American Institute of Aeronautics and Astronautics 1 Characterization of a Counterflow Thrust Vectoring Scheme on a Gas Turbine Engine Exhaust Jet Dores, D. * and Madruga Santos, M.. † Academia da Força Aérea, 2710 Sintra, Portugal Krothapalli, A ‡ . Lourenço, L § . Collins Jr., E. ** , and Alvi, F. †† Florida A&M and Florida State University, Tallahassee, Florida, 32316 and Strykowski, P. ‡‡ University of Minnesota, Minneapolis, Minnesota, 55455 Counterflow thrust vectoring is an innovative technique that uses no movable components to redirect a thrust producing jet. This system relies on fixed curved surfaces (named collars), and a secondary stream flowing in opposite direction to the main jet. This paper reports on experimental results of the application of 2-D counterflow thrust vectoring to the exhaust of a gas turbine engine. The characterization of jet response to counterflow is presented for different gap sizes between collars and nozzle. Continuous and proportional control of the jet was demonstrated for vectoring angles up to 25º. Jet attaches to the collar wall for high counterflow levels. The secondary mass flux needed to vector the main jet is less than 6% before attachment, with thrust losses below 8%. Temperature in the vacuum line rises to the point where special caution must be taken when operating electronically controlled valves, which also proved to be affected by pressure losses in the vacuum line. Different frame setups affects the vectoring results, regarding vectoring angles. Regarding the system dynamic response, a slew rate of 160º/s was observed. However, the counterflow thrust vectoring system operates on a very inhospitable environment regarding noise and interference, which degrades the measurement for high sample rates. Based on these results an optimal gap size of 0.625 times the nozzle height was chosen for further studies concerning shear layer mixing enhancement, dynamics and controls. Nomenclature p  = relative pressure  v = vectoring angle  = density AR = nozzle aspect ratio c T = thrust coefficient F gap = pressure force acting at the gap F X collar = X component of the pressure force acting on the collar F Y collar = Y component of the pressure force acting on the collar G = gap height * Captain/Professor, Laboratório de Aeronáutica, Granja do Marquês, 2710 Sintra, Portugal. † Captain/Professor, Laboratório de Aeronáutica, Granja do Marquês, 2710 Sintra, Portugal. ‡ Professor, Department of Mechanical Engineering, 2525 Pottsdamer Street, Room 229, AIAA Senior Member. § Professor, Department of Mechanical Engineering, 2525 Pottsdamer Street, Room 229, AIAA Member. ** Professor, Department of Mechanical Engineering, 2525 Pottsdamer Street, Room 229, AIAA Member. †† Associate Professor, Department of Mechanical Engineering, 2525 Pottsdamer Street, Room 229, AIAA Member. ‡‡ Professor, 111 Church Street S.E., Room 1100, AIAA Senior Member.