scholarly journals On air entrapment onset and surface velocity in high-speed turbulent prototype flows

2022 ◽  
pp. 102122
Author(s):  
Hubert Chanson
Keyword(s):  
High Speed ◽  
Surface Velocity ◽  
Air Entrapment

A New Concept in Design of Rheolytic Thrombectomy Devices: The Coanda Effect

2009 ◽  
Author(s):  
Cheng-Shiu Chung ◽  
Sergio L. Cornejo ◽  
Ming Huo ◽  
Ender A. Finol
Keyword(s):  
Pressure Distribution ◽  
High Speed ◽  
Experimental Studies ◽  
Pressure Sensors ◽  
Surface Velocity ◽  
Coanda Effect ◽  
Ambient Fluid ◽  
Mixing Rate ◽  
Coandǎ Effect ◽  
Coanda Flow

The Coanda effect, which was first named by Henri Coanda in 1910, is the phenomenon when a fluid, gas or liquid, attaches to a solid surface, called the Coanda surface. The direction of this adhered flow changes along with the surface because of the Van der Walls forces or surface tension. Therefore, the pressure distribution of the ambient fluid is also altered due to the bent attached Coanda flow. The fluid material properties, Coanda flow velocity, curvature of the Coanda surface, velocity of the ambient fluid flow, and distance to the wall above the Coanda flow are the primary factors affecting this pressure distribution. In experimental studies, Panitz and Wasan [1] evaluated the pressure distribution of the Coanda effect by using pressure sensors on the Coanda surface and a colored dye solution in the flow. By means of photographs and experimental data, they describe the influence of different heights of the shroud (a sheath plate above the Coanda surface) and the secondary flow entrainment (flow of ambient fluid) on the pressure profiles. Vortices occur beneath the Coanda flow when the height of the shroud is lower than a specified reference. Cutbill et al. [2] developed a high speed Coanda flow k-ε turbulence model in the application of PHOENICS to improve the prediction of the mixing rate, shock wave structure and flow separation. The pressure drop occurs near the Coanda surface in both experimental and computational prediction results.

Surfactant effect on path instability of a rising bubble

2013 ◽  
Vol 738 ◽  
pp. 124-142 ◽  
Author(s):  
Yoshiyuki Tagawa ◽  
Shu Takagi ◽  
Yoichiro Matsumoto
Keyword(s):  
Shear Stress ◽  
High Speed ◽  
Lift Force ◽  
Surfactant Concentration ◽  
Bubble Surface ◽  
Surface Velocity ◽  
Helical Motion ◽  
Dimensionless Numbers ◽  
Surfactant Effect ◽  
Aspect Ratios

AbstractWe report results from the first systematic experiments for investigating surfactant effects on path instability of an air bubble rising in quiescent water. The addition of surfactant to a gas–water system causes a non-uniform distribution of surfactant concentration along the bubble surface, resulting in variations in the gas–water boundary condition from zero shear stress to non-zero shear stress due to the Marangoni effect. This leads to retarded surface velocity and ends up with immobilization of the bubble surface with increasing surfactant concentration, where the drag corresponds to that of a solid sphere of the same size. Using two high-speed cameras and vertical traverse systems, we measure three-dimensional trajectories, velocities and aspect ratios of a millimetre-sized bubble simultaneously for ${\sim }1~\mathrm{m} $. Experimental parameters are the diameter of the bubble and the surfactant concentration of 1-Pentanol or Triton X-100. We explore the surfactant effect on the drag and lift forces acting on the bubble in helical motion. While the drag force monotonically increases with the surfactant concentration as expected, the lift force shows a non-monotonic behaviour. Nevertheless, the direction of the lift force in a reference frame that rotates with the bubble along its trajectory is kept almost constant. We also observe the transient trajectory starting from helical motion to zigzag, which has never been reported in the case of purified water. The instantaneous amplitude and frequency of the transient motion agree with those of the motion regarded as steady. Finally the bubble motions are categorized as straight/helical/zigzag and experimentally examined in the field of two dimensionless numbers: Reynolds number $\mathit{Re}\in $ [300 900] and the normalized drag coefficient ${ C}_{D}^{\ast } $ which represents the slip condition. Remarkably it is found that the motions of a bubble with the intermediate slip conditions between free-slip and no-slip are helical for a broad range of $\mathit{Re}$.

