Articoli di riviste: "Jets Fluid dynamics"

1

NORMAN, MICHAEL L. "Fluid Dynamics of Astrophysical Jets". Annals of the New York Academy of Sciences 617, n. 1 Nonlinear Ast (dicembre 1990): 217–33. http://dx.doi.org/10.1111/j.1749-6632.1990.tb37807.x.

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ESEN, OĞUL, e HASAN GÜMRAL. "LIFTS, JETS AND REDUCED DYNAMICS". International Journal of Geometric Methods in Modern Physics 08, n. 02 (marzo 2011): 331–44. http://dx.doi.org/10.1142/s0219887811005166.

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We show that complete cotangent lifts of vector fields, their decomposition into vertical representative and holonomic part provide a geometrical framework underlying Eulerian equations of continuum mechanics. We discuss Euler equations for ideal incompressible fluid and momentum-Vlasov equations of plasma dynamics in connection with the lifts of divergence-free and Hamiltonian vector fields, respectively. As a further application, we obtain kinetic equations of particles moving with the flow of contact vector fields both from Lie–Poisson reductions and with the techniques of present framework.

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Beutner, Thomas, e Christopher Rumsey. "Introduction: Computational Fluid Dynamics Validation for Synthetic Jets". AIAA Journal 44, n. 2 (febbraio 2006): 193. http://dx.doi.org/10.2514/1.22547.

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López-Arias, T., L. M. Gratton, G. Zendri e S. Oss. "Using jets of air to teach fluid dynamics". Physics Education 46, n. 4 (29 giugno 2011): 373–75. http://dx.doi.org/10.1088/0031-9120/46/4/f02.

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Ramos, J. I. "Fluid dynamics of slender, thin, annular liquid jets". International Journal for Numerical Methods in Fluids 21, n. 9 (15 novembre 1995): 735–61. http://dx.doi.org/10.1002/fld.1650210904.

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Murzabaeb, M. T., e A. L. Yarin. "Dynamics of sprinkler jets". Fluid Dynamics 20, n. 5 (1986): 715–22. http://dx.doi.org/10.1007/bf01050084.

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7

HERNÁNDEZ C., I., F. A. ACOSTA G., A. H. CASTILLEJOS E. e J. I. MINCHACA M. "The Fluid Dynamics of Secondary Cooling Air-Mist Jets". Metallurgical and Materials Transactions B 39, n. 5 (ottobre 2008): 746–63. http://dx.doi.org/10.1007/s11663-008-9179-x.

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8

Mitrovic, J., e A. Ricoeur. "Fluid dynamics and condensation-heating of capillary liquid jets". International Journal of Heat and Mass Transfer 38, n. 8 (maggio 1995): 1483–94. http://dx.doi.org/10.1016/0017-9310(94)00258-w.

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Miller, Steven A. E., Jérémy Veltin, Philip J. Morris e Dennis K. McLaughlin. "Assessment of Computational Fluid Dynamics for Supersonic Shock Containing Jets". AIAA Journal 47, n. 11 (novembre 2009): 2738–46. http://dx.doi.org/10.2514/1.44336.

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Milanovic, Ivana M., e K. B. M. Q. Zaman. "Fluid Dynamics of Highly Pitched and Yawed Jets in Crossflow". AIAA Journal 42, n. 5 (maggio 2004): 874–82. http://dx.doi.org/10.2514/1.2924.

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Kong, Qian, Shiqi Yang, Qisi Wang, Zhentao Wang, Qingming Dong e Junfeng Wang. "Dynamics of electrified jets in electrohydrodynamic atomization". Case Studies in Thermal Engineering 29 (gennaio 2022): 101725. http://dx.doi.org/10.1016/j.csite.2021.101725.

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Krutka, Holly M., Robert L. Shambaugh e Dimitrios V. Papavassiliou. "Using Computational Fluid Dynamics to Simulate Flow Fields from various Melt Blowing Dies". International Nonwovens Journal os-14, n. 1 (marzo 2005): 1558925005os—14. http://dx.doi.org/10.1177/1558925005os-1400101.

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This paper is an investigation of the flow fields generated by dual rectangular jets. Specifically, the jets examined are the same as the common slot dies used in the industrial melt blowing process. In this process, a molten polymer is attenuated by air discharging from dual jets. The velocity and turbulence of these flow fields determine the rate and quality of polymer fiber production. The flow field characteristics can be simulated quickly and efficiently using computational fluid dynamics (CFD). These CFD simulations require the use of an appropriate length scale to describe the flow field. This paper describes how these CFD simulations can be used to compare the flow fields generated by different jet geometries.

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Califano, F., e A. Mangeney. "Mixed layer in a stably stratified fluid". Nonlinear Processes in Geophysics 1, n. 4 (31 dicembre 1994): 199–208. http://dx.doi.org/10.5194/npg-1-199-1994.

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Abstract. We present a numerical study of the generation and evolution of a mixed layer in a stably stratified layer of Boussinesq fluid. We use an external forcing in the equation of motion to model the experimental situation where the mechanical energy input is due to an oscillating grid. The results of 2D and 3D numerical simulations indicate that the basic mechanism for the entrainment is the advection of the temperature field. This advection tends to produce horizontally thin regions of small temperature vertical gradients (jets) where the hydrodynamics forces are nearly zero. At the bottom of these structures, the buoyancy brakes the vertical motions. The jets are also characterized by the presence of very short horizontal scales where the thermal diffusion time turn out to be comparable with the dynamics time. As a result, the temperature field is well mixed in a few dynamics times. This process stops when the mechanical energy injected becomes comparable with the energy dissipated by viscosity.

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Atthanayake, I. U., P. Denissenko, Y. M. Chung e P. J. Thomas. "Formation–breakdown cycle of turbulent jets in a rotating fluid". Journal of Fluid Mechanics 868 (17 aprile 2019): 666–97. http://dx.doi.org/10.1017/jfm.2019.186.

