Molecular tagging velocimetry in turbulence using biacetyl

Abstract

We evaluate various molecular tagging velocimetry (MTV) techniques for application in turbulent flows of gases where the smallest length scales must be resolved. We argue that tracer diffusion dictates the use of large complex molecules and discuss a few candidate molecules. The accuracy of MTV is determined by the profile of written lines which widen due to molecular dynamics, including both diffusion and chemical reaction. We evaluate these profiles for tagging with phosphorescing biacetyl molecules, which is a commonly used probe in MTV. For relatively large laser power, these profiles are determined not by molecular diffusion, but by the triplet-triplet annihilation reaction of excited biacetyl molecules. We identify a new reaction pathway, and present a model for the observed line shapes. The rapid widening of tagged lines of biacetyl molecules due to chemical reaction restricts this MTV technique to large-scale turbulent motion in gases of comparable molecular weight.

Dispersion and deformation of molecular patterns written in turbulent air

“…This velocimetry scheme has been named FLEET [5]. Finally we mention tagging of added biacetyl molecules, which decay by slow phosphoresence [10,11]. It turns out that in biacetyl tagging the spatial resolution is compromised by collisional quenching [11].…”

“…Finally we mention tagging of added biacetyl molecules, which decay by slow phosphoresence [10,11]. It turns out that in biacetyl tagging the spatial resolution is compromised by collisional quenching [11]. To the best of our knowledge, only two molecular tagging techniques have been used to obtain quantitative turbulence data that can be compared to the result of more conventional techniques [6,12].…”