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Light emission during shock wave focusing in air and argon
KTH, School of Engineering Sciences (SCI), Mechanics.
University of California, Department of Mechanical Engineering, Berkeley.
KTH, School of Engineering Sciences (SCI), Mechanics.
2007 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 19, no 10, 106106-1-106106-17 p.Article in journal (Refereed) Published
Abstract [en]

The light emission from a converging shock wave was investigated experimentally. Results show that the shape of the shock wave close to the center of convergence has a large influence on the amount of emitted light. It was found that a symmetrical polygonal shock front produced more light than an asymmetrical shape. The light emission appears as the shock wave collapses. The full width at half maximum of the light pulse is about 200 ns for all geometrical shapes. It was also found that argon as a test gas produces more light than air. Numerical simulations showed good agreement with experimental results regarding the shape of the shock and the flow field behind the shock. The temperature field from the numerical simulations was investigated and shows that the triple points behind the shock front are hot spots that increase the temperature at the center as they arrive there.

Place, publisher, year, edition, pages
2007. Vol. 19, no 10, 106106-1-106106-17 p.
Keyword [en]
Argon; Computer simulation; Flow fields; Light emission; Temperature distribution
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-7431DOI: 10.1063/1.2796214ISI: 000250589600059Scopus ID: 2-s2.0-35748937956OAI: oai:DiVA.org:kth-7431DiVA: diva2:12456
Note
QC 20100707. Uppdaterad från Submitted till Published 20100707.Available from: 2007-08-31 Created: 2007-08-31 Last updated: 2010-07-07Bibliographically approved
In thesis
1. On focusing of shock waves
Open this publication in new window or tab >>On focusing of shock waves
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Both experimental and numerical investigations of converging shock waves have been performed. In the experiments, a shock tube was used to create and study converging shock waves of various geometrical shapes. Two methods were used to create polygonally shaped shocks. In the first method, the geometry of the outer boundary of the test section of the shock tube was varied. Four different exchangeable shapes of the outer boundary were considered: a circle, a smooth pentagon, a heptagon, and an octagon. In the second method, an initially cylindrical shock wave was perturbed by metal cylinders placed in various patterns and positions inside the test section. For three or more regularly spaced cylinders, the resulting diffracted shock fronts formed polygonal shaped patterns near the point of focus. Regular reflection was observed for the case with three cylinders and Mach refection was observed for cases with four or more cylinders. When the shock wave is close to the center of convergence, light emission is observed. An experimental investigation of the light emission was conducted and results show that the shape of the shock wave close to the center of convergence has a large influence on the amount of emitted light. It was found that a symmetrical polygonal shock front produced more light than an asymmetrical shape.

The shock wave focusing was also studied numerically using the Euler equations for a gas obeying the ideal gas law with constant specific heats. Two problems were analyzed; an axisymmetric model of the shock tube used in the experiments and a cylindrical shock wave diffracted by cylinders in a two dimensional test section. The results showed good agreement with the experiments. The temperature field from the numerical simulations was investigated and shows that the triple points behind the shock front are hot spots that increase the temperature at the center as they arrive there.

As a practical example of shock wave focusing, converging shocks in an electrohydraulic lithotripter were simulated. The maximum radius of a gas bubble subjected to the pressure field obtained from the lithotripter was calculated and compared for various geometrical shapes and materials of the reflector. Results showed that the shape had a large impact while the material did not influence the maximum radius of the gas bubble.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. vii, 73 p.
Series
Trita-MEK, ISSN 0348-467X ; 2007:06
Keyword
converging shock, Euler equations, imploding shock, Mach reflection, regular reflection, shock focusing, shock tube
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-4479 (URN)978-91-7178-741-5 (ISBN)
Public defence
2007-09-21, F3, Valhallavägen 79, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100706Available from: 2007-08-31 Created: 2007-08-31 Last updated: 2010-07-06Bibliographically approved

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