and the Brunt-Väisälä frequency. Our results clearly indicate that in the limit Λ →0 the problem reduces to that of the classical Rayleigh-Bénard convection.

A cyber-physical approach to experimental fluid mechanics

Science.gov (United States)

Mackowski, Andrew Williams

This Thesis documents the design, implementation, and use of a novel type of experimental apparatus, termed Cyber-Physical Fluid Dynamics (CPFD). Unlike traditional fluid mechanics experiments, CPFD is a general-purpose technique that allows one to impose arbitrary forces on an object submerged in a fluid. By combining fluid mechanics with robotics, we can perform experiments that would otherwise be incredibly difficult or time-consuming. More generally, CPFD allows a high degree of automation and control of the experimental process, allowing for much more efficient use of experimental facilities. Examples of CPFD's capabilites include imposing a gravitational force in the horizontal direction (allowing a test object to "fall" sideways in a water channel), simulating nonlinear springs for a vibrating fluid-structure system, or allowing a self-propelled body to move forward under its own force. Because experimental parameters (including forces and even the mass of the test object) are defined in software, one can define entire ensembles of experiments to run autonomously. CPFD additionally integrates related systems such as water channel speed control, LDV flow speed measurements, and PIV flowfield measurements. The end result is a general-purpose experimental system that opens the door to a vast array of fluid-structure interaction problems. We begin by describing the design and implementation of CPFD, the heart of which is a high-performance force-feedback control system. Precise measurement of time-varying forces (including removing effects of the test object's inertia) is more critical here than in typical robotic force-feedback applications. CPFD is based on an integration of ideas from control theory, fluid dynamics, computer science, electrical engineering, and solid mechanics. We also describe experiments using the CPFD experimental apparatus to study vortex-induced vibration (VIV) and oscillating-airfoil propulsion. We show how CPFD can be used to simulate

Evaporative and Convective Instabilities for the Evaporation of a Binary Mixture in a Bilayer System

Science.gov (United States)

Guo, Weidong; Narayanan, Ranga

2006-11-01

Evaporative convection in binary mixtures arises in a variety of industrial processes, such as drying of paint and coating technology. There have been theories devoted to this problem either by assuming a passive vapor layer or by isolating the vapor fluid dynamics. Previous work on evaporative and convective instabilities in a single component bilayer system suggests that active vapor layers play a major role in determining the instability of the interface. We have investigated the evaporation convection in binary mixtures taking into account the fluid dynamics of both phases. The liquid mixture and its vapor are assumed to be confined between two horizontal plates with a base state of zero evaporation but with linear vertical temperature profile. When the vertical temperature gradient reaches a critical value, the evaporative instability, Rayleigh and Marangoni convection set in. The effects of vapor and liquid depth, various wave numbers and initial composition of the mixture on the evaporative and convective instability are determined. The physics of the instability are explained and detailed comparison is made between the Rayleigh, Marangoni and evaporative convection in pure component and those in binary mixtures.

Self-sustained large-scale flow in turbulent cryogenic convection

Czech Academy of Sciences Publication Activity Database

Niemela, J. J.; Skrbek, Ladislav; Sreenivasan, K. R.; Donnelly, R. J.

2002-01-01

Roč. 126, 1/2 (2002), s. 297-302 ISSN 0022-2291 Institutional research plan: CEZ:AV0Z1010914 Keywords : thermal convection * turbulence * cryogenic Subject RIV: BK - Fluid Dynamics Impact factor: 1.139, year: 2002

Dynamics of polymeric liquids. Vol. 1, 2nd Ed.: Fluid mechanics

International Nuclear Information System (INIS)

Bird, R.B.; Armstrong, R.C.; Hassager, O.

1987-01-01

This book examines Newtonian liquids and polymer fluid mechanics. It begins with a review of the main ideas of fluid dynamics as well as key points of Newtonian fluids. Major revisions include extensive updating of all material and a greater emphasis on fluid dynamics problem solving. It presents summaries of experiments describing the difference between polymeric and simple fluids. In addition, it traces, roughly in historical order, various methods for solving polymer fluid dynamics problems

Recent developments of mathematical fluid mechanics

CERN Document Server

Giga, Yoshikazu; Kozono, Hideo; Okamoto, Hisashi; Yamazaki, Masao

2016-01-01

The book addresses recent developments of the mathematical research on the Navier-Stokes and Euler equations as well as on related problems. In particular, there are covered:   1) existence, uniqueness, and the regularity of weak solutions; 2) stability of the motion in rest and the asymptotic behavior of solutions; 3) singularity and blow-up of weak and strong solutions; 4) vorticity and energy conservation; 5) motions of rotating fluids, or of fluids surrounding a rotating body; 6) free boundary problems; 7) maximal regularity theory and other abstract results for mathematical fluid mechanics.   For this quarter century, these topics have been playing a central role in both pure and applied mathematics and having a great influence to the developm ent of the functional analysis, harmonic analysis and numerical analysis whose tools make a a substantial contribution to the investigation of nonlinear partial differential equations, particularly the Navier-Stokes and the Euler equations.      There are 24...

Mechanical testing of hydraulic fluids II; Mechanische Pruefung von Hydraulikfluessigkeiten II

Energy Technology Data Exchange (ETDEWEB)

Kessler, M.; Feldmann, D.G.; Laukart, V.

2001-09-01

Since May 1996 the Institute for Mechanical Engineering Design 1 of Technical University of Hamburg-Harburg is working on the topic of ''Mechanical Testing of Hydraulic fluids''. The first project lasting 2 1/2 years was completed in 1999, the results are published as the DGMK report 514. Within these project a testing principle for the ''mechanical testing'' of hydraulic fluids has been derived, a prototype of a test rig was designed and set in operation at the authors' institute. This DGMK-report 514-1 describes the results of the second project, which investigates the operating behaviour of the test-rig more in detail. Several test-runs with a total number of 11 different hydraulic fluids show the dependence of the different lubricating behaviour of the tested fluids and their friction and wear behaviour during the tests in a reproducible way. The aim of the project was to derive a testing principle including the design of a suitable test-rig for the mechanical testing of hydraulic fluids. Based on the described results it can be stated that with the developed test it is possible to test the lubricity of hydraulic fluids reproducible and in correlation to field experiences within a relatively short time, so the target was reached. (orig.)

Natural convection and dispersion in a tilted fracture

International Nuclear Information System (INIS)

Woods, A.W.; Linz, S.J.

1992-01-01

In many geophysical situations, fluid is contained in long narrow fractures embedded within an impermeable medium of different thermal conductivity; and there may be a uniform vertical temperature gradient imposed upon the system. We show that whenever the slot is tilted to the vertical, convection develops in the fluid, even if the background temperature increases with height. Using typical values for the physical properties of a water-filled fracture, we show that the Earth's geothermal gradient produces a convective flow in a fracture; this has an associated dispersion coefficient D T ∼10 2 -10 3 D in fractures about a centimetre wide. We show that this shear dispersion could transport radioactive material, of half-life 10 4 years, tens of metres along the fracture within one half-life; without this dispersion, the material would only diffuse a few metres along the fracture within one half-life. (author)

Education: DNA replication using microscale natural convection.

Science.gov (United States)

Priye, Aashish; Hassan, Yassin A; Ugaz, Victor M

2012-12-07

There is a need for innovative educational experiences that unify and reinforce fundamental principles at the interface between the physical, chemical, and life sciences. These experiences empower and excite students by helping them recognize how interdisciplinary knowledge can be applied to develop new products and technologies that benefit society. Microfluidics offers an incredibly versatile tool to address this need. Here we describe our efforts to create innovative hands-on activities that introduce chemical engineering students to molecular biology by challenging them to harness microscale natural convection phenomena to perform DNA replication via the polymerase chain reaction (PCR). Experimentally, we have constructed convective PCR stations incorporating a simple design for loading and mounting cylindrical microfluidic reactors between independently controlled thermal plates. A portable motion analysis microscope enables flow patterns inside the convective reactors to be directly visualized using fluorescent bead tracers. We have also developed a hands-on computational fluid dynamics (CFD) exercise based on modeling microscale thermal convection to identify optimal geometries for DNA replication. A cognitive assessment reveals that these activities strongly impact student learning in a positive way.

Numerical method for studying the circulation patterns of a fluid in a cavity

International Nuclear Information System (INIS)

Stephani, L.M.; Butler, T.D.

1975-10-01

The method incorporates three circulation-inducing mechanisms: (1) buoyancy induced by nonuniform initial distribution of heat throughout the fluid, (2) buoyancy induced by removal of heat from the fluid, and (3) forced convection induced by withdrawal of heated fluid and return of cooled fluid. A two-dimensional computer program, CIRCO, based on the Marker-and-Cell (MAC) technique, is used to study the circulation patterns. The report discusses the code and illustrates its capabilities by means of examples from studies conducted for the Pacer project, which investigates the concept of producing electrical power from energy released by thermonuclear explosions in a salt dome. Efficient engineering for withdrawing energy from the cavity requires an understanding of the circulation patterns of the heated fluid. CIRCO provides this information in the form of computer-generated plots

Solar Hot Water Heating by Natural Convection.

Science.gov (United States)

Noble, Richard D.

1983-01-01

Presents an undergraduate laboratory experiment in which a solar collector is used to heat water for domestic use. The working fluid is moved by natural convection so no pumps are required. Experimental apparatus is simple in design and operation so that data can be collected quickly and easily. (Author/JN)

The Weight Loss Effect of Heated Inner Cylinder by Free Convection in Horizontal Cylindrical Enclosure

Science.gov (United States)

Sboev, I. O.; Kondrashov, A. N.; Rybkin, K. A.; Burkova, L. N.; Goncharov, M. M.

2018-03-01

The work presents results of numerical simulations of natural convection in cavity formed by the surfaces of two horizontal coaxial cylinders. The temperature of the outer cylinder is constant. The area between the cylinders is filled with an ideal incompressible fluid. The inner cylinder is set as the heater. The solution of the equations of thermal convection in a two-dimensional approximation performed by the software package ANSYS Fluent with finite volume method. The study compares the results of numerical simulation with several well-known theoretical and experimental results. The nature of interaction of the inner cylinder with a convection current created in the gap was observed. It was shown that the flux appeared around a heated cylinder affects the weight of the heat source and causes an additional lift force from the surrounding fluid. The various Rayleigh numbers (from 1.0 ṡ 103 to 1.5 ṡ 106) and fluid with different Prandtl number (from 0.5 to 1.0 ṡ 105) are considered.

