Characteristics of cavity collapse behind a high-speed projectile entering the water

2021 ◽  
Vol 33 (6) ◽  
pp. 062110
Author(s):  
Q. Zhang ◽  
Z. Zong ◽  
T. Z. Sun ◽  
Y. Q. Yu ◽  
H. T. Li
Keyword(s):  
High Speed ◽  
Cavity Collapse

Mechanism of Cavitation Erosion at the Exit of a Long Orifice

2003 ◽  
Author(s):  
Yoshinori Yagi ◽  
Michio Murase ◽  
Keiichi Sato ◽  
Shuji Hattori
Keyword(s):  
High Speed ◽  
Cavitation Erosion ◽  
Propagation Speed ◽  
Video Camera ◽  
Concentric Circle ◽  
Collapse Mechanism ◽  
Pressurized Water ◽  
Flow Passage ◽  
Cavity Collapse ◽  
A Chain

We carried out experiments to clarify the mechanism of cavitation erosion at the exit of a long orifice equipped at a pressure-reducing line in a pressurized water reactor (PWR). In order to ascertain the mechanism of cavitation erosion at the first stage and progression stage, we used a high-speed video camera. As a result, we observed cavity collapse near the exit of the orifice under oscillating flow conditions, which might be a major factor in the first stage of erosion at the exit of the orifice. To simulate the progression stage, we used an orifice with a cone-shaped flow passage at its exit, corresponding to an orifice diffuser. We observed cavity collapse near the exit, after which cavities that existed upstream in the cone shape collapsed in a manner similar to a chain reaction. The propagation speed varied with the quantity of cavities in the cone-shaped flow passage and cavities collapsed in a concentric circle pattern. Thus, the cavity collapse mechanism was concluded as follows: a pressure wave (shock wave) was generated by cavity collapse near the exit, then propagated upwards, and consequently caused cavity collapse upstream. This mechanism might promote cavitation erosion in an upward direction.

scholarly journals High-speed X-ray imaging of a ball impacting on loose sand

2015 ◽  
Vol 777 ◽  
pp. 690-706 ◽  
Author(s):  
Tess Homan ◽  
Rob Mudde ◽  
Detlef Lohse ◽  
Devaraj van der Meer
Keyword(s):  
High Speed ◽  
Packing Fraction ◽  
Loose Sand ◽  
X Ray ◽  
Air Bubble ◽  
Cavity Collapse ◽  
X Ray Imaging ◽  
Custom Made ◽  
Set Up ◽  
Entrapped Air

When a ball is dropped in fine very loose sand, a splash and subsequently a jet are observed above the bed, followed by a granular eruption. To directly and quantitatively determine what happens inside the sand bed, high-speed X-ray tomography measurements are carried out in a custom-made set-up that allows for imaging of a large sand bed at atmospheric pressures. Herewith, we show that the jet originates from the pinch-off point created by the collapse of the air cavity formed behind the penetrating ball. Subsequently, we measure how the entrapped air bubble rises through the sand, and show that this is consistent with bubbles rising in continuously fluidized beds. Finally, we measure the packing fraction variation throughout the bed. From this we show that there is (i) a compressed area of sand in front of and next to the ball while the ball is moving down, (ii) a strongly compacted region at the pinch-off height after the cavity collapse and (iii) a relatively loosely packed centre in the wake of the rising bubble.

scholarly journals Ultra-high-speed x-ray imaging of shock-induced cavity collapse in a solid medium

2020 ◽  
Author(s):  
Emilio M. Escauriza ◽  
Joao P. Duarte ◽  
David J. Chapman ◽  
Lukasz Farbaniec ◽  
John C. Jonsson ◽  
...  
Keyword(s):  
High Speed ◽  
Solid Medium ◽  
X Ray ◽  
Cavity Collapse ◽  
Ultra High Speed ◽  
X Ray Imaging

Generation and breakup of Worthington jets after cavity collapse. Part 2. Tip breakup of stretched jets

2010 ◽  
Vol 663 ◽  
pp. 331-346 ◽  
Author(s):  
J. M. GORDILLO ◽  
STEPHAN GEKLE
Keyword(s):  
High Speed ◽  
Local Strain ◽  
External Noise ◽  
Creeping Flow ◽  
Liquid Density ◽  
Dimensionless Time ◽  
Cavity Collapse ◽  
Flow Limit ◽  
Theoretical Predictions ◽  
High Reynolds

The capillary breakup of the high-speed Worthington jets ejected after a cavity collapse in water occurs due to the high-Reynolds-number version of the capillary end-pinching mechanism first described, in the creeping flow limit, by Stone & Leal (J. Fluid Mech., vol. 198, 1989, p. 399). Using potential flow numerical simulations and theory, we find that the resulting drop ejection process does not depend on external noise and can be described as a function of a single dimensionless parameter, WeS = ρ R30S20/σ, which expresses the ratio of the capillary time to the inverse of the local strain rate, S0. Here, ρ and σ indicate the liquid density and the interfacial tension coefficient, respectively, and R0 is the initial radius of the jet. Our physical arguments predict the dimensionless size of the drops to scale as Ddrop/R0 ~ We−1/7S and the dimensionless time to break up as TS0 ~ We2/7S. These theoretical predictions are in good agreement with the numerical results.

