Digital color holography applied to fluid and structural mechanics

In various domains such as acoustics, vibrations or fluid mechanics, non-invasive metrological tools, giving full-field measurements with very high spatial and temporal resolutions, need to be developed to validate the models and/or numerical simulations of the studied phenomena. In this way, ONERA and LAUM have developed optical real-time methods based on three-wavelength digital holographic interferometry to analyze either unsteady wake flows or vibrating kinematics or complex fields. These digital color holographic methods aim at avoiding panchromatic holographic plates and their related constraints. In the domain of fluids mechanics, an interferometric set-up is presented to generate micro fringes from the observed area. The data are processed thanks to direct and inverse Fourier transforms to obtain a gas density field and to study its evolution in time. In structural mechanics, a versatile interferometric imaging set-up, based on digital Fresnel holography, is presented. These new optical imaging methods result in full-field measurements with a high spatial resolution. This research ultimately aims at analyzing, in time, unsteady complex wake flows, vibrating kinematics and acoustic fields. A few examples are given and the possibilities and limits of these methods are discussed.

► Digital color holography is demonstrated in fluid and structural mechanics. ► Color allows quantifying the initial optical path difference due to external vibrations. ► Opportunity for a real-time three-dimensional sensing in given. ► Digital Fresnel holography is adapted to simultaneous 3D deformation measurements. ► The applications to real-time 3D measurement shows quite satisfactory results.