Particle Streak Velocimetry of Supersonic Nozzle Flows

A novel velocimetry technique to probe the exhaust flow of a laboratory scale combustor is being developed. The technique 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. This “Particle Streak Velocimetry” technique tracks laser illuminated seed particles at up to 236 picosecond temporal resolution allowing time-resolved measurement of one-dimensional flows exceeding 2000 m/s as are found in rocket nozzles and many other applications. Developmental tests with cold nitrogen have been performed to validate and troubleshoot the technique with supersonic flows of much lower velocity and without background noise due to combusting flow. Flow velocities on the order of 500 m/s have been probed with titanium dioxide particles and a continuous-wave laser diode. Single frame images containing multiple streaks are analyzed to find the average slope of all incident particles corresponding to the centerline axial flow velocity. Long term objectives for these tests are correlation of specific impulse to theoretical combustion predictions and direct comparisons between candidate green fuels and the industry standard, monomethylhydrazine, each tested under identical conditions. α = time constant for spheres in Stokes drag [ s ] β = oblique shock angle [ ° ] d = diameter [ m ] Isp = specific impulse [ s ] n = correction factor for Stokes drag at high Reynolds number [ ] O/F = oxidizer to fuel mass flow ratio [ ] P0 = stagnation pressure [psia] ρ = density [kg/m3] φ = particle to flow velocity ratio [ ] Re = Reynolds number [ ] r = radius [mm] T0 = stagnation temperature [ K ] ∆t = time step [ s ] ts = temporal scaling factor [μs/pixel] θ = streak angle [ ° ] μ = dynamic viscosity [Pa-s] u = velocity [m/s] x = nozzle position [mm] ys = spatial scaling factor [μm/pixel] λ = dimensionless parameter from 2nd order ODE solution [ ] f = fluid subscript p = particle subscript