FLEET System for Global Velocimetry at High Repetition Rates in Nitrogen-Based Hypersonic Ground Test Facilities.

ABSTRACT: Femtosecond Laser Electronic Excitation Tagging (FLEET) is proposed for time accurate and spatially resolved measurement of transport processes in unseeded nitrogen containing flows. A kHz rate, sub picosecond pulse laser will be focused into the flow to create lines and/or patterns through the multiphoton dissociation of nitrogen molecules. As the nitrogen atoms in the tagged regions recombine during the tens of microseconds following tagging, they emit red light, and the motion of those tagged regions can be followed with high sensitivity, time gated cameras. Multiple gating of the camera intensifiers allows the motion of each pattern to be sampled at rates of 100 kHz or greater, providing essentially real time imaging of the transport. Two cameras provide a capability for full three dimensional transport measurements. Velocity accuracies of better than +/- 10 meters per second, operation at temperatures ranging from 50K to 2000K and operation at pressures ranging from 0.1 to 1000 kPa are anticipated. The proposed Phase I research will use a new Princeton University kHz rate laser facility and wind tunnels to determine the potential and establish a system configuration for the application of FLEET kHz imaging of transport in large scale hypersonic nitrogen flow facilities. BENEFIT: FLEET opens a unique capability to the ground testing community, eliminating the requirement for seeding and providing a method for the instantaneous imaging of flow structure. Methods for the acquisition of flow data are wide spread and include particle imaging and laser induced fluorescence, both of which require seeding the flow. Once the configuration and capabilities of a FLEET system are established by this SBIR project, systems that are virtually identical can be marketed to other laboratories including many government, university and industrial customers. The need for such a capability has already been identified by NASA Langley and there has been significant interest at the Air Force Research Laboratory in Dayton, Ohio. The cost of the competing PIV systems is in the $200K range depending on the requirements. The FLEET system is expected to be more expensive due to the requirement for a femtosecond laser, but the absence of the requirement for seeding will offset that cost disadvantage. New high energy pulsed disk and fiber lasers are on the horizon and are expected to significantly reduce the price of the system. The marketing plan is to use the personnel team and laboratory space established under the Phase II effort to build similar units, initially in response to special requests from customers. The Phase II support will allow Plasma TEC to determine the cost and performance specifications for such units and to promulgate those to prospective customers. Further development of the FLEET system is expected to involve the use of new fiber based lasers for the reduction of cost and foot print with the expectation that in the future similar systems can be implemented for in flight applications including in-flight air data acquisition. Our expectation is to offer a system similar to the one designed for AEDC as soon as the performance is verified