Hybrid 2D method for molecular tagging velocimetry with application to supersonic flow over a bluff-body with a centerline fuel-jet

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Abstract 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.

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