Adverse Effects of Using Laser Diagnostics in High-Speed Compressible Flows

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This proposal focuses on studying the adverse effects that laser diagnostics can have on high-speed, compressible flows. Two broad diagnostic areas are targeted: particle-based and spectroscopic methods. It is expected that particle-gas interactions, which occur with particle-image velocimetry (PIV), can lead to rapid exchanges of momentum and energy in a high-speed flow and alter major gas-dynamic features, such as shock waves. It is also expected that gas seeding associated with planar laser-induced fluorescence (PLIF) and dissociation associated with femtosecond laser electronic excitation and tagging (FLEET) can also alter the separation in the near wake of a re-entry capsule flow. While gas-particle and gas-laser interactions can adversely alter the flow and lead to measurement uncertainty, these mechanisms will be exploited in this program to improve aerospace systems including intakes, thermal protection, and flow-control technologies. Using a shock tunnel, two canonical cases will be analyzed to assess any adverse diagnostic effects: the under-expanded jet and circular cylinder. Artificial flow responses will be monitored as inputs such as particle loading level, seed gas flow rates, and laser energy levels are varied. It is hypothesized that there are conditions where particle cooling has a larger effect than particle drag on displacing the Mach disk location in an under-expanded jet. It is also hypothesized that gas seeding and laser energy deposition near the lip-shock boundary-layer interaction region will perturb the free shear layer in the near wake of the circular cylinder and move the point of separation region (affecting base pressure and heating loads). Through an on-going 7-yr collaboration, Mach 6 and Mach 10 experiments using FLEET and PLIF will be performed at the NASA Langley on the circular cylinder case. Results will be compared to the impulse facility measurements at the University of Calgary. Computational flow imaging (CFI) will be used to both predict and correct for the unwanted gas-particle and gas-laser interactions that are expected to occur. CFI and experiments will be used to assess how cooled particles can be used to improve supersonic intake performance and how gas seeding and laser energy deposition can be used for flow control on the aft-bodies of re-entry capsules. This program is expected to have a large impact on extending more conventional laser diagnostics to high Mach number flows as well as to quantify the limitations of some newer diagnostics in general. The canonical problems chosen are relevant to rocket propulsion, hypersonic air-breathing propulsion, re-entry aerodynamics, missiles, and high-speed ballistics. Training of highly qualified personnel (HQP) in the area of laser diagnostics, numerical simulation, wind tunnel experiments, and aerospace technologies is a valuable output to grow Canada's knowledge-based economy.