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Strong blast wave interaction with multiphase media
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-2915-6303
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 [en]
Blast waves, negative pressure, cavitation, blast wave attenuation, RMI, KHI
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-228198ISBN: 978-91-7729-813-7 (print)OAI: oai:DiVA.org:kth-228198DiVA, id: diva2:1207069
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
List of papers
1. Plane shock wave interaction with a cylindrical water column
Open this publication in new window or tab >>Plane shock wave interaction with a cylindrical water column
2016 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 28, no 5, article id 056102Article in journal (Refereed) Published
Abstract [en]

A complex system of waves propagating inside a water column due to the impact of plane shock wave is investigated both experimentally and numerically. Flow features, such as, focusing of expansion waves generating large negative pressure, nucleation of cavitation bubbles, and a re-circulation zone are observed and discussed qualitatively and quantitatively. Experiments are conducted on a 22 mm diametrical water column hit by shock waves with Mach numbers 1.75 and 2.4 in a newly constructed exploding wire facility. A new technique to create a properly shaped, repeatable, large diameter water column with straight walls is presented. Qualitative features of the flow are captured using the shadowgraph technique. With the aid of numerical simulations the wave motions inside the column are analyzed; the spatial location of the expansion wave focusing point and the corresponding negative peak pressures is estimated.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2016
Keywords
Cavitation, Exploding wires, Cavitation bubble, Expansion wave, Large diameter, Negative pressures, Qualitative features, Shadowgraph technique, Shock wave interaction, Spatial location
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-189693 (URN)10.1063/1.4948274 (DOI)000377709500038 ()2-s2.0-84969134528 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20160711

Available from: 2016-07-11 Created: 2016-07-11 Last updated: 2018-05-18Bibliographically approved
2. An experimental time-based analysis and numerical parameter study on shock-water column interaction
Open this publication in new window or tab >>An experimental time-based analysis and numerical parameter study on shock-water column interaction
(English)Manuscript (preprint) (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-228205 (URN)
Note

QC 20180518

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-05-18Bibliographically approved
3. Attenuation of strong external blast by foam barriers
Open this publication in new window or tab >>Attenuation of strong external blast by foam barriers
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
Keywords
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:nbn:se:kth:diva-194875 (URN)10.1063/1.4963243 (DOI)000384878900039 ()2-s2.0-84989361083 (Scopus ID)
Note

QC 20161213

Available from: 2016-12-13 Created: 2016-11-01 Last updated: 2018-05-18Bibliographically approved
4. Plane blast wave propagation in air with a transverse thermal inhomogeneity
Open this publication in new window or tab >>Plane blast wave propagation in air with a transverse thermal inhomogeneity
2018 (English)In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 67, p. 220-230Article in journal (Refereed) Published
Abstract [en]

An alternate mechanism explaining the shock broadening and splitting effects observed during its propagation through an elongated region with transverse thermal inhomogeneity is described. The shock wave is generated by exploding wire technique and its propagation is captured optically using shadowgraph method. Visualizing the flow provided distinct advantage not only for obtaining detailed information on the propagation characteristics but also for validating the numerical scheme used in the analysis. Three physical features namely shock jump, precursor region and vorticity induced flow, are identified to contribute to the shock structure with the latter two being responsible for the pressure profile ‘broadening’. The physical behavior of the incident shock is also analyzed along with other factors like temperature and curvature effects.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Exploding wire, Shock broadening/splitting, Shock curvature, Thermal inhomogeneity, Shock waves, Wave propagation, Blast wave propagation, Exploding wire technique, Physical behaviors, Propagation characteristics, Shadowgraph method, Exploding wires
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-216806 (URN)10.1016/j.euromechflu.2017.09.011 (DOI)000418726900021 ()2-s2.0-85030309669 (Scopus ID)
Funder
Swedish Research Council, 621-2014-5678
Note

QC 20180111

Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2018-05-18Bibliographically approved
5. Plane blast wave interaction with an elongated straight and inclined heat-generated inhomogeneity
Open this publication in new window or tab >>Plane blast wave interaction with an elongated straight and inclined heat-generated inhomogeneity
(English)Manuscript (preprint) (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-228208 (URN)
Note

QC 20180518

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-05-22Bibliographically approved

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