Acoustic analysis of starting jets in an anechoic chamber: implications for volcano monitoring

Fernández, Juan José Peña; Cigala, Valeria; Kueppers, Ulrich; Sesterhenn, Jörn

doi:10.1038/s41598-020-69949-1

Cited by 11 publications

(26 citation statements)

References 27 publications

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“…The visibility of the gas is due to condensation upon expansion-driven cooling. After diaphragm rupture, the gas is expanding vertically and the flow requires some time to develop and generate quasi-static conditions for a short moment (Peña Fernández et al 2020). As long as the jet is underexpanded at the vent (i.e.…”

Section: Methodsmentioning

confidence: 99%

“…the vent radius (in our case) (Clarke 2013) or the jet diameter (Kieffer and Sturtevant 1984), and μ is the viscosity at the temperature of the fully expanded condition. The reference quantities in our experiments were calculated by using the one-dimensional isentropic theory (Oswatitsch 1952) by estimating gas density, viscosity and flow velocity for our experimental temperature and pressures (see Table 1 for gas properties of argon). The Re for our experiments was between 2.22 × 10 7 (cylindrical, 5 MPa) at the vent exit and 9.09 × 10 8 (diverging, 25 MPa) at fully expanded conditions.…”

Section: Scalingmentioning

confidence: 99%

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Release characteristics of overpressurised gas from complex vents: implications for volcanic hazards

et al. 2020

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Many explosive volcanic eruptions produce underexpanded starting gas-particle jets. The dynamics of the accompanying pyroclast ejection can be affected by several parameters, including magma texture, gas overpressure, erupted volume and geometry. With respect to the latter, volcanic craters and vents are often highly asymmetrical. Here, we experimentally evaluate the effect of vent asymmetry on gas expansion behaviour and gas jet dynamics directly above the vent. The vent geometries chosen for this study are based on field observations. The novel element of the vent geometry investigated herein is an inclined exit plane (5, 15, 30° slant angle) in combination with cylindrical and diverging inner geometries. In a vertical setup, these modifications yield both laterally variable spreading angles as well as a diversion of the jets, where inner geometry (cylindrical/diverging) controls the direction of the inclination. Both the spreading angle and the inclination of the jet are highly sensitive to reservoir (conduit) pressure and slant angle. Increasing starting reservoir pressure and slant angle yield (1) a maximum spreading angle (up to 62°) and (2) a maximum jet inclination for cylindrical vents (up to 13°). Our experiments thus constrain geometric contributions to the mechanisms controlling eruption jet dynamics with implications for the generation of asymmetrical distributions of proximal hazards around volcanic vents.

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Section: Methodsmentioning

confidence: 99%

Section: Scalingmentioning

confidence: 99%

Release characteristics of overpressurised gas from complex vents: implications for volcanic hazards

et al. 2020

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“…Peña Fernández et al. (2020) performed laboratory measurements of a shock tube in an anechoic chamber and studied the acoustic signal of a starting supersonic jet. Our simulations of the start‐up of a supersonic jet are complementary to this study, although our jet was pressure‐balanced with the atmosphere rather than over‐pressurized.…”

Section: Introductionmentioning

confidence: 99%

Infrasound Radiation From Impulsive Volcanic Eruptions: Nonlinear Aeroacoustic 2D Simulations

