Counterflow thrust vector control of subsonic jets: Continuous and bistable regimes

Fluidic thrust vectoring of a subsonic jet was examined by the asymmetric application of counterflow to the jet shear layers. When counterflow is applied to one side of a 4:1 aspect ratio rectangular jet in the proximity of a control surface, the shear-layer entrainment characteristics are altered asymmetrically giving rise to a cross-stream pressure gradient and flow vectoring. Thrust vector control up to 20 deg was possible at Mach numbers up to 0.5 using counterflow. Two regimes of fluidic control were identified, a continuous regime and a bistable one. During continuous vectoring, proportional control could be achieved between jet response and the pressure conditions established in the counterflowing stream. However, under certain circumstances, proportional control was lost leading to jet bistability. Since such bistability is undesirable for aircraft control applications, the phenomenon was studied in detail. A parametric study of the collar geometry was used to minimize jet attachment and expand the operating domain over which proportional control could be maintained.