Computational Fluid Dynamics (CFD) validation experiments require careful documentation of the boundary conditions. Many validation experiments contain complex geometries or facilities that are not accesible for meaurement using calipers. This paper describes a method for providing accurate optical measurement of physical geometries using an Nd:YAG laser, a CCD camera, and two 1-dimensional traverses. The facility used is a cylinder array test section. The laser sheet is aligned perpendicular to the cylinder span and the camera is aligned parallel to the cylinders.
After images were acquired, a code was written to analyze the images based on the Gaussian-like intensity profiles of the illuminated cylinder edges and walls in the facility. The peaks were extracted and a least squares fit applied to the peaks resulting in the center coordinates and diameter of the cross-sections. These were then reconstructed into a surface which can be imported into a CFD simulation package. This study shows that the cylinder diameters and x- and y-coordinates can be determined accurately.
The effects of various surface finishes are also compared. Three finishes were used: transparent, painted flat black, and a rhodamine painted surface with an appropriate band pass filter. The intensity profiles were compared using a single laser power setting.