Cavity collapse in a liquid with solid particles

1994 ◽  
Vol 259 ◽  
pp. 149-165 ◽  
Author(s):  
N. K. Bourne ◽  
J. E. Field
Keyword(s):  
Shock Front ◽  
Solid Particle ◽  
High Speed ◽  
Thin Sheet ◽  
Weak Shock ◽  
Incident Shock ◽  
Solid Particles ◽  
Cavity Collapse ◽  
Collapse Time ◽  
Axis Parallel

An experimental study of the interaction of weak shock waves in a liquid with bubbles and solid particles has been conducted. Cavities were punched, and solid particles were cast, into a thin sheet of gelatine clamped between two transparent blocks. A shock of pressure 0.3 GPa was introduced by impacting the gelatine layer with a flyer plate. The subsequent collapse of the cavities was photographed using high-speed framing cameras, and waves in the gelatine were visualized using schlieren optics. Assorted cavity/particle geometries were studied. In the first, cavity and particle were aligned on an axis parallel to the incident shock front. The jet crossing the cavity was found to deviate from the perpendicular to the shock front. This deviation was towards the solid particle when separations were small and away from the particle when separations were increased. When a cavity was placed upstream of a solid particle the collapse time was reduced. Conversely, when a cavity was placed downstream of a solid particle, collapse time was increased and the closure was more symmetrical. These observations were explained in terms of wave reflections. Collapses where the cavity/particle axis was inclined to the incident shock showed features of each of the geometries described above.

Tandem cavity collapse in a high-speed droplet impinging on a constrained wall

2021 ◽  
Vol 932 ◽  
Author(s):  
Wangxia Wu ◽  
Bing Wang ◽  
Qingquan Liu
Keyword(s):  
Shock Wave ◽  
High Speed ◽  
High Energy ◽  
Tandem Array ◽  
Small Scale ◽  
Two Phase ◽  
Collapse Pressure ◽  
Cavity Collapse ◽  
Pressure Peak ◽  
Energy Convergence

A focusing shock wave can be generated during the high-speed impact of a droplet on a $180^\circ$ constrained wall, which can be used to realise energy convergence on a small scale. In this study, to realise high energy convergence and peak pressure amplification, a configuration of droplets embedded with cavities is proposed for high-speed impingement on a $180^\circ$ constrained wall. A multicomponent two-phase compressible flow model considering the phase transition is used to simulate the high-speed droplet impingement process. The properties of the embedded cavities can influence the collapse pressure peak. The collapse of an embedded single air cavity or vapour cavity, as well as the cavities in a tandem array, is simulated in this study. The physical evolution mechanisms of the impinging droplet and the embedded cavities are investigated qualitatively and quantitatively by characterising the focusing shock wave generated inside the droplet and its interaction with different cavity configurations. The interaction dynamics between the cavities is analysed and a theoretical prediction model for the intensity of each cavity collapse in the tandem array is established. With the help of this theoretical model, the influencing factors for the collapse intensities of the tandem cavities are identified. The results reveal that the properties of the initial shock wave and the interval between the cavities are two predominant factors for the amplification of the collapse intensity. This study enhances the understanding of the physical process of shock-induced tandem-cavity collapse.

scholarly journals An Experimental Study on the Water Hammer with Cavity Collapse under Multiple Interruptions

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2566
Author(s):  
Li Zhao ◽  
Yusi Yang ◽  
Tong Wang ◽  
Wensheng Han ◽  
Rongchu Wu ◽  
...  
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Cavity Length ◽  
Transition States ◽  
Pressure Rise ◽  
Water Hammer ◽  
Pipeline System ◽  
Horizontal Pipe ◽  
Initial Flow ◽  
Cavity Collapse

Pressurized pipeline system damage is primarily caused by the highly destructive water hammer force. Currently, research on water hammer-caused collapse is mostly based on single-point collapse cases, but water hammer research, which involves multipoint collapse, is insufficient. Here, we establish an experimental platform to realize water hammers with multipoint collapse. With different schemes, i.e., various initial flow rates and valve closing speeds, we observed the hydraulic transient process with a high-speed camera, analyzed its characteristics and explained experimental phenomena with theoretical knowledge. Using experimental data analysis, we summarized the influencing factors and laws of the cavity length and water hammer pressure. Flow and pressure data for the different schemes were recorded to provide basic simulation data. Water column separation experimental phenomena were observed: completely atomized, completely cavitated and partially cavitated, and both cavitated and atomized. At the pump outlet, three hydraulic transition states occurred simultaneously in the horizontal pipe section: completely atomized, completely cavitated, and both cavitated and atomized. Two hydraulic transition states occurred in the knee region: completely and partially cavitated, and without atomization. The experimental results reveal that the initial flow rate and valve closing speed greatly affect the water hammer pressure rise and cavity length. The higher the initial flow rate and valve closing speed are, the larger the water hammer pressure rise and cavity length are.