Magnetic particle mixing with magnetic micro-convection for microfluidics

International Nuclear Information System (INIS)

Kitenbergs, Guntars; Erglis, Kaspars; Perzynski, Régine; Cēbers, Andrejs

2015-01-01

In this paper we discuss the magnetic micro-convection phenomenon as a tool for mixing enhancement in microfluidics systems in cases when one of the miscible fluids is a magnetic particle colloid. A system of a water-based magnetic fluid and water is investigated experimentally under homogeneous magnetic field in a Hele–Shaw cell. Subsequent image analysis both qualitatively and quantitatively reveals the high enhancement of mixing efficiency provided by this method. The mixing efficiency dependence on the magnetic field and the physical limits is discussed. A suitable model for a continuous-flow microfluidics setup for mixing with magnetic micro-convection is also proposed and justified with an experiment. In addition, possible applications in improving the speed of ferrohydrodynamic sorting and magnetic label or selected tracer mixing in lab on a chip systems are noted. - Highlights: • We study the magnetic micro-convection as a mixing method in microfluidics. • We show that the method enhances mixing with magnetic field squared dependency. • We propose a flow cell setup for mixing and justify it with a sample experiment. • The mixing method can be easily implemented in an existing microfluidics setup

Electroresponsive Aqueous Silk Protein As “Smart” Mechanical Damping Fluid

Science.gov (United States)

2015-01-01

Here we demonstrate the effectiveness of an electroresponsive aqueous silk protein polymer as a smart mechanical damping fluid. The aqueous polymer solution is liquid under ambient conditions, but is reversibly converted into a gel once subjected to an electric current, thereby increasing or decreasing in viscosity. This nontoxic, biodegradable, reversible, edible fluid also bonds to device surfaces and is demonstrated to reduce friction and provide striking wear protection. The friction and mechanical damping coefficients are shown to modulate with electric field exposure time and/or intensity. Damping coefficient can be modulated electrically, and then preserved without continued power for longer time scales than conventional “smart” fluid dampers. PMID:24750065

Heat Transfer and Fluid Mechanics Institute, 30th, California State University, Sacramento, May 28, 29, 1987, Proceedings

International Nuclear Information System (INIS)

Reardon, F.H.; Thinh, N.D.

1987-01-01

Experimental and analytical techniques in heat transfer and fluid dynamics and state-of-the-art applications are examined in reviews and reports. Topics discussed include the recirculation characteristics of a vortex pump, simulation of radial-flow impellers using the Navier-Stokes equations, the transient effect in composite-medium conduction or diffusion, flow in a tube with a porous obstruction, the measurement of the physical heat-transfer coefficient, and a penalty FEM for combined forced and free convection in a rectangular enclosure. Consideration is given to heat transfer in the entrance region of multiply connected ducts, working-fluid selection for low-temperature Rankine cycles, a computational-experimental method for monitoring particulate flux in fluid streams, medical applications of a vortex aerosol generator, and the interaction of unlike propellant droplets in various reactive environments

Hydromagnetic natural convection flow between vertical parallel plates with time-periodic boundary conditions

International Nuclear Information System (INIS)

Adesanya, S.O.; Oluwadare, E.O.; Falade, J.A.; Makinde, O.D.

2015-01-01

In this paper, the free convective flow of magnetohydrodynamic fluid through a channel with time periodic boundary condition is investigated by taking the effects of Joule dissipation into consideration. Based on simplifying assumptions, the coupled governing equations are reduced to a set of nonlinear boundary valued problem. Approximate solutions are obtained by using semi-analytical Adomian decomposition method. The effect of pertinent parameters on the fluid velocity, temperature distribution, Nusselt number and skin friction are presented graphically and discussed. The result of the computation shows that an increase in the magnetic field intensity has significant influence on the fluid flow. - Highlights: • The influence of magnetic field on the free convective fluid flow is considered. • The coupled equations are solved by using Adomian decomposition method. • The Adomian series solution agreed with previously obtained result. • Magnetic field decreases the velocity maximum but enhances temperature field

Thermal radiation and chemical reaction effects on MHD free convection heat and mass transfer in a micropolar fluid

International Nuclear Information System (INIS)

Srinivasacharya, D.; Mendu, Upendar

2011-01-01

The steady laminar free convection heat and mass transfer boundary layer flow of a thermomicropolar fluid past a non-isothermal vertical flat plate in the presence of a homogeneous first order chemical reaction and a radiation with transverse magnetic field has been reported. It has been established that the flow problem has similarity solutions when the variation in temperature of the plate and variation in concentration of the fluid are linear functions of the distance from the leading edge measured along the plate. The nonlinear governing equations of the flow along with their appropriate boundary conditions are initially cast into dimensionless forms using similarity transformations which are used to reduce the governing partial differential equations into ordinary differential equations. The resulting system of equations thus formed is then solved numerically by using the Keller-box method. The non-dimensional Nusselt number, Sherwood number and the skin friction coefficient and wall couple stress at the plate are derived, and a parametric study of the governing parameters, namely the magnetic field strength parameter, radiation parameter, chemical reaction parameter, Sherwood number profiles against to the coupling number as well as the skin friction coefficient, wall couple stress coefficient is conducted. (author)

Influence of Thermal Radiation on Unsteady Free Convection MHD Flow of Brinkman Type Fluid in a Porous Medium with Newtonian Heating

Directory of Open Access Journals (Sweden)

Farhad Ali

2013-01-01

Full Text Available The focus of this paper is to analyze the influence of thermal radiation on some unsteady magnetohydrodynamic (MHD free convection flows of an incompressible Brinkman type fluid past a vertical flat plate embedded in a porous medium with the Newtonian heating boundary condition. The fluid is considered as a gray absorbing-emitting but nonscattering medium and the Rosseland approximation in the energy equations is used to describe the radiative heat flux for optically thick fluid. For a detailed analysis of the problem, four important situations of flow due to (i impulsive motion of the plate (ii uniform acceleration of the plate (iii nonuniform acceleration of the plate, and (iv highly nonuniform acceleration of the plate are considered. The governing equations are first transformed into a system of dimensionless equations and then solved analytically using the Laplace transform technique. Numerical results for temperature and velocity are shown graphically, while skin friction and Nusselt number are computed in tables. The results show that temperature and velocity increase on increasing radiation and Newtonian heating parameters. However, the results of magnetic and porosity parameters on velocity are found quite opposite.

Direct simulation of natural convection in square porous enclosure

International Nuclear Information System (INIS)

Pourshaghaghy, A.; Hakkaki-Fard, A.; Mahdavi-Nejad, A.

2007-01-01

In this article, natural convection in a square porous enclosure is simulated by a direct numerical method. The solution method is based on a random distribution of solid blocks, which resembles the porous media within the cavity. The Navier-Stokes equations are solved directly in the fluid region without the assumption of volume averaging. The no-slip condition is applied on the surface of any solid particle, and the energy transport equation is solved separately for the solid phase and fluid flow. The local and average Nusselt numbers are presented for steady state for two different cases of thermal boundary conditions of the cavity walls. An oscillatory solution is observed for the local Nu number on the surface of the enclosure, and the critical Ra numbers are found in which natural convection flow is started within the cavity

Anti-collapse mechanism of CBM fuzzy-ball drilling fluid

Directory of Open Access Journals (Sweden)

Lihui Zheng

2016-03-01

Full Text Available Although fuzzy-ball drilling fluid has been successfully applied in CBM well drilling, it is necessary to study its anti-collapse mechanism so that adjustable coalbed sealing effects, controllable sealing strength, rational sealing cost and controllable reservoir damage degree can be realized. In this paper, laboratory measurement was performed on the uniaxial compressive strength of the plungers of No. 3 coalbed in the Qinshui Basin and the inlet pressure of Ø38 mm coal plunger displacement. The strengths of coal plungers were tested and compared after 2% potassium chloride solution, low-solids polymer drilling fluid and fuzzy-ball drilling fluid were injected into the coal plungers respectively. It is shown that coal strength rises by 38.46% after the fuzzy-ball drilling fluid is injected (in three groups; and that no fuzzy-ball drilling fluid is lost at the displacement pressures of 20.73 and 21.46 MPa, nor 2% potassium chloride solution is leaked at such pressures of 24.79 and 25.64 MPa after the plunger was sealed by the fuzzy-ball drilling fluid. This indicates that the fuzzy-ball drilling fluid can increase the formation resistance to fluid. Indoor microscopic observation was conducted on the sealing process of the fuzzy-ball drilling fluid in sand packs with coal cuttings of three grain sizes (60–80, 80–100 and 100–120 mesh. It is shown that the leakage pathways of different sizes are sealed by the vesicles in the form of accumulation, stretch and blockage. And there are vesicles at the inlet ends of the flowing pathways in the shape of beaded blanket. The impact force of drilling tools on the sidewalls is absorbed by the vesicles due to their elasticity and tenacity, so the sidewall instability caused by drilling tools is relieved. It is concluded that the main anti-collapse mechanisms of the CBM fuzzy-ball drilling fluid are to raise the coal strength, increase the formation resistance to fluid, and buffer the impact of

Convection flows driven by laser heating of a liquid layer

OpenAIRE

Rivière , David; Selva , Bertrand; Chraibi , Hamza; Delabre , Ulysse; Delville , Jean-Pierre

2016-01-01

International audience; When a fluid is heated by the absorption of a continuous laser wave, the fluid density decreases in the heated area. This induces a pressure gradient that generates internal motion of the fluid. Due to mass conservation, convection eddies emerge in the sample. To investigate these laser-driven bulk flows at the microscopic scale, we built a setup to perform temperature measurements with a fluorescent-sensitive dye on the one hand, and measured the flow pattern at diffe...

[Present status and trend of heart fluid mechanics research based on medical image analysis].

Science.gov (United States)

Gan, Jianhong; Yin, Lixue; Xie, Shenghua; Li, Wenhua; Lu, Jing; Luo, Anguo

2014-06-01

With introduction of current main methods for heart fluid mechanics researches, we studied the characteristics and weakness for three primary analysis methods based on magnetic resonance imaging, color Doppler ultrasound and grayscale ultrasound image, respectively. It is pointed out that particle image velocity (PIV), speckle tracking and block match have the same nature, and three algorithms all adopt block correlation. The further analysis shows that, with the development of information technology and sensor, the research for cardiac function and fluid mechanics will focus on energy transfer process of heart fluid, characteristics of Chamber wall related to blood fluid and Fluid-structure interaction in the future heart fluid mechanics fields.