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Results of comprehensive particle image velocimetry measurements investigating the dynamics of turbulent jets in a rotating fluid are presented. It is observed that background system rotation induces a time-periodic formation–breakdown cycle of the jets. The flow dynamics associated with this process is studied in detail. It is found that the frequency of the cycle increases linearly with the background rotation rate. The data show that the onset of the breakdown phase and of the reformation phase of the cycle can be characterized in terms of a local Rossby number employing an internal velocity and a length scale of the jet. The critical values for this local Rossby number, for onset of breakdown and reformation, scale linearly with a global Rossby number based on the flow conditions at the source. The analysis of the experimental data suggests centrifugal instability as the potential origin of the formation–breakdown cycle.

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Nguyen, Anh V., e Geoffrey M. Evans. "Computational fluid dynamics modelling of gas jets impinging onto liquid pools". Applied Mathematical Modelling 30, n. 11 (novembre 2006): 1472–84. http://dx.doi.org/10.1016/j.apm.2006.03.015.

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Bons, Jeffrey P., Rolf Sondergaard e Richard B. Rivir. "The Fluid Dynamics of LPT Blade Separation Control Using Pulsed Jets". Journal of Turbomachinery 124, n. 1 (1 febbraio 2001): 77–85. http://dx.doi.org/10.1115/1.1425392.

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The effects of pulsed vortex generator jets on a naturally separating low-pressure turbine boundary layer have been investigated experimentally. Blade Reynolds numbers in the linear turbine cascade match those for high-altitude aircraft engines and industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets (30 deg pitch and 90 deg skew angle) are pulsed over a wide range of frequency at constant amplitude and selected duty cycles. The resulting wake loss coefficient versus pulsing frequency data add to previously presented work by the authors documenting the loss dependency on amplitude and duty cycle. As in the previous studies, vortex generator jets are shown to be highly effective in controlling laminar boundary layer separation. This is found to be true at dimensionless forcing frequencies F+ well below unity and with low (10 percent) duty cycles. This unexpected low-frequency effectiveness is due to the relatively long relaxation time of the boundary layer as it resumes its separated state. Extensive phase-locked velocity measurements taken in the blade wake at an F+ of 0.01 with 50 percent duty cycle (a condition at which the flow is essentially quasi-steady) document the ejection of bound vorticity associated with a low-momentum fluid packet at the beginning of each jet pulse. Once this initial fluid event has swept down the suction surface of the blade, a reduced wake signature indicates the presence of an attached boundary layer until just after the jet termination. The boundary layer subsequently relaxes back to its naturally separated state. This relaxation occurs on a timescale which is five to six times longer than the original attachment due to the starting vortex. Phase-locked boundary layer measurements taken at various stations along the blade chord illustrate this slow relaxation phenomenon. This behavior suggests that some economy of jet flow may be possible by optimizing the pulse duty cycle and frequency for a particular application. At higher pulsing frequencies, for which the flow is fully dynamic, the boundary layer is dominated by periodic shedding and separation bubble migration, never recovering its fully separated (uncontrolled) state.

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Souza, Pedro R. C., Odenir de Almeida e Carlos R. Ilário da Silva. "Aeroacoustic Investigation of High Subsonic Jets in Crossflow". Journal of Theoretical and Computational Acoustics 26, n. 04 (dicembre 2018): 1850031. http://dx.doi.org/10.1142/s2591728518500317.

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The present work investigates the flow and the sound field generated by high subsonic jets in crossflow (JICF). The problem arises when a jet is exhausted perpendicularly into a moving medium. Although being characterized as a very complex flow, the JICF has a well-known fluid dynamics, but a sound field yet to be more explored. Therefore, a hybrid methodology of low computational cost aeroacoustic prediction tool is applied in this work for the complete investigation of this problem. A single jet operating at Mach number 0.75 in a crossflow regime with effective velocity ratios of 4 and 8 is studied herein. The fluid dynamics is solved by the Reynolds Average Navier–Stokes (RANS) equations, and the noise calculations are performed using a statistical method known as the Lighthill Ray-Tracing (LRT) method. The numerical results for the acoustic and flow fields were in reasonable agreement with the experimental data available showing good applicability of this kind of methodology for solving JICF.

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Khatri, Hemant, e Pavel Berloff. "Role of Eddies in the Maintenance of Multiple Jets Embedded in Eastward and Westward Baroclinic Shears". Fluids 3, n. 4 (11 novembre 2018): 91. http://dx.doi.org/10.3390/fluids3040091.

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Multiple zonal jets observed in many parts of the global ocean are often embedded in large-scale eastward and westward vertically sheared background flows. Properties of the jets and ambient eddies, as well as their dynamic interactions, are found to be different between eastward and westward shears. However, the impact of these differences on overall eddy dynamics remains poorly understood and is the main subject of this study. The roles of eddy relative vorticity and buoyancy fluxes in the maintenance of oceanic zonal jets are studied in a two-layer quasigeostrophic model. Both eastward and westward uniform, zonal vertically sheared cases are considered in the study. It is shown that, despite the differences in eddy structure and local characteristics, the fundamental dynamics are essentially the same in both cases: the relative-vorticity fluxes force the jets in the entire fluid column, and the eddy-buoyancy fluxes transfer momentum from the top to the bottom layer, where it is balanced by bottom friction. It is also observed that the jets gain more energy via Reynolds stress work in the layer having a positive gradient in the background potential vorticity, and this is qualitatively explained by a simple reasoning based on Rossby wave group velocity.

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Xianzhi, Song, Li Gensheng, Huang Zhongwei, Zhang Laibin, Tian Shouceng e Wang Haizhu. "Mechanism and Characteristics of Horizontal-Wellbore Cleanout by Annular Helical Flow". SPE Journal 19, n. 01 (25 giugno 2013): 45–54. http://dx.doi.org/10.2118/156335-pa.

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Summary Horizontal-wellbore cleanout by rotating jets and annular helical flow has developed rapidly in past decades, in which the annular helical flow is one of the most significant factors to transport the solids in a horizontal wellbore. Because of its complexity and lack of research approaches, the mechanism and characteristics of annular helical flow by high-pressure jets were never revealed comprehensively. By the computational-fluid-dynamics (CFD) method, the flow field of annular helical flow (such as its generation, continuation, and attenuation) was first manifested. The axial velocity and tangential velocity vary regarding cleaning distance, flow rate, and nozzle assemblies. Furthermore, the dynamic simulation of sandbed sweeping by rotating jets and annular helical flow in a horizontal wellbore was accomplished, and the influences on sweeping efficiency were discussed. Finally, the recommended nozzle assembly and its flow-rate distribution in front jets, lateral jets, and rear jets were provided. This study is beneficial in designing the cleaning tool and in optimizing the hydraulic parameters and operation procedures.

