摘要

The speckle-photographic method that has become an attractive alternative to traditional optical flow visualization methods is described and modeled by means of the Fourier analysis. The speckle displacement due to the presence of a flow with varying fluid density is verified with numerical simulation in the case studied. The speckle displacement as the signal is a measure of the refractive light deflection, similar to the information obtainable with a schlieren system; but the analysis visualizes the principal differences between the physical effects used for schlieren and speckle measurements. In order to avoid the shortcomings of this "line-of-sight" method in resolving three-dimensional test objects, an attempt is made to combine the speckle technique with the "sharp-focusing" effect known from schlieren technology. Preliminary experiments with a flow of known density distribution demonstrate that the implementation of "sharp-focusing" can deliver spatially resolved results.