, Volume 7, Issue 3, pp 217-224

Real-time color holographic interferometry devoted to 2D unsteady wake flows

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A new optical technique based on real time holographic interferometry in true colors has been implemented around the transonic wind tunnel of the ONERA-Lille center to analyze 2D unsteady wake flows. Tests realized in color interferometry, real time and double exposure, use simultaneously three wavelengths of a continuous waves laser (argon and krypton mixed) and holograms are recorded on silver-halide single-layer panchromatic Slavich PFG03c plates. The very principle of real-time true color holographic interferometry uses three primary wavelengths (red, green and blue) to record, under no-flow conditions, the interference among the three measurement beams and the three reference beams simultaneously on a single reference hologram. After the holographic plate is developed, it is placed on the test setup again in the position it occupied during exposure and the hologram is illuminated again by the three reference beams and three measurement beams. A flat, uniform color can then be observed behind the hologram. So a horizontal, vertical, or even circular fringe pattern can be formed and the achromatic central fringe can be made out very clearly. The single color is used to determine the path difference zero on the interferograms. The flow studied was the unsteady flow downstream of a cylinder placed crosswise in the test section. A sequence of hundred interferograms was recorded on the flow around the cylinder at Mach 0.37. The vortex formation and dissipation phases can be seen very clearly, along with the fringe beat to either side of the cylinder.

Félix Albe: Doctor/engineer, specialist in color holography using continuous and pulsed lasers, he worked in the Institute Franco-Allemand de Saint-Louis. Now retired, he brought his contribution to perform and implement the optical technique around the wind tunnel.
Jean-Michel Desse: Doctor/engineer, he works in ONERA, Centre de Lille from 1979. His research interests high speed visualizations based on the gas density measurements and more specially, the real-time color holographic interferometry.
Jean-Louis Tribillon: Doctor/engineer, famous specialist in color holography. He has a very large experience in color holography using pulsed lasers and he has recorded a lot of color interferograms known in the entire world. He works in the Direction des systèmes de Forces et de la prospective, Service Recherche Etude Amont.