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Greenblatt, David, e David R. Williams. "Flow Control for Unmanned Air Vehicles". Annual Review of Fluid Mechanics 54, n. 1 (5 gennaio 2022): 383–412. http://dx.doi.org/10.1146/annurev-fluid-032221-105053.

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The pervasiveness of unmanned air vehicles (UAVs), from insect to airplane scales, combined with active flow control maturity, has set the scene for vehicles that differ markedly from present-day configurations. Nano and micro air vehicles, with characteristic Reynolds numbers typically less than 105, rely on periodically generated leading-edge vortices for lift generation, propulsion, and maneuvering. This is most commonly achieved by mechanical flapping or pulsed plasma actuation. On larger UAVs, with Reynolds numbers greater than 105, externally driven and autonomous fluidic systems continue to dominate. These include traditional circulation control techniques, autonomous synthetic jets, and discrete sweeping jets. Plasma actuators have also shown increased technological maturity. Energy efficiency is a major challenge, whether it be batteries and power electronics on nano and micro air vehicles or acceptably low compressor bleed on larger UAVs. Further challenges involve the development of aerodynamic models based on experiments or numerical simulations, as well as flight dynamics models.

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Xu, Peng, Agus Sasmito e Arun Mujumdar. "A computational study of heat transfer under twin turbulent slot jets impinging on planar smooth and rough surfaces". Thermal Science 20, suppl. 1 (2016): 47–57. http://dx.doi.org/10.2298/tsci151130016x.

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The flow and heat transfer characteristics of twin turbulent slot jets impinging on planar smooth and rough surfaces are examined using a computational fluid dynamics model. The interaction between jets lowers the heat transfer performance of each jet in the zone where the wall jets collide. A single jet performs better than the equivalent twin jet. The average heat transfer under twin jets which are injected alternately so that each one of the pair of jets behaves like a single jet, is found to be better than twin jets issuing simultaneously. It is proposed that alternating jet flows in the twin jet arrangement is a simple novel way to enhance thermal performance of jet pairs. Along with parametric studies of the key flow and geometric parameters, effects of large temperature differences between the jet air and the target surface being heated, and model roughness of the target surface are also evaluated. Interestingly, roughness can lower the heat transfer performance in the impingement zone as the fluid can get trapped in the valleys in the rough surface.

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GRINSTEIN, FERNANDO F. "Vortex dynamics and entrainment in rectangular free jets". Journal of Fluid Mechanics 437 (22 giugno 2001): 69–101. http://dx.doi.org/10.1017/s0022112001004141.

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Simulations of low-aspect-ratio, rectangular free jets are presented. The investigations focus on the entrainment and transitional vortex dynamics in compressible (subsonic) jets initialized with laminar conditions, a thin vortex sheet with slightly rounded-off corner regions, and uniform initial momentum thickness. A monotonically integrated large-eddy simulation approach based on the solution of the unsteady flow equations with high-resolution monotone algorithms is used. Inherent uncertainties in the jet entrainment measurement process are addressed using the database from laboratory experiments and simulations. Vorticity geometries characterizing the near flow field of low aspect-ratio (A) rectangular jets are demonstrated, involving: (i) self-deforming and (ii) splitting vortex rings; interacting ring and braid (rib) vortices including (iii) single ribs aligned with corner regions (A [ges ] 2) and (iv) rib pairs aligned with the corners (A = 1); (v) a more disorganized flow regime in the far jet downstream, where the rotational-fluid volume is occupied by a relatively weak vorticity background with strong, slender tube-like filament vortices filling a small fraction of the domain – as observed in fully developed turbulent flows. The near field entrainment properties of low-A rectangular jets are shown to be largely determined by the characteristic A-dependent coupling geometry of interacting rib and ring vortices and by vortex-ring axis-switching times.

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Yakhya, Saleh, Sami Ernez e François Morency. "Computational Fluid Dynamics Investigation of Transient Effects of Aircraft Ground Deicing Jets". Journal of Thermophysics and Heat Transfer 33, n. 1 (gennaio 2019): 117–27. http://dx.doi.org/10.2514/1.t5428.

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Rumsey, C. L., T. B. Gatski, W. L. Sellers, V. N. Vasta e S. A. Viken. "Summary of the 2004 Computational Fluid Dynamics Validation Workshop on Synthetic Jets". AIAA Journal 44, n. 2 (febbraio 2006): 194–207. http://dx.doi.org/10.2514/1.12957.

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Morris, R. M., J. A. Snyman e J. P. Meyer. "Jets in Crossflow Mixing Analysis Using Computational Fluid Dynamics and Mathematical Optimization". Journal of Propulsion and Power 23, n. 3 (maggio 2007): 618–28. http://dx.doi.org/10.2514/1.22136.

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Azim, M. A. "Isothermal free jets in high-temperature surroundings". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 225, n. 8 (16 maggio 2011): 1913–18. http://dx.doi.org/10.1177/0954406211401488.

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Two types of isothermal free jets, named positively and negatively buoyant, have been studied numerically to discern the effect of surrounding temperatures on their flow dynamics. Turbulence closure in those jets was achieved by standard k - ε model. The governing equations were solved using Implicit θ-Scheme and Tridiagonal Matrix Algorithm. Calculations were made for the jets having constant temperature at 20 °C and by varying surrounding temperatures from 20°C to 1000°C. It is clear that negatively buoyant jets but not the positively buoyant jets are nearly invariant to the change in surrounding temperatures compared to non-buoyant jet. Change in fluid dynamical behaviour of positively buoyant jets due to surrounding temperature change seems promising as it may offer the advantages of fuel jets in high-temperature air combustion.

