Planar laser-induced fluorescence imaging of shock-tube flows with vibrational nonequilibrium

Abstract

Single-shot planar laser-induced fluorescence images of nitric oxide in shock-heated flows with vibrational nonequilibrium are reported. The results demonstrate that planar laser-induced fluorescence imaging is a promising diagnostic technique for multidimensional high-speed flows because of its ability to examine shock structure and to visualize and measure vibrational nonequilibrium. The flows studied were generated within a shock tube and were composed of dilute mixtures of NO in argon. A narrow-band ArF laser tuned to the D +-X (0,1) R 2 (28.5) transition of NO at 193.346 nm was used as the excitation source. The broadband fluorescence was collected at 90 deg to the path of excitation using an intensified, two-dimensional photodiode array. Images presented include a normal incident shock, a normal reflected shock, and a four-image sequence of the development of high-temperature supersonic flow over a two-dimensional blunt body. The vibrational relaxation in the downstream region of the normal shocks is analyzed and compared with calculations based on known relaxation rates.

Comparison of theoretical laser-induced fluorescence images with measurements performed in a hypersonic shock tunnel

“…The short duration of the laser pulse and resulting fluorescence gives PLIF the ability to freeze the motion of hypersonic flows which makes it particularly applicable to shock tunnels. For supersonic flows, PLIF has been used to measure rotational temperatures, 5 -7 vibrational temperatures, 8,9 velocity, 10 pressure 11 and mole fraction. 12 Free-piston shock tunnels present a challenging environment for PLIF.…”

Demonstration of NO production in air plasma–metallic surface interaction by broadband laser-induced fluorescence

“…Laser-induced fluorescence (LIF) remains the most accurate way to get data about the ground state of the NO radical. It was used in various high enthalpy facilities using the γ band as excitation path (mainly at 226 nm) as well as the band (mainly at 193 nm) [11][12][13] and especially for air plasma-surface interaction studies [14,15]. Schulz et al [16] showed that NO could be excited near 248 nm using a narrowband KrF exciplex laser.…”