Decrease in Volcano Jet Noise Peak Frequency from Crater Expansion

2021 ◽  
Author(s):  
Kathleen McKee ◽  
Eveanjelene Snee ◽  
Sean Maher ◽  
Cassandra Smith ◽  
Kevin Reath ◽  
...  
Keyword(s):  
Strouhal Number ◽  
Satellite Data ◽  
Jet Noise ◽  
Peak Frequency ◽  
Nozzle Geometry ◽  
Jet Flows ◽  
Crater Diameter ◽  
Jet Velocity ◽  
Frequency Changes ◽  
Volcanic Jet

<p>Volcanic jet noise is the sound, often below the human audible range (<20 Hz and termed infrasound), generated by momentum-driven fluid flow through a volcanic vent. Assuming the self-similarity of jet flows and audible jet noise extends to infrasonic volcanic jet noise, the Strouhal number, <em>St=D<sub>j</sub>f/U<sub>j</sub></em>, connects frequency changes, <em>f</em>, to changes in the jet length (expanded jet diameter, <em>D<sub>j</sub></em>) and/or velocity scale (jet velocity, <em>U<sub>j</sub></em>). We examine the infrasound signal characteristics from the June 2019 VEI 4 eruptions of Raikoke, Kuril Islands and Ulawun, Papua New Guinea volcanoes with changes in crater geometry. We use data from the International Monitoring System (IMS) infrasound network and pre- and post-eruption satellite data (RADARSAT-2 and PlanetScope imaging for Raikoke and Ulawun, respectively). During both eruptions we observe a decrease in infrasound peak frequency during the transition to a Plinian phase, which remains through the end of the eruptions. The RADARSAT-2 data show a qualitative increase in the crater area at Raikoke; quantitative analysis is limited by shadows. At Ulawun, however, we estimate an increase in crater area from ~35,000 m<sup>2</sup> on May 25, 2019 to ~66,000 m<sup>2</sup> on July 17, 2019. We assume a constant Strouhal number and use the crater diameter as a proxy for expanded jet diameter. Our analysis suggests that the increase in crater diameter alone cannot account for the decrease in peak frequency during the Ulawun eruption. This suggests that the jet velocity also increased, which fits satellite data, and or the fluid properties (e.g. particle loading, nozzle geometry and roughness, etc.) changed. This is reasonable as the Ulawun eruption went Plinian, which likely involved an increase in jet velocity and erosion of the crater walls. This is the first study to corroborate the decrease in infrasound peak frequency with documented increase in crater area. The fortuitous satellite overpass timing, clear skies, and high spatial resolution enabled the quantitative examination of the Ulawun eruption.</p>

Impact of Mechanical Chevrons on Supersonic Jet Flow and Noise

2009 ◽  
Author(s):  
K. Kailasanath ◽  
Junhui Liu ◽  
Ephraim Gutmark ◽  
David Munday ◽  
Steven Martens
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Near Field ◽  
Supersonic Jet ◽  
Initial Step ◽  
Nozzle Geometry ◽  
Jet Flows ◽  
Flow Conditions ◽  
Nozzle Geometries ◽  
The Impact

In this paper, we present observations on the impact of mechanical chevrons on modifying the flow field and noise emanated by supersonic jet flows. These observations are derived from both a monotonically integrated large-eddy simulation (MILES) approach to simulate the near fields of supersonic jet flows and laboratory experiments. The nozzle geometries used in this research are representative of practical engine nozzles. A finite-element flow solver using unstructured grids allows us to model the nozzle geometry accurately and the MILES approach directly computes the large-scale turbulent flow structures. The emphasis of the work is on “off-design” or non-ideally expanded flow conditions. LES for several total pressure ratios under non-ideally expanded flow conditions were simulated and compared to experimental data. The agreement between the predictions and the measurements on the flow field and near-field acoustics is good. After this initial step on validating the computational methodology, the impact of mechanical chevrons on modifying the flow field and hence the near-field acoustics is being investigated. This paper presents the results to date and further details will be presented at the meeting.

