| Digital holographic interferometry and computed tomography for studying turbulent flows are developed in this research. It has three aspects: (1) applying digital holographic interferometry to fluid mechanics, (2) developing a computational method for limited-data tomography, and (3) visualizing a helium jet with integral imaging and computed tomography.; Digital holographic interferometry, a hybrid optical-digital technique for measuring interferometric phase, is developed for studying fluid flow. By measuring the two-dimensional distribution of the optical path integrals through a flow field, the technique forms integral projection images of the flow's refractive index field. These images visualize flow field structures well, accentuating field variations normal to the viewing direction, just as medical x-ray images illustrate structures within the body. Unlike schlieren of shadowgraph, integral interferometric images do not accentuate field gradients and are interpreted unambiguously. Practical aspects of digital interferometry, including implementation, accuracy, and use of pulsed lasers, and visualizations of two- and three-dimensional flows are presented.; Computed tomography uses an invertible integral transform relation between a field and its projections to recover a field's cross-sectional distribution. From a phase object's interferometric integral projections, one can obtain its refractive index distribution. In the absence of sufficient data, the transform can not be inverted without image artifacts and reconstruction errors. In part two, this "limited data" problem is discussed and a new formulation and algorithmn for attacking it are developed. The formulation enforces consistency between the reconstructed image and its integral projections, constrains it with known information and iteratively estimates the missing integral data.; In part three, a visualization study with integral imaging and computed tomography of a round helium jet under both laminar and turbulent conditions is presented. The integral image data demonstrates the various flow regimes of a laminar buoyant jet and illuminates large scale motions within the turbulent flows. The tomographic images of the turbulent flow demonstrate unmixed ambient fluid within the jet, a two-level concentration field structure, and stream-wise vorticity in the jet. The image artifacts in the reconstructions and the potential of interferometric tomographic measurements in turbulent flows are discussed. |
