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Shock dynamics of strong imploding cylindrical and spherical shock waves with real gas effects
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.
2010 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 22, no 11, 116102- p.Article in journal (Refereed) Published
Abstract [en]

Strong cylindrical and spherical shock implosion in a monatomic gas is considered A simple solution is obtained by Whitham's geometrical shock dynamics approach modified to account for the real gas effects The real gas effects are introduced by jump relations over the shock and include several levels of ionization, Coulomb interaction as well as internal energy of the excited electrons It is shown that ionization has a major effect on temperature and density behind the converging shock as well as on the shock acceleration The temperature and acceleration being substantially reduced and density substantially increased as compared to the ideal nonionizing case The ionization effect on the pressure behind the converging shock is less pronounced It is also shown that for the considered test case of initial Mach number M-0=8 the gas becomes completely ionized behind the spherical shock at approximately 1% of the initial radius from the focal point and its speed being decreased by a factor of 1 8 as compared to the ideal case

Place, publisher, year, edition, pages
2010. Vol. 22, no 11, 116102- p.
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-30509DOI: 10.1063/1.3500684ISI: 000285486600058Scopus ID: 2-s2.0-79251560971OAI: oai:DiVA.org:kth-30509DiVA: diva2:404261
Funder
Swedish Research Council
Note
QC 20110316Available from: 2011-03-16 Created: 2011-02-28 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Energy concentration by converging shock waves in gases
Open this publication in new window or tab >>Energy concentration by converging shock waves in gases
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Converging shock waves have been studied experimentally in a shock tube, and numerically using inviscid calculations and the theory of geometrical shock dynamics. The converging shock waves were created in a shocktube with two modular test sections designed to create cylindrical respectively spherical waves. In the spherical case the shock waves take the shape of spherical cap before propagating into a cone, while the cylindrical shocks converge in a fully circular cylindrical chamber.

The dynamics and symmetry of circular and polygonal cylindrical shock waves with initial Mach numbers ranging from 2 to 4 were studied. The shocked gas at the centre of convergence attains temperatures high enough to emit radiation which is visible to the human eye. The strength and duration of the light pulse due to shock implosion depends on the medium. In this study, shock waves converging in air, argon, nitrogen and propane have been studied. Circular shock waves are very sensitive to disturbances which deform the shock front, decreasing repeatability. Shocks consisting of plane sides making up a symmetrical polygon have a more stable behaviour during focusing, which provides less run-to-run variance in light strength. The radiation from the gas at the implosion centre has been studied photometrically and spectrometrically. The full visible spectrum of the light pulse created by a shock wave in argon has been recorded, showing the gas behaving as a blackbody radiator with apparent temperatures up to 6,000 K. This value is interpreted as a modest estimation of the temperatures actually achieved at the centre as the light has been collected from an area larger than the bright gas core. Circular shock waves attained higher temperatures but the run-to-run variation was significant. The propagation of circular and polygonal shocks was also studied using schlieren photography and compared to the self-similar theory and geometrical shock dynamics, showing good agreement.

Real gas effects must be taken into consideration for calculations at the implosion focal point. Ideal gas numerical and analytical solutions show temperatures and pressures approaching infinity, which is clearly not physical. Real gas effects due to ionisation of the argon atoms have been considered in the numerical work and its effect on the temperature has been calculated.

A second convergent test section was manufactured, designed to smoothly transform a plane shock wave into the shape of a spherical cap. After the convergent transformation the spherical shock propagates through a conical section, where it is aimed to retain the spherical shape and converge in the tip of the truncated cone, which has an end radius of 0.3 mm. Spherical implosion is more efficient than cylindrical and the target volume is much smaller than that in the cylindrical chamber. The new set-up does not suffer from large losses through reflections. Spectrometric and photometrical measurements of the implosion show significantly stronger radiation of longer duration. Preliminary results show measured apparent blackbody temperatures up to 27,000 K during implosion of shock waves of initial Mach number MS = 3.9.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. vii, 80 p.
Series
Trita-MEK, ISSN 0348-467X ; 2012:09
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-95186 (URN)978-91-7501-368-8 (ISBN)
Public defence
2012-05-25, D2, Lindstedtsvägen 5, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Note
QC 20120521Available from: 2012-05-21 Created: 2012-05-15 Last updated: 2012-05-21Bibliographically approved

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