An <i>m</i> by <i>n</i> FLDI Array for Single-Shot Multipoint Disturbance Measurements in High-Speed Flows
Mark Gragston, Theron J. Price, Kirk Davenport, John D. Schmisseur, Zhili Zhang
Abstract
View Video Presentation: https://doi.org/10.2514/6.2021-0599.vid In this work, the capabilities of the traditional focused-laser differential interferometry (FLDI) technique are expanded in an efficient manner to allow for simultaneous probing of several spatial locations using a diffractive optical element. The technique, called linear array- focused-laser differential interferometry (LA-FLDI), is demonstrated for measurements of well-characterized screech tones in an under-expanded Mach 1.5 jet and for measurements in the UTSI Mach 4 Ludwieg tube turbulent floor boundary layer. A measurement of convective velocity in the turbulent boundary layer is also made using signal correlation between beams in the array. The increased probing capability provided by LA-FLDI is ideal for impulse facilities, where spatial scanning via measurement system translation is not possible for a single run. While the work shown here utilizes a six-point array, the creation of a 2D array of FLDI beam pairs is also demonstrated. Finally, a custom geometric optics calculator is used to analyze the effect the diffractive optical element and its placement has on the beam geometry at the focal point of the system.