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Interaction of weak shock waves and discrete gas inhomogeneities

Citation

Haas, Jean-Francois Luc (1984) Interaction of weak shock waves and discrete gas inhomogeneities. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-06232005-110318

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. An experimental investigation of the interaction of shock waves with discrete gas inhomogeneities is conducted in the GALCIT 15 cm diameter shock tube. The gas volumes are cylindrical refraction cells of 5 cm diameter with a 0.5 [...] thick membrane separating the test gas (helium or Freon 22) from the ambient air and large spherical soap bubbles containing the same gases. The incident wave Mach numbers are nominally 1.09 and 1.22. The wave pattern and the deformation of the gas volumes are documented by shadowgraphs. The transmitted and diffracted wave pressure profiles are recorded by pressure transducers at various distances behind the cylinders. The basic phenomena of acoustic wave refraction, reflection and diffraction by cylindrical acoustic lenses, with indices of refraction appropriate to the gases used in the experiments, are illustrated with computer-generated ray and wave-front diagrams. In the case of a Freon 22-filled cylinder, the wave diffracted externally around the body precedes the wave transmitted from the interior which goes through a focus just behind the cylinder, while in the case of the helium-filled cylinder the expanding transmitted wave runs ahead of the diffracted wave. Both sets of waves merge a few cylinder diameters downstream. The wave patterns inside the cylinder, showing initially the refracted waves and later the same waves reflected internally, present some interesting phenomena. The mechanisms by which the gas volumes are transformed into vertical structures by the shock motion are observed. The unique effect of shock acceleration and Rayleigh-Taylor instability on the spherical volume of helium leads to the formation of a strong vortex ring which rapidly separates from the main volume of helium. Measurements of the wave and gas-interface velocities are compared to values calculated for one-dimensional interactions and for a simple model of shock-induced Taylor instability. The behavior of thin liquid membranes accelerated by shocks under varying conditions is documented by high speed photography. In a related experiment, shock waves of Mach number between 1.005 and 1.36 interact with a dense random array of 2 mm diameter helium filled soap bubbles. Experimental results (based on shadowgraphs and pressure measurements) show that very weak shock waves ([...][...] 1.01) are strongly scattered by the array, which is left undisturbed by the shock, and that stronger shock waves, only locally disturbed by each bubble, maintain undisturbed pressure profiles because of nonlinear effects, while the array undergoes shock-induced mixing. A simple criterion for multiple scattering shows that the combined effect of many bubbles is necessary in order to produce important modifications on the shock wave pressure profile.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Major Option:Aeronautics
Thesis Availability:Public (worldwide access)
Thesis Committee:
  • Sturtevant, Bradford (chair)
Defense Date:15 June 1983
Record Number:CaltechETD:etd-06232005-110318
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-06232005-110318
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2701
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:24 Jun 2005
Last Modified:26 Dec 2012 02:53

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