Investigation of Initial Stage of Cavitation by Diffraction Optic Method

Besov, A. S.; Bichenkov, E. I.; Kedrinskii, V. K.; Pal'chikov, Ye. I.

doi:10.1007/978-3-642-82459-3_17

Cited by 4 publications

(13 citation statements)

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“…Various types of hydrodynamic shock tubes designed for generation of shock waves with controlled parameters under laboratory conditions may be used in experimental modeling of explosive eruptions [4][5][6]. For modeling the processes developed in the compressed magma subjected to decompression, it suffices to change the places of the gas and the liquid sample in the static scheme proposed by Glass and Heuckroth [4].…”

Section: Hydrodynamic Shock Tubes As Analogs Of the Scheme Of The Prementioning

confidence: 99%

“…For modeling the processes developed in the compressed magma subjected to decompression, it suffices to change the places of the gas and the liquid sample in the static scheme proposed by Glass and Heuckroth [4]. Dynamic schemes [5,6] that allow generation of shock waves with given parameters involve only liquid samples with the free surface and do not operate with notions of the high-pressure chamber and diaphragm in the sense of the static scheme [4]. In this case, the gas-dynamic scheme of the pre-explosion state of the volcano is formed in the dynamic mode.…”

Section: Hydrodynamic Shock Tubes As Analogs Of the Scheme Of The Prementioning

confidence: 99%

“…In this case, the gas-dynamic scheme of the pre-explosion state of the volcano is formed in the dynamic mode. The sample, which has an interface with the atmosphere (free surface), is compressed to a given pressure by a shock wave generated by some external source [5,6] and propagating over the sample up to the interface, thus, simulating the hydrostatic situation in the volcanic chamber. The wave reflected from the interface is a rarefaction wave, which propagates over the compressed sample in the opposite direction and acts as a decompression wave.…”

Section: Hydrodynamic Shock Tubes As Analogs Of the Scheme Of The Prementioning

confidence: 99%

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Gas-dynamic signs of explosive eruptions of volcanoes. 1. Hydrodynamic analogs of the pre-explosion state of volcanoes, dynamics of the three-phase magma state in decompression waves

Kedrinskii

2008

J Appl Mech Tech Phy

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Experimental data and results of numerical simulations of the magma state dynamics in explosive eruptions of volcanoes are presented. The pre-explosion state of volcanoes and the cavitation processes developed in the magma under explosive decompression are studied under the assumption that the intensity of explosive volcanoes does not exert any significant effect on the eruption mechanisms. In terms of the structural features of the pre-explosion state, a number of explosive volcanic systems are close to hydrodynamic shock-tube schemes proposed by Glass and Heuckroth. High-velocity processes initiated by shock-wave loading of the liquid may be considered as analogs of natural volcanic processes, which have common gas-dynamic features and common kinetics responsible for their mechanisms, regardless of the eruption intensity.Introduction. Explosive volcanic eruptions comprise a wide range of predictable processes, which primarily involve phase transitions induced by decompression of the liquid magma previously compressed to high pressures. As a consequence, the magma solution containing large amounts of dissolved gases becomes oversaturated. Homogeneous nucleation generates cavitation nuclei growing, in particular, by the mechanism of gas diffusion from the melt. The melt viscosity dynamically increases during the degassing process. At the same time, the mechanisms of many processes that occur in the magma and determine the magma state dynamics and the formation of the flow structure in decompression waves, as well as the character of the eruption proper, remain unclear. As the answers to these questions cannot be unambiguous because the phenomena are extremely complicated and involve many aspects and many scales, a classification of volcanic systems was obviously needed.Apparently, the first classification (in terms of the eruption character) was proposed at the end of the 19th century. In this classification, all known volcanoes were divided into three groups: 1) quiet volcanoes (which produce flowing lava); 2) explosive volcanoes; 3) intermediate volcanoes (violent eruptions followed by lava flows). A physical model was formulated for the initial state of explosive volcanoes, where the magma becomes sufficiently cooled to produce a lava plug blocking the gases and the magma in the volcanic conduit. When the pressure in the conduit reaches a value sufficient to destroy the plug, the hot gases and the magma explode out of the volcano.In 1908, Lacroix refined the notion of explosive volcanoes on the basis of the eruption intensity. In his classification, explosive volcanoes are divided into the following groups (of increasing intensity): Hawaiian (eruptions that rarely have an explosive character), Strombolian (moderate eruptions), Plinian/Vulcanian (strong eruptions), and Pelean (greatest eruptions) volcanoes. A question arises: Are these processes with many aspects governed by identical mechanisms? Obviously, the answer to this question will provide better understanding of the processes inside the magma and allow...

