Multiparameter Laser Absorption Tomography System for High-Speed Flows

Characterization of hypersonic flow in a large-scale ground test facility is challenging due to the extreme thermodynamic and fluid dynamic environment, which exhibits drastic spatio-temporal variations. Physical probes can be inserted into the flow, but point data is insufficient and the probe will invariably alter the flow field, potentially affecting the quantities of interest by changing the flow pattern, quenching key reactions, or acting as a catalyst. Optical diagnostics are non-intrusive, but existing techniques cannot provide robust velocity data in a high enthalpy flow, let alone surrogate parameters like temperature, species, and pressure. Therefore, there is a need for diagnostics that can measure these thermo-fluid properties over the wide field-of-view typical of large-scale supersonic and hypersonic applications. ISSI proposes to address this need using Linear Absorption Tomography with Velocimetry (LATV). LATV is based on laser absorption spectroscopy, a molecular diagnostic that is directly sensitive to the absorbance of a target fluid along the measurement path. The diagnostic utilizes a network of laser beams and tomographic reconstruction algorithm to produce 2D measurements of velocity, temperature, species, and pressure in a tilted plane. This diagnostic has been demonstrated for internal supersonic reacting flows as well as jet plumes. Our implementation is unique in that it utilizes Bayesian physics-informed neural networks to conduct data assimilation with built in uncertainty quantification. Use of the LATV technique at hypersonic flight conditions requires application-specific considerations, which will be explored in the Phase I effort. Quantifying spatio-temporally resolved exit conditions in NASArsquo;s 8 ft. hypersonic tunnel using this technique is a long-term goal of the Phase II program. Accuracy and precision will be assessed by comparing LATV measurements to conventional probe data in a controlled setting.