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Attenuation of strong external blast by foam barriers
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-2915-6303
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0003-1475-5351
KTH, School of Engineering Sciences (SCI), Mechanics.
2016 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 28, no 9, article id 096105Article in journal (Refereed) Published
Abstract [en]

The mitigation of externally generated strong blast waves by an aqueous foam barrier of varying configurations within fixed distance between the explosion origin and the object to be protected is investigated and quantified both experimentally and numerically. The blast waves of shock Mach number 4.8 at 190 mm from the explosion plane are generated using exploding wire technique. The initially cylindrical blast waves are transformed into a plane blast wave in a specially constructed test unit in which the experiments are performed. The shock waves emanating from the foam barrier are captured using shadowgraph technique. A simple numerical model treating the foam by a pseudo-gas approach is used in interpreting and reconstructing the experimental results. The additional contribution of the impedance mismatch factor is analysed with the aid of numerical simulation and exploited for achieving greater blast wave pressure reduction.

Place, publisher, year, edition, pages
American Institute of Physics Inc , 2016. Vol. 28, no 9, article id 096105
Keywords [en]
Numerical models, Shock waves, A-plane, Aqueous foams, Blast waves, Exploding wire technique, Impedance mismatch factors, Shadowgraph technique, Test unit, Exploding wires
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-194875DOI: 10.1063/1.4963243ISI: 000384878900039Scopus ID: 2-s2.0-84989361083OAI: oai:DiVA.org:kth-194875DiVA, id: diva2:1055773
Note

QC 20161213

Available from: 2016-12-13 Created: 2016-11-01 Last updated: 2018-05-18Bibliographically approved
In thesis
1. Strong blast wave interaction with multiphase media
Open this publication in new window or tab >>Strong blast wave interaction with multiphase media
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The interaction of a blast wave propagating in air with different fluids like water column, aqueous foam and thermal/density inhomogeneity have been studied both experimentally and numerically. The blast waves were generated at atmospheric conditions in a newly constructed exploding wire facility. For fixed capacitance and wire size, the intensity of the shock front (measured typically at 200 mm from the wire explosion plane) was varied by controlling the charges stored in the capacitor and the size of the test section. Qualitative features of the interaction were captured using shadowgraph technique. Numerical simulations were performed to better analyze and understand the flow features observed in experiments. The main points across each fluid interactions are as follow:

Water column: A new technique was implemented to create highly repeatable, properly shaped, large diameter water column. The impact of a blast wave with shock Mach number ranging from 1.75 to 2.4 on a 22 mm diameter water column resulted in a complex system of waves propagating inside the column. Due to the concave boundary of the downstream interface, the reflected expansion wave naturally focused at a point before travelling upstream resulting in the generation of large negative pressures leading to nucleation of cavitation bubbles. Through high speed photography, various aspects of the flow features were discussed qualitatively and quantitatively. With the aid of numerical simulation, the effect of size of water column and shock strength on the maximum attainable negative pressures in the absence of cavitation were quantified.

Aqueous foam: The performance of various aqueous foam barrier configurations on the attenuation of externally generated blast wave peak pressure was examined. Here a blast wave with shock Mach number 4.8 was allowed to interact with an aqueous foam barrier of initial liquid fraction 0.1. The dominant process responsible for reduction of peak pressure was the `catching up' of the rarefaction wave with the wave front travelling in the foam barrier. Additional reduction was provided by the impedance mismatch factor at the foam-air interface which was further exploited to achieve greater reduction. A simple numerical model treating the foam by a pseudo-gas approach was used for re-constructing the experimental results.

Density inhomogeneity: The unstable evolution of a 2D elongated, elliptically-shaped inhomogeneity embedded in ambient air and aligned both normal and at an angle to the incident plane blast wave of impact Mach number 2.15 was studied. The inhomogeneity was created on the basis of `Joule heating' wherein heat produced by a current carrying wire was used to heat its surrounding air. Two counter-rotating vortices primarily due to Richtmyer-Meshkov instability (RMI) and a train of vortices primarily due to Kelvin-Helmholtz instability (KHI) were observed for two different inclination angles. Similarly circulation, calculated from numerical simulation solving Navier-Stokes equation, was also found to vary from a linear to a quadratic function when the inhomogeneity was inclined.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 190
Series
TRITA-SCI-FOU ; 2018:21
Keywords
Blast waves, negative pressure, cavitation, blast wave attenuation, RMI, KHI
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-228198 (URN)978-91-7729-813-7 (ISBN)
Public defence
2018-06-07, F3, Lindstedsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20180518

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-06-20Bibliographically approved

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Liverts, MichaelApazidis, Nicholas

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