scholarly journals Generation and breakup of Worthington jets after cavity collapse. Part 1. Jet formation

2010 ◽  
Vol 663 ◽  
pp. 293-330 ◽  
Author(s):  
STEPHAN GEKLE ◽  
J. M. GORDILLO
Keyword(s):  
Flow Structure ◽  
High Speed ◽  
Liquid Surface ◽  
Circular Disk ◽  
Boundary Integral ◽  
Analytical Modelling ◽  
Acceleration Region ◽  
Jet Formation ◽  
Cavity Collapse ◽  
The Impact

At the beginning of the last century Worthington and Cole discovered that the high-speed jets ejected after the impact of an axisymmetric solid on a liquid surface are intimately related to the formation and collapse of an air cavity created in the wake of the impactor. In this paper, we combine detailed boundary-integral simulations with analytical modelling to describe the formation of such Worthington jets after the impact of a circular disk on water. We extend our earlier model in Gekle et al. (Phys. Rev. Lett., vol. 102, 2009a, 034502), valid for describing only the jet base dynamics, to describe the whole jet. We find that the flow structure inside the jet may be divided into three different regions: the axial acceleration region, where the radial momentum of the incoming liquid is converted to axial momentum; the ballistic region, where fluid particles experience no further acceleration and move constantly with the velocity obtained at the end of the acceleration region; and the jet tip region, where the jet eventually breaks into droplets. From our modelling of the ballistic region we conclude that, contrary to the case of other physical situations where high-speed jets are also ejected, the types of Worthington jets studied here cannot be described using the theory of hyperbolic jets of Longuet-Higgins (J. Fluid Mech., vol. 127, 1983, p. 103). Most importantly, we find that the velocity and the shape of the ejected jets can be well predicted at any instant in time with the only knowledge of quantities obtained before pinch-off occurs. This fact allows us to provide closed expressions for the jet velocity and the sizes of the ejected droplets as a function of the velocity and the size of the impactor. We show that our results are also applicable to Worthington jets emerging after the collapse of a bubble growing from an underwater nozzle, although this system creates thicker jets than the disk impact.

scholarly journals Spectral content of cloud cavitation about a sphere

2016 ◽  
Vol 812 ◽  
Author(s):  
K. L. de Graaf ◽  
P. A. Brandner ◽  
B. W. Pearce
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Cavity Growth ◽  
Leading Edge ◽  
Transition To Turbulence ◽  
Variable Pressure ◽  
Dynamic Surface ◽  
Spectral Content ◽  
Cloud Cavitation ◽  
Cavity Collapse

The physics and spectral content of cloud cavitation about a sphere are investigated in a variable-pressure water tunnel using dynamic surface pressure measurement and high-speed imaging. Experiments are conducted using a polyvinyl chloride sphere at a Reynolds number of $1.5\times 10^{6}$ with cavitation numbers, $\unicode[STIX]{x1D70E}$, ranging from inception to supercavitation. Three distinct shedding regimes are identified: a uni-modal regime for $\unicode[STIX]{x1D70E}>0.9$ and two bi-modal regimes for $0.9>\unicode[STIX]{x1D70E}>0.675$ and $0.675>\unicode[STIX]{x1D70E}>0.3$. For small cavity lengths ($\unicode[STIX]{x1D70E}>0.9$), Kelvin–Helmholtz instability and transition to turbulence in the overlying separated boundary layer form the basis for cavity breakup and coherent vortex formation. At greater lengths ($\unicode[STIX]{x1D70E}<0.9$), larger-scale shedding ensues, driven by coupled re-entrant jet formation and shockwave propagation. Strong adverse pressure gradients about the sphere lead to accumulation and radial growth of re-entrant flow, initiating breakup, from which, in every case, a condensation shockwave propagates upstream causing cavity collapse. When the shedding is most energetic, shockwave propagation upstream may cause large-scale leading edge extinction. The bi-modal response is due to cavity shedding being either axisymmetric or asymmetric. The two bi-modal regimes correspond to $\unicode[STIX]{x1D70E}$ ranges where the cavity and re-entrant jet either remain attached or become detached from the sphere. There is a distinct frequency offset at transition between regimes in both shedding modes. Despite the greater cavity lengths at lower $\unicode[STIX]{x1D70E}$ values, the second bi-modal regime initially exhibits shorter shedding periods due to increased cavity growth rates. The second regime persists until supercavitation develops for $\unicode[STIX]{x1D70E}<0.3$.

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