Dual hologram shearing interference technique for wind tunnel flow fields testing |
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Authors: | G Toker D Levin J Stricker |
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Institution: | (1) Department of Aerospace Engineering, Technion-I.T.T., 32000 Haifa, Israel, IL |
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Abstract: | A novel optical diagnostic technique, dual hologram shearing interferometry, for measuring density gradients of different
phase objects is proposed and demonstrated. The lateral shearing is achieved by using a phase grating. A holographic interferometer
has been developed and designed on the base of a single pass Z type conventional schlieren device. The interferometer’s scheme is insensitive to acoustical disturbances, similarly to the
conventional schlieren layout, and is capable of recording holograms with a continuous wave laser during the wind tunnel run.
The features of the technique make it tolerant to both the temporal coherence of the laser light source and to the relatively
low, schlieren quality optical windows of the wind tunnel’s test section. The obtained reconstructed lateral shearing interferograms
with a large region of overlap have high contrast and may have an arbitrary orientation and/or spacing of the background interference
fringes.
It is believed that the proposed approach will become a useful tool for visualization and accurate mapping of the density
gradients of gas dynamic flow fields, in wind and shock tunnels, where acoustic noise problems may dramatically affect reference
beam holographic schemes.
Received: 9 January 1997 / Accepted: 12 April 1997 |
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