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 NASAs 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. Potential NASA Applications (Limit 1500 characters, approximately 150 words): The LATV diagnostic can be used to probe internal and external flows of both reacting and non-reacting fluids. As such, the diagnostic has a wide range of potential ground and flight test applications. One application of LATV is real time characterization of NASAs extreme condition wind tunnels. The ability to quantify and time resolve flow field parameters such as velocity, temperature, species, and pressure in real time could drastically improve online interpretation of results and decision-making during test campaigns. Potential Non-NASA Applications (Limit 1500 characters, approximately 150 words): The final product from this program will be a system capable of producing 2D tomographic reconstructions of velocity, temperature, species, and pressure for high-speed wind tunnels. This technological capability is of interest to ISSIs current commercial, research, and military wind tunnel customers. ISSI expects to aggressively market this capability to these customers. Duration: 6