Fluid mechanics of environmental interfaces

CERN Document Server

Gualtieri, Carlo

2008-01-01

Fluid Mechanics of Environmental Interfaces describes the concept of the environmental interface, defined as a surface between two either abiotic or biotic systems. These are in relative motion and exchange mass, heat and momentum through biophysical and/or chemical processes. These processes are fluctuating temporally and spatially.The book will be of interest to graduate students, PhD students as well as researchers in environmental sciences, civil engineering and environmental engineering, (geo)physics and applied mathematics.

Heat transfer by natural convection into an horizontal cavity

International Nuclear Information System (INIS)

Arevalo J, P.

1998-01-01

At this thesis it is studied the heat transfer by natural convection in an horizontal cavity, it is involved a boiling's part that is described the regimes and correlations differences for boiling's curve. It is designed a horizontal cavity for realize the experimental part and it's mention from equipment or instrumentation to succeed in a experimentation that permits to realize the analysis of heat transfer, handling as water fluid at atmospheric pressure and where it's present process from natural convection involving part boiling's subcooled. The system consists of heater zone submerged in a horizontal cavity with water. Once part finished experimental with information to obtained it's proceeded to obtain a correlation, realized starting from analysis dimensionless such as: Jakob, Bond and Grasoft (Boiling) besides of knows in natural convection: Prandtl and Nusselt. The mathematical model explains the behavior for natural convection continued part boiling's subcooled. It is realize analysis graphics too where it's show comparing with Globe Dropkin and Catton equations by natural convection with bottom heating. (Author)

Magnetohydrodynamic free convection in a strong cross field

NARCIS (Netherlands)

Kuiken, H.K.

1970-01-01

The problem of magnetohydrodynamic free convection of an electrically conducting fluid in a strong cross field is investigated. It is solved by using a singular perturbation technique. The solutions presented cover the range of Prandtl numbers from zero to order one. This includes both the important

Simulation of Thermomagnetic Convection in a Cavity Using the Lattice Boltzmann Model

Directory of Open Access Journals (Sweden)

Mahshid Hadavand

2011-01-01

Full Text Available Thermomagnetic convection in a differentially heated square cavity with an infinitely long third dimension is numerically simulated using the single relaxation time lattice Boltzmann method (LBM. This problem is of considerable interest when dealing with cooling of microelectronic devices, in situations where natural convection does not meet the cooling requirements, and forced convection is not viable due to the difficulties associated with pumping a ferrofluid. Therefore, circulation is achieved by imposing a magnetic field, which is created and controlled by placing a dipole at the bottom of the enclosure. The magnitude of the magnetic force is controlled by changing the electrical current through the dipole. In this study, the effects of combined natural convection and magnetic convection, which is commonly known as “thermomagnetic convection,” are analysed in terms of the flow modes and heat transfer characteristics of a magnetic fluid.

An integrated fluid-chemical model toward modeling the formation of intra-luminal thrombus in abdominal aortic aneurysms.

Science.gov (United States)

Biasetti, Jacopo; Spazzini, Pier Giorgio; Swedenborg, Jesper; Gasser, T Christian

2012-01-01

Abdominal Aortic Aneurysms (AAAs) are frequently characterized by the presence of an Intra-Luminal Thrombus (ILT) known to influence their evolution biochemically and biomechanically. The ILT progression mechanism is still unclear and little is known regarding the impact of the chemical species transported by blood flow on this mechanism. Chemical agonists and antagonists of platelets activation, aggregation, and adhesion and the proteins involved in the coagulation cascade (CC) may play an important role in ILT development. Starting from this assumption, the evolution of chemical species involved in the CC, their relation to coherent vortical structures (VSs) and their possible effect on ILT evolution have been studied. To this end a fluid-chemical model that simulates the CC through a series of convection-diffusion-reaction (CDR) equations has been developed. The model involves plasma-phase and surface-bound enzymes and zymogens, and includes both plasma-phase and membrane-phase reactions. Blood is modeled as a non-Newtonian incompressible fluid. VSs convect thrombin in the domain and lead to the high concentration observed in the distal portion of the AAA. This finding is in line with the clinical observations showing that the thickest ILT is usually seen in the distal AAA region. The proposed model, due to its ability to couple the fluid and chemical domains, provides an integrated mechanochemical picture that potentially could help unveil mechanisms of ILT formation and development.

Numerical Investigations of Mixed Convection of Incompressible Viscous Fluid in LNG Storage with a Various Locations of Input and Output Mass

Directory of Open Access Journals (Sweden)

Sklyarenko Kristina A.

2015-01-01

Full Text Available The article shows the results of mathematical simulation of mixed convection in the low-temperature storage of liquefied natural gas with a regenerative cooling. The regimes of mixed convection in a closed area with the different arrangement of the input and output sections of the masses are investigated. Two-dimensional nonstationary problem in the model of the Navier-Stokes in dimensionless variables “vorticity - stream function - temperature” was examined. Are obtained distributions of the hydrodynamic parameters and temperatures, characteristic basic laws governing the processes being investigated. Detailed circulating currents and carried out analysis of the mechanism of vortices formation and the temperature distribution in the solution for mixed convection mode with low Reynolds and Grashof numbers (Gr = 106, 100

Self-regulation in self-propelled nematic fluids.

Science.gov (United States)

Baskaran, A; Marchetti, M C

2012-09-01

We consider the hydrodynamic theory of an active fluid of self-propelled particles with nematic aligning interactions. This class of materials has polar symmetry at the microscopic level, but forms macrostates of nematic symmetry. We highlight three key features of the dynamics. First, as in polar active fluids, the control parameter for the order-disorder transition, namely the density, is dynamically convected by the order parameter via active currents. The resulting dynamical self-regulation of the order parameter is a generic property of active fluids and destabilizes the uniform nematic state near the mean-field transition. Secondly, curvature-driven currents render the system unstable deep in the nematic state, as found previously. Finally, and unique to self-propelled nematics, nematic order induces local polar order that in turn leads to the growth of density fluctuations. We propose this as a possible mechanism for the smectic order of polar clusters seen in numerical simulations.

Spinning Up Interest: Classroom Demonstrations of Rotating Fluid Dynamics

Science.gov (United States)

Aurnou, J.

2005-12-01

The complex relationship between rotation and its effect on fluid motions presents some of the most difficult and vexing concepts for both undergraduate and graduate level students to learn. We have found that student comprehension is greatly increased by the presentation of in-class fluid mechanics experiments. A relatively inexpensive experimental set-up consists of the following components: a record player, a wireless camera placed in the rotating frame, a tank of fluid, and food coloring. At my poster, I will use this set-up to carry out demonstrations that illustrate the Taylor-Proudman theorem, flow within the Ekman layer, columnar convection, and flow around high and low pressure centers. By sending the output of the wireless camera through an LCD projection system, such demonstrations can be carried out even for classes in large lecture halls.

Mechanics of solids and fluids

International Nuclear Information System (INIS)

Ziegler, F.

1991-01-01

This book is a comprehensive treatise on the mechanics of solids and fluids, with a significant application to structural mechanics. In reading through the text, I can not help being impressed with Dr. Ziegler's command of both historical and contemporary developments of theoretical and applied mechanics. The book is a unique volume which contains information not easily found throughout the related literature. The book opens with a fundamental consideration of the kinematics of particle motion, followed by those of rigid body and deformable medium .In the latter case, both small and finite deformation have been presented concisely, paving the way for the constitutive description given later in the book. In both chapters one and two, the author has provided sufficient applications of the theoretical principles introduced. Such a connection between theory and appication is a common theme throughout every chapter, and is quite an attractive feature of the book

Carbon Sequestration in Saline Aquifers: Modeling Diffusive and Convective Transport Of a Carbon-­Dioxide Cap

KAUST Repository

Allen, Rebecca

2011-01-01

done on the diffusive-convective transport that occurs under a cap of CO2-saturated fluid, which results after CO2 is injected into an aquifer and spreads laterally under an area of low permeability. The diffusive-convective modeling reveals an enhanced

Interpreting Students’ Perceptions in Fluid Mechanics Learning Outcomes

Directory of Open Access Journals (Sweden)

Filomena SOARES

2015-11-01

Full Text Available The objective of this study is to analyse the impact of introducing a practical work in the learning process of the Fluid Transport Systems course in Chemical Engineering degree. The students, in groups of two or three elements, were free to choose the application case in order to develop the practical work proposed by the responsible teachers. The students selected a centrifugal pump to supply water to houses or buildings and designed the piping system. The practical work was evaluated through the written report. The students’ perceptions were analysed through a questionnaire. The learning outcomes were also considered in order to understand how the fluid mechanics concepts were acquired. In the teachers’ point of view the teamwork should enable the development of students’ soft skills and competencies, promoting the ability to integrate and work in teams. The students changed their learning processing and perception becoming more reflective and less accommodative, forcing them to think critically and share opinions. Regarding the Fluid Mechanics assessment, the practical work increased, in average, the final grade at least one value.

Fluid mechanics and heat transfer spirally fluted tubing

Science.gov (United States)

Larue, J. C.; Libby, P. A.; Yampolsky, J. S.

1981-08-01

The objective of this program is to develop both a qualitative and a quantitative understanding of the fluid mechanics and heat transfer mechanisms that underlie the measured performance of the spirally fluted tubes under development at General Atomic. The reason for the interest in the spirally fluted tubes is that results to date have indicated three advantages to this tubing concept: The fabrication technique of rolling flutes on strip and subsequently spiralling and simultaneously welding the strip to form tubing results in low fabrication costs, approximately equal to those of commercially welded tubing. The heat transfer coefficient is increased without a concomitant increase of the friction coefficient on the inside of the tube. In single-phase axial flow of water, the helical flutes continuously induce rotation of the flow both within and without the tube as a result of the effect of curvature. An increase in condensation heat transfer on the outside of the tube is achieved. In a vertical orientation with fluid condensing on the outside of the helically fluted tube, the flutes provide a channel for draining the condensed fluid.

