Robert Wendell Pitz

A hybrid method for 2D molecular tagging velocimetry is developed to overcome the limitations of template-based methods in high-speed flows. The method integrates a Hough line transform for grid detection at arbitrary grid orientations with a multi-scale optical-flow method for sub-pixel tracking of intersections. The method was validated using synthetic datasets, achieving < 0.1 pixel root-mean-square error for translational and shear-dominated flows for signal-to-noise ratio ⩾ 4. The method is applied to analyze experimental hydroxyl tagging velocimetry measurements in a Mach 1.5 supersonic flow over an axisymmetric bluff-body with a centerline sonic N 2 fuel-jet. Time-resolved imaging of a photodissociated 11 × 11 OH grid reveals the complex velocity field, capturing a high-speed supersonic fuel-jet, expansion waves, shear layers, and the recirculation zone behind the bluff-body. By eliminating template dependency, this method provides robust, automated, and accurate velocity fields for validating high-fidelity computational fluid dynamics simulations.

Spark discharges were parametrically examined for a cylindrical air-gap electrode configuration. The aim of this study was to elucidate spark discharge characteristics, arc penetration, and exhaust plume development to guide designers of relevant ignition devices. Spark gaps ranged from 0.5 to 2.3 mm, nominal pressures ranged from 150 to 2200 kPa, and two exciter types (bipolar and unipolar) were tested. Positive correlations were observed between the pressure–distance product and multiple dependent variables: breakdown voltage, energy discharged, and percentage of sparks quenched. Positive correlations were observed between the pressure–distance quotient and various other dependent variables: spark duration, channel resistance, and plume velocity. This study also discusses the effects of quenching on electrical measurements, how these effects are nontrivial, and the subtle irregularities in electrical results that are indicative of quenching.

We report a new molecular tagging velocimetry method for use in pure nitrogen gas with a small impurity of water vapor on the order of 0.1%. This two laser method can produce a 25 mm long tag line of NH (imidogen) radicals at a standoff of 1 m which is imaged by laser-induced fluorescence after a delay of a few microseconds. The signal-to-noise ratio of the tag image can exceed 50 at standard temperature and pressure, allowing excellent spatial resolution. This new method called imidogen tagging velocimetry is useful for measuring spatially resolved velocity in flow facilities which run pure nitrogen rather than air, contain or can be seeded with trace water vapor, and in which other seeded or intrusive velocimetry methods are impractical.