Demonstration and Characterization of Particle Streak Velocimetry in Supersonic Nozzle Flows

摘要

This work describes the development and implementation of a novel velocimetry technique to probe the exhaust flow of a cold gas thruster. The diagnostic combines the advantages of standard particle velocimetry techniques and the ultra-fast imaging capabilities of a streak camera to probe high speed flows near continuously with improved spatial and velocity resolution compared to Particle Image Velocimetry. This "Particle Streak Velocimetry" technique tracks illuminated seed particles at up to 4.2 GHz allowing time-resolved measurement of one-dimensional flows exceeding 2000 m/s as are found in rocket nozzles and many other applications. Single frame images containing multiple streaks are analyzed to find the slope of each incident particle. Tests with inert gas have been performed to validate and develop the technique in supersonic flows without background noise due to combustion. Exhaust centerline flow velocities of a cold gas nozzle flowing pure nitrogen have been probed with 300 nm titanium dioxide seed particles and a 450 nm, continuous-wave laser diode. Measured velocities on the order of 500 m/s were validated against schlieren images of the plume and stagnation temperature measurements, which can also be correlated to velocity for known flow compositions. Further tests using a mixture of helium and nitrogen have been performed with measured velocities of over 1100 m/s that are shown to agree with predicted behavior from 1-D flow analyses.