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Madaliev, Murodil, Zokhidjon Abdulkhaev, Jamshidbek Otajonov, Khasanboy Kadyrov, Inomjan Bilolov, Sharabiddin Israilov e Nurzoda Abdullajonov. "Comparison of numerical results of turbulence models for the problem of heat transfer in turbulent molasses". E3S Web of Conferences 508 (2024): 05007. http://dx.doi.org/10.1051/e3sconf/202450805007.

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The study introduces Malikov's two-fluid methodology along with the RSM turbulence model for simulating turbulent heat transfer phenomena. It elucidates that temperature fluctuations within turbulent flows arise from temperature differentials between the respective fluids. Leveraging the two-fluid paradigm, the researchers develop a mathematical framework to characterize turbulent heat transfer dynamics. This resultant turbulence model is then applied to analyze heat propagation in turbulent flows around a flat plate and in scenarios involving submerged jets. To validate the model's efficacy, numerical outcomes are juxtaposed against established RSM turbulence models and experimental findings. The comparative analysis reveals that the two-fluid turbulent transport model aptly captures the thermodynamic behaviors inherent in turbulent flows with exceptional precision.

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Castillo, Luis G., José M. Carrillo e Álvaro Sordo-Ward. "Simulation of overflow nappe impingement jets". Journal of Hydroinformatics 16, n. 4 (18 gennaio 2014): 922–40. http://dx.doi.org/10.2166/hydro.2014.109.

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Rectangular jets constitute one of the energy dissipation methods in the overtopping of dams. The high turbulence and aeration phenomena that appear in falling jets and dissipation basins make it difficult to carry out studies based only on classical methodologies. There are studies modelling spillways with computational fluid dynamics which produces accurate results. However, the study of overflow nappe impingement jets has not been sufficiently examined. Simulations of free air–water overflow weirs are scarce, and require small mesh sizes and a high computational effort. This work seeks to address such simulation. Results obtained with ANSYS CFX are compared with laboratory measurements and empirical formulae. To identify the level of reliability of computed parameters, validation of air entrainment and velocity along free falling jets, thickness and break-up of jets, and pressures on the bottom of the plunge pool, are carried out by using a two-fluid model, turbulence models and mesh-size analysis. Good agreement is obtained with experimental and theoretical data. The results show that air entrainment in the jet is highly sensitive to the mesh size, while the choice of the turbulence model seems to have only a relative effect on the stagnation point.

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Fromm, C. M., Z. Younsi, A. Baczko, Y. Mizuno, O. Porth, M. Perucho, H. Olivares et al. "Using evolutionary algorithms to model relativistic jets". Astronomy & Astrophysics 629 (22 agosto 2019): A4. http://dx.doi.org/10.1051/0004-6361/201834724.

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Context. High-resolution very long baseline interferometry (VLBI) observations of NGC 1052 show a two sided jet with several regions of enhanced emission and a clear emission gap between the two jets. This gap shrinks with increasing frequency and vanishes around ν ∼ 43 GHz. The observed structures are due to both the macroscopic fluid dynamics interacting with the surrounding ambient medium including an obscuring torus and the radiation microphysics. In order to model the observations of NGC 1052 via state-of-the art numerical simulations both the fluid-dynamical and emission processes have to be taken into account. Aims. In this paper we investigate the possible physical conditions in relativistic jets of NGC 1052 by directly modelling the observed emission and spectra via state-of-the-art special-relativistic hydrodynamic (SRHD) simulations and radiative transfer calculations. Methods. We performed SRHD simulations of over-pressured and pressure-matched jets using the special-relativistic hydrodynamics code Ratpenat. To investigate the physical conditions in the relativistic jet we coupled our radiative transfer code to evolutionary algorithms and performed simultaneous modelling of the observed jet structure and the broadband radio spectrum. During the calculation of the radiation we consider non-thermal emission from the jet and thermal absorption in the obscuring torus. In order to compare our model to VLBI observations we take into account the sparse sampling of the u-v plane, the array properties and the imaging algorithm. Results. We present for the first time an end-to-end pipeline for fitting numerical simulations to VLBI observations of relativistic jets taking into account the macro-physics including fluid dynamics and ambient medium configurations together with thermal and non-thermal emission and the properties of the observing array. The detailed analysis of our simulations shows that the structure and properties of the observed relativistic jets in NGC 1052 can be reconstructed by a slightly over-pressured jet (dk ∼ 1.5) embedded in a decreasing pressure ambient medium

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Valizadeh, Alireza, Jason P. Antenucci e Grant Griffith. "REGULAR WAVE EFFECTS ON NEGATIVELY BUOYANT JETS". Coastal Engineering Proceedings, n. 36v (28 dicembre 2020): 13. http://dx.doi.org/10.9753/icce.v36v.waves.13.

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Seawater desalination is an increasingly important technology in the supply of potable water to municipal communities. Brine created by this process is typically released back to the ocean via a nearshore diffuser into a wave-exposed climate. Despite this, little work has been published on the effect of waves on negatively buoyant jets. In this paper we outline the literature on this topic and the results of a series of computational fluid dynamics (CFD) simulations that address the role of regular waves on negatively buoyant jets.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/0085wAVVybc

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Selimefendigil, Fatih, Hakan F. Oztop e Mikhail A. Sheremet. "Thermoelectric Generation with Impinging Nano-Jets". Energies 14, n. 2 (18 gennaio 2021): 492. http://dx.doi.org/10.3390/en14020492.

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In this study, thermoelectric generation with impinging hot and cold nanofluid jets is considered with computational fluid dynamics by using the finite element method. Highly conductive CNT particles are used in the water jets. Impacts of the Reynolds number of nanojet stream combinations (between (Re1, Re2) = (250, 250) to (1000, 1000)), horizontal distance of the jet inlet from the thermoelectric device (between (r1, r2) = (−0.25, −0.25) to (1.5, 1.5)), impinging jet inlet to target surfaces (between w2 and 4w2) and solid nanoparticle volume fraction (between 0 and 2%) on the interface temperature variations, thermoelectric output power generation and conversion efficiencies are numerically assessed. Higher powers and efficiencies are achieved when the jet stream Reynolds numbers and nanoparticle volume fractions are increased. Generated power and efficiency enhancements 81.5% and 23.8% when lowest and highest Reynolds number combinations are compared. However, the power enhancement with nanojets using highly conductive CNT particles is 14% at the highest solid volume fractions as compared to pure water jet. Impacts of horizontal location of jet inlets affect the power generation and conversion efficiency and 43% variation in the generated power is achieved. Lower values of distances between the jet inlets to the target surface resulted in higher power generation while an optimum value for the highest efficiency is obtained at location zh = 2.5ws. There is 18% enhancement in the conversion efficiency when distances at zh = ws and zh = 2.5ws are compared. Finally, polynomial type regression models are obtained for estimation of generated power and conversion efficiencies for water-jets and nanojets considering various values of jet Reynolds numbers. Accurate predictions are obtained with this modeling approach and it is helpful in assisting the high fidelity computational fluid dynamics simulations results.

