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Published May 2021 | public
Journal Article

Focused laser differential interferometer response to shock waves


The focused laser differential interferometer (FLDI) can be used to measure rapid density fluctuations non-intrusively in high-speed flow applications. Being a non-imaging shearing interferometer, FLDI response can be accurately modeled using a paraxial ray-tracing scheme. We present the details of a new numerical implementation of this scheme, capable of accepting flow-field input from analytical models, computational fluid dynamics (CFD) results, and experimental data. This implementation has previously been validated for static (laminar jet) and dynamic (ultrasound-generated) changes in index of refraction by Lawson et al. In this work, we examine the FLDI response to shock waves propagating at up to Mach 10, in Caltech's hypervelocity expansion tube. While the timescale and approximate form of the signal can be recovered using a simple inviscid, planar shock model, it is found that the inclusion of viscous shock effects allows an accurate simulation of both the magnitude and detailed shape of the experimental response. This is a further analytical validation of the FLDI model that extends beyond the results of the existing dynamic validation case. The model implementation is then coupled to a CFD code, and predictions reproduce experimental FLDI response to a complex shock-dominated flow-field.

Additional Information

© 2021 IOP Publishing Ltd. Received 12 November 2020, revised 16 December 2020; Accepted for publication 14 January 2021; Published 12 March 2021. The authors gratefully acknowledge Prof J E Shepherd of Caltech for his ongoing interest in furthering our understanding and application of FLDI. They would also like to thank Prof R Deiterding of the University of Southampton for his patient assistance with the operation of AMROC. This work was partially supported by the Office of Naval Research award N00014-16-1-2503 with Dr Eric Marineau.

Additional details

August 20, 2023
October 23, 2023