Academic literature on the topic 'Dynamic meteorology Air entrainment'
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Journal articles on the topic "Dynamic meteorology Air entrainment"
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Vandre, E., M. S. Carvalho, and S. Kumar. "Characteristics of air entrainment during dynamic wetting failure along a planar substrate." Journal of Fluid Mechanics 747 (April 14, 2014): 119–40. http://dx.doi.org/10.1017/jfm.2014.110.
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AbstractCharacteristic substrate speeds and meniscus shapes associated with the onset of air entrainment are studied during dynamic wetting failure along a planar substrate. Using high-speed video, the behaviour of the dynamic contact line (DCL) is recorded as a tape substrate is drawn through a bath of a glycerol/water solution. Air entrainment is identified by triangular air films that elongate from the DCL above some critical substrate speed. Meniscus confinement within a narrow gap between the substrate and a stationary plate is shown to delay air entrainment to higher speeds for a wide range of liquid viscosities, expanding upon the findings of Vandre, Carvalho & Kumar (J. Fluid Mech., vol. 707, 2012, pp. 496–520). A pressurized liquid reservoir controls the meniscus position within the confinement gap. It is found that liquid pressurization further postpones air entrainment when the meniscus is located near a sharp corner along the stationary plate. Meniscus shapes recorded near the DCL demonstrate that operating conditions influence the size of entrained air films, with smaller films appearing in the more viscous solutions. Regardless of size, air films become unstable to thickness perturbations and ultimately rupture, leading to the entrainment of air bubbles. Recorded critical speeds and air-film sizes compare well to predictions from a hydrodynamic model for dynamic wetting failure, suggesting that strong air stresses near the DCL trigger the onset of air entrainment.
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Kamal, Catherine, James E. Sprittles, Jacco H. Snoeijer, and Jens Eggers. "Dynamic drying transition via free-surface cusps." Journal of Fluid Mechanics 858 (November 12, 2018): 760–86. http://dx.doi.org/10.1017/jfm.2018.794.
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We study air entrainment by a solid plate plunging into a viscous liquid, theoretically and numerically. At dimensionless speeds $Ca=U\unicode[STIX]{x1D702}/\unicode[STIX]{x1D6FE}$ of order unity, a near-cusp forms due to the presence of a moving contact line. The radius of curvature of the cusp’s tip scales with the slip length multiplied by an exponential of $-Ca$. The pressure from the air flow drawn inside the cusp leads to a bifurcation, at which air is entrained, i.e. there is ‘wetting failure’. We develop an analytical theory of the threshold to air entrainment, which predicts the critical capillary number to depend logarithmically on the viscosity ratio, with corrections coming from the slip in the gas phase.
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Andre´s, Luis San, and Sergio E. Diaz. "Flow Visualization and Forces From a Squeeze Film Damper Operating With Natural Air Entrainment." Journal of Tribology 125, no. 2 (March 19, 2003): 325–33. http://dx.doi.org/10.1115/1.1510878.
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Measurements of dynamic film pressures and high-speed photographs of the flow field in an open-ended Squeeze Film Damper (SFD) operating with natural free air entrainment are presented for increasing whirl frequencies (8.33–50 Hz), and a range of feed pressures to 250 kPa (37 psig). The flow conditions range from lubricant starvation (air ingestion) to a fully flooded discharge operation. The test dynamic pressures and video recordings show that air entrainment leads to large and irregular gas fingering and striation patterns. This is a natural phenomenon in SFDs operating with low levels of external pressurization (reduced lubricant through flow rates). Air ingestion and entrapment becomes more prevalent as the whirl frequency raises, and increasing the feed pressure aids little to ameliorate the loss in dynamic forced performance. As a result of the severity of air entrainment, experimentally estimated damping forces decrease steadily as the whirl frequency (operating speed) increases.
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Sprittles, James E. "Air entrainment in dynamic wetting: Knudsen effects and the influence of ambient air pressure." Journal of Fluid Mechanics 769 (March 25, 2015): 444–81. http://dx.doi.org/10.1017/jfm.2015.121.
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Recent experiments on coating flows and liquid drop impact both demonstrate that wetting failures caused by air entrainment can be suppressed by reducing the ambient gas pressure. Here, it is shown that non-equilibrium effects in the gas can account for this behaviour, with ambient pressure reductions increasing the mean free path of the gas and hence the Knudsen number $\mathit{Kn}$. These effects first manifest themselves through Maxwell slip at the boundaries of the gas, so that for sufficiently small $\mathit{Kn}$ they can be incorporated into a continuum model for dynamic wetting flows. The resulting mathematical model contains flow structures on the nano-, micro- and millimetre scales and is implemented into a computational platform developed specifically for such multiscale phenomena. The coating flow geometry is used to show that for a fixed gas–liquid–solid system (a) the increased Maxwell slip at reduced pressures can substantially delay air entrainment, i.e. increase the ‘maximum speed of wetting’, (b) unbounded maximum speeds are obtained, as the pressure is reduced only when slip at the gas–liquid interface is allowed for, and (c) the observed behaviour can be rationalised by studying the dynamics of the gas film in front of the moving contact line. A direct comparison with experimental results obtained from a dip-coating process shows that the model recovers most trends but does not accurately predict some of the high viscosity data at reduced pressures. This discrepancy occurs because the gas flow enters the ‘transition regime’, so that more complex descriptions of its non-equilibrium nature are required. Finally, by collapsing onto a master curve experimental data obtained for drop impact in a reduced pressure gas, it is shown that the same physical mechanisms are also likely to govern splash suppression phenomena.
