After switching to the 400 nm read light, the picture gradually brightened, and the contrast of the schlieren images gradually faded to invisibility after several minutes. An image was then collected of this scene as a reference to obtain information about the fading of the schlieren effect with time. The gas is 1,1,1,2-Tetrafluoroethane. Each distinct section of the jet appears darker on its left side and lighter on its right. 7 presents BR schlieren results for a low velocity flow of He gas.
Turbulence is observed.
Again, identifiable regions are darker on the left side and lighter on the right. The heavy curves are BR schlieren data. The light curves in Figs. 8 and 9 are profiles of images taken with the standard schlieren set-up. An attempt was made to locate high contrast regions in these images with spatial frequencies similar to those plotted for BR schlieren.