Effect of density inversion on the transient natural convection of liquids in a cavity with a non darcian porous material

International Nuclear Information System (INIS)

Moraga, Nelson O; Vega, Sylvana A

2004-01-01

This work aims to describe the mechanics of fluids and heat transfer by natural convection in porous materials, full of liquid phase elements like gallium and water. The transient process occurs inside a cavity with two adiabatic and two isothermic walls, at different temperatures. The properties vary with the temperature and specifically include the non lineal variation of the density with the temperature, that is typical of these elements. The study uses a mathematical model based on continuity equations, lineal moment and energy, including transport by convection and by diffusion. The method of finite volumes is used for the numerical simulation. The results generated include the variation in time of the distributions of speed and temperature (CW)

A perturbational h4 exponential finite difference scheme for the convective diffusion equation

International Nuclear Information System (INIS)

Chen, G.Q.; Gao, Z.; Yang, Z.F.

1993-01-01

A perturbational h 4 compact exponential finite difference scheme with diagonally dominant coefficient matrix and upwind effect is developed for the convective diffusion equation. Perturbations of second order are exerted on the convective coefficients and source term of an h 2 exponential finite difference scheme proposed in this paper based on a transformation to eliminate the upwind effect of the convective diffusion equation. Four numerical examples including one- to three-dimensional model equations of fluid flow and a problem of natural convective heat transfer are given to illustrate the excellent behavior of the present exponential schemes. Besides, the h 4 accuracy of the perturbational scheme is verified using double precision arithmetic

A blended learning approach to teach fluid mechanics in engineering

Science.gov (United States)

Rahman, Ataur

2017-05-01

This paper presents a case study on the teaching and learning of fluid mechanics at the University of Western Sydney (UWS), Australia, by applying a blended learning approach (BLA). In the adopted BLA, various flexible learning materials have been made available to the students such as online recorded lectures, online recorded tutorials, hand written tutorial solutions, discussion board and online practice quizzes. The lecture and tutorial class times have been primarily utilised to discuss confusing topics and engage students with practical issues in applying the theories learnt in fluid mechanics. Based on the data of over 734 students over a 4-year period, it has been shown that a BLA has improved the learning experience of the fluid mechanics students in UWS. The overall percentage of student satisfaction in this subject has increased by 18% in the BLA case compared with the traditional one.

Magnetic Fields in the Solar Convection Zone

Directory of Open Access Journals (Sweden)

Fan Yuhong

2004-07-01

Full Text Available Recent studies of the dynamic evolution of magnetic flux tubes in the solar convection zone are reviewed with focus on emerging flux tubes responsible for the formation of solar active regions. The current prevailing picture is that active regions on the solar surface originate from strong toroidal magnetic fields generated by the solar dynamo mechanism at the thin tachocline layer at the base of the solar convection zone. Thus the magnetic fields need to traverse the entire convection zone before they reach the photosphere to form the observed solar active regions. This review discusses results with regard to the following major topics: 1. the equilibrium properties of the toroidal magnetic fields stored in the stable overshoot region at the base of the convection zone, 2. the buoyancy instability associated with the toroidal magnetic fields and the formation of buoyant magnetic flux tubes, 3. the rise of emerging flux loops through the solar convective envelope as modeled by the thin flux tube calculations which infer that the field strength of the toroidal magnetic fields at the base of the solar convection zone is significantly higher than the value in equipartition with convection, 4. the minimum twist needed for maintaining cohesion of the rising flux tubes, 5. the rise of highly twisted kink unstable flux tubes as a possible origin of d -sunspots, 6. the evolution of buoyant magnetic flux tubes in 3D stratified convection, 7. turbulent pumping of magnetic flux by penetrative compressible convection, 8. an alternative mechanism for intensifying toroidal magnetic fields to significantly super-equipartition field strengths by conversion of the potential energy associated with the superadiabatic stratification of the solar convection zone, and finally 9. a brief overview of our current understanding of flux emergence at the surface and post-emergence evolution of the subsurface magnetic fields.

Topology optimisation of natural convection problems

DEFF Research Database (Denmark)

Alexandersen, Joe; Aage, Niels; Andreasen, Casper Schousboe

2014-01-01

This paper demonstrates the application of the density-based topology optimisation approach for the design of heat sinks and micropumps based on natural convection effects. The problems are modelled under the assumptions of steady-state laminar flow using the incompressible Navier-Stokes equations...... coupled to the convection-diffusion equation through the Boussinesq approximation. In order to facilitate topology optimisation, the Brinkman approach is taken to penalise velocities inside the solid domain and the effective thermal conductivity is interpolated in order to accommodate differences...... in thermal conductivity of the solid and fluid phases. The governing equations are discretised using stabilised finite elements and topology optimisation is performed for two different problems using discrete adjoint sensitivity analysis. The study shows that topology optimisation is a viable approach...

Interfacial Fluid Mechanics A Mathematical Modeling Approach

CERN Document Server

Ajaev, Vladimir S

2012-01-01

Interfacial Fluid Mechanics: A Mathematical Modeling Approach provides an introduction to mathematical models of viscous flow used in rapidly developing fields of microfluidics and microscale heat transfer. The basic physical effects are first introduced in the context of simple configurations and their relative importance in typical microscale applications is discussed. Then,several configurations of importance to microfluidics, most notably thin films/droplets on substrates and confined bubbles, are discussed in detail.  Topics from current research on electrokinetic phenomena, liquid flow near structured solid surfaces, evaporation/condensation, and surfactant phenomena are discussed in the later chapters. This book also:  Discusses mathematical models in the context of actual applications such as electrowetting Includes unique material on fluid flow near structured surfaces and phase change phenomena Shows readers how to solve modeling problems related to microscale multiphase flows Interfacial Fluid Me...

Temperature-Driven Convection

Science.gov (United States)

Bohan, Richard J.; Vandegrift, Guy

2003-02-01

Warm air aloft is stable. This explains the lack of strong winds in a warm front and how nighttime radiative cooling can lead to motionless air that can trap smog. The stability of stratospheric air can be attributed to the fact that it is heated from above as ultraviolet radiation strikes the ozone layer. On the other hand, fluid heated from below is unstable and can lead to Bernard convection cells. This explains the generally turbulent nature of the troposphere, which receives a significant fraction of its heat directly from the Earth's warmer surface. The instability of cold fluid aloft explains the violent nature of a cold front, as well as the motion of Earth's magma, which is driven by radioactive heating deep within the Earth's mantle. This paper describes how both effects can be demonstrated using four standard beakers, ice, and a bit of food coloring.

Computational modelling in fluid mechanics

International Nuclear Information System (INIS)

Hauguel, A.

1985-01-01

The modelling of the greatest part of environmental or industrial flow problems gives very similar types of equations. The considerable increase in computing capacity over the last ten years consequently allowed numerical models of growing complexity to be processed. The varied group of computer codes presented are now a complementary tool of experimental facilities to achieve studies in the field of fluid mechanics. Several codes applied in the nuclear field (reactors, cooling towers, exchangers, plumes...) are presented among others [fr

Heat Transfer and Flows of Thermal Convection in a Fluid-Saturated Rotating Porous Medium

Directory of Open Access Journals (Sweden)

Jianhong Kang

2015-01-01

Full Text Available Thermal convection at the steady state for high Rayleigh number in a rotating porous half space is investigated. Taking into account the effect of rotation, Darcy equation is extended to incorporate the Coriolis force term in a rotating reference frame. The velocity and temperature fields of thermal convection are obtained by using the homotopy analysis method. The influences of Taylor number and Rayleigh number on the Nusselt number, velocity profile, and temperature distribution are discussed in detail. It is found that the Nusselt number decreases rapidly with the increase of Taylor number but tends to have an asymptotic value. Besides, the rotation can give rise to downward flow in contrast with the upward thermal convection.

Magnetohydrodynamics (MHD flow of a tangent hyperbolic fluid with nanoparticles past a stretching sheet with second order slip and convective boundary condition

Directory of Open Access Journals (Sweden)

Wubshet Ibrahim

Full Text Available This article presents the effect of thermal radiation on magnetohydrodynamic flow of tangent hyperbolic fluid with nanoparticle past an enlarging sheet with second order slip and convective boundary condition. Condition of zero normal flux of nanoparticles at the wall is used for the concentration boundary condition, which is the current topic that have yet to be studied extensively. The solution for the velocity, temperature and nanoparticle concentration is governed by parameters viz. power-law index (n, Weissenberg number We, Biot number Bi, Prandtl number Pr, velocity slip parameters δ and γ, Lewis number Le, Brownian motion parameter Nb and the thermophoresis parameter Nt. Similarity transformation is used to metamorphosed the governing non-linear boundary-value problem into coupled higher order non-linear ordinary differential equation. The succeeding equations were numerically solved using the function bvp4c from the matlab for different values of emerging parameters. Numerical results are deliberated through graphs and tables for velocity, temperature, concentration, the skin friction coefficient and local Nusselt number. The results designate that the skin friction coefficient Cf deplete as the values of Weissenberg number We, slip parameters γ and δ upturn and it rises as the values of power-law index n increase. The local Nusselt number -θ′(0 decreases as slip parameters γ and δ, radiation parameter Nr, Weissenberg number We, thermophoresis parameter Nt and power-law index n increase. However, the local Nusselt number increases as the Biot number Bi increase. Keywords: Tangent hyperbolic fluid, Second order slip flow, MHD, Convective boundary condition, Radiation effect, Passive control of nanoparticles

Analysis Of Convective Plane Stagnation Point Chemically Reactive Mhd Flow Past A Vertical Porous Plate With A Convective Boundary Condition In The Presence Of A Uniform Magnetic Field.

OpenAIRE

Adeniyan, A.,

2013-01-01

The numerical investigation of a stagnation point boundary layer flow , mass and heat transfer of a steady two dimensional , incompressible , viscous electrically conducting, chemically reacting laminar fluid over a vertical convectively heated , electrically neutral flat plate exposed to a transverse uniform magnetic field has been carried out to examine the influence of the simultaneous presence of the effects of a convective boundary condition, chemical reaction, heat transfer and suctio...

COUPLED CHEMOTAXIS FLUID MODEL

KAUST Repository

LORZ, ALEXANDER

2010-01-01

We consider a model system for the collective behavior of oxygen-driven swimming bacteria in an aquatic fluid. In certain parameter regimes, such suspensions of bacteria feature large-scale convection patterns as a result of the hydrodynamic

STAFAN, Fluid Flow, Mechanical Stress in Fractured Rock of Nuclear Waste Repository

International Nuclear Information System (INIS)

Huyakorn, P.; Golis, M.J.