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Esmail, M. N., and M. T. Ghannam. "Air entrainment and dynamic contact angles in hydrodynamics of liquid coating." Canadian Journal of Chemical Engineering 68, no. 2 (April 1990): 197–203. http://dx.doi.org/10.1002/cjce.5450680203.
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Zhang, Wei, Bingbing Han, Kunpeng Zhang, and Qian Ding. "Dynamic Analysis of a Rotor System Supported on Squeeze Film Damper with Air Entrainment." International Journal of Bifurcation and Chaos 27, no. 14 (December 30, 2017): 1750212. http://dx.doi.org/10.1142/s0218127417502121.
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Squeeze film dampers (SFDs) are widely used in compressors and turbines to suppress the vibration while traversing critical speeds. In practical applications, air ingestion from the outside environment and cavitation may lead to a foamy lubricant that weakens oil film damping and dynamic performance of rotor system. In this paper, a rigid rotor model is established considering both lateral and pitching vibration under different imbalance excitations to evaluate the effect of air entrainment on rotor system. Tests with three different imbalances are carried out on a rotor-SFD apparatus. Volume controlled air in mixture ranging from pure oil to all air are supplied to the SFD. The transient response of rotor is measured in the experiments. The results show that two-phase flow produces significant influence on the system stability and dynamical response. The damping properties are weakened by entrained air, such as the damping on high frequency components of rolling ball bearing. Super-harmonic resonance and bifurcation are observed, as well as the low frequency components due to air entrainment.
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Wang, Yan, Xiao-dong Ren, Xue-song Li, and Chun-wei Gu. "Numerical investigation of subsynchronous vibration in floating ring bearings." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 232, no. 11 (January 19, 2018): 1390–401. http://dx.doi.org/10.1177/1350650117753915.
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Floating ring bearings are popular among turbochargers due to their simplicity and reliability. The disappearance of subsynchronous vibration with the increase of shaft speed in a low oil-supplied pressure floating ring bearing is reported by Hatakenaka and Yanai. This finding may help eliminate the noise and decrease the loss of turbochargers. This work aims to explain this phenomenon in the low oil-supplied floating ring bearing using computational fluid dynamic. Steady computational fluid dynamic calculation is conducted to validate the effect of air entrainment. Transient computational fluid dynamic calculation method with mesh motion method is established. The subsynchronous vibration of the shaft can be obtained by discrete Fourier transform analysis. The results are validated by comparing them with those in the literature. It is found that the disappearance of the subsynchronous vibration is the result of the change in lubricant properties caused by the air entrainment.
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San Andre´s, Luis, and Oscar De Santiago. "Forced Response of a Squeeze Film Damper and Identification of Force Coefficients From Large Orbital Motions." Journal of Tribology 126, no. 2 (April 1, 2004): 292–300. http://dx.doi.org/10.1115/1.1611503.
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Experimentally derived damping and inertia force coefficients from a test squeeze film damper for various dynamic load conditions are reported. Shakers exert single frequency loads and induce circular and elliptical orbits of increasing amplitudes. Measurements of the applied loads, bearing displacements and accelerations permit the identification of force coefficients for operation at three whirl frequencies (40, 50, and 60 Hz) and increasing lubricant temperatures. Measurements of film pressures reveal an early onset of air ingestion. Identified damping force coefficients agree well with predictions based on the short length bearing model only if an effective damper length is used. A published two-phase flow model for air entrainment allows the prediction of the effective damper length, and which ranges from 82% to 78% of the damper physical length as the whirl excitation frequency increases. Justifications for the effective length or reduced (flow) viscosity follow from the small through flow rate, not large enough to offset the dynamic volume changes. The measurements and analysis thus show the pervasiveness of air entrainment, whose effect increases with the amplitude and frequency of the dynamic journal motions. Identified inertia coefficients are approximately twice as large as those derived from classical theory.
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Katta, V. R., and W. M. Roquemore. "Numerical Studies on Trapped-Vortex Concepts for Stable Combustion." Journal of Engineering for Gas Turbines and Power 120, no. 1 (January 1, 1998): 60–68. http://dx.doi.org/10.1115/1.2818088.
