EXCITATION AND PHOTOGRAMMETRY ANALYSIS OF FLUID-STRUCTURAL VIBRATIONS

Abstract

The field of fluid-structural interactions (FSI) requires specifically designed measurementsystems that can be used to interpret the results of experiments without interfering with any aspects of the tests. In our hypersonic experiments, the chosen method of measurement is photogrammetry, the processing of 2-dimensional images to obtain 3-dimensional positional information about a structure exposed to a flow. To examine vibrations, the test specimen is painted with evenly spaced markers which are then photographed by a stereo digital image correlation setup of two high-speed cameras. There exists an effective algorithm for processing these images to obtain displacement and deflection data that can in turn be analyzed using spectral proper orthogonal decomposition (SPOD) to find vibrational modes. However, the current method for locating markers within an image is computationally expensive and slow, so a new algorithm was adapted to perform the same task. This adapted method differs from the old method by not being iterative, allowing it to run more quickly as it detects the markers and tracks them between images. We verified the efficacy of this new algorithm with two calibration tests, one with artificial marker images and one with real images of a painted plate translated at known displacements. After characterizing the errors of the method, it was tested on FSI experimental data collected at the NASA Langley Facility in their Mach 10 wind tunnel. The results of these tests showed that the algorithm can be quick and accurate, but it is not robust with regards to non-ideal image conditions. The images obtained in FSI photogrammetry are often not ideal, so this method must be developed further. A mechanism for test specimen excitation was also explored. We evaluated a solenoid-based prototype by performing a modal test on a compliant panel with a vibrometer. The results of this test show that the prototype is effective in producing strong and reliable vibrations in the test panel, and as such this should be developed further for use in hypersonic wind tunnel tests.