Computational Modeling and Simulations of Isothermal Plane (Linear) Air Jet Velocity Profile for Slot Diffusers

2014 ◽  
Author(s):  
Deify Law ◽  
Agustin Valdez
Keyword(s):  
Velocity Profile ◽  
Jet Flows ◽  
Air Velocity ◽  
Flow Simulations ◽  
Air Jet ◽  
Isothermal Plane ◽  
Jet Velocity ◽  
Semi Empirical ◽  
Plane Jet ◽  
Free Plane

In the present work, computational modeling and simulations of isothermal plane (linear) air jet velocity profile for slot diffusers are performed. Plane air jets are formed by linear slots or rectangular openings with a large aspect ratio. Numerical simulations are performed using the commercial computational fluid dynamics (CFD) code ANSYS FLUENT. Three plane air jet flow simulations will be investigated such as free plane (linear) jets, attached jets, and air flow through a slot diffuser in a room setting. The purpose of simulating the free plane jet through a slot diffuser is to study the behavior of jet velocity profile that is not blocked by side walls or ceilings. The jet velocity profile is modified when obstructed by the walls and the air jet desires to attach to the surfaces along its path. For this reason, attached jet simulations through a slot diffuser will be conducted. The CFD study of plane air jet flows will eventually be extended to jet flows through a slot diffuser to a room to investigate the fluid flow behavior that enters a room under a ceiling. In addition, effects of two-equation turbulence models such as standard, renormalization group (RNG), and realizable k-ε on the CFD simulations will be investigated. Predicted velocity profiles and decays of free plane jet through a slot diffuser will be validated with a semi-empirical model [1]. Predicted velocity profiles of attached jet simulations will also be compared with a semi-empirical expression [2]. The slot diffuser air flow simulations will be compared with experimental data by the work of Chen and Srebric [3]. All simulations will be conducted at a specified inlet air velocity. The effects of grid resolution are also examined. It is established that the standard k-ε turbulence model best simulates attached and free jet flows. The standard k-ε turbulence model is applied to a room setting under isothermal conditions. The results are compared with non-isothermal experimental data [3]. It is shown that temperature which is a passive scalar has less influence on the flow pattern at a high air velocity than at a low air velocity in a room setting.

Supersonic Jet Noise Suppression by Coaxial Cold/Heated Jet Flows

AIAA Journal ◽  
1978 ◽  
Vol 16 (3) ◽  
pp. 268-270 ◽  
Author(s):  
D.S. Dosanjh ◽  
P.K. Bhutiani ◽  
K.K. Ahuja
Keyword(s):  
Noise Suppression ◽  
Supersonic Jet ◽  
Jet Noise ◽  
Jet Flows ◽  
Supersonic Jet Noise ◽  
Heated Jet

scholarly journals Standing shock prevents propagation of sparks in supersonic explosive flows

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Jens von der Linden ◽  
Clare Kimblin ◽  
Ian McKenna ◽  
Skyler Bagley ◽  
Hsiao-Chi Li ◽  
...  
Keyword(s):  
Radio Frequency ◽  
High Frequency ◽  
Fluid Dynamic ◽  
Supersonic Jet ◽  
Explosive Eruptions ◽  
Jet Flows ◽  
Frequency Content ◽  
Frequency Regime ◽  
High Frequency Content ◽  
Volcanic Jet

AbstractVolcanic jet flows in explosive eruptions emit radio frequency signatures, indicative of their fluid dynamic and electrostatic conditions. The emissions originate from sparks supported by an electric field built up by the ejected charged volcanic particles. When shock-defined, low-pressure regions confine the sparks, the signatures may be limited to high-frequency content corresponding to the early components of the avalanche-streamer-leader hierarchy. Here, we image sparks and a standing shock together in a transient supersonic jet of micro-diamonds entrained in argon. Fluid dynamic and kinetic simulations of the experiment demonstrate that the observed sparks originate upstream of the standing shock. The sparks are initiated in the rarefaction region, and cut off at the shock, which would limit their radio frequency emissions to a tell-tale high-frequency regime. We show that sparks transmit an impression of the explosive flow, and open the way for novel instrumentation to diagnose currently inaccessible explosive phenomena.