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Spatially locked vortices in the cavities of a combustor aid in stabilizing the flames. On the other hand, these stationary vortices also restrict the entrainment of the main air into the cavity. For obtaining good performance characteristics in a trapped-vortex combustor, a sufficient amount of fuel and air must be injected directly into the cavity. This paper describes a numerical investigation performed to understand better the entrainment and residence-time characteristics of cavity flows for different cavity and spindle sizes. A third-order-accurate time-dependent Computational Fluid Dynamics with Chemistry (CFDC) code was used for simulating the dynamic flows associated with forebody-spindle-disk geometry. It was found from the nonreacting flow simulations that the drag coefficient decreases with cavity length and that an optimum size exists for achieving a minimum value. These observations support the earlier experimental findings of Little and Whipkey (1979). At the optimum disk location, the vortices inside the cavity and behind the disk are spatially locked. It was also found that for cavity sizes slightly larger than the optimum, even though the vortices are spatially locked, the drag coefficient increases significantly. Entrainment of the main flow was observed to be greater into the smaller-than-optimum cavities. The reacting-flow calculations indicate that the dynamic vortices developed inside the cavity with the injection of fuel and air do not shed, even though the cavity size was determined based on cold-flow conditions.
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Diaz, S. E., and L. A. San Andre´s. "Air Entrainment Versus Lubricant Vaporization in Squeeze Film Dampers: An Experimental Assessment of Their Fundamental Differences." Journal of Engineering for Gas Turbines and Power 123, no. 4 (October 1, 1998): 871–77. http://dx.doi.org/10.1115/1.1383258.
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Squeeze film dampers (SFDs) provide structural isolation and energy dissipation in air-breathing engines and process gas compressors. However, SFDs are prone to develop a flow regime where the ingestion of air leads to the formation of a bubbly lubricant. This pervasive phenomenon lacks proper physical understanding and sound analytical modeling, although actual practice demonstrates that it greatly reduces the damper force response. Measurements of film pressures in a test SFD describing circular centered orbits at whirl frequencies varying from 0 to 100 Hz are presented for fully flooded and vented discharge operating conditions. The experiments demonstrate that operation with low levels of external pressurization, moderate to large whirl frequencies, and lubricant discharge to ambient leads to the entrapment of air within the damper film lands. The experiments also elucidate fundamental differences in the generation of film pressures and forces for operation in a flooded condition that evidences vapor cavitation. Damping forces for the vented end with air entrainment are just 15 percent of the forces measured for the flooded damper. Further measurements at constant whirl frequencies demonstrate that increasing the lubricant pressure supply retards the onset of air entrainment. Classical fluid film cavitation models predict well the pressures and forces for the lubricant vapor cavitation condition. However, prevailing models fail to reproduce the dynamic forced response of vented (open-ended) SFDs where air entrainment makes a foamy lubricant, which limits severely the damper film pressures and forces.
Dissertations / Theses on the topic "Dynamic meteorology Air entrainment"
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Veverka, Peter John. "An investigation of interfacial instability during air entrainment." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/5800.
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Elgadafi, Mansour M. "Angled curtain coating: An experimental study. An experimental investigation into the effect of die angle on air entrainment velocity in curtain coating under a range of operating conditions." Thesis, University of Bradford, 2010. http://hdl.handle.net/10454/4464.
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In all coating applications, a liquid film displaces air in contact with a dry solid substrate. At a low substrate speed a thin uniform wetting line is formed on the substrates surface, but at a high speed the wetting line becomes segmented and unsteady as air becomes entrained between the substrate and the liquid. These air bubbles affect the quality of the coated product and any means to postpone this at higher speeds without changing the specifications of the coating liquid is desirable. This research assesses the validity of a theoretically based concept developed by Blake and Rushack [1] and exploited by Cohu and Benkreira [2] for dip coating. The concept suggests that angling the wetting line by an angle ß would increase the speed at which air is entrained by a factor 1/cos ß. In practice, if achieved this is a significant increase that would result in more economical operation. This concept was tested in a fast coating operation that of curtain coating which is already enhanced by what is known as hydrodynamic assistance [2]. Here we are effectively checking an additional assistance to wetting. The work, performed on a purposed built curtain coater and a rotating die, with a range of fluids showed the concept to hold but provided the data are processed in a way that separate the effect of curtain impingement from the slanting of the wetting line.
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Elgadafi, Mansour Masoud. "Angled curtain coating : an experimental study : an experimental investigation into the effect of die angle on air entrainment velocity in curtain coating under a range of operating conditions." Thesis, University of Bradford, 2010. http://hdl.handle.net/10454/4464.
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In all coating applications, a liquid film displaces air in contact with a dry solid substrate. At a low substrate speed a thin uniform wetting line is formed on the substrates surface, but at a high speed the wetting line becomes segmented and unsteady as air becomes entrained between the substrate and the liquid. These air bubbles affect the quality of the coated product and any means to postpone this at higher speeds without changing the specifications of the coating liquid is desirable. This research assesses the validity of a theoretically based concept developed by Blake and Rushack [1] and exploited by Cohu and Benkreira [2] for dip coating. The concept suggests that angling the wetting line by an angle ß would increase the speed at which air is entrained by a factor 1/cos ß. In practice, if achieved this is a significant increase that would result in more economical operation. This concept was tested in a fast coating operation that of curtain coating which is already enhanced by what is known as hydrodynamic assistance [2]. Here we are effectively checking an additional assistance to wetting. The work, performed on a purposed built curtain coater and a rotating die, with a range of fluids showed the concept to hold but provided the data are processed in a way that separate the effect of curtain impingement from the slanting of the wetting line.