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Scott, Lewis, Antonia Borissova, Alan Burns e Mojtaba Ghadiri. "Analysis of hold-up and grinding pressure in a spiral jet mill using CFD-DEM". EPJ Web of Conferences 249 (2021): 12004. http://dx.doi.org/10.1051/epjconf/202124912004.

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A spiral jet mill was simulated using Discrete Element Method modelling and Computational Fluid Dynamics. The particle behaviour and fluid motion were analysed as a function of hold-up and grinding pressure. Particle collision energy was predicted to be prevalent along the bed surface and in front of the grinding jets, as shown through the collision data recorded. The bed itself affects the fluid flow field, as momentum is transferred to the particles. Increasing the grinding pressure does not result in a proportional increase in the kinetic energy of the particle system, as the high pressure jets begin to penetrate the bed with greater ease. The particle bed moves as ‘plug-flow’, with the layers of the bed closest to chamber wall.

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Voropayev, S. I., Ya D. Afanasyev e I. A. Filippov. "Horizontal jets and vortex dipoles in a stratified fluid". Journal of Fluid Mechanics 227 (giugno 1991): 543–66. http://dx.doi.org/10.1017/s0022112091000241.

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When a horizontal force is applied locally to some volume of a viscous densitystratified fluid, flows with high concentration of vertically oriented vorticity (vortex dipoles) are generated. The processes of generation and evolution with time of these unsteady flows in a stratified fluid are studied. A convenient way to produce and study these flows in the laboratory is to use a submerged horizontal jet as a ‘point’ source of momentum. The main governing parameter (the ‘force’) is easily controlled in this case. Two regimes were studied: starting jets with dipolar vortex fronts (the force acts continuously) and impulsive vortex dipoles (the force acts for a short period of time). A conductivity microprobe, aluminium powder, shadowgraph, thymol-blue and other techniques have been used to measure the velocity and density distributions in the flows. It is found that in both regimes the flows are self-similar: the lengthscale of the flows increases with time as t½ for starting jets and as t1/3 for vortex dipoles. Detailed information about the generation mechanism, kinematics and dynamics of the flows is obtained. On the basis of similarity principles a theoretical explanation of the experimental results is given. The theory is in good agreement with the results obtained.

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Bogy, D. B., e F. E. Talke. "Mechanics-Related Problems of Magnetic Recording Technology and Ink-Jet Printing". Applied Mechanics Reviews 39, n. 11 (1 novembre 1986): 1665–77. http://dx.doi.org/10.1115/1.3149508.

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In this paper, mechanical aspects of magnetic recording technology and nonimpact printing are discussed. In the recording area, theoretical and experimental aspects of air bearing theory, head/disk dynamics, and head/disk tribology are studied. Flutter of rotating disks is investigated, the flow field between rotating disks is described, and nonrepeatable run-out of disk file spindles is studied. Furthermore, the head/disk interface for flexible media is discussed and dimensional stability of flexible substrate is examined. In the printing area, experimental and theoretical investigations using continuous and drop-on-demand fluid jets are presented, and numerical calculations of the drop formation process in drop-on-demand fluid jets are described.

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Song, XiaoWen, e MingXiao Zhang. "Turbulent Drag Reduction Characteristics of Bionic Nonsmooth Surfaces with Jets". Applied Sciences 9, n. 23 (24 novembre 2019): 5070. http://dx.doi.org/10.3390/app9235070.

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Aiming at aerodynamic drag reduction for transportation systems, a new active surface is proposed that combines a bionic nonsmooth surface with a jet. Simulations were performed in the computational fluid dynamics software STAR-CCM+ to investigate the flow characteristics and drag reduction efficiency. The SST K-Omega model was used to enclose the equations. The simulation results showed that when the active surface simultaneously reduced the skin friction and overcame the sharp increase of pressure drag caused by a common nonsmooth surface, the total net drag decreased. The maximum drag reduction ratio reached 19.35% when the jet velocity was 11 m/s. Analyses of the turbulent kinetic energy, pressure distribution, and velocity profile variations showed that the active surface reduced the peak pressure on the windward side of the nonsmooth unit cell, thereby reducing the total pressure drag. Moreover, the recirculation formed in the unit cell transformed the fluid–wall sliding friction into fluid–fluid rolling friction like a rolling bearing, thereby reducing the skin friction. This study provides a new efficient way for turbulent drag reduction to work.

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36

Balk, A. M. "The Rossby wave extra invariant in the dynamics of 3-D fluid layers and the generation of zonal jets". Nonlinear Processes in Geophysics 21, n. 1 (10 gennaio 2014): 49–59. http://dx.doi.org/10.5194/npg-21-49-2014.

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Abstract. We consider an adiabatic-type (approximate) invariant that was earlier obtained for the quasi-geostrophic equation and the shallow water system; it is an extra invariant, in addition to the standard ones (energy, enstrophy, momentum), and it is based on the Rossby waves. The presence of this invariant implies the energy transfer from small-scale eddies to large-scale zonal jets. We show that this extra invariant can be extended to the dynamics of a three-dimensional (3-D) fluid layer on the beta plane. Combined with the investigation of other researchers, this 3-D extension implies enhanced generation of zonal jets. For a general physical system, the presence of an extra invariant (in addition to the energy–momentum and wave action) is extremely rare. We summarize the unique conservation properties of geophysical fluid dynamics (with the beta effect) that allow for the existence of the extra invariant, and argue that its presence in various geophysical systems is a strong indication that the formation of zonal jets is indeed related to the extra invariant. Also, we develop a new, more direct, way to establish extra invariants (without using cubic corrections). For this, we introduce the small denominator lemma.

