scholarly journals Bi-stability of a pendular disk in laminar and turbulent flows

2013 ◽  
Vol 728 ◽  
Author(s):  
M. Obligado ◽  
M. Puy ◽  
M. Bourgoin
Keyword(s):  
Turbulent Flows ◽  
Fluid Dynamic ◽  
Inclined Plate ◽  
Strongly Coupled ◽  
Turbulent Drag ◽  
Wide Range ◽  
Broad Variety ◽  
Fundamental Systems ◽  
The Impact ◽  
Laminar And Turbulent Flows

AbstractThe simple pendulum remains one of the most fundamental systems studied in physics. It is commonly used as a model to illustrate a broad variety of mechanisms in a wide range of areas. However, in spite of this popularity, subtle behaviours still remain to be discovered and to be explored when the pendulum is strongly coupled to fluid mechanics. This is for instance illustrated in recent studies by Neill, Livelybrooks & Donnelly (Am. J. Phys., vol. 75, 2007, pp. 226–229) and Bolster, Hershberger & Donnelly (Phys. Rev. E, vol. 81, 2010, pp. 1–6) which highlight the impact on a simple spherical pendulum of vortex shedding and added mass effects. In the present work we show that the equilibrium of a pendular disk facing a flow exhibits bi-stability and hysteresis. We give a simple interpretation of this behaviour in terms of a two-potential-well description, only requiring to know the angular dependence of the normal drag coefficient of an inclined plate. We investigate the influence of turbulence on the equilibrium of the pendulum in general and on the observed bi-stability in particular. Our results have potentially important fundamental and practical consequences: (i) they extend the attractiveness of the pendulum as a model to investigate generic questions related to bi-stable stochastic processes, (ii) they highlight important fluid dynamic mechanisms, including turbulent drag enhancement and fluid–structure interaction issues.

Coupled CFD-DEM modelling to assess settlement velocity and drag coefficient of microplastics

2020 ◽  
Author(s):  
Robin Jérémy ◽  
Latessa Pablo Gaston ◽  
Manousos Valyrakis
Keyword(s):  
Fluid Dynamics ◽  
Fresh Water ◽  
Turbulent Flows ◽  
Transport Processes ◽  
Water Bodies ◽  
World Health ◽  
Drinking Water Source ◽  
Drag Coefficients ◽  
Wide Range ◽  
The Impact

<p>Several studies have documented high concentration of microplastics on fresh water sources, oceans and even on treated tap and bottled water. Understanding the physics behind these particles in the water environment has become one of the key research needs identified in the World Health Organization Report (2019). In order to develop novel and efficient methodologies for sampling, treating and removing microplastics from water bodies, a thorough understanding of the sources and transportation and storage mechanisms of these particles is required.</p><p>In this article, the settlement velocity affecting the transport [1, 2] of low-density particles (1<r<1.4 g.cm<sup>-3</sup>) and drag coefficients is assessed through numerical modelling. The effects of fluid and particle relative densities and media temperatures are analysed, as well as the impact of the particle size and shapes [3].</p><p>Computational Fluid Dynamics (CFD) techniques are applied to solve the fluid dynamics while the Discrete Element Method (DEM) approach is used to model the particle trajectories [4]. These two modules are coupled under the CFDEM module, which transmits the forces from the fluid into the particle and from the particle into the surrounding water through the Fictitious Boundary Method approach.</p><p>Several tests are run under the same particle conditions in order to estimate the influence of turbulent flows on these experiments. The influence from different particle densities and diameters on settling velocities and drag coefficients is assessed. The numerical results are validated against a wide range of experimental data [2, 3] and compared against empirical predictions.</p><p>There is an urge for gaining a better understanding of the sources and transport of microplastics through fresh water bodies. In this sense, sampling and quantification of microplastics in a drinking water source is key to evaluate the environment status and to design the most appropriate techniques to reduce or remove the microplastics from the aquatic environments. The implementation of coupled CFD-DEM models provides a very powerful tool for the understanding and prediction of the transport processes and the accumulation of microplastics along the fluvial vectors.</p><p> </p><p>References</p><p>[1] Valyrakis M., Diplas P. and Dancey C.L. 2013. Entrainment of coarse particles in turbulent flows: An energy approach. J. Geophys. Res. Earth Surf., Vol. 118, No. 1., pp 42- 53, doi:340210.1029/2012JF002354.</p><p>[2] Valyrakis, M., Farhadi, H. 2017. Investigating coarse sediment particles transport using PTV and “smart-pebbles” instrumented with inertial sensors, EGU General Assembly 2017, Vienna, Austria, 23-28 April 2017, id. 9980.</p><p>[3] Valyrakis, M., J. Kh. Al-Hinai, D. Liu (2018), Transport of floating plastics along a channel with a vegetated riverbank, 12th International Symposium on Ecohydraulics, Tokyo, Japan, August 19-24, 2018, a11_2705647.</p><p>[4] Valyrakis M., P. Diplas, C.L. Dancey, and A.O. Celik. 2008. Investigation of evolution of gravel river bed microforms using a simplified Discrete Particle Model, International Conference on Fluvial Hydraulics River Flow 2008, Ismir, Turkey, 03-05 September 2008, 10p.</p>