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Crum, Timothy D. "Case studies of the structure of the atmospheric boundary layer entrainment zone." 1985. http://catalog.hathitrust.org/api/volumes/oclc/41870232.html.
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Cohu, O., and Hadj Benkreira. "Air entrainment in angled dip coating." 1998. http://hdl.handle.net/10454/812.
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YesThe coating flow examined here, labelled angled dip coating, is that where a substrate enters a pool of liquid forming an angle ß with the vertical so that it intersects the liquid along a wetting line which is not perpendicular to the direction of its motion. This flow situation is distinctly different from that where the substrate, inclined in the other dimension by the so-called angle of entry ¿, intersects the liquid surface perpendicularly to its motion. Experiments were carried out with various liquids to determine the effect of ß on the substrate velocity at which air is entrained into the liquid. It was observed that as this angle departs from zero, air entrainment is delayed to higher speeds. The data show that the speed which is relevant to air entrainment is not the velocity of the substrate itself but its component normal to the wetting line. This result has important practical implications and suggests that this fundamental principle is also applicable to other coating flows.
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Benkreira, Hadj, and M. I. Khan. "Air entrainment in dip coating under reduced air pressures." 2008. http://hdl.handle.net/10454/808.
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YesThis study examines experimentally and for the first time the effect of reduced air pressure on dynamic wetting. The purpose is to assess the role of air viscosity on dynamic wetting failure which hitherto has been speculated on but not measured. In this paper we used dip coating as the model experimental flow and report data on air entrainment velocity Vae we measured with a series of silicone oils in a range of viscosities in a vacuum chamber where the pressure can be reduced from atmospheric down to a few mbar when the mean molecular free path of air is large and air ceases to have a viscosity. To complement earlier work, we carried out the experiments with a range of substrates of varying roughness. The substrates were chosen so that for each one, their two sides differ in roughness. This enables simultaneous comparative observation of their wetting performance and reduces the experimental error in assessing the role of roughness. The data presented here capture the effects of viscosity, roughness and air pressure but the important result of this study is that Vae can be increased considerably (exponentially) when the pressure is reduced with the suggestion that Vae approaches infinity as pressure approaches zero. In other words, the role of the surrounding air viscosity is important in dynamic wetting. The data from this study have significant implication to the fundamental understanding of dynamic wetting. Indeed they form the missing data link to fully understand this phenomenon. The data presented in this work also confirm the complex role of roughness, in that it can increase or decrease the air entrainment speed depending on the value on the viscosity of the coating solution. The results presented in this paper are very useful in practice as they imply that if one chooses carefully roughness one can coat viscous formulation at unexpectedly very high speeds with a moderate vacuum (50 mbar typically).
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Benkreira, Hadj. "The effect of substrate roughness on air entrainment in dip coating." 2004. http://hdl.handle.net/10454/807.
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YesDynamic wetting failure was observed in the simple dip coating flow with a series of substrates, which had a rough side and a comparatively smoother side. When we compared the air entrainment speeds on both sides, we found a switch in behaviour at a critical viscosity. At viscosity lower than a critical value, the rough side entrained air at lower speeds than the smooth side. Above the critical viscosity the reverse was observed, the smooth side entraining air at lower speed than the rough side. Only substrates with significant roughness showed this behaviour. Below a critical roughness, the rough side always entrained air at lower speeds than the smooth side. These results have both fundamental and practical merits. They support the hydrodynamic theory of dynamic wetting failure and imply that one can coat viscous fluids at higher speeds than normal by roughening substrates. A mechanism and a model are presented to explain dynamic wetting failure on rough surfaces.
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Benkreira, Hadj, and O. Cohu. "Angling the dynamic wetting line retards air entrainment in pre-metered coating processes." 1998. http://hdl.handle.net/10454/2235.
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Benkreira, Hadj. "Dynamic wetting in metering and pre-metered roll coating." 2002. http://hdl.handle.net/10454/806.
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Benkreira, Hadj, and J. Bruce Ikin. "Slot Coating Minimum Film Thickness in Air and in Rarefied Helium." 2016. http://hdl.handle.net/10454/8260.