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37

Liu, Yong, Jia Li, Yu Tian, Jian Liu e Jie Fan. "Multi-Physics Coupled FEM Method to Simulate the Formation of Crater-Like Taylor Cone in Electrospinning of Nanofibers". Journal of Nano Research 27 (marzo 2014): 153–62. http://dx.doi.org/10.4028/www.scientific.net/jnanor.27.153.

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Crater-like Taylor cone electrospinning is a novel, simple, and powerful approach to mass produce nanofibers. The Taylor cone, crater-like liquid bump on the free liquid surface, in this electrospinning process plays a key role to produce multiple fluid jets which finally solidifies nanofibers. A multi-physics coupled FEM method was employed to simulate the dynamic formation process of crater-like Taylor Cone in crater-like electrospinning. A blended k−ω /k−ε model for turbulence and dynamic overset grids to resolve large amplitude motions were used to simulate two-dimensional uncompressed flow, which was described in axisymmetrical coordinates. The numerical calculation results were obtained by a computational fluid dynamics (CFD) method. The effect of gas flow on the formation of crater-like Taylor cone and the production of nanofibers were also discussed. The experiments were carried out to validate the numerical results. The Polyvinyl Alcohol (PVA)/ distilled water solution with 18wt% and the air pressures ranged varied from 4 to 50kPa were used in our experiments. The results showed that the numerical results were in good agreement with the experimental results. This work provides a deep understanding of the mechanisms of micro fluid jets production in electrospinning processes and two-phase flow in specific type of industrial equipment.

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38

Rhines, P. B. "Jets and Orography: Idealized Experiments with Tip Jets and Lighthill Blocking". Journal of the Atmospheric Sciences 64, n. 10 (1 ottobre 2007): 3627–39. http://dx.doi.org/10.1175/jas4008.1.

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Abstract This paper describes qualitative features of the generation of jetlike concentrated circulations, wakes, and blocks by simple mountainlike orography, both from idealized laboratory experiments and shallow-water numerical simulations on a sphere. The experiments are unstratified with barotropic lee Rossby waves, and jets induced by mountain orography. A persistent pattern of lee jet formation and lee cyclogenesis owes its origins to arrested topographic Rossby waves above the mountain and potential vorticity (PV) advection through them. The wake jet occurs on the equatorward, eastern flank of the topography. A strong upstream blocking of the westerly flow occurs in a Lighthill mode of long Rossby wave propagation, which depends on βa2/U, the ratio of Rossby wave speed based on the scale of the mountain, to zonal advection speed, U (β is the meridional potential vorticity gradient, f is the Coriolis frequency, and a is the diameter of the mountain). Mountains wider (north–south) than the east–west length scale of stationary Rossby waves will tend to block the oncoming westerly flow. These blocks are essentially β plumes, which are illustrated by their linear Green function. For large βa2/U, upwind blocking is strong; the mountain wake can be unstable, filling the fluid with transient Rossby waves as in the numerical simulations of Polvani et al. For small values, βa2/U ≪ 1 classic lee Rossby waves with large wavelength compared to the mountain diameter are the dominant process. The mountain height, δh, relative to the mean fluid depth, H, affects these transitions as well. Simple lee Rossby waves occur only for such small heights, δh/h ≪ aβ/f, that the f/h contours are not greatly distorted by the mountain. Nongeostrophic dynamics are seen in inertial waves generated by geostrophic shear, and ducted by it, and also in a texture of finescale, inadvertent convection. Weakly damped circulations induced in a shallow-water numerical model on a sphere by a lone mountain in an initially simple westerly wind are also described. Here, with βa2/U ∼1, potential vorticity stirring and transient Rossby waves dominate, and drive zonal flow acceleration. Low-latitude critical layers, when present, exert strong control on the high-latitude waves, and with no restorative damping of the mean zonal flow, they migrate poleward toward the source of waves. While these experiments with homogeneous fluid are very simplified, the baroclinic atmosphere and ocean have many tall or equivalent barotropic eddy structures owing to the barotropization process of geostrophic turbulence.

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39

Liu, C. M., A. Vaivads, Y. V. Khotyaintsev, H. S. Fu, D. B. Graham, K. Steinvall, Y. Y. Liu e J. L. Burch. "Cross-scale Dynamics Driven by Plasma Jet Braking in Space". Astrophysical Journal 926, n. 2 (1 febbraio 2022): 198. http://dx.doi.org/10.3847/1538-4357/ac4979.

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Abstract Plasma jets are ubiquitous in space. In geospace, jets can be generated by magnetic reconnection. These reconnection jets, typically at fluid scale, brake in the near-Earth region, dissipate their energies, and drive plasma dynamics at kinetic scales, generating field-aligned currents that are crucial to magnetospheric dynamics. Understanding of the cross-scale dynamics is fundamentally important, but observation of coupling among phenomena at various scales is highly challenging. Here we report, using unprecedentedly high-cadence data from NASA's Magnetospheric Multiscale Mission, the first observation of cross-scale dynamics driven by jet braking in geospace. We find that jet braking causes MHD-scale distortion of magnetic field lines and development of an ion-scale jet front that hosts strong Hall electric fields. Parallel electric fields arising from the ion-scale Hall potential generate intense electron-scale field-aligned currents, which drive strong Debye-scale turbulence. Debye-scale waves conversely limit intensity of the field-aligned currents, thereby coupling back to the large-scale dynamics. Our study can help in understanding how energy deposited in large-scale structures is transferred into small-scale structures in space.

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40

Ezhova, E. V., D. A. Sergeev, A. A. Kandaurov e Yu I. Troitskaya. "Nonsteady dynamics of turbulent axisymmetric jets in stratified fluid: Part 1. Experimental study". Izvestiya, Atmospheric and Oceanic Physics 48, n. 4 (luglio 2012): 409–17. http://dx.doi.org/10.1134/s0001433812040081.

