Affiliations: Office National d'Etudes et Recherches
Aérospatiales, Centre de Lille, 5, Boulevard Paul
Painlevé, 50045 Lille, France. E-mail: desse@imf-lille.fr | Institut Franco-allemand de Recherches de Saint-Louis,
5, rue du Général Cassagnou, BP 34, 68301 Saint-Louis,
France | Direction des Systèmes de Forces et de la
Prospective, Service Recherche Etude Amont, 4bis, Avenue de la porte
d'Issy, 75075 Paris Cedex, France
Abstract: 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.
Keywords: Color Holography, Interferometry, High Speed Flow, Gas Density Field
