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Generation And Evaluation Of Projected Moving Patterns For Reference-Free BOS With Increased Spatial Resolution

M. Raffel (1), N.T. Smith (2), C.C. Wolf (1), J.T. Heineck (3), A.D. Gardner (1)

(1) Institute of Aerodynamics and Flow Technology, DLR Göttingen, Germany

(2) Metis Technology Solutions Inc., Experimental Aero-Physics Branch, NASA Ames Research Center, Moffett Field, CA, USA

(3) Experimental Aero-Physics Branch, NASA Ames Research Center, Moffett Field, CA, USA

DOI:

A method of taking background oriented schlieren technique (BOS) images using projected

backgrounds is shown. The projected backgrounds can be scaled to the measurement

requirements, providing more flexibility than printed backgrounds. The evaluation of the BOS

image pairs using cross correlation or optical flow analysis was shown to produce equivalent

results. The background can be dynamically moved using a rotating mirror, allowing evaluation

using the reference-free shadowgraphy or reference-free BOS methods. Forward BOS is shown,

where the projected speckle pattern shines through the density object onto a screen, and is

recorded by a camera focused on the screen. In contrast to standard shadowgraphy, this technique

is robust when the lighting of the field is uneven, and the point movement is related to the first

derivative of density.

20th Edition
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