Investigations and subsequent advancement of a holographic interferometry system

Non-intrusive measurement techniques for various flow parameters are important in the future of ground testing. The most promising such technique for hypersonic wind tunnels with low densities is Holographic Interferometry. Several improvements were made to an existing Holographic Interferometry system in an effort to advance the technique. An existing single plate Holographic Interferometry system was modified for use in the laboratory environment. Holograms created in a previous wind tunnel test were examined to validate the use of Phase-shift Interferometry to remove any effects due to any illumination disparities. Using this phase map, a qualitative view of a flow was created. During the reconstruction of the holograms, difficulties with the alignment of the two reference beams were discovered with the single plate method. In an effort to reduce these errors, the single plate system was modified to a dual plate system, reducing the alignment problems. This dual plate system was used in a laboratory setting to validate the new system. The reader system was modified to perform in Phase-Shift Interferometry for the dual pate system. System validation was performed ona candle, heat gun, and a blowing jet. A phase map for each of these items was created using this modified system. A user-friendly Windows-based data reduction program was developed to provide qualitative results for all of the images taken. Two computer algorithms were developed to remove the 2k ambiguities resulting from the finite fringes. These algorithms, spiral method and the largest neighbor method, were both developed in an attempt to provide noise insensitive unwrapping of the images. Both of these methods are explained and compared. Once the 2k ambiguities have been removed, the linearly changing reference fringes are subtracted off and the final phase maps are created. From these unwrapped phase maps, a computer code was developed to calculate the density. The density calculations were attempted on two-dimensional and axisymmetric flows. The flows examined were taken from a 10 degree half-angle wedge at Mach 3, an 8 degree half-angle sharp-nose cone at Mach 6, and a blowing jet taken in the laboratory