Session Hj - Shocks, Combustion & Hypersonic Flows.
ORAL session, Tuesday, November 25
310, Moscone Center
The nature of shock waves in soap films is investigated theoretically and experimentally. For one-dimensional flows in soap films, the basic normal shock relations and Rankine-Hugoniot equations are derived. At low concentrations, the results are similar to those of compressible gases. On short time scales, soap films are analogous to compressible gases of \gamma = 1.0. The role of pressure in gases is played by surface tension in the film and that of compressibility by Gibbs or Marangoni elasticity, depending on the time scales of the film stretching. The thickness of the film is an active scalar which responds to the dynamics of the film motion in a manner similar to shallow water flows. A series of experiments is performed. The bursting of plane vertical soap films is studied by means of the high-speed flash photography and the line scan CCD imaging technique. An aureole and a shock wave preceding the expanding hole are clearly observed. The analogy between thickness jumps in soap films and shock waves in gases are then investigated experimentally. Photographs of supersonic flows over blunt bodies are presented. The results suggest the feasibility of the soap film shock tube.