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Published December 25, 2009 | Published
Journal Article Open

Shock focusing in a planar convergent geometry: experiment and simulation


The behaviour of an initially planar shock wave propagating into a linearly convergent wedge is investigated experimentally and numerically. In the experiment, a 25° internal wedge is mounted asymmetrically in a pressure-driven shock tube. Shock waves with incident Mach numbers in the ranges of 1.4–1.6 and 2.4–2.6 are generated in nitrogen and carbon dioxide. During each run, the full pressure history is recorded at fourteen locations along the wedge faces and schlieren images are produced. Numerical simulations performed based on the compressible Euler equations are validated against the experiment. The simulations are then used as an additional tool in the investigation. The linearly convergent geometry strengthens the incoming shock repeatedly, as waves reflected from the wedge faces cross the interior of the wedge. This investigation shows that aspects of this structure persist through multiple reflections and influence the nature of the shock-wave focusing. The shock focusing resulting from the distributed reflected waves of the Mach 1.5 case is distinctly different from the stepwise focusing at the higher incoming shock Mach number. Further experiments using CO_2 instead of N_2 elucidate some relevant real-gas effects and suggest that the presence or absence of a weak leading shock on the distributed reflections is not a controlling factor for focusing.

Additional Information

© 2009 Cambridge University Press. Received 26 March 2008; revised 7 August 2009; accepted 8 August 2009; first published online 16 November 2009. We would like to acknowledge the code development and contributions undertaken as part of the Caltech DOE ASC Alliance Program by R. Deiterding, documented above, on which the numerical simulations relied, the early exploratory discussions and investigations in collaboration with R. Samtaney, the preliminary experimental work by A. Lam, and the mechanical engineering and design assistance of G. Kaztenstein and B. Valiferdowsi. This work was supported by the Advanced Simulation and Computing (ASC) Program under subcontract no. B341492 of DOE contract W-7405-ENG-48.

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