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YesThis study assesses experimentally the role of gas viscosity in controlling the minimum film thickness in slot coating in both the slot over roll and tensioned web modes. The minimum film thickness here is defined with respect to the onset of air entrainment rather than rivulets, the reason being that rivulets are an extreme form of instabilities occurring at much higher speeds. The gas viscosity effects are simulated experimentally by encasing the coaters in a sealed gas chamber in which various gases can be admitted. An appropriate choice of two gases was used to compare performances: air at atmospheric pressure and helium at sub-ambient pressure (25mbar), which we establish has a significantly lower “thin film” viscosity than atmospheric air. A capacitance sensor was used to continuously measure the film thickness on the web, which was ramped up in speed at a fixed acceleration whilst visualizations of the film stability were recorded through a viewing port in the chamber. The data collected show clearly that by coating in rarefied helium rather that atmospheric air we can reduce the minimum film thickness or air/gas entrainment low-flow limit. We attribute this widening of the stable coating window to the enhancement of dynamic wetting that results when the thin film gas viscosity is reduced. These results have evident practical significance for slot coating, the coating method of choice in many new technological applications, but it is their fundamental merit which is new and one that should be followed with further data and theoretical underpinning.
Books on the topic "Dynamic meteorology Air entrainment"
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1919-, Scorer R. S., ed. Dynamics of meteorology and climate. Chichester, England: Wiley, 1997.
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Gordon, Adrian H., and Ronald C. Taylor. Computations of Surface Layer Air Trajectories and Weather in the Oceanic Tropics (International Indian Ocean Expedition meteorological monographs). University of Hawaii Press, 1986.
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V, Penenko V., and Akademii͡a︡ nauk SSSR. Sibirskoe otdelenie. Vychislitelʹnyĭ t͡s︡entr., eds. Chislennoe modelirovanie dli͡a︡ zadach dinamiki atmosfery i okhrany okruzhai͡u︡shcheĭ sredy: Sbornik nauchnykh trudov. Novosibirsk: Akademii͡a︡ nauk SSSR, Sibirskoe otd-nie, Vychislitelʹnyĭ t͡s︡entr, 1989.
Find full textBook chapters on the topic "Dynamic meteorology Air entrainment"
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Yiannikopoulou, I., D. Deligiorgi, H. A. Flocas, and K. Philippopoulos. "A Dynamic-Statistical Downscaling Approach for Simulating Air Temperature Time Series." In Advances in Meteorology, Climatology and Atmospheric Physics, 811–17. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-29172-2_114.
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Quante, Markus, and David O’C Starr. "Dynamic Processes in Cirrus Clouds: A Review of Observational Results." In Cirrus. Oxford University Press, 2002. http://dx.doi.org/10.1093/oso/9780195130720.003.0021.
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Local dynamical processes are a key factor determining the microphysical characteristics and typically heterogeneous macroscopic structure of cirrus cloud fields. The internal and background flow fields are correspondingly heterogeneous, albeit only weakly turbulent in most instances, as is discussed here. Nucleation processes and ice crystal growth and habit are intrinsically governed by the local temperature and humidity (saturation ratio) conditions that, in turn, are strongly regulated by the intensity and duration of local updrafts and downdrafts. The microphysical result of equivalent lift by a 50cm/s updraft over a cell width of 200m is quite different from that by a 0.5 cm/s updraft over a 2-km width, even though the overall mass fluxes are equivalent. The great degree of horizontal structure seen in fallstreaks emanating from cirrus likely reflects corresponding variability in microphysical properties, primarily ice crystal size, resulting from variability in the dynamical conditions in the ice-crystal-generating layer. The ice fallout process is a first-order effect in determining overall cloud ice water path. Entrainment of noncloudy environmental air and internal mixing processes are other dynamical aspects that likely play a significant role in cloud life cycle. Dynamical processes provide an important coupling between cirrus cloud microphysical and radiative processes, as described in chapter 18 and illustrated in figure 17.1. Cirrus cloud microphysical properties and macroscopic structure strongly affect the overall radiative properties of a cirrus cloud field and thus the important radiative effect of cirrus in the climate system. Knowledge of the dynamical processes influencing cloud macrophysical properties and microphysical structure is important to understanding the origin of these characteristics. Moreover, cloud-resolving models of cirrus cloud systems must be evaluated in these respects due to the importance of cloud dynamical processes in determining overall cloud properties. Dynamical processes in cirrus are linked to the state of the background flow field that, in general, is characterized by significant wind shear and a stable thermal stratification. Gravity waves are ubiquitous and occur over a range of scales. Upper tropospheric turbulence tends to occur intermittently in patches, likely a result of sporadic shear generation (Kelvin-Helmholtz instabilities) or breaking gravity waves. Turbulent mixing in stratified shear flows is a notoriously difficult subject, and advances in its description have been obtained only recently (e.g., Fernando 1991; Schumann and Gerz 1995; Vanneste and Haynes 2000).
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Brock, Fred V., and Scott J. Richardson. "Barometry." In Meteorological Measurement Systems. Oxford University Press, 2001. http://dx.doi.org/10.1093/oso/9780195134513.003.0004.