scholarly journals High-beta turbulence in two-dimensional magnetohydrodynamics

1976 ◽  
Vol 16 (2) ◽  
pp. 181-191 ◽  
Author(s):  
David Fyfe ◽  
David Montgomery
Keyword(s):  
Magnetic Fields ◽  
Turbulent Flows ◽  
Fluid Dynamic ◽  
Fluid Velocity ◽  
Navier Stokes ◽  
Magnetic Islands ◽  
Dissipation Energy ◽  
Energy Cascades ◽  
Wide Range ◽  
Current Filaments

Incompressible turbulent flows are investigated in the framework of ideal magnetohydrodynamics. All the field quantities vary with only two spatial dimensions. Equilibrium canonical distributions are determined in a phase space whose co-ordinates are the real and imaginary parts of the Fourier coefficients for the field variables. In the geometry considered, the magnetic field and fluid velocity have variable x and y components, and all field quantities are independent of z. Three constants of the motion are found (one of them new) which survive the truncation in Fourier space and permit the construction of canonical distributions with three independent temperatures. Spectral densities are calculated. One of the more novel physical effects is the appearance of macroscopic structures involving long wavelength, self-generated, magnetic fields (‘magnetic islands’) for a wide range of initial parameters. Current filaments show a tendency toward consolidation in much the same way that vorticity filaments do in the guiding-centre plasma case. In the presence of finite dissipation, energy cascades to higher wavenumbers can be accompanied by vector potential cascades to lower wavenumbers, in much the same way as, in the fluid dynamic (Navier-Stokes) case, energy cascades to lower wavenumbers accompany enstrophy cascades to higher wavenumbers. It is suggested that the techniques may be relevant to theories of the magnetic dynamo problem and to the generation of megagauss magnetic fields when pellets are irradiated by lasers.

Multiphase CFD Model Development for a Rotating Centrifugal Separator

2012 ◽  
Author(s):  
Daniel DeMore ◽  
William Maier
Keyword(s):  
Separation Efficiency ◽  
Fluid Dynamic ◽  
Model Development ◽  
Modeling Method ◽  
Operating Conditions ◽  
Cfd Modeling ◽  
Separation Performance ◽  
Centrifugal Separator ◽  
Wide Range ◽  
The Impact

The present paper describes the development of a Computational Fluid Dynamic (CFD) modeling approach suitable for the analysis, design, and optimization of rotating centrifugal separator stage geometries. The Homogeneous Multiple Size Group (MUSIG) model implemented in the commercial code CFX V13.0 was utilized as a basis for the CFD modeling method. The model was developed through a series of studies to understand the impact of droplet size distribution, particle coalescence, rotor/stator interface treatment, and mesh resolution on the prediction of separation efficiency for a given rotating separator geometry. This model was then validated against the OEM’s extensive in-house experimental separation testing database. The resulting CFD modeling method is shown to adequately reproduce observed trends in separation performance over a wide range of operating conditions.

scholarly journals Análisis CFD de flujos turbulentos desplazados por bombas centrífugas con bajo número de Reynolds

2020 ◽  
Vol 1 (1) ◽  
pp. 1-9
Author(s):  
José Sánchez ◽  
Brando Hernández ◽  
Jorge Duarte Forero
Keyword(s):  
Virtual Environment ◽  
Centrifugal Pump ◽  
Turbulent Flows ◽  
Computational Effort ◽  
Laminar Flows ◽  
Science And Engineering ◽  
Wide Range ◽  
Mathematical Algorithms ◽  
Mechanical Devices ◽  
Laminar And Turbulent Flows

