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Techniques for creating precursors in shock tubes

Techniken zur Erzeugung von Precursor in Stoßrohren
: Kuhl, A.L.; Reichenbach, H.

Grönig, H.:
16th International Symposium on Shock Tubes and Waves '87. Proceedings
Weinheim: VCH Verlagsgesellschaft, 1987
pp.847-853 : Abb.,Lit.
International Symposium on Shock Tubes and Waves <16, 1987, Aachen>
Conference Paper
Fraunhofer EMI ()
precursor; simulation; Stoßrohr; Stoßwelle; Stoßwellenbrechung

The airblast precursor is a shock refraction effect formed by the interaction of a shock wave with a high-sound-speed layer. Various techniques are described for simulating precursors in small shock tubes. Three successful methods were developed to create high-sound-speed layers: helium layers contained by thin membranes, helium injected through a porous plate, and hot air layers formed by a heated foil technique. The flow was made visible by schlieren, shadow, and interferometer photography. Incident shock Mach numbers of M = 1.7 were used. The results indicate that strong precursors could be formed by these techniques. A prominent feature of the flow was an unstable, supersonic wall jet that developed large-scale, turbulent structures. Such experiments can be used to study the fluid mechanics of precursors and to evaluate the accuracy of computer simulations of this problem. (EMI)