1989-01-01

1 - Description of program or function: STAFAN (Stress And Flow Analysis) is a two-dimensional, finite-element code designed to model fluid flow and the interaction of fluid pressure and mechanical stresses in a fractured rock surrounding a nuclear waste repository. STAFAN considers flow behavior of a deformable fractured system with fracture-porous matrix interactions, the coupling effects of fluid pressure and mechanical stresses in a medium containing discrete joints, and the inelastic response of the individual joints of the rock mass subject to the combined fluid pressure and mechanical loading. 2 - Restrictions on the complexity of the problem: STAFAN does not presently contain thermal coupling, and it is unable to simulate inelastic deformation of the rock mass and variably saturated or two-phase flow in the fractured porous medium system

Fluid mechanics and heat transfer advances in nonlinear dynamics modeling

CERN Document Server

Asli, Kaveh Hariri

2015-01-01

This valuable new book focuses on new methods and techniques in fluid mechanics and heat transfer in mechanical engineering. The book includes the research of the authors on the development of optimal mathematical models and also uses modern computer technology and mathematical methods for the analysis of nonlinear dynamic processes. It covers technologies applicable to both fluid mechanics and heat transfer problems, which include a combination of physical, mechanical, and thermal techniques. The authors develop a new method for the calculation of mathematical models by computer technology, using parametric modeling techniques and multiple analyses for mechanical system. The information in this book is intended to help reduce the risk of system damage or failure. Included are sidebar discussions, which contain information and facts about each subject area that help to emphasize important points to remember.

Computational simulation of two-dimensional transient natural convection in volumetrically heated square enclosure

International Nuclear Information System (INIS)

Vieira, Camila Braga; Jian Su

2010-01-01

Natural convection is a physical phenomenon that has been investigated in nuclear engineering so as to provide information about heat transfer in severe accident conditions involving nuclear reactors. This research reported transient natural convection of fluids with uniformly distributed volumetrically heat generation in square cavity with isothermal side walls and adiabatic top/bottom walls. Two Prandtl numbers were considered, 0:0321 and 0:71. Direct numerical simulations were applied in order to obtain results about the velocities of the fluid in directions x and y. These results were used in Fast Fourier Transform, which showed the periodic, quasi-chaotic and chaotic behavior of transient laminar flow. (author)

Numerical simulation of helical-vortex effects in Rayleigh-Bénard convection

Directory of Open Access Journals (Sweden)

G. V. Levina

2006-01-01

Full Text Available A numerical approach is substantiated for searching for the large-scale alpha-like instability in thermoconvective turbulence. The main idea of the search strategy is the application of a forcing function which can have a physical interpretation. The forcing simulates the influence of small-scale helical turbulence generated in a rotating fluid with internal heat sources and is applied to naturally induced fully developed convective flows. The strategy is tested using the Rayleigh-Bénard convection in an extended horizontal layer of incompressible fluid heated from below. The most important finding is an enlargement of the typical horizontal scale of the forming helical convective structures accompanied by a cells merging, an essential increase in the kinetic energy of flows and intensification of heat transfer. The results of modeling allow explaining how the helical feedback can work providing the non-zero mean helicity generation and the mutual intensification of horizontal and vertical circulation, and demonstrate how the energy of the additional helical source can be effectively converted into the energy of intensive large-scale vortex flow.

Ten iterative steps for model development and evaluation applied to Computational Fluid Dynamics for Environmental Fluid Mechanic

NARCIS (Netherlands)

Blocken, B.J.E.; Gualtieri, C.

2012-01-01

Computational Fluid Dynamics (CFD) is increasingly used to study a wide variety of complex Environmental Fluid Mechanics (EFM) processes, such as water flow and turbulent mixing of contaminants in rivers and estuaries and wind flow and air pollution dispersion in urban areas. However, the accuracy

Natural convection in square enclosure induced by inner circular cylinder with time-periodic pulsating temperature

KAUST Repository

Huang, Zhu

2015-03-01

The periodic unsteady natural convection flow and heat transfer in a square enclosure containing a concentric circular cylinder is numerically studied. The temperature of the inner circular cylinder fluctuates periodically with time at higher averaged value while the temperature of the enclosure keeps lower constant, and the natural convection is driven by the temperature difference. The two-dimensional natural convection is simulated with high accuracy temporal spectral method and local radial basis functions method. The Rayleigh number is studied in the range 103 ≤ Ra ≤ 106, the temperature pulsating period ranges from 0.01 to 100 and the temperature pulsating amplitudes are a = 0.5, 1.0 and 1.5. Numerical results reveal that the fluid flow and heat transfer is strongly dependent on the pulsating temperature of inner cylinder. Comparing with the steady state natural convection, the heat transfer is enhanced generally for the time-periodic unsteady natural convection, and the local maximum heat transfer rate is observed for Ra = 105 and 106. Moreover, the phenomenon of backward heat transfer is discussed quantitatively. Also, the influence of pulsating temperature on the unsteady fluid flow and heat transfer are discussed and analyzed.

Oscillatory fluid flow influences primary cilia and microtubule mechanics.

Science.gov (United States)

Espinha, Lina C; Hoey, David A; Fernandes, Paulo R; Rodrigues, Hélder C; Jacobs, Christopher R

2014-07-01

Many tissues are sensitive to mechanical stimuli; however, the mechanotransduction mechanism used by cells remains unknown in many cases. The primary cilium is a solitary, immotile microtubule-based extension present on nearly every mammalian cell which extends from the basal body. The cilium is a mechanosensitive organelle and has been shown to transduce fluid flow-induced shear stress in tissues, such as the kidney and bone. The majority of microtubules assemble from the mother centriole (basal body), contributing significantly to the anchoring of the primary cilium. Several studies have attempted to quantify the number of microtubules emanating from the basal body and the results vary depending on the cell type. It has also been shown that cellular response to shear stress depends on microtubular integrity. This study hypothesizes that changing the microtubule attachment of primary cilia in response to a mechanical stimulus could change primary cilia mechanics and, possibly, mechanosensitivity. Oscillatory fluid flow was applied to two different cell types and the microtubule attachment to the ciliary base was quantified. For the first time, an increase in microtubules around primary cilia both with time and shear rate in response to oscillatory fluid flow stimulation was demonstrated. Moreover, it is presented that the primary cilium is required for this loading-induced cellular response. This study has demonstrated a new role for the cilium in regulating alterations in the cytoplasmic microtubule network in response to mechanical stimulation, and therefore provides a new insight into how cilia may regulate its mechanics and thus the cells mechanosensitivity. Copyright © 2014 Wiley Periodicals, Inc.

A consideration on pipe-wall thinning mechanisms from an aspect of fluid-mechanics

International Nuclear Information System (INIS)

Inada, Fumio; Yoneda, Kimitoshi; Morita, Ryo; Fujiwara, Kazutoshi; Furuya, Masahiro

2008-01-01

The contribution of the fluid mechanics to the piping wall thinning phenomena was investigated. It was shown that the fluid force to the wall was quite different between flow accelerated corrosion (FAC) and erosion. The turbulent mass transfer, which is one of the primary factors of FAC, was analogous to the turbulent heat transfer. The model that the molecular transport in the viscous sublayer nearby soon of wall was predominant was practicable. In addition, the mass transport was predicted using commercial codes of computational fluid dynamics. Some prediction results of the mass transfer in orifice and the elbow using above techniques were explained. (author)

Fluid Dynamics for Physicists

Science.gov (United States)

Faber, T. E.

1995-08-01

This textbook provides an accessible and comprehensive account of fluid dynamics that emphasizes fundamental physical principles and stresses connections with other branches of physics. Beginning with a basic introduction, the book goes on to cover many topics not typically treated in texts, such as compressible flow and shock waves, sound attenuation and bulk viscosity, solitary waves and ship waves, thermal convection, instabilities, turbulence, and the behavior of anisotropic, non-Newtonian and quantum fluids. Undergraduate or graduate students in physics or engineering who are taking courses in fluid dynamics will find this book invaluable.

Stanley Corrsin Award Talk: Fluid Mechanics of Fungi and Slime

Science.gov (United States)

Brenner, Michael

2013-11-01

There are interesting fluid mechanics problems everywhere, even in the most lowly and hidden corners of forest floors. Here I discuss some questions we have been working on in recent years involving fungi and slime. A critical issue for the ecology of fungi and slime is nutrient availability: nutrient sources are highly heterogeneous, and strategies are necessary to find food when it runs out. In the fungal phylum Ascomycota, spore dispersal is the primary mechanism for finding new food sources. The defining feature of this phylum is the ascus, a fluid filled sac from which spores are ejected, through a build up in osmotic pressure. We outline the (largely fluid mechanical) design constraints on this ejection strategy, and demonstrate how it provides strong constraints for the diverse morphologies of spores and asci found in nature. The core of the argument revisits a classical problem in elastohydrodynamic lubrication from a different perspective. A completely different strategy for finding new nutrient is found by slime molds and fungi that stretch out - as a single organism- over enormous areas (up to hectares) over forest floors. As a model problem we study the slime mold Physarum polycephalum, which forages with a large network of connected tubes on the forest floors. Localized regions in the network find nutrient sources and then pump the nutrients throughout the entire organism. We discuss fluid mechanical mechanisms for coordinating this transport, which generalize peristalsis to pumping in a heterogeneous network. We give a preliminary discussion to how physarum can detect a nutrient source and pump the nutrient throughout the organism.

Comparison of CFD Natural Convection and Conduction-only Models for Heat Transfer in the Yucca Mountain Project Drifts

International Nuclear Information System (INIS)

Hadgu, T.; Webb, S.; Itamura, M.

