Examination of Nitric Oxide Formation for Unseeded Molecular Tagging Velocimetry

Abstract

In order to fully understand a fluid flow (and the resulting implications, e.g. lift, drag, turbulence, etc.) accurate velocity measurements under experimental conditions are critical. Nonintrusive techniques are essential to accurate measurements whereas more common instrumentation affects the flow. Molecular Tagging Velocimetry (MTV) is a technique which utilizes a nonintrusive molecule as a tracer in a flow. An ideal molecular candidate for such work is NO because of its stable nature. Prior work has shown that NO can be produced through photo-ionization of N2 using a 193 nm Argon Fluoride (ArF) laser. Chemical kinetic simulations were performed to determine the effect of photo-ionization levels and pressure on the production of NO. The simulations predict that the NO production is nonlinearly dependent on the amount of N2 ionization and the NO production increases with increasing pressure. They further show a positive correlation with increasing pressure. An alternate photo-ionization scheme to the ArF laser was investigated utilizing a pulsed 10 ns 355 nm Nd:YAG laser. The alternate has benefits over the ArF in safety, versatility, prevalence, storage, etc. but has not been shown to be able to produce NO before. The investigation determined that NO can be produced by 355 nm light, however MTV work is precluded due to low NO production rate. Therefore, the ns Nd:YAG is found to be an unsuitable replacement to the ArF laser for NO tag formation.