Abstract

The limits of applicability of the invisible ink variant of the vibrationally excited nitric oxide monitoring (VENOM) technique for three distinct flow fields is reported in this work. This technique involves the generation of a grid of vibrationally excited NO ($\mathrm{X},{}^2\mathsf{\Pi }$) by exciting the NO A-X electronic transition at 226 nm, which subsequently relaxes via fluorescence and collisional quenching to produce vibrationally excited NO ($\mathrm{X},{}^2\mathsf{\Pi }$). This grid is then probed by two laser sheets tuned to distinct rotational states. The resulting images allow for the simultaneous measurement of temperature and velocity. The flow fields presented in this work provide a range of NO concentrations, vibrational lifetimes, pressures, temperatures, and collisional quenching, which explore the applicability of the invisible ink variant to a wide range of conditions. We have modelled the initial NO, ${\mathrm{O}}_2$, and ${\mathrm{N}}_2$ vibrational and rotational energy distribution resulting from the combination of fluorescence and quenching of electronically excited NO. The subsequent rethermalization of the sample, in particular the long-time vibrational relaxation, has been modelled using a forced harmonic oscillator model. The time-dependent temperature perturbation due to the invisible ink technique is evaluated for two distinct timescales: a short-timescale temperature rise resulting from collisional quenching and rotational/translational thermalization and a long-timescale temperature rise caused by vibrational thermalization. Under low pressures where fluorescence dominates quenching, there is minimal temperature perturbation of the flow field on the timescale of a VENOM measurement, and the short-timescale temperature perturbation only becomes significant at high NO seed concentrations. The predicted signal-to-noise ratio of the invisible ink method is unaffected for low-pressure, low-temperature flow fields. However, preserving signal-to-noise ratio for a high-temperature, high-pressure flow field could prove challenging due to the impact of quenching and self-absorption. Overall, we find that the invisible ink method is predicted to be a viable laser-based diagnostic for velocimetry and thermometry over a wide range of experimental conditions.

© 2019 Optical Society of America

Simultaneous velocity and temperature measurements in gaseous flowfields using the vibrationally excited nitric oxide monitoring technique: a comprehensive study

Rodrigo Sánchez-González, Rodney D. W. Bowersox, and Simon W. North
Appl. Opt. 51(9) 1216-1228 (2012)

Vibrationally excited hydroxyl tagging velocimetry

Nathan Grady and Robert W. Pitz
Appl. Opt. 53(31) 7182-7188 (2014)

Simultaneous three-dimensional velocimetry and thermometry in gaseous flows using the stereoscopic vibrationally excited nitric oxide monitoring technique

Feng Pan, Rodrigo Sánchez-González, Madison H. McIlvoy, Rodney D. W. Bowersox, and Simon W. North
Opt. Lett. 41(7) 1376-1379 (2016)

Vibrationally excited NO tagging by NO(A²Σ⁺) fluorescence and quenching for simultaneous velocimetry and thermometry in gaseous flows

Rodrigo Sánchez-González, Rodney D. W. Bowersox, and Simon W. North
Opt. Lett. 39(9) 2771-2774 (2014)

Two-component molecular tagging velocimetry utilizing NO fluorescence lifetime and NO₂ photodissociation techniques in an underexpanded jet flowfield

Andrea G. Hsu, Ravi Srinivasan, Rodney D. W. Bowersox, and Simon W. North
Appl. Opt. 48(22) 4414-4423 (2009)