Laser Dynamic Disturbance Mitigation

The innovation proposed for Phase I is the examination of two concepts for reducing turbulence-generated pressure-oscillations in a 90¿ bend and in a tee-duct. The first concept is based on introducing fine-grain, high-frequency turbulence just upstreamof the separated zone via a thin-rod shedding mechanism. The thickness of the rod and its placement in the approach boundary layer is critical to the proper operation of this concept and will be established by use of LES numerics. This concept has beendemonstrated to work in laboratory cavity studies and has been scaled-up for aircraft weapons bay applications. The second concept entails the use of flexible filaments which extract energy from the turbulent eddies using dispersed-phase interactionconcepts. Both concepts will be tested at the National Center for Physical Acoustic (at U.Miss) using models with glass sections to permit use of non-intrusive (PIV) diagnostics. This work relates to what we are performing for the AF in controllingturbulence about laser cavities and turrets, and, for NASA in analyzing fuel flows from cryogenic tanks through ducts and valves for launch applications. Phase II work will entail examining application of these to other plumbing zones (valves, etc.), and,demonstrating their effectiveness at full scale. Much of the work done in reducing vibrations stemming from turbulence-driven pressure oscillations is done at the heuristic level without a detailed understanding of the physics, and, without the use ofvery advanced CFD tools that can lead to a concept that works effectively. We have developed using hybrid RANS/LES CFD a pulsatile device that has been shown to reduce oscillations in cavities. We have applied for a patent on this device and it is nowbeing tested on a military fighter. This same device has also been shown to work at reducing jet noise and in reducing IR signatures and we are working with industry to see how it can be integrated into current and developmental aircraft. The sameopportunity is provided in this program. The concepts we proposed are fundamental but getting them to work properly is very complex, but once done, the technology is applicable to a broad variety of ducted flow problems of interest to DoD, to NASA and tocommercial industries (heating/cooling systems, etc.).