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Early development of a spatio-temporally resolved filtered Rayleigh scattering (STR-FRS) instrument to measure temperature and density in compressible flows is discussed. This technique relies on new detector technology and FPGA data acquisition which promises many point, high repetition rate measurements. Results from a small cold jet are presented using similar technology as the full STRFRS technique, showing the robust fundamentals of the technique. Expected ratios of filtered-to-unfiltered Rayleigh scattering agree with theoretical predictions within a few percent. Additionally, numerical results are presented for using two iodine cells to maximize temperature and density measurement sensitivity in transonic jet flows. Future plans are to couple this technique with time resolved velocity measurements in flows of interest to the aeroacoustics community to correlate density and temperature fluctuations with noise production.

Gliding flight-moving horizontally downward through the air without power-has evolved in a broad diversity of taxa and serves numerous ecologically relevant functions such as predator escape, expanding foraging locations, and finding mates, and has been suggested as an evolutionary pathway to powered flight. Historically, gliding has been conceptualized using the idealized conditions of equilibrium, in which the net aerodynamic force on the glider balances its weight. While this assumption is appealing for its simplicity, recent studies of glide trajectories have shown that equilibrium gliding is not the norm for most species. Furthermore, equilibrium theory neglects the aerodynamic differences between species, as well as how a glider can modify its glide path using control. To investigate non-equilibrium glide behavior, we developed a reduced-order model of gliding that accounts for self-similarity in the equations of motion, such that the lift and drag characteristics alone determine the glide trajectory. From analysis of velocity polar diagrams of horizontal and vertical velocity from several gliding species, we find that pitch angle, the angle between the horizontal and chord line, is a control parameter that can be exploited to modulate glide angle and glide speed. Varying pitch results in changing locations of equilibrium glide configurations in the velocity polar diagram that govern passive glide dynamics. Such analyses provide a new mechanism of interspecies comparison and tools to understand experimentally-measured kinematics data and theory. In addition, this analysis suggests that the lift and drag characteristics of aerial and aquatic autonomous gliders can be engineered to passively alter glide trajectories with minimal control effort.

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