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The objective of barometry is to measure the static pressure exerted by the atmosphere. Static pressure is the force per unit area that would be exerted against any surface in the absence of air motion. It is an isotropic, scalar quantity. Dynamic pressure is the force per unit area due to air motion. It is a vector quantity, following the wind vector. This chapter is concerned with determining the static air pressure and doing so in the presence of air motion (wind) that requires special measurement techniques. The Earth’s atmosphere exerts a pressure on the surface of the Earth equal to the weight of a vertical column of air of unit cross-section. Since air is a fluid, this pressure, or force, is exerted equally in all directions. The static pressure at the surface is given by where g(z) = acceleration due to gravity at height z above sea level in ms-2, and ρ = density as a function of height, kg-3. The SI unit of pressure is the pascal, abbreviated as Pa. In meteorology, the preferred unit of pressure is the mb or the hPa (equivalent magnitude). Table 2-1 lists some conversion factors for units currently in use in pressure measurement and also for some units no longer favored. Standard sea level pressure in various units is shown in table 2-2. The last line of table 2-2 refers to the units of Ibf in-2,also called psi (pounds per square inch). Pressure measurements are often called absolute (psia), gauge (psig), or differential (psid). Absolute pressure is simply the total static pressure exerted by the gas (or fluid) and so the barometric pressure is also the absolute pressure. Gauge pressure is the pressure relative to ambient atmospheric pressure. Pressure in an automobile tire is measured relative to atmospheric pressure so it is gauge pressure, not absolute pressure. Differential pressure is the pressure relative to some other pressure. Gauge pressure is a special case of differential pressure. In addition to the static pressure there is a dynamic pressure exerted by wind flow.
Conference papers on the topic "Dynamic meteorology Air entrainment"
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Bourgin, Patrick, and Sylvie Saintlos. "Dynamic Effects of Air Entrainment in High Velocity Coating Flows." In ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-0453.
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Abstract The problem of a liquid sheet issuing from an ejector and being coated on a moving solid substrate (generally flexible such as for instance paper or plastic film) is considered here. Such a situation resorts of dynamic wetting and the classical free surface boundary conditions at the air/liquid interface are applied. The ambient air viscosity is classically neglected in comparison with that of the liquid, which corresponds to consider the surrounding air as steady. However, it is well known that one of the limiting factors in high velocity coaling flows is the onset of air entrainment into the wedge between the moving solid substrate and the liquid layer. The mechanics of air entrainment of the dynamic wetting line has been studied.
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Liu, C. S. L., and S. H. K. Lee. "A Numerical Study of Dynamic Meniscus." In ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-33717.
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Air entrainment is one of the bottlenecks during high speed coating process. Numerous studies concerned with the mechanics of air entrainment in coating process have been reported during the last four decades. The difficulty in visualization of three-phase contact point due to small dimension made it a hard task to unveil the mechanism of air entrainment experimentally. In most numerical studies on free surface flow, the effect of air upon dynamic meniscus was usually neglected, which induced the coarse accuracy in air entrainment study. In the present study, the numerical simulation of free surface coating flow as well as airflow upon dynamic meniscus was given. The effect of several parameters, such as coating material viscosity, and coating cup geometry, especially airflow upon free surface on the dynamic meniscus, was studied. The results showed that the dynamic effects of air in the vicinity of dynamic meniscus should not be disregarded. The pressure near the dynamic meniscus, especially at the dynamic contact point in the coating flow simulation, was much smaller than the atmosphere pressure, while in the gas phase calculation, the value was larger than the atmosphere one at the same position. These results indicated another explanation of the mechanics of air entrainment: the low pressure in the vicinity of dynamic contact point in the liquid makes the gas dissolve easily into the coating material, and the gas flow will even break the dynamic meniscus when the pressure difference between the gas and liquid phase is large enough. The effects of several factors on pressure distribution at the dynamic meniscus were also presented.
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Colby, Patrick J., Manoj Tandon, and Raymond F. Watts. "Determination of the Air Entrainment Characteristics of Automatic Transmission Fluids Using a Dynamic Flow Apparatus." In International Fall Fuels and Lubricants Meeting and Exposition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 1998. http://dx.doi.org/10.4271/982669.
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Molki, Arman, Lyes Khezzar, and Afshin Goharzadeh. "Characterization of Air-Entrainment in a Plunging Water Jet System Using Image Processing: An Educational Approach." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-62371.
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This paper outlines a proposed experimental setup and image processing techniques using MATLAB for the characterization of the average dynamic behavior of the air/water mixture under the free surface of water penetrated by a plunging jet. The proposed setup focuses on the dynamics of air entrainment below the free surface and the identification of the major regimes related to the entrainment process of bubbles in water, namely: (a) no-entrainment, (b) incipient entrainment, (c) intermittent entrainment, and (d) continuous entrainment. The experimental setup allows students to observe the flow behavior below the free liquid surface and determine the penetration depth of the bubble plumes using image processing techniques in MATLAB. The focal point of the experiment is image analysis for qualitative and quantitative characterization of the bubble plume.
