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.