Particle Tracking in Combustion Chamber of Solid Rocket Motor

2001 ◽  
Author(s):  
Yumin Xiao ◽  
R. S. Amano ◽  
Timin Cai ◽  
Jiang Li ◽  
Guoqiang He
Keyword(s):  
Boundary Conditions ◽  
Combustion Chamber ◽  
High Speed ◽  
Rocket Motor ◽  
Surface Velocity ◽  
Surface Boundary ◽  
Solid Rocket Motor ◽  
Two Phase ◽  
Solid Rocket ◽  
Propellant Surface

Abstract It has been a challenge to investigate how to trace particles in a solid rocket motor (SRM) using aluminized composite solid propellant and submerged nozzle. In using CFD simulations, the boundary conditions for the ejecting particles constrain their trajectories, hence these affect the two-phase flow calculations, and thus significantly affect the evaluation of the slag accumulation. The RTR (X-ray Real-time Radiography) technique is a new method to detect the particles in a firing SRM. A method was developed to simulate the particle ejection from the propellant surface. The moving trajectories of metal particles in a firing combustion chamber were measured by using the RTR high-speed motion analyzer. Numerical simulations with different propellant-surface boundary conditions were performed to calculate particle trajectories. Through this study an appropriate surface velocity condition on the propellant surface was discovered. The method developed here can be used for the future CRM research.

Optimum Velocity Control of Die Casting Plunger Accounting for Air Entrapment and Shutting

2008 ◽  
Vol 2 (4) ◽  
pp. 259-265 ◽  
Author(s):  
Ken'ichi Yano ◽  
◽  
Kotaro Hiramitsu ◽  
Yoshifumi Kuriyama ◽  
Seishi Nishido ◽  
...  
Keyword(s):  
Mass Production ◽  
High Speed ◽  
Die Casting ◽  
Control Input ◽  
Velocity Control ◽  
Air Entrapment ◽  
Fluid Behavior ◽  
Complex Shapes ◽  
Computational Fluid Dynamics Cfd ◽  
Optimum Velocity

Die casting in mass production has the advantage of producing complex shapes precisely, but the disadvantage of air entrapment in high-speed injection molding. Plunger velocity control very effectively avoids air entrapment. Using computational fluid dynamics (CFD), we analyzed fluid behavior, the amount of air trapped, and air shutting caused by die casting plunger movement. We calculated optimum die casting plunger velocity control input to reduce or prevent air entrapment and air shutting in die casting products. We also conducted optimization using a genetic algorithm incorporating a CFD simulator.

Dynamic Impact Characterization of Al+Fe2O3+30% Epoxy Composites Using Time Synchronized High-Speed Camera and VISAR Measurements

2005 ◽  
Vol 896 ◽  
Author(s):  
Louis Ferranti ◽  
Naresh N. Thadhani
Keyword(s):  
Dynamic Loading ◽  
High Speed ◽  
Elastic Recovery ◽  
Axial Strain ◽  
Epoxy Composites ◽  
Surface Velocity ◽  
High Speed Camera ◽  
Wave Interactions ◽  
Impact Experiments

AbstractReverse Taylor anvil-on-rod impact experiments were conducted on Al+Fe2O3+30% epoxy composites to measure their viscoelastic and fracture response to dynamic loading. Impact velocities ranged from 80 to 200 m/s. High-speed camera images capturing transient deformation reveal these materials exhibit significant elastic recovery in both the longitudinal and radial directions. Images were time synchronized with free surface velocity measurements, using VISAR, to track elastic/plastic wave interactions attributed to the material’s dynamic loading response. Some specimens underwent brittle fracture once a critical areal strain was exceeded while the axial strain response appeared unaltered.