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Yan, Wang, and Li Yuhong. "Investigation of Air-Oil Distribution of Low Oil-Supplied Pressure Grooved Ring Floating Ring Bearing." In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-75887.
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Oil lubricated floating ring bearings (FRBs) are popular among the passenger vehicle turbochargers. Air entrainment occurs in the inner film of the FRB under low oil-supplied pressure. Air entrainment has great impact on the bearing performance. Experiments reported that FRB with a circumferential groove on the ring shows lower ring-to-shaft speed and improved stabilizing capacity at high shaft speed. This study aims to construct the numerical simulation method to predict the multiphase flow in the grooved ring (GR) FRB. Computational fluid dynamic (CFD) method is adopted to obtain the bearing performance considering air entrainment. CFD calculation can obtain detailed air entrainment results that experiment cannot provide. Calculation results are compared with the experimental results to validate the proposed CFD method. Analysis shows the great influence of grooved ring on the air entrainment. Air entrainment contributes to the decrease of the ring-to-shaft speed ratio in the GR FRB. The proposed CFD calculation considering air entrainment can give good prediction of the ring rotation speed under different shaft speed. Besides, detailed analysis of the effective viscosity indicates that outer film is mainly affected by thermal effect. Inner film is affected by both thermal effect and air entrainment effect, where latter is more predominant.
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San Andre´s, Luis, and Oscar C. De Santiago. "Dynamic Response of Squeeze Film Dampers Operating With Bubbly Mixtures." In ASME Turbo Expo 2002: Power for Land, Sea, and Air. ASMEDC, 2002. http://dx.doi.org/10.1115/gt2002-30317.
Full textAbstract:
Squeeze film dampers (SFDs) aid to attenuate vibrations in compressors and turbines while traversing critical speeds. In actual applications, gas ingestion from the environment may lead to the formation of a foamy lubricant that degrades the rotor/bearing system dynamic performance. Impact and imbalance response tests conducted on a rigid rotor supported on SFDs, and aimed to emulate the pervasive effect of air ingestion into the damper film lands, are reported. Two types of squeeze film damper support the test rotor, one is a conventional cylindrical design with a squirrel cage type elastic support, and the other is a compact four-pad damper with integral wire EDM elastic supports. Both dampers have identical diameter and radial clearance. Controlled (air in oil) mixtures ranging from pure oil to all air conditions are supplied to the SFDs, and measurements of the transient rotor response to calibrated impact loads are conducted. System damping coefficients, identified from acceleration/load transfer functions, decrease steadily as the air content in the mixture increases. However, measurements of the rotor synchronous imbalance response conducted with a lubricant bubbly mixture (50% air volume) show little difference with test results obtained with pure lubricant supplied to the dampers. The experimental results show that air entrainment is process and device dependent, and that small amounts of lubricant enable the effective action of SFDs when the rotor traverses a critical speed.
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Torres, Jorge E., and Sergio E. Di´az. "Finite Length Squeeze Film Dampers With Air Entrainment: Non-Dimensional Maps and Their Applicability." In ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-22561.
Full textAbstract:
Squeeze Film Dampers (SFDs) are bearings that support large motion amplitudes when traversing rotor-bearing systems critical speeds. Actual practice demands bearings with operating conditions of low oil supply pressure and high frequency. In open-ended SFDs, large amplitudes of journal motion draw air into the film gap. The air ingested and entrapped results in a bubbly mixture that affects the dynamic performance and the overall damping capability of the SFDs. Diaz and San Andre´s [11] developed a model to predict the amount of air ingested into SFDs with open-ends. They proposed an innovative non-dimensional number to estimate the amount of air entrapped in the film gap, but their analytical results are limited to short length bearings. Mendez et al. [13] extended the results of Diaz and San Andre´s to finite length bearings, devising a Finite Volume Method (FVM) scheme. Even though their research presented new and significant results, they lack wider applicability that includes different geometries or boundary conditions. The present research proposes the solution of the Reynolds equation by the finite element method. Results computed by this formulation explore non-dimensional maps for determination of the amount of entrapped air. The results show that for fixed lubricant properties the amount of entrapped air depends exclusively on three dimensionless parameters: feed-squeeze flow number, length to diameter ratio, and dimensionless orbit radius.
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Me´ndez, Tilmer H., Marco A. Ciaccia, Jorge E. Torres, and Sergio E. Di´az. "On the Numerical Prediction of Finite Length Squeeze Film Dampers Performance With Free Air Entrainment." In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-50368.