2004-01-01

Yucca Mountain, Nevada has been designated as the nation's high-level radioactive waste repository and the U.S. Department of Energy has been approved to apply to the U.S. Nuclear Regulatory Commission for a license to construct a repository. Heat transfer in the Yucca Mountain Project (YMP) drift enclosures is an important aspect of repository waste emplacement. Canisters containing radioactive waste are to be emplaced in tunnels drilled 500 m below the ground surface. After repository closure, decaying heat is transferred from waste packages to the host rock by a combination of thermal radiation, natural convection and conduction heat transfer mechanism?. Current YMP mountain-scale and drift-scale numerical models often use a simplified porous medium code to model fluid and heat flow in the drift openings. To account for natural convection heat transfer, the thermal conductivity of the air was increased in the porous medium model. The equivalent thermal conductivity, defined as the ratio of total heat flow to conductive heat flow, used in the porous media models was based on horizontal concentric cylinders. Such modeling does not effectively capture turbulent natural convection in the open spaces as discussed by Webb et al. (2003) yet the approach is still widely used on the YMP project. In order to mechanistically model natural convection conditions in YMP drifts, the computational fluid dynamics (CFD) code FLUENT (Fluent, Incorporated, 2001) has been used to model natural convection heat transfer in the YMP emplacement drifts. A two-dimensional (2D) model representative of YMP geometry (e.g., includes waste package, drip shield, invert and drift wall) has been developed and numerical simulations made (Francis et al., 2003). Using CFD simulation results for both natural convection and conduction-only heat transfer in a single phase, single component fluid, equivalent thermal conductivities have been calculated for different Rayleigh numbers. Correlation

Heat transfer and thermal stress analysis in fluid-structure coupled field

International Nuclear Information System (INIS)

Li, Ming-Jian; Pan, Jun-Hua; Ni, Ming-Jiu; Zhang, Nian-Mei

2015-01-01

In this work, three-dimensional simulation on conjugate heat transfer in a fluid-structure coupled field was carried out. The structure considered is from the dual-coolant lithium-lead (DCLL) blanket, which is the key technology of International Thermo-nuclear Experimental Reactor (ITER). The model was developed based on finite element-finite volume method and was employed to investigate mechanical behaviours of Flow Channel Insert (FCI) and heat transfer in the blanket under nuclear reaction. Temperature distribution, thermal deformation and thermal stresses were calculated in this work, and the effects of thermal conductivity, convection heat transfer coefficient and flow velocity were analyzed. Results show that temperature gradients and thermal stresses of FCI decrease when FCI has better heat conductivity. Higher convection heat transfer coefficient will result in lower temperature, thermal deformations and stresses in FCI. Analysis in this work could be a theoretical basis of blanket optimization. - Highlights: • We use FVM and FEM to investigate FCI structural safety considering heat transfer and FSI effects. • Higher convective heat transfer coefficient is beneficial for the FCI structural safety without much affect to bulk flow temperature. • Smaller FCI thermal conductivity can better prevent heat leakage into helium, yet will increase FCI temperature gradient and thermal stress. • Three-dimensional simulation on conjugate heat transfer in a fluid-structure coupled field was carried out

Fluid Temperature of Aero Hydraulic Systems

Directory of Open Access Journals (Sweden)

I. S. Shumilov

2016-01-01

Full Text Available In modern supersonic aircrafts due to aerodynamic skin heating a temperature of hydraulics environment significantly exceeds that of permissible for fluids used. The same problem exists for subsonic passenger aircrafts, especially for Airbuses, which have hydraulics of high power where convective heat transfer with the environment is insufficient and there is no required temperature control of fluid. The most significant in terms of heat flow is the flow caused by the loss of power to the pump and when designing the hydraulic system (HS it is necessary to pay very serious attention to it. To use a constant capacity pump is absolutely unacceptable, since HS efficiency in this case is extremely low, and the most appropriate are variable-capacity pumps, cut-off pumps, dual-mode pumps. The HS fluid cooling system should provide high reliability, lightweight, simple design, and a specified heat transfer in all flight modes.A system cooling the fluid by the fuel of feeding lines of the aircraft engines is the most effective, and it is widely used in supersonic aircrafts, where power of cooling system is essential. Subsonic aircrafts widely use convective heat exchangers. In thermal design of the aircraft hydraulics, the focus is generally given to the maximum and minimum temperatures of the HS fluid, the choice of the type of heat exchanger (convective or flow-through, the place of its installation. In calculating the operating temperature of a hydraulic system and its cooling systems it is necessary to determine an increase of the working fluid temperature when throttling it. There are three possible formulas to calculate the fluid temperature in throttling, with the error of a calculated temperature drop from 30% to 4%.The article considers the HS stationary and noon-stationary operating conditions and their calculation, defines temperatures of fluid and methods to control its specified temperature. It also discusses various heat exchanger schemes

Introductory fluid mechanics for physicists and mathematicians

CERN Document Server

Pert, Geoffrey J

2013-01-01

This textbook presents essential methodology for physicists of the theory and applications of fluid mechanics within a single volume.  Building steadily through a syllabus, it will be relevant to almost all undergraduate physics degrees which include an option on hydrodynamics, or a course in which hydrodynamics figures prominently.

Flippin' Fluid Mechanics--Comparison Using Two Groups

Science.gov (United States)

Webster, Donald R.; Majerich, David M.; Madden, Amanda G.

2016-01-01

A flipped classroom approach was implemented in an undergraduate fluid mechanics course. Students watched short, online video lectures before class, participated in active in-class problem solving sessions (in pairs), and completed individualized online quizzes weekly. In-class activities were designed to develop problem-solving skills and teach…

Magnetic particle mixing with magnetic micro-convection for microfluidics

OpenAIRE

Kitenbergs , Guntars; Erglis , Kaspars; Perzynski , Régine; Cēbers , Andrejs

2015-01-01

International audience; In this paper we discuss the magnetic micro-convection phenomenon as a tool for mixing enhancement in microfluidics systems in cases when one of the mis-cible fluids is a magnetic particle colloid. A system of a water-based magnetic fluid and water is investigated experimentally under homogeneous magnetic field in a Hele-Shaw cell. Subsequent image analysis both qualitatively and quan-titatively reveals the high enhancement of mixing efficiency provided by this method....

Flask fluid flow simulation using CFD

International Nuclear Information System (INIS)

Swindlehurst, W.E.; Livesey, E.; Worthington, D.

1989-01-01

BNFL and its subsidiary Company, PNTL, design and operate waterfilled LWR fuel transport flasks for the international transport of irradiated fuel. Although some 150 flasks are currently in operation, new flask designs are being developed. As part of the supporting R and D program, Computational Fluid Dynamics (CFD) codes are being investigated as a means of predicting fluid movements and temperatures within the complex internal geometry of flasks. The ability to simulate fluid flow is particularly important when convection heat transfer is significant. Although obviously relevant to water filled flasks, the technique is applicable to dry flask thermal assessments (where experience shows that convection heat transfer is often underestimated). Computational Fluid Dynamics has emerged in recent years as an important technique in engineering design and safety assessments. Cheaper computing and the development of general CFD codes allows complex engineering structures to be analyzed. However, because of this complexity, it is essential that the application and associated modeling assumptions are critically reviewed. To assess the ability of a CFD code to model flask internals, the code PHOENICS has been used to model the fluid movements in a BNFL Excellox-type flask and the results compared with test data

Axisymmetric free convection boundary-layer flow past slender bodies

NARCIS (Netherlands)

Kuiken, H.K.

1968-01-01

Radial curvature effects on axisymmetric free convection boundary-layer flow are investigated for vertical cylinders and cones for some special non-uniform temperature differences between the surface and the ambient fluid. The solution is given as a power series expansion, the first term being equal

An investigation of transition boiling mechanisms of subcooled water under forced convective conditions

Energy Technology Data Exchange (ETDEWEB)

Kwang-Won, Lee; Sang-Yong, Lee

1995-09-01

A mechanistic model for forced convective transition boiling has been developed to investigate transition boiling mechanisms and to predict transition boiling heat flux realistically. This model is based on a postulated multi-stage boiling process occurring during the passage time of the elongated vapor blanket specified at a critical heat flux (CHF) condition. Between the departure from nucleate boiling (DNB) and the departure from film boiling (DFB) points, the boiling heat transfer is established through three boiling stages, namely, the macrolayer evaporation and dryout governed by nucleate boiling in a thin liquid film and the unstable film boiling characterized by the frequent touches of the interface and the heated wall. The total heat transfer rates after the DNB is weighted by the time fractions of each stage, which are defined as the ratio of each stage duration to the vapor blanket passage time. The model predictions are compared with some available experimental transition boiling data. The parametric effects of pressure, mass flux, inlet subcooling on the transition boiling heat transfer are also investigated. From these comparisons, it can be seen that this model can identify the crucial mechanisms of forced convective transition boiling, and that the transition boiling heat fluxes including the maximum heat flux and the minimum film boiling heat flux are well predicted at low qualities/high pressures near 10 bar. In future, this model will be improved in the unstable film boiling stage and generalized for high quality and low pressure situations.

Carbon Sequestration in Saline Aquifers: Modeling Diffusive and Convective Transport Of a Carbon-­Dioxide Cap

KAUST Repository

Allen, Rebecca

2011-05-01

An increase in the earth’s surface temperature has been directly linked to the rise of carbon dioxide (CO2) levels In the atmosphere and an enhanced greenhouse effect. CO2 sequestration is one of the proposed mitigation Strategies in the effort to reduce atmospheric CO2 concentrations. Globally speaking, saline aquifers provide an adequate storage capacity for the world’s carbon emissions, and CO2 sequestration projects are currently underway in countries such as Norway, Germany, Japan, USA, and others. Numerical simulators serve as predictive tools for CO2 storage, yet must model fluid transport behavior while coupling different transport processes together accurately. With regards to CO2 sequestration, an extensive amount of research has been done on the diffusive-convective transport that occurs under a cap of CO2-saturated fluid, which results after CO2 is injected into an aquifer and spreads laterally under an area of low permeability. The diffusive-convective modeling reveals an enhanced storage capacity in saline aquifers, due to the density increase between pure fluid and CO2‐saturated fluid. This work presents the transport modeling equations that are used for diffusive- convective modeling. A cell-centered finite difference method is used, and simulations are run using MATLAB. Two cases are explored in order to compare the results from this work’s self-generated code with the results published in literature. Simulation results match relatively well, and the discrepancy for a delayed onset time of convective transport observed in this work is attributed to numerical artifacts. In fact, onset time in this work is directly attributed to the instability of the physical system: this instability arises from non-linear coupling of fluid flow, transport, and convection, but is triggered by numerical errors in these simulations. Results from this work enable the computation of a value for the numerical constant that appears in the onset time equation that

Annual review of fluid mechanics. Volume 22

International Nuclear Information System (INIS)

Lumley, J.L.; Van Dyke, M.; Reed, H.L.

