Flow Visualization by a Simplified BOS Technique
Junichi Akatsuka, Shinji Nagai · 29th AIAA Applied Aerodynamics Conference · 2011
This paper proposes a simplified background oriented schlieren (S-BOS) technique for flow visualization. Our new method does not require a cross-correlation algorithm, which results in a more straightforward and automated technique. The difficulty in optimizing parameters and removing incorrect vectors, which is typical in the conventional BOS technique, is eliminated. It allows us to output images easily in real time. In the proposed BOS method, the image displacement associated with density gradient is algebraically calculated from the image intensities using a periodic background pattern. Because the proposed optical setup is simpler than the conventional schlieren technique, it could be used in various situations including field tests. A wind tunnel test was conducted using the proposed and conventional methods in a 1 m × 1 m supersonic wind tunnel and the images displayed the value of the new, simplified technique. Nomenclature A = resolution [mm] c = circle of confusion [mm] d = image dimension [mm] f = focal length [mm] f# = aperture value G = sensor size of 1 pixel [m] I = intensity K = Gladstone-Dale constant M = Mach number m = magnification factor n = refractive index P0 = tunnel stagnation pressure [Pa] X = displacement in the image along the x-direction [pixel] Y = displacement in the image along the y-direction [pixel] Zbo = distance between background and object [mm] Zoc = distance between object and camera lens [mm] Zbc = distance between background and camera lens [mm] Zs = depth of view [mm] = angle of view [rad] = deflection angle [rad] = wavelength of light [m] i = incident angle [rad] r = refractive angle [rad]