scholarly journals Numerical Computation of Shock Waves in a Spherical Cloud of Cavitation Bubbles

1999 ◽  
Vol 121 (4) ◽  
pp. 872-880 ◽  
Author(s):  
Yi-Chun Wang ◽  
Christopher E. Brennen
Keyword(s):  
Pressure Pulse ◽  
Ambient Pressure ◽  
Transient Behavior ◽  
Damage Potential ◽  
Cloud Cavitation ◽  
Cavitation Bubbles ◽  
Large Pressure ◽  
Spherical Cloud ◽  
Bubble Interaction ◽  
Physical Phenomena

The nonlinear dynamics of a spherical cloud of cavitation bubbles have been simulated numerically in order to learn more about the physical phenomena occurring in cloud cavitation. A finite cloud of nuclei is subject to a decrease in the ambient pressure which causes the cloud to cavitate. A subsequent pressure recovery then causes the cloud to collapse. This is typical of the transient behavior exhibited by a bubble cloud as it passes a body or the blade of a ship propeller. The simulations employ the fully nonlinear continuum bubbly mixture equations coupled with the Rayleigh-Plesset equation for the dynamics of bubbles. A Lagrangian integral method is developed to solve this set of equations. It was found that, with strong bubble interaction effects, the collapse of the cloud is accompanied by the formation of an inward propagating bubbly shock wave. A large pressure pulse is produced when this shock passes the bubbles and causes them to collapse. The focusing of the shock at the center of the cloud produces a very large pressure pulse which radiates a substantial impulse to the far field and provides an explanation for the severe noise and damage potential in cloud cavitation.

Pressure Gradients Affecting the Labyrinth during Hypobaric Pressure

1997 ◽  
Vol 106 (6) ◽  
pp. 495-502 ◽  
Author(s):  
Konrád S. Konrádsson ◽  
Björn I. R. Carlborg ◽  
Joseph C. Farmer
Keyword(s):  
Cerebrospinal Fluid ◽  
Eustachian Tube ◽  
Ambient Pressure ◽  
Pressure Gradients ◽  
Cochlear Aqueduct ◽  
Fluid Compartment ◽  
Large Pressure ◽  
Fluid Compartments ◽  
Pressure Changes ◽  
Considerable Pressure

Hypobaric effects on the perilymph pressure were investigated in 18 cats. The perilymph, tympanic cavity, cerebrospinal fluid, and systemic and ambient pressure changes were continuously recorded relative to the atmospheric pressure. The pressure equilibration of the eustachian tube and the cochlear aqueduct was studied, as well as the effects of blocking these channels. During ascent, the physiologic opening of the eustachian tube reduced the pressure gradients across the tympanic membrane. The patent cochlear aqueduct equilibrated perilymph pressure to cerebrospinal fluid compartment levels with a considerable pressure gradient across the oval and round windows. With the aqueduct blocked, the pressure decrease within the labyrinth and tympanic cavities was limited, resulting in large pressure gradients toward the chamber and the cerebrospinal fluid compartments, respectively. We conclude that closed cavities with limited pressure release capacities are the cause of the pressure gradients. The strain exerted by these pressure gradients is potentially harmful to the ear.

A Scaling Analysis Inquiring Into Two-Phase Flow Reversal

2008 ◽  
Author(s):  
C. M. Rops ◽  
R. Lindken ◽  
L. F. G. Geers ◽  
J. Westerweel
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Pressure Fluctuations ◽  
Small Diameter ◽  
Flow Instabilities ◽  
Scaling Analysis ◽  
Two Phase ◽  
Large Pressure ◽  
Small Channels ◽  
Physical Phenomena

Physical processes limit the maximum achievable heat flux when miniaturising heat transfer equipment. In case of boiling heat transfer literature reports large pressure fluctuations, flow instabilities, and possible vapour backflow. The occurrence of the flow instabilities during boiling in small channels (defined by the Confinement Number, Co > 0.5) are explained by the formation of slug bubbles blocking the entire channel. These particular bubbles are likely to emerge during nucleate flow boiling in small diameter channels. Slug bubble blockage during flow boiling is investigated experimentally by creating a single hotspot in a small-diameter channel (Co∼5). For different liquid flow rates the detachment length of such a blocking slug bubble is determined. A scaling analysis offers to insight into the physical phenomena causing the flow instabilities. The position of the bubble caps as a function of time is identified as an important parameter.