Numerical methodologies have presented an inexpensive solution of laminar and turbulent flows capable of predicting a wide range of mechanical devices in science and engineering. Computational tools have been employed in recent years to analyze the conservation equations behavior used to describe the interaction between turbulent and laminar flows used to transfer the energy needed to perform a complex mechanical system. Due to the above, this paper purpose the application of the numerical method linked to mathematical algorithms capable of generating an approximated solution of the partial differential equations system which determines pressure, and velocity values related to the centrifugal pump performance under low Re conditions in a virtual environment through OpenFOAM software, and Salome 8.3.0. An independence mesh analysis was computed to study the computational effort required to establish an approximated turbulence phenomena description performed by the centrifugal pump into the virtual environment supported by MRFSimpleFoam solver.

scholarly journals Dos and Don’ts When Developing a System to Investigate Spontaneous Imbibition in Unconsolicdated Porous Media

2019 ◽  
Vol 89 ◽  
pp. 01005 ◽  
Author(s):  
Bergit Brattekås ◽  
Tore L. Føyen ◽  
Trond Vabø ◽  
Håkon Haugland ◽  
Simon I. Reite ◽  
...  
Keyword(s):  
Porous Media ◽  
Oil Recovery ◽  
Fluid Dynamic ◽  
Water Soluble ◽  
Spontaneous Imbibition ◽  
Displacement Front ◽  
Wide Range ◽  
Unconsolidated Porous Media ◽  
The Impact ◽  
Wetting Fluid

This paper describes the development of a consistent model system to measure spontaneous imbibition and determine saturation functions in unconsolidated porous media. Sand grains or glass beads were packed in up to 0.5 m long, transparent glass tubes with optical access to local saturation development during spontaneous imbibition processes. The Two Ends Open-Free spontaneous imbibition (TEOFSI) boundary condition was used, where one end face is exposed to the wetting fluid and the other end to the non-wetting fluid. Dynamic measurement of the advancing displacement front and volumetric production from each open end-face enabled estimation of capillary pressure and relative permeability for the system. A range of wetting- and non-wetting phase viscosities and viscosity ratios was used during spontaneous imbibition in unconsolidated sand or glass packs. Wetting phase (water) viscosity was increased using water soluble glycerol or polymers. Air or mineral oil of varying composition provided a wide range of non-wetting phase viscosities. High permeable systems are extremely sensitive to laboratory properties, which may dominate the viscous resistance and determine flow behaviour. Systematic discrepancies observed in early testing indicated that end effects were present, even in long systems, in the filters at each end of the glass tube to maintain the grains or beads in place. Different filters were tested (no filter, glass, paper and micro-porous discs) to determine the impact of the filter on spontaneous imbibition. In addition to slower oil recovery than anticipated, developmentof a non-uniform displacement front was observed, demonstrating the large influence from minute heterogeneities within the packs, and at the end faces. A standard sand grain packing procedure, using a custom-designed packing device, was therefore developed to ensure homogeneous properties throughout theporous media, and limited the spread in porosity and permeability values. Homogeneous sand packs with reproducible properties are necessary, to systematically investigate flow parameters and changes in wettability in unconsolidated porous media.

Heat Transfer and Drag Reduction in Flows Over Riblet Mounted Surfaces

2003 ◽  
Author(s):  
Stefan aus der Wiesche
Keyword(s):  
Heat Transfer ◽  
Drag Reduction ◽  
Turbulent Flows ◽  
Numerical Data ◽  
Smooth Wall ◽  
Reynolds Analogy ◽  
Turbulent Drag ◽  
Prandtl Numbers ◽  
Laminar And Turbulent Flows ◽  
Good Agreement

The heat transfer in a channel with its lower wall mounted with streamwise V-shaped riblets is investigated numerically using a LES approach. Both laminar and turbulent flows are considered. At the riblet wall the turbulent drag is reduced by 6% in comparison to the smooth wall, whereas for laminar flow the riblets lead to a significant drag increase. The effect of riblets on heat transfer is investigated explicitly for small Prandtl numbers Pr and an appropriate correlation is derived. This correlation indicates that the Reynolds analogy is not violated in case of Pr = 1 despite the extraordinary turbulent drag reducing mechanism. The numerical results for drag reduction are in good agreement with available experimental and numerical data, and the results are faced with corresponding heat transfer results found in the literature.

