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Title: Nonlinear reflection of a spherically divergent N-wave from a plane surface: Optical interferometry measurements in air

Mach stem is a well-known structure typically observed in the process of strong (acoustic Mach numbers greater than 0.4) step-shock waves reflection from a rigid boundary. However, this phenomenon has been much less studied for weak shocks in nonlinear acoustic fields where Mach numbers are in the range from 0.001 to 0.01 and pressure waveforms have more complicated waveforms than step shocks. The goal of this work was to demonstrate experimentally how nonlinear reflection occurs in air for very weak spherically divergent acoustic spark-generated pulses resembling an N-wave. Measurements of reflection patterns were performed using a Mach-Zehnder interferometer. A thin laser beam with sub-millimeter cross-section was used to obtain the time resolution of 0.4 µs, which is 6 times higher than the time resolution of the condenser microphones. Pressure waveforms were reconstructed using the inverse Abel transform applied to the phase of the signal measured by the interferometer. The Mach stem formation was observed experimentally as a result of collision of the incident and reflected shock pulses. It was shown that irregular reflection of the pulse occurred in a dynamic way and the length of the Mach stem increased linearly while the pulse propagated along the surface. Since the frontmore » shock of the spark-generated pulse was steeper than the rear shock, irregular type of reflection was observed only for the front shock of the pulse while the rear shock reflection occurred in a regular regime.« less
Authors:
 [1] ;  [2] ; ;  [3] ; ;  [1]
  1. Laboratoire de Mécanique des Fluides et d’Acoustique, Ecole Centrale de Lyon, 36 Avenue Guy de Collongue, 69134 Ecully (France)
  2. (Russian Federation)
  3. Physics Faculty, Moscow State University, Leninskie Gory, 119991 Moscow (Russian Federation)
Publication Date:
OSTI Identifier:
22492655
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1685; Journal Issue: 1; Conference: 20. international symposium on nonlinear acoustics, Ecully (France), 29 Jun - 3 Jul 2015, 2. international sonic boom forum, Ecully (France), 29 Jun - 3 Jul 2015; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 42 ENGINEERING; AIR; CROSS SECTIONS; HEAT EXCHANGERS; INTERFEROMETRY; LASER RADIATION; LENGTH; MACH-ZEHNDER INTERFEROMETER; NONLINEAR PROBLEMS; PULSES; REFLECTION; SHOCK WAVES; SIGNALS; SOUND WAVES; SPHERICAL CONFIGURATION; SURFACES; TIME RESOLUTION; VAPOR CONDENSERS; WAVE FORMS