Upscaling and Development of Linear Array Focused Laser Differential Interferometry for Simultaneous 1D Velocimetry and Spectral Profiling in High-Speed Flows

In this research a new configuration of linear array-focused laser differential interferometry (LA-FLDI) is described. This measurement expands on previous implementations of LA-FLDI through the use of an additional Wollaston prism. This additional prism expands the typical single LA-FLDI column into two columns of FLDI point pairs. The additional column of probed locations allows for increased spatial sampling of frequency spectra as well as the addition of simultaneous wall normal velocimetry measurements. The new configuration is used to measure the velocity profile and frequency content across a Mach 2 turbulent boundary layer at six wall normal locations simultaneously. Features of the measured spectra are shown to agree with expectations and the obtained boundary layer velocity profile is compared with previously obtained PIV measurements. The increase in simultaneously probed points provided by LA-FLDI is ideal for impulse facilities where spatial scanning via measurement system translation is not possible for a single run and techniques such as PIV may not be feasible. Initial testing was also carried out to determine if FLDI-based velocimetry can provide reasonable velocity profiles for adverse pressure gradients and over distributed roughness. Finally, a prototype photodiode array is proposed to simplify the optical setup for LA-FLDI and initial test results are provided comparing the impulse response of the prototype array to that of the amplified photodetectors currently in use.