Air entrapment by a falling water mass

1995 ◽  
Vol 294 ◽  
pp. 181-207 ◽  
Author(s):  
Hasan N. Oguz ◽  
Andrea Prosperetti ◽  
Ali R. Kolaini
Keyword(s):  
High Speed ◽  
Water Mass ◽  
Boundary Integral ◽  
Surface Shape ◽  
Water Tank ◽  
Air Entrapment ◽  
Free Surface Shape ◽  
Large Water ◽  
The Impact ◽  
Good Agreement

The impact of a nearly cylindrical water mass on a water surface is studied both experimentally and theoretically. The experiments consist of the rapid release of water from the bottom of a cylindrical container suspended above a large water tank and of the recording of the free-surface shape of the resulting crater with a high-speed camera. A bubble with a diameter of about twice that of the initial cylinder remains entrapped at the bottom of the crater when the aspect ratio and the energy of the falling water mass are sufficiently large. Many of the salient features of the phenomenon are explained on the basis of simple physical arguments. Boundary-integral potential-flow simulations of the process are also described. These numerical results are in fair to good agreement with the observations.

Influence of Surfactants on Bubble Entrainment

2010 ◽  
Author(s):  
Christopher N. Layman ◽  
John S. Allen ◽  
In Mei Sou
Keyword(s):  
High Speed ◽  
Sound Production ◽  
Liquid Surface ◽  
Acoustic Emissions ◽  
Surface Velocity ◽  
Optical Data ◽  
Formation Mechanisms ◽  
Significant Difference ◽  
Bubble Entrainment

A drop impacting on a liquid surface may entrain a bubble resulting in sounds from the bubble oscillation in addition to that of the initial drop impact. This subject has received considerable interest with respect to the underwater sound produced by rain. The previous optical and acoustical studies have extensively examined the role of drop size and impact velocity as well entrainment formation mechanisms. However, the role of surfactants on the liquid surface has received less attention especially with respect to sound production. One previous study [1] of two different surfactants (Kodak Photoflo and a sulfo detergent) reports that these suppress entrainment resulting in diminished or negligible bubble noise. However, we have found bubble entrainment and acoustic emissions associated with the addition of a heptane layer on the water surface. Using a synchronized hydrophone and a high-speed camera, acoustical and optical data of the bubble drop dynamics were obtained. Particle image velocimetry (PIV) was also utilized to measure the surface velocity produced by the drop. These results show a significant difference in the drop rebound and subsequent fluid column dynamics, which results in a dual acoustic emission for the surfactant case.

scholarly journals Direct observation of microcavitation in underwater adhesion of mushroom-shaped adhesive microstructure

2014 ◽  
Vol 5 ◽  
pp. 903-909 ◽  
Author(s):  
Lars Heepe ◽  
Alexander E Kovalev ◽  
Stanislav N Gorb
Keyword(s):  
High Speed ◽  
Video Recording ◽  
High Temporal Resolution ◽  
Contact Interface ◽  
Ambient Conditions ◽  
Air Entrapment ◽  
Underwater Adhesion ◽  
Challenges And Opportunities ◽  
Further Development ◽  
Very High

In this work we report on experiments aimed at testing the cavitation hypothesis [Varenberg, M.; Gorb, S. J. R. Soc., Interface 2008, 5, 383–385] proposed to explain the strong underwater adhesion of mushroom-shaped adhesive microstructures (MSAMSs). For this purpose, we measured the pull-off forces of individual MSAMSs by detaching them from a glass substrate under different wetting conditions and simultaneously video recording the detachment behavior at very high temporal resolution (54,000–100,000 fps). Although microcavitation was observed during the detachment of individual MSAMSs, which was a consequence of water inclusions present at the glass–MSAMS contact interface subjected to negative pressure (tension), the pull-off forces were consistently lower, around 50%, of those measured under ambient conditions. This result supports the assumption that the recently observed strong underwater adhesion of MSAMS is due to an air layer between individual MSAMSs [Kizilkan, E.; Heepe, L.; Gorb, S. N. Underwater adhesion of mushroom-shaped adhesive microstructure: An air-entrapment effect. In Biological and biomimetic adhesives: Challenges and opportunities; Santos, R.; Aldred, N.; Gorb, S. N.; Flammang, P., Eds.; The Royal Society of Chemistry: Cambridge, U.K., 2013; pp 65–71] rather than by cavitation. These results obtained due to the high-speed visualisation of the contact behavior at nanoscale-confined interfaces allow for a microscopic understanding of the underwater adhesion of MSAMSs and may aid in further development of artificial adhesive microstructures for applications in predominantly liquid environments.

