Unseeded molecular flow tagging in cold and hot flows using ozone and hydroxyl tagging velocimetry

Two complementary unseeded molecular Row tagging techniques for gas-flow velocity held measurement at low and high temperature are demonstrated. Ozone tagging velocimetry (OTV) is applicable to low-temperature air Rows whereas hydroxyl tagging velocimetry (HTV) is amenable to use in high-temperature reacting Rows containing water vapour. Tn OTV, a grid of ozone lines is created by photodissociation of O-2 by a narrowband 193 nm ArF excimer laser. After a fixed time delay, the ozone grid is imaged with a narrowband KrF laser sheet that photodissociates the ozone and produces vibrationally excited O-2 that is: subsequently made to fluoresce by the same KrF laser light sheet via the O-2 transition B (3)Sigma(u)(-) (v' = 0, 2) <-- X (3)Sigma(g)(-) (v = 6, 7). in HTV, a molecular grid of hydroxyl (OH) radicals is written into a flame by single-photon photodissociation of vibrationally excited H2O by a 193 nm ArF excimer laser. After displacement, the OH tag line position is revealed through fluorescence caused by OH A (2)Sigma(1) - X-2 Pi (3 <-- 0) excitation using a 248 nm tunable KrF excimer laser. OTV and HTV use the same lasers and can simultaneously measure velocities in low and high temperature regions. Instantaneous flow-tagging grids are measured in air flows and a flame. The velocity field is extracted from OTV images in an air jet using the image correlation velocimetry (ICV) method.