scholarly journals Predicting frequency changes of global-scale solar Rossby modes due to solar cycle changes in internal rotation

2020 ◽  
Vol 640 ◽  
pp. L10 ◽  
Author(s):  
C. R. Goddard ◽  
A. C. Birch ◽  
D. Fournier ◽  
L. Gizon
Keyword(s):  
Internal Rotation ◽  
Large Scale ◽  
Peak Frequency ◽  
Global Scale ◽  
Frequency Change ◽  
Theory Approach ◽  
Time Varying ◽  
Solar Cycles ◽  
Frequency Changes ◽  
The Impact

Context. Large-scale equatorial Rossby modes have been observed on the Sun over the last two solar cycles. Aims. We investigate the impact of the time-varying zonal flows on the frequencies of Rossby modes. Methods. A first-order perturbation theory approach is used to obtain an expression for the expected shift in the mode frequencies due to perturbations in the internal rotation rate. Results. Using the time-varying rotation from helioseismic inversions we predict the changes in Rossby mode frequencies with azimuthal orders from m = 1 to m = 15 over the last two solar cycles. The peak-to-peak frequency change is less than 1 nHz for the m = 1 mode, grows with m, and reaches 25 nHz for m = 15. Conclusions. Given the observational uncertainties on mode frequencies due to the finite mode lifetimes, we find that the predicted frequency shifts are near the limit of detectability.

Analysis of nozzle geometry effect on supersonic jet noise using Schlieren

2016 ◽  
Vol 140 (4) ◽  
pp. 3043-3043
Author(s):  
Yuta Ozawa ◽  
Akira Oyama ◽  
Masayuki Anyoji ◽  
Akira Oyama ◽  
Hiroya Mamori ◽  
...  
Keyword(s):  
Supersonic Jet ◽  
Jet Noise ◽  
Nozzle Geometry ◽  
Geometry Effect ◽  
Supersonic Jet Noise

scholarly journals Numerical Simulation and Experiment on Impulse Noise in a Small Caliber Rifle with Muzzle Brake

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Xin Yi Zhao ◽  
Ke Dong Zhou ◽  
Lei He ◽  
Ye Lu ◽  
Jia Wang ◽  
...  
Keyword(s):  
Flow Field ◽  
Impulse Noise ◽  
Jet Noise ◽  
Blast Waves ◽  
Jet Flows ◽  
Data Sets ◽  
Negative Effects ◽  
Aeroacoustic Noise ◽  
Noise Characteristics ◽  
Simulation And Experiment

Blast waves generated from the muzzles of weapons may exert negative effects, such as shock waves and impulse noise. If the weapon is fired with a muzzle brake, these effects are recognized to be more severe. This paper discusses the influence of the muzzle brake on certain aeroacoustic noise characteristics based on numerical simulations and a corresponding experiment. The impulse noise, which is induced by complex jet flows discharging from small caliber rifles with muzzle brakes, is focused in this study. Computational fluid dynamics (CFD) and computational aeroacoustics (CAA) are combined to calculate the muzzle flow field and jet noise for cases with and without a muzzle brake, and then the data sets are carefully compared. The simulations indicate that the muzzle brake alters the muzzle flow field and directional distribution of the jet noise compared to a rifle sans muzzle brake. Deviations less than 7.6% between experimental data and simulation results validate the simulation model. The results presented in this paper may provide a workable reference for the prediction of muzzle noise and the optimization of muzzle brake designs.

Sign in / Sign up

Export Citation Format

Share Document