et al. 2021

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Infrasound observations are increasingly used to constrain properties of volcanic eruptions. In order to better interpret infrasound observations, however, there is a need to better understand the relationship between eruption properties and sound generation. Here we perform two‐dimensional computational aeroacoustic simulations where we solve the compressible Navier‐Stokes equations for pure‐air with a large‐eddy simulation approximation. We simulate idealized impulsive volcanic eruptions where the exit velocity is specified and the eruption is pressure‐balanced with the atmosphere. Our nonlinear simulation results are compared with the commonly used analytical linear acoustics model of a compact monopole source radiating acoustic waves isotropically in a half space. The monopole source model matches the simulations for low exit velocities (<100 m/s or M0.3333em≈0.3333em0.3 where M is the Mach number); however, the two solutions diverge as the exit velocity increases with the simulations developing lower peak amplitude, more rapid onset, and anisotropic radiation with stronger infrasound signals recorded above the vent than on Earth's surface. Our simulations show that interpreting ground‐based infrasound observations with the monopole source model can result in an underestimation of the erupted volume for eruptions with sonic or supersonic exit velocities. We examine nonlinear effects and show that nonlinear effects during propagation are relatively minor for the parameters considered. Instead, the dominant nonlinear effect is advection by the complex flow structure that develops above the vent. This work demonstrates the need to consider anisotropic radiation patterns and jet dynamics when interpreting infrasound observations, particularly for eruptions with sonic or supersonic exit velocities.

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“…Kieffer and Sturtevant 1984;Chojnicki et al 2006;Cigala et al 2017). Acoustic analysis of gas-only experiments using the same setup (Peña-Fernández et al 2020) revealed that most transient jets are composed of three stages, 1) an early vortex head phase, 2) a quasi-static phase and 3) a trailing phase, depending on pressure ratio and reservoir volume. Thus, by scaling experiments and volcanic eruption non-dimensionally, it is possible to infer from the former which variables are likely influencing the latter.…”

Section: Discussionmentioning

confidence: 99%

Linking gas and particle ejection dynamics to boundary conditions in scaled shock-tube experiments

et al. 2021

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Predicting the onset, style and duration of explosive volcanic eruptions remains a great challenge. While the fundamental underlying processes are thought to be known, a clear correlation between eruptive features observable above Earth’s surface and conditions and properties in the immediate subsurface is far from complete. Furthermore, the highly dynamic nature and inaccessibility of explosive events means that progress in the field investigation of such events remains slow. Scaled experimental investigations represent an opportunity to study individual volcanic processes separately and, despite their highly dynamic nature, to quantify them systematically. Here, impulsively generated vertical gas-particle jets were generated using rapid decompression shock-tube experiments. The angular deviation from the vertical, defined as the “spreading angle”, has been quantified for gas and particles on both sides of the jets at different time steps using high-speed video analysis. The experimental variables investigated are 1) vent geometry, 2) tube length, 3) particle load, 4) particle size, and 5) temperature. Immediately prior to the first above-vent observations, gas expansion accommodates the initial gas overpressure. All experimental jets inevitably start with a particle-free gas phase (gas-only), which is typically clearly visible due to expansion-induced cooling and condensation. We record that the gas spreading angle is directly influenced by 1) vent geometry and 2) the duration of the initial gas-only phase. After some delay, whose length depends on the experimental conditions, the jet incorporates particles becoming a gas-particle jet. Below we quantify how our experimental conditions affect the temporal evolution of these two phases (gas-only and gas-particle) of each jet. As expected, the gas spreading angle is always at least as large as the particle spreading angle. The latter is positively correlated with particle load and negatively correlated with particle size. Such empirical experimentally derived relationships between the observable features of the gas-particle jets and known initial conditions can serve as input for the parameterisation of equivalent observations at active volcanoes, alleviating the circumstances where an a priori knowledge of magma textures and ascent rate, temperature and gas overpressure and/or the geometry of the shallow plumbing system is typically chronically lacking. The generation of experimental parameterisations raises the possibility that detailed field investigations on gas-particle jets at frequently erupting volcanoes might be used for elucidating subsurface parameters and their temporal variability, with all the implications that may have for better defining hazard assessment.

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Acoustic analysis of starting jets in an anechoic chamber: implications for volcano monitoring

Cited by 11 publications

References 27 publications

Release characteristics of overpressurised gas from complex vents: implications for volcanic hazards

Release characteristics of overpressurised gas from complex vents: implications for volcanic hazards

Infrasound Radiation From Impulsive Volcanic Eruptions: Nonlinear Aeroacoustic 2D Simulations

Linking gas and particle ejection dynamics to boundary conditions in scaled shock-tube experiments

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