1990-01-01

Topics presented include rapid granular flows, issues in viscoelastic fluid mechanics, wave loads on offshore structures, boundary layers in the general ocean circulation, parametrically forced surface waves, wave-mean flow interactions in the equatorial ocean, and local and global instabilities in spatially developing flows. Also presented are aerodynamics of human-powered flight, aerothermodynamics and transition in high-speed wind tunnels at NASA-Langley, wakes behind blunt bodies, and mixing, chaotic advection, and turbulence. Also addressed are the history of the Reynolds number, panel methods in computational fluid dynamics, numerical multipole and boundary integral equation techniques in Stokes flow, plasma turbulence, optical rheometry, and viscous-flow paradoxes

Boiling Suppression in Convective Flow

International Nuclear Information System (INIS)

Aounallah, Y.

2004-01-01

The development of convective boiling heat transfer correlations and analytical models has almost exclusively been based on measurements of the total heat flux, and therefore on the overall two-phase heat transfer coefficient, when the well-known heat transfer correlations have often assumed additive mechanisms, one for each mode of heat transfer, convection and boiling. While the global performance of such correlations can readily be assessed, the predictive capability of the individual components of the correlation has usually remained elusive. This becomes important when, for example, developing mechanistic models for subcooled void formation based on the partitioning of the wall heat flux into a boiling and a convective component, or when extending a correlation beyond its original range of applications where the preponderance of the heat transfer mechanisms involved can be significantly different. A new examination of existing experimental heat transfer data obtained under fixed hydrodynamic conditions, whereby the local flow conditions are decoupled from the local heat flux, has allowed the unequivocal isolation of the boiling contribution over a broad range of thermodynamic qualities (0 to 0.8) for water at 7 MPa. Boiling suppression, as the quality increases, has consequently been quantified, thus providing valuable new insights on the functionality and contribution of boiling in convective flows. (author)

Teaching Fluid Mechanics to the Beginning Graduate Student--An Objective-Oriented Approach.

Science.gov (United States)

Liu, Henry

A premature embarkation in specialized areas of fluid mechanics by the beginning graduate student, without having first thoroughly learned the basics, leads to learning difficulties and destroys zeal for learning. To avoid these problems, many schools in the U.S. offer beginning graduate courses in fluid mechanics (BGCFM). Because the success or…

The Role of Rotation in Convective Heat Transport: an Application to Low-Mass Stars

Science.gov (United States)

Matilsky, Loren; Hindman, Bradley W.; Toomre, Juri; Featherstone, Nicholas

2018-06-01

It is often supposed that the convection zones (CZs) of low-mass stars are purely adiabatically stratified. This is thought to be because convective motions are extremely efficient at homogenizing entropy within the CZ. For a purely adiabatic fluid layer, only very small temperature variations are required to drive convection, making the amplitude and overall character of the convection highly sensitive to the degree of adiabaticity established in the CZ. The presence of rotation, however, fundamentally changes the dynamics of the CZ; the strong downflow plumes that are required to homogenize entropy are unable to penetrate through the entire fluid layer if they are deflected too soon by the Coriolis force. This talk discusses 3D global models of spherical-shell convection subject to different rotation rates. The simulation results emphasize the possibility that for stars with a high enough rotation rate, large fractions of their CZs are not in fact adiabatically stratified; rather, there is a finite superadiabatic gradient that varies in magnitude with radius, being at a minimum in the CZ’s middle layers. Two consequences of the varying superadiabatic gradient are that the convective amplitudes at the largest length scales are effectively suppressed and that there is a strong latitudinal temperature gradient from a cold equator to a hot pole, which self-consistently drives a thermal wind. A connection is naturally drawn to the Sun’s CZ, which has supergranulation as an upper limit to its convective length scales and isorotational contours along radial lines, which can be explained by the presence of a thermal wind.

Characterization of the Mechanical Properties of Electrorheological Fluids Made of Starch and Silicone Fluid

Science.gov (United States)

Vieira, Sheila Lopes; de Arruda, Antonio Celso Fonseca

In the majority of published articles on the topic, ER fluids have been studied as if they were viscous liquids. In this work, electrorheological fluids were characterized as solids and their mechanical properties were determined. The results infer that ER materials are controllably resistant to compression, tensile and shear stress, in this order of magnitude. More precisely, fluids made of starch have elasticity modulus similar to that of rubber, they have tensile strength 103 to 5×104 times lower than that of low density polyethylene (LDPE), static yield stress 4×104 to 8×105 times lower than that of acrylonitrile-butadiene-styrene terpolymer (ABS) and fatigue life similar to some polymers like polyethylene(PE) and polypropylene (PP).

Simulating deep convection with a shallow convection scheme

Directory of Open Access Journals (Sweden)

C. Hohenegger

2011-10-01

Full Text Available Convective processes profoundly affect the global water and energy balance of our planet but remain a challenge for global climate modeling. Here we develop and investigate the suitability of a unified convection scheme, capable of handling both shallow and deep convection, to simulate cases of tropical oceanic convection, mid-latitude continental convection, and maritime shallow convection. To that aim, we employ large-eddy simulations (LES as a benchmark to test and refine a unified convection scheme implemented in the Single-column Community Atmosphere Model (SCAM. Our approach is motivated by previous cloud-resolving modeling studies, which have documented the gradual transition between shallow and deep convection and its possible importance for the simulated precipitation diurnal cycle.

Analysis of the LES reveals that differences between shallow and deep convection, regarding cloud-base properties as well as entrainment/detrainment rates, can be related to the evaporation of precipitation. Parameterizing such effects and accordingly modifying the University of Washington shallow convection scheme, it is found that the new unified scheme can represent both shallow and deep convection as well as tropical and mid-latitude continental convection. Compared to the default SCAM version, the new scheme especially improves relative humidity, cloud cover and mass flux profiles. The new unified scheme also removes the well-known too early onset and peak of convective precipitation over mid-latitude continental areas.

Has the ultimate state of turbulent thermal convection been observed?

Czech Academy of Sciences Publication Activity Database

Skrbek, L.; Urban, Pavel

2015-01-01

Roč. 785, DEC (2015), s. 270-282 ISSN 0022-1120 R&D Projects: GA ČR GA14-02005S Institutional support: RVO:68081731 Keywords : turbulent convection * turbulent flows Subject RIV: BK - Fluid Dynamics Impact factor: 2.514, year: 2015

Temperature structure function in the Bolgiano regime of thermal convection

Czech Academy of Sciences Publication Activity Database

Skrbek, Ladislav; Niemela, J. J.; Sreenivasan, K. R.; Donnelly, J.

2002-01-01

Roč. 66, č. 3 (2002), 036303/1-036303/6 ISSN 1063-651X Institutional research plan: CEZ:AV0Z1010914 Keywords : thermal convection * temperature fluctuations * Bolgiano regime Subject RIV: BK - Fluid Dynamics Impact factor: 2.397, year: 2002

Analysis of natural convection heat transfer and flows in internally heated stratified liquid pools

International Nuclear Information System (INIS)

Gubaidullin, A.A. Jr.; Dinh, T.N.; Sehgal, B.R.

1999-01-01

In this paper, natural convection flows and heat transfer in a liquid pool, with two superposed immiscible fluid layers, are analyzed. The objective of the study is to examine the effect of interfacial hydrodynamics and to develop a method which enables energy splitting to be evaluated in a stratified liquid pool. The thermal convection, with and without an internal heat source, in a rectangular cavity with different pairs of fluids was numerically simulated by a CFD code FLOW-3D. It was found that the code performs very well for prediction of heat transfer coefficients for different conditions. The hydrodynamic coupling between immiscible layers was found to have minor, if any, impact on the natural convection heat transfer for the conditions examined. Calculated results were used to develop, and validate, a new correlation for energy splitting and for heat transfer in stratified liquid pools

Hydrothermal fluid flow within a tectonically active rift-ridge transform junction: Tjörnes Fracture Zone, Iceland

Science.gov (United States)

Lupi, M.; Geiger, S.; Graham, C. M.

2010-05-01

We investigate the regional fluid flow dynamics in a highly faulted transform area, the Tjörnes Fracture Zone in northern Iceland which is characterized by steep geothermal gradients, hydrothermal activity, and strong seismicity. We simulate fluid flow within the Tjörnes Fracture Zone using a high-resolution model that was based on the available geological and geophysical data and has the aim to represent the complex geological structures and the thermodynamical processes that drive the regional fluid flow in a physically realistic way. Our results show that convective heat flow and mixing of cold and saline seawater with deep hydrothermal fluids controls the large-scale fluid flow. The distribution of faults has a strong influence on the local hydrodynamics by focusing flow around clusters of faults. This explains the nature of isolated upflow zones of hot hydrothermal fluids which are observed in the Tjörnes Fracture Zone. An important emergent characteristic of the regional fluid flow in the Tjörnes Fracture Zone are two separate flow systems: one in the sedimentary basins, comprising more vigorous convection, and one in the crystalline basement, which is dominated by conduction. These two flow systems yield fundamental insight into the connection between regional hydrothermal fluid flow and seismicity because they form the basis of a toggle switch mechanism that is thought to have caused the hydrogeochemical anomalies recorded at Húsavik before and after the 5.8 M earthquake in September 2002.

Model of two-temperature convective transfer in porous media

Science.gov (United States)

Gruais, Isabelle; Poliševski, Dan

2017-12-01

In this paper, we study the asymptotic behaviour of the solution of a convective heat transfer boundary problem in an ɛ -periodic domain which consists of two interwoven phases, solid and fluid, separated by an interface. The fluid flow and its dependence with respect to the temperature are governed by the Boussinesq approximation of the Stokes equations. The tensors of thermal diffusion of both phases are ɛ -periodic, as well as the heat transfer coefficient which is used to describe the first-order jump condition on the interface. We find by homogenization that the two-scale limits of the solutions verify the most common system used to describe local thermal non-equilibrium phenomena in porous media (see Nield and Bejan in Convection in porous media, Springer, New York, 1999; Rees and Pop in Transport phenomena in porous media III, Elsevier, Oxford, 2005). Since now, this system was justified only by volume averaging arguments.

10,000 - A reason to study granular heat convection

Energy Technology Data Exchange (ETDEWEB)

Einav, I.; Rognon, P.; Gan, Y.; Miller, T.; Griffani, D. [Particles and Grains Laboratory, School of Civil Engineering, University of Sydney, Sydney, NSW 2006 (Australia)

2013-06-18

In sheared granular media, particle motion is characterized by vortex-like structures; here this is demonstrated experimentally for disks system undergoing indefinite deformation during simple shear, as often imposed by the rock masses hosting earthquake fault gouges. In traditional fluids it has been known for years that vortices represent a major factor of heat transfer enhancement via convective internal mixing, but in analyses of heat transfer through earthquake faults and base planes of landslides this has been continuously neglected. Can research proceed by neglecting heat convection by internal mixing? Our answer is astonishingly far from being yes.