Fluid-Dynamic Characterization of a CNG Injection System

2012 ◽  
Author(s):  
Mirko Baratta ◽  
Daniela Misul ◽  
Ezio Spessa ◽  
Giuseppe Gazzilli ◽  
Andrea Gerini
Keyword(s):  
Mass Flow ◽  
Fluid Dynamic ◽  
Injection System ◽  
Rail Pressure ◽  
Dynamic Characterization ◽  
Pressure Regulator ◽  
Fuel Mass ◽  
Wide Range ◽  
The Impact

A renewed interest in CNG fuelled engines, which has recently been boosted by the even more stringent emissions regulations, has generated considerable R&D activity in the last few years. In order to fulfill such limits, most current CNG vehicles combine advanced technical and control solutions such as VVA intake systems, new turbocharging solutions, enhanced ECU strategies, etc. The present work focuses on the complete fluid-dynamic characterization of a gaseous injection system so as to support the design of the related control module and devices. To that end, a numerical investigation into the fluid-dynamic behavior of a commercial CNG injection system has been extensively carried out by means of the GT-POWER code. A detailed geometrical model including the rail, the injectors as well as the pipe connecting the pressure regulator to the rail has been built in the GT-POWER environment. The model has been validated by comparing the experimental to the numerical outputs for the rail pressure and for the injected mass quantity. The model has hence been applied to the prediction of the pressure waves produced by the injection event and of their effect on the actually injected fuel mass. Moreover, the influence of the pressure regulator dynamics has been assessed by simulating the impact on the system behavior of a pressure noise downstream from the regulator. Finally, the possibility of reducing the rail volume, thus enhancing its dynamic response, has been investigated. The results have shown a good agreement between the predicted and the measured rail pressure and injected fuel mass flow rates over a wide range of engine operation conditions. Moreover, the dynamic simulations sketched a dependence of the injected fuel mass on the average rail pressure level, which in turn appeared to reduce for increasing engine power outputs. Finally, the reduction in the rail volume has proved not to significantly affect the injected mass flow rate.

THE IMPACT OF LEADERSHIP PRACTICES TO TEAM MEMBERS’ SATISFACTION

2009 ◽  
Vol 8 (1) ◽  
Author(s):  
Chalimah .
Keyword(s):  
Conflict Resolution ◽  
Leadership Practices ◽  
Hotel Industry ◽  
Leader Behavior ◽  
Team Leader ◽  
Shop Floor ◽  
Team Members ◽  
Top Executives ◽  
Wide Range ◽  
The Impact

eamwork is becoming increasingly important to wide range of operations. It applies to all levels of the company. It is just as important for top executives as it is to middle management, supervisors and shop floor workers. Poor teamwork at any level or between levels can seriously damage organizational effectiveness. The focus of this paper was therefore to examine whether leadership practices consist of team leader behavior, conflict resolution style and openness in communication significantly influenced the team member’s satisfaction in hotel industry. Result indicates that team leader behavior and the conflict resolution style significantly influenced team member satisfaction. It was surprising that openness in communication did not affect significantly to the team members’ satisfaction.

Strongly Coupled Redox-Linked Conformational Switching at the Active Site of the Non-Heme Iron-Dependent Dioxygenase, TauD

2019 ◽  
Author(s):  
Christopher John ◽  
Greg M. Swain ◽  
Robert P. Hausinger ◽  
Denis A. Proshlyakov
Keyword(s):  
Active Site ◽  
Structural Model ◽  
Heme Iron ◽  
Chemical Transformations ◽  
Experimental Conditions ◽  
Strongly Coupled ◽  
Non Heme Iron ◽  
Reversible Redox ◽  
Wide Range ◽  
Complex Structural

2-Oxoglutarate (2OG)-dependent dioxygenases catalyze C-H activation while performing a wide range of chemical transformations. In contrast to their heme analogues, non-heme iron centers afford greater structural flexibility with important implications for their diverse catalytic mechanisms. We characterize an <i>in situ</i> structural model of the putative transient ferric intermediate of 2OG:taurine dioxygenase (TauD) by using a combination of spectroelectrochemical and semi-empirical computational methods, demonstrating that the Fe (III/II) transition involves a substantial, fully reversible, redox-linked conformational change at the active site. This rearrangement alters the apparent redox potential of the active site between -127 mV for reduction of the ferric state and 171 mV for oxidation of the ferrous state of the 2OG-Fe-TauD complex. Structural perturbations exhibit limited sensitivity to mediator concentrations and potential pulse duration. Similar changes were observed in the Fe-TauD and taurine-2OG-Fe-TauD complexes, thus attributing the reorganization to the protein moiety rather than the cosubstrates. Redox difference infrared spectra indicate a reorganization of the protein backbone in addition to the involvement of carboxylate and histidine ligands. Quantitative modeling of the transient redox response using two alternative reaction schemes across a variety of experimental conditions strongly supports the proposal for intrinsic protein reorganization as the origin of the experimental observations.

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