Analysis of digital speckle tomography for reconstruction of density distribution of unsteady and asymmetric flow

Abstract

Transient and asymmetric density distributions have been investigated by a digital speckle tomography with a novel integration method. Multiple CCD images captured movements of speckles in three angles of view simultaneously because the flows were asymmetric and unsteady. The speckle movements which have been formed by a ground glass between no flow and downward butane flow from an elliptical nozzle have been calculated by a cross-correlation tracking method so that those distances can be transferred to deflection angles of laser rays for density gradients. A novel integration method has been developed to obtain projection data from the deflection angles for the speckle tomography. Also, basis functions including a cubic B-spline method have been compared with each other and a projection matrix has been analyzed to improve the accuracy of the reconstruction. The unsteady density fields have been reconstructed from the accurate projection values by the digital speckle tomography method using the developed integration method and improved basis function.