Full textAbstract:
Squeeze Film Dampers (SFDs) are commonly used in turbomachinery to dampen shaft vibrations in rotor-bearing systems. The main factor deterring the success of analytical models for the prediction of SFD’s performance lays on the modeling of dynamic film rupture. Usually, the cavitation models developed for journal bearings are applied to SFDs. Yet, the characteristic motion of the SFD results in the entrapment of air into the oil film, producing a bubbly mixture that cannot be represented by these models. There is a need to identify and understand the parameters that affect air entrainment and subsequent formation of a bubbly air-oil mixture within the lubricant film. A previous model by Diaz and San Andre´s advanced estimation of the amount of film-entrapped air, based on a non-dimensional number that related both geometrical and operating parameters but limited to the short bearing approximation (i.e., neglecting circumferential flow). The present study extends their work to consider the effects of finite length-to-diameter ratios. This is achieved by means of a finite volume integration of the two-dimensional, Newtonian, compressible Reynolds equation combined with the effective mixture density and viscosity defined in the work of Diaz and San Andre´s. A flow balance at the open end of the film is devised to estimate the amount of air entrapped within the film. The results show, in dimensionless plots, a map of the amount of entrained air as a function of the Feed-Squeeze Flow Number, defined by Diaz and San Andre´s, and the Length-to-Diameter Ratio of the Damper. Entrained air is shown to decrease as the L/D ratio increases, going from the approximate solution of Diaz and San Andre´s for infinitely short SFDs down to no air entrainment for an infinite length SFD. The results of this research are of immediate engineering applicability. Furthermore, they represent a firm step to advance the understanding of the effects of air entrapment on the performance of SFDs.
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Diaz, Sergio E., and Luis A. San Andrés. "Air Entrainment vs. Lubricant Vaporization in Squeeze Film Dampers: An Experimental Assessment of Their Fundamental Differences." In ASME 1999 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/99-gt-187.
Full textAbstract:
Squeeze film dampers (SFDs) provide structural isolation and energy dissipation in air breathing engines and process gas compressors. However, SFDs are prone to develop a flow regime where the ingestion of air leads to the formation of a bubbly lubricant. This pervasive phenomenon lacks proper physical understanding and sound analytical modeling, although actual practice demonstrates that it greatly reduces the damper force response. Measurements of film pressures in a test SFD describing circular centered orbits at whirl frequencies varying from 0 to 100 Hz are presented for fully flooded and vented discharge operating conditions. The experiments demonstrate that operation with low levels of external pressurization, moderate to large whirl frequencies, and lubricant discharge to ambient leads to the entrapment of air within the damper film lands. The experiments also elucidate fundamental differences in the generation of film pressures and forces for operation in a flooded condition that evidences vapor cavitation. Damping forces for the vented end with air entrainment are just 15% percent of the forces measured for the flooded damper. Further measurements at constant whirl frequencies demonstrate that increasing the lubricant pressure supply retards the onset of air entainment. Classical fluid film cavitation models predict well the pressures and forces for the lubricant vapor cavitation condition. However, prevailing models fail to reproduce the dynamic forced response of vented (open ended) SFDs where air entrainment makes a foamy lubricant, which limits severely the damper film pressures and forces.
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Yousef, Khaled, Ahmed Hegazy, and Abraham Engeda. "Mixing of Dry Air With Water-Liquid Flowing Through an Inverted U-Tube for Power Plant Condenser Applications." In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-4901.
Full textAbstract:
Abstract This paper presents a Computational Fluid Dynamic (CFD) simulation for dry air/water-liquid and two-phase flow mixing in a vertical inverted U-tube using the mixture multiphase and turbulence models. This study is to investigate the flow behaviors and underlying some physical mechanisms encountered in dry air/water-liquid flow in the inverted U-tube. Water flows through the inverted U-tube while the dry air is entrained using the side-tube installed after the water flow downward. The inverted U-tube is tested at water mass flow rates of 2,4,6 and 8 kg/s, air mass flow rates, 0.000614–0.02292 kg/s, with dry air volume fractions 0.2–0.9. The obtained results are compared with the experimental data for model validation and the present CFD model is able to give an acceptable agreement. Also, the results show that, at water mass flow rate of 2 kg/s, there are vortices and turbulent intensity disturbances are noticed at the inverted U-tube higher part, which refers to an air entrainment occurrence from the side-tube. Theses disturbances starts to be stabilized at air mass flow rate around 0.00736 kg/s and air volume fraction, αa = 0.75. This means, if the air mass flow rate increases above this limit, the air entrainment may be blocked. On the other side, at water mass flow rate of 4 kg/s, there are little noticed disturbances until air mass flow rate of 0.00368 kg/s and αa = 0.43 and thereafter stabilized. After this point for water mass flow rate of 4 kg/s, increasing air mass flow rate may block the water flow and the whole inverted U-tube system possible stop flowing. Therefore, this study is able to estimate the required operational conditions and mass ratios for stable air entrainment process. Beyond these operational conditions, air entrainment may be blocked and the whole system discontinues its normal induced gravitational flow. In addition, this study proves that the inverted U-tube is able to generate a vacuum pressure up to 53.382 kPa based on the present geometrical configuration. This generated low-pressure by the inverted U-tube can be used for engineering applications which are working under vacuum and need continuous evacuating form the dry air and non-condensable gases. Furthermore, these findings motivate the utilizing of inverted U-tube for the air evacuation purposes for less power consuming in power plants.