Date(s) - 05/07/2021
3:00 pm - 4:00 pm
“Laser-Flow Coupling: A Double-Edged Sword in Hypersonic Flow Control, Diagnostics and Aero-Optics”
By: Dr. Christopher M. Limbach
Assistant Professor of Aerospace Engineering at Texas A&M University
ABSTRACT: Understanding and exploiting the interaction between high-energy lasers and high-speed flows has enabled a diverse range of applications including advanced laser diagnostics and new stand-off flow control strategies. However, the efficacy of these approaches can be significantly enhanced by carefully tailoring the interaction and mitigating unwanted side-effects. The first part of the talk focuses on gas heating as applied to flow control and diagnostics. In particular, tailoring vorticity and heating profiles can be achieved using dual-pulse excitation schemes, with demonstrated improvements in energy efficiency and lean ignition limits. In other applications, such as femtosecond laser electronic excitation tagging (FLEET) velocimetry, heat release is traded against signal strength. These considerations are discussed in the context of the first implementation of FLEET in the TAMU Actively Controlled Expansion (ACE) tunnel at Mach 6.
The second part of the talk will focus on aero-optics, beginning with the influence of non-equilibrium excitation on refractivity in hypersonic environments. For low-speed atmospheric propagations, a sub-scale 80-ft path length environmental chamber has recently been built as a pre-cursor to a 1 km enclosed directed energy facility known as the Ballistics Aero-optics and Materials (BAM) range. Baseline optical characterization of crossflow and buoyancy-driven turbulence generators will be described. Initial scintillation measurements have shown transition from L3 to L11/6 scaling occurs within the facility, highlighting the importance of flow characterization in sub-scale testing. The talk will end by describing future directions and challenge problems with two-way coupling between beam propagation and flow physics.
BIO: Dr. Limbach joined Texas A&M University (TAMU) as an Assistant Professor of Aerospace Engineering in 2018 and conducts his research at the Aerospace Laboratory for Lasers, Electromagnetics and Optics (ALLEMO). He received his PhD from Princeton University where he studied laser energy deposition and developed adjoint-based optimization methods for flow control and new diagnostic techniques for dissociated and ionized plasma flows. Dr. Limbach is the 2017 recipient of the Nakayama Award for Fluid Measurement and Visualization, is a NASA Innovative Advanced Concepts Program Fellow, and currently serves on the AIAA Plasmadynamics and Lasers Technical Committee. At TAMU, he founded the Laser Diagnostics and Plasma Devices Laboratory which focuses on fundamental and applied experimental research developing optical and plasma solutions to aerospace challenges. His research thrusts include the application of high-speed diagnostics and femtosecond laser tagging to hypersonic measurements at the TAMU National Aerothermochemistry Laboratory and development of new diagnostic approaches for remote sensing and optical air data based on atomic and molecular vapor filters. Finally, an emerging area of research has been applications of flow-optical coupling for aero-optics and space propulsion.
Friday, May 7, 3-4pm, Zoom meeting link: https://nmsu.zoom.us/j/99609263954