Measurement of three-dimensional temperature fields using multidirectional holographic interferometry

The study of three-dimensional flow phenomena is applicable to a large number of thermal engineering systems. Optical tomography using multidirectional interferometric data holds great promise to quantitatively investigate three-dimensional flow and heat transfer phenomena. In this study, multiview holographic interferometry is coupled with optical tomographic techniques to measure the three-dimensional temperature fields in a differentially-heated cubic enclosure. The experimental apparatus, test procedures, and tomographic reconstruction techniques are described herein, highlighting the specific challenges that were overcome to apply these techniques to enclosure flows. Additional experimental and computational investigations to verify the reconstruction results, such as flow visualization, independent temperature measurements, and numerical computations performed, are also described.; In addition to developing the experimental apparatus to perform the measurements and adapting existing phase extraction methods to the peculiarities of our experiment, two notable contributions were made to the field of optical tomography. First, the lack of a visible reference in the interferograms obtained from the enclosure required the development of the modified complementary field method, which allows quantitative reconstruction of the object fields using only relative fringe data. High spatial resolution in the boundary layers and thermal plume region is critical for the study of heat transfer but is problematical using existing reconstruction methods. A newly developed finite element reconstruction method significantly improved the spatial resolution by placing arbitrarily shaped reconstruction elements within the domain. These methods were demonstrated to allow more accurate reconstruction of complex refractive index fields.; By applying these new techniques, an interesting three-dimensional temperature field inside the enclosure was observed and quantified. The results of the tomographic reconstructions are verified by comparison with the flow visualization, independent temperature measurements, and computational analysis. The present results indicate that this experimental technique can yield three-dimensional perspectives of complex flows with sufficient spatial resolution to verify direct three-dimensional numerical simulations. The completion of this research lays the groundwork for development of a three-dimensional, time-dependent diagnostic for the measurement of complex flow fields.