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41

Moore, Eric M., Robert L. Shambaugh e Dimitrios V. Papavassiliou. "Analysis of isothermal annular jets: Comparison of computational fluid dynamics and experimental data". Journal of Applied Polymer Science 94, n. 3 (2004): 909–22. http://dx.doi.org/10.1002/app.20963.

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42

Lotfiani, Amin, Shahram Khalilarya e Samad Jafarmadar. "A semi-analytical model for the prediction of the behavior of turbulent coaxial gaseous jets". Thermal Science 17, n. 4 (2013): 1221–32. http://dx.doi.org/10.2298/tsci110701140l.

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In diffusion combustion systems, fuel and oxidizer (usually air) are admitted into the combustion chamber separately in the form of turbulent jets. Most often, fuel enters the furnace from a round nozzle and air is admitted through an annulus surrounding the central fuel nozzle. Momentum of the fuel and air jets is utilized for directing the flame and controlling the mixture formation which is typically the rate-limiting step of the combustion process. Hence the behavior of turbulent coaxial jets must be well understood prior to any detailed analysis of these systems. In this study, a set of relations is proposed to predict the behavior of turbulent coaxial gaseous jets using curve-fits to the computational fluid dynamics (CFD) solutions and the fluid flow governing equations as well as the ideal gas equation of state. A computer program is developed to implement the presented model. Results are compared with existing data and reasonable agreement is observed. According to the results, the presented model makes sufficiently accurate estimates of the flow and concentration fields in a very short time.

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43

Untuç, Ahmet Hikmet, e Salih Ozen Unverdi. "Heat Transfer Enhancement by Mitigating the Adverse Effects of Crossflow in a Multi-Jet Impingement Cooling System in Hexagonal Configuration by Coaxial Cylindrical Protrusion—Guide Vane Pairs". Applied Sciences 13, n. 20 (13 ottobre 2023): 11260. http://dx.doi.org/10.3390/app132011260.

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A novel compound multi-jet impingement system for enhanced cooling of a flat surface by augmenting its area with cylindrical protrusions (CPs) equipped with coaxial guide vanes (CGVs) and reducing deflection of jets by crossflow has been developed for high-heat removal applications. The cooling performance of coaxial circular jets impinging on the top faces of CPs placed in hexagonal configuration on a flat plate is evaluated by three-dimensional (3D) computational fluid dynamics (CFD) simulations. Jets impinging on the top faces of the protrusions are directed to their lateral faces and then to the base plate by the CGVs around the protrusions, resulting in up to 62.8% improvement in heat transfer rate with a minor increase in pressure drop. Effects of protrusion height and diameter on the pressure drop and cooling performance are studied for jet Reynolds (Re number range of 5000–20,000. Due to both shortened jet impingement lengths as the height of protrusions is increased and directing the expended fluid away from the impinging jets by CGVs, adverse effects of jet–crossflow interactions on cooling performance and fluid pumping power are significantly reduced. Performance evaluation criterion (PEC) of the novel compound multi-jet impingement cooling system (CMJICS) can be as high as 1.52.

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44

Joshi, Raj Kishor, Sanjit Debnath e Indranil Chattopadhyay. "Shocks in Radiatively Driven Time-dependent, Relativistic Jets around Black Holes". Astrophysical Journal 933, n. 1 (1 luglio 2022): 75. http://dx.doi.org/10.3847/1538-4357/ac70de.

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Abstract We study time-dependent relativistic jets under the influence of the radiation field of the accretion disk. The accretion disk consists of an inner compact corona and an outer sub-Keplerian disk. The thermodynamics of the fluid is governed by a relativistic equation of state (EOS) for multispecies fluid that enables us to study the effect of composition on jet dynamics. Jets originate from the vicinity of the central black hole, where the effect of gravity is significant and traverses large distances where only special relativistic treatment is sufficient. So we have modified the flat metric to include the effect of gravity. In this modified relativistic framework we have developed a new total variation diminishing routine along with a multispecies EOS for the purpose. We show that the acceleration of jets crucially depends on flow composition. All the results presented are transonic in nature; starting from very low injection velocities, the jets can achieve high Lorentz factors. For sub-Eddington luminosities, lepton-dominated jets can be accelerated to Lorentz factors >50. The change in radiation field due to variation in the accretion disk dynamics will be propagated to the jet in a finite amount of time. Hence, any change in radiation field due to a change in disk configuration will affect the lower part of the jet before it affects the outer part. This can drive shock transition in the jet flow. Depending on the disk oscillation frequency, amplitude, and jet parameters, these shocks can collide with each other and may trigger shock cascades.

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45

Loureiro, Juliana Braga Rodrigues, e Atila Pantaleão Silva Freire. "Erosion Characterization Of Gas-Solid Jets Impinging Onto Inclined Surfaces". Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 21 (8 luglio 2024): 1–5. http://dx.doi.org/10.55037/lxlaser.21st.194.

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Erosion caused by solid particles is an important phenomenon in many industrial applications. Wear modelling is a complex phenomenon due to the many relevant variables. In any event, the dynamics of the fluid flow and particles need to be characterized so that their interrelations are well understood and models can be advanced. Depending on their sizes, particles immersed in solid-gas flows may deviate from the fluid stream, meaning that any deployed measuring technique must take this into account. The work describes through PIV and PTV the flow and particle dynamics of a round air-jet loaded with carbon silicate particles (SiO2) impinging onto an inclined surface. Flow conditions are set for two different Reynolds numbers and four impinging angles. The experimental results are compared with numerical simulations furnished by a two-way coupling scheme. The results show that erosion wear is highly dependent on the kinetic energy of the particle at impact. The larger the size of the particle or the larger its velocity, the larger is the damage it causes. A correlation between the thickness of removed material with particle size distribution and flow rate is presented. For low flow rates, the distinction between the damage caused by particles of various sizes is small.

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Wang, Zhifeng, Zhengyang Feng, Jinsen Hu, Yuning Zhang e Yuning Zhang. "Numerical Investigations on the Jet Dynamics during Cavitation Bubble Collapsing between Dual Particles". Symmetry 16, n. 5 (29 aprile 2024): 535. http://dx.doi.org/10.3390/sym16050535.

