Analysis of Screech Phenomena in a Mach 1.0 Jet with Linear Array Focused Laser Differential Interferometry

In this work, an underexpanded Mach 1.0 jet will be analyzed using an expansion of the traditional focused laser differential interferometer (FLDI). This expansion is known as linear array FLDI (LA-FLDI), and permits simultaneous probing of multiple spatial locations by means of a diffractive optical element. An array of six points is used to probe the jet in several spatial locations both inside and outside of the flowfield. The jet flowfield is measured in six distinct locations, oriented parallel with the nozzle axis, leading to a total of 36 distinct measurement points. Spectral analysis is used to determine that two screech modes—the flapping B mode and helical C mode—are present in the jet across broad spectrum of supply pressures. Four nozzle pressure ratios of interest were selected. The spectral content at these pressure ratios indicate there are several instances where these modes undergo mode-staging, as well as exist simultaneously. In general, this work is an extension of an earlier work on single-point FLDI applied to a Mach 1.5 jet, and it is expected that this work will demonstrate the utility and power of multi-point FLDI for making spatially-resolved, high-speed jet measurements—particularly for jet screech measurements.