Analysis of Tangent Molecular Tagging Velocimetry Using Simulated Measurements

Laminar and turbulent computational fluid dynamics (CFD) solutions of hypersonic flow around a hollow-cylinder model are used in tandem with a synthetic formulation of femtosecond laser electronic excitation tagging velocimetry to understand the parametric sensitivities and possible limitations of the tangent molecular tagging velocimetry (MTV) method for boundary-layer measurements. Velocity profiles obtained from the synthetic tangent MTV experiments are compared to exact CFD counterparts and previous experimental data to understand how boundary-layer velocity profiles, inferred boundary-layer thickness, and determined skin friction are affected by beam alignment, beam parameters, and signal-to-noise ratio. Uncertainty in the measurement technique and parametric sensitivity is analyzed using a Monte Carlo simulation. Synthetic results show that the tangent MTV method is able to successfully resolve skin-friction and boundary-layer height values, with a mean skin-friction error of approximately 1.3% and 7.6% for laminar and turbulent boundary layers, respectively. Recommendations for the future use of tangentially oriented MTV techniques are provided based on the results. This synthetic data framework also provides a means for CFD and experimental data to be compared in a manner that removes analysis bias while better reflecting measurement uncertainties and limitations.