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The jet dynamics during cavitation bubble collapsing between unequal-sized dual particles are investigated utilizing a numerical model that combines the finite volume approach alongside the volume of fluid approach. The model incorporates the compressibility of the two-phase fluid and accounts for mass and heat transfer between two phases. The computational model utilizes an axisymmetric model, where the axis of symmetry is defined as the line that connects the centers of the particles and the bubble. A comprehensive analysis is presented on the influence of the particle radius and bubble–particle distance on the jet behavior. Furthermore, the variations of surface pressure on the particles induced by jet impingement are quantitatively analyzed. Four distinct jet behaviors are categorized, depending on the formation mechanism, as well as the number and the direction of the jets. For case 1, the bubble produces a single jet directed toward a small particle; for case 2, the bubble fragments produces double jets receding from each other; for case 3, the bubble produces double jets approaching each other; and for case 4, the bubble produces a single jet directed toward a large particle. The pressure perturbations induced by jet impingement upon the particles exceed those caused by shock wave impacts. The larger the bubble volume at the moment of jet formation, the longer the duration of the pressure variation caused by the jet impinging on the particles.

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47

Díaz-Figueroa, Elton Everardo, Gonzalo Ares de Parga e José Juan González-Avilés. "Influence of the Magnetic Field Topology in the Evolution of Small-Scale Two-Fluid Jets in the Solar Atmosphere". Physics 5, n. 1 (27 febbraio 2023): 261–75. http://dx.doi.org/10.3390/physics5010020.

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In this paper, a series of numerical simulations is performed to recreate small-scale two-fluid jets using the JOANNA code, considering the magnetohydrodynamics of two fluids (ions plus electrons and neutral particles). First, the jets are excited in a uniform magnetic field by using velocity pulse perturbations located at y0= 1.3, 1.5, and 1.8 Mm, considering the base of the photosphere at y=0. Then, the excitation of the jets is repeated in a magnetic field that mimics a flux tube. Mainly, the jets excited at the upper chromosphere (y∼1.8 Mm) reach lower heights than those excited at the lower chromosphere (y∼1.3 Mm); this is due to the higher initial vertical location because of the lesser amount of plasma dragging. In both scenarios, the dynamics of the neutral particles and ions show similar behavior, however, one can still identify some differences in the velocity drift, which in the simulations here is of the order of 10−3 km/s at the tips of the jets once they reached their maximum heights. In addition, the heat due to the friction between ions and neutrals (Qi,nin) is estimated to be of the order of 0.002–0.06 W/m3. However, it hardly contributes to the heating of the surroundings of the solar corona. The jets in the two magnetic environments do not show substantial differences other than a slight variation in the maximum heights reached, particularly in the uniform magnetic field scenario. Finally, the maximum heights reached by the three different jets are found in the range of some morphological parameters corresponding to macrospicules, Type I spicules, and Type II spicules.

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48

Kranz, Michael, Tracy Hudson, Michael Whitley e Brian English. "Integrated Localized Cooling using Piezoelectrically-Driven Synthetic Jets". Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2014, DPC (1 gennaio 2014): 001072–106. http://dx.doi.org/10.4071/2014dpc-tp35.

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RF communication and radar systems present an extreme thermal management challenge. These systems are comprised of tightly packaged and high wattage components requiring a controlled temperature to meet performance and reliability parameters. In these systems, there is little space available for air flow or other traditional cooling methods. In addition, the heat generating components are typically microscale semiconductor devices fabricated on integrated circuit substrates buried deep within the system. Localized cooling using integrated microsystems may provide a solution to these thermal management issues. One approach being pursued to meet this thermal challenge is the integration of miniature synthetic air jets near the heat generating components. These synthetic jets are generated using oscillating piezoelectric actuators that force air through a small nozzle at high flow rates and in very close proximity to the heat generating component. The resulting jets provide vorticity within the fluid, leading to enhanced mixing with the surrounding lower temperature fluid, and a subsequent increase in the heat transfer coefficient. The US Army AMRDEC is developing and operating microactuator test beds to mature these concepts and implement practical integration solutions. This investigation has modeled potential actuators and jets in using computational fluid dynamics and heat transfer codes, verified the results of these models with the prototype test beds, and demonstrated high-levels of localized cooling. This paper will present actuator designs, thermal modeling results, and actual cooling results using a high-stroke piezoelectric actuator as the drive element.

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49

Zhang, Qiang, Yu Tamanoi e Kotaro Sato. "Influence of secondary flow with a Coanda surface on the direction of jets". Journal of Physics: Conference Series 2252, n. 1 (1 aprile 2022): 012003. http://dx.doi.org/10.1088/1742-6596/2252/1/012003.

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Abstract We propose a method for fluidic thrust vectoring by studying the effect of excited secondary Coanda flow on the direction of jets. The primary flow is the steady continuous jet, while the the secondary flow is synthetic jet or continuous flow. In this experiment, speaker is used to adjusted the frequency and velocity amplitude of synthetic jets, while a blower is used to adjust the continuous jet and suction flow.We visualize and compare the primary flow under the influence of various secondary flows. Additionally, computational fluid dynamics is used to investigate the flow characteristics, including the deflection angle. The main results of this study is that both synthetic jets and continuous suction flow are capable of deflection.

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50

Zhang, Qiang, Yu Tamanoi e Kotaro Sato. "Influence of secondary flow with a Coanda surface on the direction of jets". Journal of Physics: Conference Series 2252, n. 1 (1 aprile 2022): 012003. http://dx.doi.org/10.1088/1742-6596/2252/1/012003.

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Abstract (sommario):

Abstract We propose a method for fluidic thrust vectoring by studying the effect of excited secondary Coanda flow on the direction of jets. The primary flow is the steady continuous jet, while the the secondary flow is synthetic jet or continuous flow. In this experiment, speaker is used to adjusted the frequency and velocity amplitude of synthetic jets, while a blower is used to adjust the continuous jet and suction flow.We visualize and compare the primary flow under the influence of various secondary flows. Additionally, computational fluid dynamics is used to investigate the flow characteristics, including the deflection angle. The main results of this study is that both synthetic jets and continuous suction flow are capable of deflection.

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