Revisiting Newtonian and Non-Newtonian Fluid Mechanics Using Computer Algebra

Science.gov (United States)

Knight, D. G.

2006-01-01

This article illustrates how a computer algebra system, such as Maple[R], can assist in the study of theoretical fluid mechanics, for both Newtonian and non-Newtonian fluids. The continuity equation, the stress equations of motion, the Navier-Stokes equations, and various constitutive equations are treated, using a full, but straightforward,…

Onset of oscillatory binary fluid convection in three-dimensional cells

Energy Technology Data Exchange (ETDEWEB)

Alonso, Arantxa; Batiste, Oriol [Universitat Politecnica de Catalunya, Departament de Fisica Aplicada, Barcelona (Spain)

2004-11-01

The purpose of this work is to investigate the influence of the transverse walls on the onset of convection in a horizontal rectangular cavity of infinite length filled with a binary mixture when heated from below. For the first time we take into account the effect of the third dimension without making any approximation and considering realistic boundary conditions. In previous numerical works the width of the cell was either taken to be infinity (bulk mixtures) or different approximations usually valid in the narrow cell limit were assumed (i.e., Hele-Shaw and non-ideal Hele-Shaw approximations). The results we find show that the presence of the walls has a considerable effect on the onset of convection even for intermediate transverse aspect ratio cells. They also show that the approximations generally assumed fail to reproduce the correct behaviour of the critical parameters in an important range of aspect ratio values when the primary bifurcation is oscillatory. We have compared the critical values of the Rayleigh number and the frequency with those reported in the literature (Ohlsen et al. [1]) and we find a quantitative agreement within the experimental error. (orig.)

Heat Flux Sensors for Infrared Thermography in Convective Heat Transfer

Science.gov (United States)

Carlomagno, Giovanni Maria; de Luca, Luigi; Cardone, Gennaro; Astarita, Tommaso

2014-01-01

This paper reviews the most dependable heat flux sensors, which can be used with InfraRed (IR) thermography to measure convective heat transfer coefficient distributions, and some of their applications performed by the authors' research group at the University of Naples Federico II. After recalling the basic principles that make IR thermography work, the various heat flux sensors to be used with it are presented and discussed, describing their capability to investigate complex thermo-fluid-dynamic flows. Several applications to streams, which range from natural convection to hypersonic flows, are also described. PMID:25386758

Heat Flux Sensors for Infrared Thermography in Convective Heat Transfer

Directory of Open Access Journals (Sweden)

Giovanni Maria Carlomagno

2014-11-01

Full Text Available This paper reviews the most dependable heat flux sensors, which can be used with InfraRed (IR thermography to measure convective heat transfer coefficient distributions, and some of their applications performed by the authors’ research group at the University of Naples Federico II. After recalling the basic principles that make IR thermography work, the various heat flux sensors to be used with it are presented and discussed, describing their capability to investigate complex thermo-fluid-dynamic flows. Several applications to streams, which range from natural convection to hypersonic flows, are also described.

CISM course on stochastic methods in fluid mechanics

CERN Document Server

Chibbaro, Sergio

2013-01-01

Since their first introduction in natural sciences through the work of Einstein on Brownian motion in 1905 and further works, in particular by Langevin, Smoluchowski and others, stochastic processes have been used in several areas of science and technology. For example, they have been applied in chemical studies, or in fluid turbulence and for combustion and reactive flows. The articles in this book provide a general and unified framework in which stochastic processes are presented as modeling tools for various issues in engineering, physics and chemistry, with particular focus on fluid mechan

Transitions in rapidly rotating convection dynamos

Science.gov (United States)

Tilgner, A.

2013-12-01

It is commonly assumed that buoyancy in the fluid core powers the geodynamo. We study here the minimal model of a convection driven dynamo, which is a horizontal plane layer in a gravity field, filled with electrically conducting fluid, heated from below and cooled from above, and rotating about a vertical axis. Such a plane layer may be viewed as a local approximation to the geophysically more relevant spherical geometry. The numerical simulations have been run on graphics processing units with at least 960 cores. If the convection is driven stronger and stronger at fixed rotation rate, the flow behaves at some point as if it was not rotating. This transition shows in the scaling of the heat transport which can be used to distinguish slow from rapid rotation. One expects dynamos to behave differently in these two flow regimes. But even within the convection flows which are rapidly rotating according to this criterion, it will be shown that different types of dynamos exist. In one state, the magnetic field strength obeys a scaling indicative of a magnetostrophic balance, in which the Lorentz force is in equilibrium with the Coriolis force. The flow in this case is helical. A different state exists at higher magnetic Reynolds numbers, in which the magnetic energy obeys a different scaling law and the helicity of the flow is much reduced. As one increases the Rayleigh number, all other parameters kept constant, one may find both types of dynamos separated by an interval of Rayleigh numbers in which there are no dynamos at all. The effect of these transitions on energy dissipation and mean field generation have also been studied.

Multidomain multiphase fluid mechanics

International Nuclear Information System (INIS)

Sha, W.T.; Soo, S.L.

1976-10-01

A set of multiphase field equations--conversion of mass, momentum and energy--based on multiphase mechanics is developed. Multiphase mechanics applies to mixtures of phases which are separated by interfaces and are mutually exclusive. Based on the multiphase mechanics formulation, additional terms appear in the field equations when the physical size of the dispersed phase (bubble or droplet) is many times larger than the inter-molecular spacing. These terms are the inertial coupling due to virtual mass and the additional viscous coupling due to unsteadiness of the flow field. The multiphase formulation given here takes into account the discreteness of particles of dispersed phases and, at the same time, the necessity of the distributive representation of field variables via space-time averaging when handling a large number of particles. The provision for multidomain transition further permits us to treat dispersed phases which are large compared to the characteristic dimension of the flow system via interdomain relations. The multidomain multiphase approach provides a framework for us to model the various flow regimes. Because some of the transport parameters associated with the system equations are not well known at the present time, an idealized two-domain two-phase solution approach is proposed as a first step. Finally, comparisons are made between the field equations formulated based on the multidomain-multiphase fluid mechanics and the pertinent existing models, and their relative significances are discussed. The desirability of consistent approximation and simplifications possible for dilute suspensions are discussed

Effects of Thermal Radiation and Chemical Reaction on MHD Free Convection Flow past a Flat Plate with Heat Source and Convective Surface Boundary Condition

OpenAIRE

E.Hemalatha; N. Bhaskar Reddy

2015-01-01

This paper analyzes the radiation and chemical reaction effects on MHD steady two-dimensional laminar viscous incompressible radiating boundary layer flow over a flat plate in the presence of internal heat generation and convective boundary condition. It is assumed that lower surface of the plate is in contact with a hot fluid while a stream of cold fluid flows steadily over the upper surface with a heat source that decays exponentially. The Rosseland approximation is used to desc...

Teaching fluid mechanics to high schoolers: methods, challenges, and outcome

Science.gov (United States)

Manikantan, Harishankar

2017-11-01

This talk will summarize the goals, methods, and both short- and long-term feedback from two high-school-level courses in fluid mechanics involving 43 students and cumulatively spanning over 100 hours of instruction. The goals of these courses were twofold: (a) to spark an interest in science and engineering and attract a more diverse demographic into college-level STEM programs; and (b) to train students in a `college-like' method of approaching the physics of common phenomena, with fluid mechanics as the context. The methods of instruction included classes revolving around the idea of dispelling misconceptions, group activities, `challenge' rounds and mock design projects to use fluid mechanics phenomena to achieve a specified goal, and simple hands-on experiments. The feedback during instruction was overwhelmingly positive, particularly in terms of a changing and favorable attitude towards math and engineering. Long after the program, a visible impact lies in a diverse group of students acknowledging that the course had a positive effect in their decision to choose an engineering or science major in a four-year college.

New numerical approaches for modeling thermochemical convection in a compositionally stratified fluid

Science.gov (United States)

Puckett, Elbridge Gerry; Turcotte, Donald L.; He, Ying; Lokavarapu, Harsha; Robey, Jonathan M.; Kellogg, Louise H.

2018-03-01

Geochemical observations of mantle-derived rocks favor a nearly homogeneous upper mantle, the source of mid-ocean ridge basalts (MORB), and heterogeneous lower mantle regions. Plumes that generate ocean island basalts are thought to sample the lower mantle regions and exhibit more heterogeneity than MORB. These regions have been associated with lower mantle structures known as large low shear velocity provinces (LLSVPS) below Africa and the South Pacific. The isolation of these regions is attributed to compositional differences and density stratification that, consequently, have been the subject of computational and laboratory modeling designed to determine the parameter regime in which layering is stable and understanding how layering evolves. Mathematical models of persistent compositional interfaces in the Earth's mantle may be inherently unstable, at least in some regions of the parameter space relevant to the mantle. Computing approximations to solutions of such problems presents severe challenges, even to state-of-the-art numerical methods. Some numerical algorithms for modeling the interface between distinct compositions smear the interface at the boundary between compositions, such as methods that add numerical diffusion or 'artificial viscosity' in order to stabilize the algorithm. We present two new algorithms for maintaining high-resolution and sharp computational boundaries in computations of these types of problems: a discontinuous Galerkin method with a bound preserving limiter and a Volume-of-Fluid interface tracking algorithm. We compare these new methods with two approaches widely used for modeling the advection of two distinct thermally driven compositional fields in mantle convection computations: a high-order accurate finite element advection algorithm with entropy viscosity and a particle method that carries a scalar quantity representing the location of each compositional field. All four algorithms are implemented in the open source finite

Sparse identification of a predator-prey system from simulation data of a convection model

DEFF Research Database (Denmark)

Dam, Magnus; Brøns, Morten; Rasmussen, Jens Juul

2017-01-01

of a convection problem. A convection model with a pressure source centered at the inner boundary models the edge dynamics of a magnetically confined plasma. The convection problem undergoes a sequence of bifurcations as the strength of the pressure source increases. The time evolution of the energies......The use of low-dimensional dynamical systems as reduced models for plasma dynamics is useful as solving an initial value problem requires much less computational resources than fluid simulations. We utilize a data-driven modeling approach to identify a reduced model from simulation data...

Chaotic dynamics of large-scale double-diffusive convection in a porous medium

Science.gov (United States)