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Section: Hydrodynamic Shock Tubes As Analogs Of the Scheme Of The Prementioning

confidence: 99%

Section: Hydrodynamic Shock Tubes As Analogs Of the Scheme Of The Prementioning

confidence: 99%

Section: Hydrodynamic Shock Tubes As Analogs Of the Scheme Of The Prementioning

confidence: 99%

See 1 more Smart Citation

Gas-dynamic signs of explosive eruptions of volcanoes. 1. Hydrodynamic analogs of the pre-explosion state of volcanoes, dynamics of the three-phase magma state in decompression waves

Kedrinskii

2008

J Appl Mech Tech Phy

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“…This method offers a unique possibility of real-time realization of pulsed processes in the examined sample, which are adequate to natural effects in many aspects. As the real liquid (such as distilled water) contains microinhomoheneities with a density of approximately 10 12 m −3 [6], small volumes of the liquid can be used as samples to be tested. For example, a liquid drop with a 0.5-cm radius contains potential nucleation centers with a density approximately equal to 10 11 m −3 .…”

Section: Crystal Clusters In the Cavitating Magma (Experimental Modelmentioning

confidence: 99%

Gas-dynamic signs of explosive eruptions of volcanoes. 2. Model of homogeneous-heterogeneous nucleation. Specific features of destruction of the cavitating magma

Kedrinskii

2009

J Appl Mech Tech Phy

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The dynamics of state of the crystallite-containing magma is studied within the framework of the gas-dynamic model of bubble cavitation. The effect of crystallites on flow evolution is considered for two cases: where the crystallites are cavitation nuclei (homogeneous-heterogeneous nucleation model) and where large clusters of crystallites are formed in the magma in the period between eruptions. In the first case, decompression jumps are demonstrated to arise as early as in the wave precursor; the intensity of these jumps turns out to be sufficient to form a series of discrete zones of nucleation ahead of the front of the main decompression wave. Results of experimental modeling of an explosive eruption with ejection of crystallite clusters (magmatic "bombs") suggest that a cocurrent flow of the cavitating magma with dynamically varying properties (mean density and viscosity) transforms to an independent unsteady flow whose velocity is greater than the magma flow velocity. Experimental results on modeling the flow structure during the eruption show that coalescence of bubbles in the flow leads to the formation of spatial "slugs" consisting of the gas and particles. This process is analyzed within a combined nucleation model including the two-phase Iordansky-Kogarko-van Wijngaarden model and the model of the "frozen" field of mass velocities in the cavitation zone.The present paper describes the dynamics of the magma flow structure studied in model experiments and the gas dynamics of its bubble state in decompression waves. Specific Features of the Structure of the Bubble Cavitation Zone under the Conditions of Homogeneous-Heterogeneous Nucleation.As was noted in [1, 2], cavitation nuclei can form on crystallites whose volume concentration can be substantially greater than the concentration of gas nuclei; as a result, heterogeneous nucleation proceeds in the melt, in addition to homogeneous nucleation. The gas-dynamic model proposed in [3], which describes the above-mentioned processes, remains valid. The specific feature of the physical formulation of the problem is the fact that the heterogeneous mechanism is "triggered" in each layer after the homogeneous nucleation is completed; at this moment, the initial sizes of all nuclei, regardless of their nature, are assumed to be identical.It follows from calculations (see the initial conditions in [3]) that the flow structure becomes significantly different if the model of homogeneous-heterogeneous nucleation is used. As in usual bubble and cavitating media [4], the incident wave (either a shock wave or a rarefaction wave) is divided into a precursor with the front 1 [curve P (x) in Fig. 1a] propagating in a homogeneous medium with a velocity of sound c 0 and the main perturbation with the front 2 propagating in a bubble medium with a phase velocity of sound c ph . The emergence of heterogeneous nuclei in the melt leads to an increase in their total density by one or two orders, as compared with the case of homogeneous nucleation. The precursor structure becomes subs...

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“…The presence of free gas microbubbles (with dimensions of about a micrometer) in water that has been allowed to settle for several days was mentioned in [7][8][9][10][11][12][13][14][15][16][17][18][19]. At the same time, according to classical ideas about the solubility of gas in a liquid, the charac teristic lifetime of microbubbles must not be longer than tenths or even hundredths of a second.…”

Section: Introductionmentioning

confidence: 99%