Simulations of pressure pulse–bubble interaction using boundary element method

2006 ◽  
Vol 195 (33-36) ◽  
pp. 4287-4302 ◽  
Author(s):  
Evert Klaseboer ◽  
Cary Turangan ◽  
Siew Wan Fong ◽  
Tie Gang Liu ◽  
Kin Chew Hung ◽  
...  
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Pressure Pulse ◽  
Bubble Interaction ◽  
Element Method

SUPPRESSION OF SPIN FLUCTUATIONS IN YMn2 BY HYDROSTATIC PRESSURE

1993 ◽  
Vol 07 (01n03) ◽  
pp. 826-829 ◽  
Author(s):  
E. BAUER ◽  
I.S. DUBENKO ◽  
E. GRATZ ◽  
R. HAUSER ◽  
A. MARKOSYAN ◽  
...  
Keyword(s):  
Hydrostatic Pressure ◽  
Neutron Diffraction ◽  
Pressure Dependence ◽  
Ambient Pressure ◽  
Paramagnetic State ◽  
Spin Fluctuations ◽  
Interatomic Distances ◽  
Effective Moment ◽  
Large Pressure ◽  
Phase Compound

The cubic Laves phase compound YMn2 exhibits a huge spontaneous volume magnetostriction at the Néel temperature (TN=100 K). The magnetic moment per Mn atom is 2.7 μB at 2 K. From polarized neutron diffraction in the paramagnetic state it has been shown that the effective moment persisting above TN is reduced (1.6 μB at 120 K). The anomalously large pressure dependence of TN (dTN/dp=–35 K/kbar) is an evidence for the sensitive role played by the Mn—Mn interatomic distances. In the paramagnetic state, the influence of spin fluctuations dominates the physical properties. We have studied the effect of pressure on the resistivity up to 16 kbar. From dρ/dT we have estimated the spinfluctuation temperature as a function of pressure. The value at ambient pressure is 15 K which is in agreement with that determined in the paramagnetic Y0.9Lu0.1Mn2 compound.

scholarly journals Numerical Investigation of the Transient Behavior of a Hot Gas Duct under Rapid Depressurization

2016 ◽  
Vol 2016 ◽  
pp. 1-8
Author(s):  
JingBao Liu ◽  
ShengYao Jiang ◽  
Tao Ma ◽  
RiQiang Duan
Keyword(s):  
High Temperature ◽  
Numerical Investigation ◽  
Structural Integrity ◽  
Transient Behavior ◽  
Pressure Differential ◽  
Key Factors ◽  
Pressure Transient ◽  
Hot Gas ◽  
Large Pressure ◽  
Decisive Parameter

A hot gas duct is an indispensable component for the nuclear-process heat applications of the Very-High-Temperature Reactor (VHTR), which has to fulfill three requirements: to withstand high temperature, high pressure, and large pressure transient. In this paper, numerical investigation of pressure transient is performed for a hot gas duct under rapid depressurization. System depressurization imposes an imploding pressure differential on the internal structural elements of a hot gas duct, the structural integrity of which is susceptible to being damaged. Pressure differential and its imposed duration, which are two key factors to evaluate the damage severity of a hot gas duct under depressurization, are examined in regard to depressurization rate and insulation packing tightness. It is revealed that depressurization rate is a decisive parameter for controlling the pressure differential and its duration, whereas insulating-packing tightness has little effect on them.

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