High-strain-rate dynamic mechanical behavior of a bulk metallic glass composite

2008 ◽  
Vol 23 (4) ◽  
pp. 998-1008 ◽  
Author(s):  
Morgana Martin ◽  
Laszlo Kecskes ◽  
Naresh N. Thadhani
Keyword(s):  
Metallic Glass ◽  
High Strain Rate ◽  
Strain Rate ◽  
Bulk Metallic Glass ◽  
High Speed ◽  
High Strain ◽  
Microstructural Analysis ◽  
Surface Velocity ◽  
Fracture Characteristics ◽  
Transient Deformation

The high-strain-rate mechanical properties, deformation mechanisms, and fracture characteristics of a bulk metallic glass (BMG)-matrix composite, consisting of an amorphous Zr57Nb5Cu15.4Ni12.6Al10 (LM106) matrix with crystalline tungsten reinforcement particles, were investigated using gas gun anvil-on-rod impact experiments instrumented with velocity interferometry (VISAR) and high-speed digital photography. The time-resolved elastic-plastic wave propagation response obtained through VISAR and the transient deformation states captured with the camera provided information about dynamic strength and deformation modes of the composite. Comparison of experimental measurements with AUTODYN-simulated transient deformation profiles and free surface velocity traces allowed for validation of the pressure-hardening Drucker–Prager model, which was used to describe the deformation response of the composite. The impacted specimens recovered for post-impact microstructural analysis provided further information about the mechanisms of dynamic deformation and fracture characteristics. The overall results from experiments and modeling revealed a strain to failure of ∼45% along the length and ∼7% in area, and the fracture initiation stress was found to decrease with increasing impact velocity because of the negative strain-rate sensitivity of the BMG.

The Ablation Mechanism of Magnetic Driven Flyer Plate

2014 ◽  
Vol 574 ◽  
pp. 416-420
Author(s):  
Gang Hua Wang ◽  
Ming Xian Kan ◽  
Yi Fei Niu ◽  
Hai Long Zhao
Keyword(s):  
Free Surface ◽  
Stress Wave ◽  
Thermal Conduction ◽  
High Speed ◽  
Ohmic Heating ◽  
Surface Velocity ◽  
Free Surface Velocity ◽  
Magnetic Diffusion ◽  
Ablation Mechanism ◽  
Velocity History

It is found that the samples usually melt and even gasify in the magnetic driven high-speed flying plate experiments, which phenomenon goes against the investigation on materials’ equation of state (EOS). To understand this phenomenon, the whole process of magnetic driven flying plate experiment is simulated by the magnetohydrodynamic code MDSC. The ablation mechanism of magnetic driven flying plate is analyzed through the control of thermal conduction coefficient, and resistivity coefficient which is related to the magnetic diffusion velocity, in the energy conversing equation. Inside the flying plate the velocity of stress wave is much higher than that of magnetic diffusion, and hence the current goes into the inside of sample no early than the stress wave, so the magnetic diffusion doesn’t play an important role in the first stage of flyer free surface velocity history. The thermal conduction doesn’t influence the whole free surface velocity history of the flying plate much, while the Ohmic heating has a big effect on it, without which more than 20% error will be produced. The energy transportation in the flying plate medium is mainly caused by the Ohmic heating from magnetic diffusion. Besides, the relationship between the magnetic diffusion and temperature of flying plate is also analyzed.

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