Stereoscopic Imaging of Transverse Detonations in Diffraction

Abstract

Diffraction of gaseous detonations has received considerable attention for many years, yet there is limited understanding of the failure and initiation phenomena due to the complex coupling between the combustion and the fluid dynamics. A variety of optical techniques such as streak imaging, open shutter photography, high-speed schlieren imaging, and, more recently, planar laser induced fluorescence (PLIF) has been used to visualize the diffraction process in detonations. To overcome the integrating nature of visualization techniques and also allow for sooted foil records, many diffraction experiments in the past were carried out in narrow channels, studying detonation transition from planar to cylindrical geometry. The experimental investigation on spherically diffracting detonations described in this paper uses stereoscopic image reconstruction of the transverse detonations. The aim is to obtain further insight into the transverse detonations, which are the re-coupling phenomena identified to occur in the critical diffraction regime following a re-initiation event. The 3D reconstruction technique visualizes the transverse detonation as defined by the volume in space with high luminosity. The reconstruction technique is based on gradients, in contrast to those techniques based on target points as used, for example, in 3D particle image velocimetry. Together with a simultaneously obtained schlieren image, the location of the transverse detonation could be determined to be just below the shock surface.

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