Hydroxyl Tagging Velocimetry in Supersonic Flow Over a Wall Cavity Flameholder
Lahr, Michael David
Hydroxyl tagging velocimetry (HTV) in supersonic flow over a cavity flameholder is presented in this thesis. HTV is an “unseeded”, non-intrusive method to measure gas velocity that produces a hydroxyl tag from water vapor naturally occurring in humid air. These types of gas phase velocity measurements are needed in supersonic flows where probes can easily cause flow disturbances. Typical gas phase velocity measurements are accomplished through laser scattering from particles naturally occurring in the flow or of those inserted in the flow. However, these particles can coat test section windows and exhibit drag biasing, altering the accuracy of the gas phase velocity data. The ambitions and motivation for this work under direction of Vanderbilt University and the United States Air Force are first presented. An overview of HTV, and the reasons associated with its ideality for supersonic application are also presented. In addition, the alternate velocimetry techniques and their subsequent downfalls to this area are discussed. Hydroxyl tagging velocimetry is demonstrated in Mach 2 flow in the combustor test section of a model scramjet engine at Wright-Patterson Air Force Base. Instantaneous, single-shot measurements of two-dimensional flow patterns are made in the non-reacting Mach 2 flow with a wall cavity under both low and high backpressure conditions. The single-shot profiles are analyzed to yield mean and root-mean-squared velocity profiles in the Mach 2 non-reacting flow. A description of the post-processing technique for the HTV images is presented and the subsequent results are provided. Finally, hydroxyl tagging velocimetry work that is in progress and that which is planned for the future is discussed.