NASA’s Langley Research Center has created novel flow effector technology for separation control and enhanced mixing. The technology allows for variable shape control of aircraft structure through actively deformable surfaces. The flow effectors are made by embedding shape memory alloy actuator material in a composite structure. When thermally actuated, the flow effector deflects into or out of the flow in a prescribed manner to enhance mixing or induce separation for a variety of applications, including aeroacoustic noise reduction, drag reduction, and flight control. NASA developed the active flow effectors for noise reduction as an alternative to fixed-configuration effectors, such as static chevrons, that cannot be optimized for airframe installation effects or variable operating conditions, and cannot be retracted for off-design or failsafe conditions.
The technology involves embedding pre-strained SMA actuators on one side of the chevron neutral axis in order to generate a thermal moment and deflect the structure out of plane when heated. The force developed in the host structure during deflection and the aerodynamic load are used for returning the structure to the retracted position. The NASA chevron design is highly scalable and versatile, and easily affords active and/or autonomous (environmental) control.
Prototype chevrons at 1:9 scale have been built and tested at NASA Langley. This included thermal cycling tests, repeatability tests, and tests with representative flow conditions. All aspects of the chevron performance were found to be very repeatable, including closed-loop performance of the chevron tip to prescribed positions while immersing into and retracting from the flow.
This technology can be used in aerospace applications for distributed spoilers, jet noise control, airframe noise control, and flow separation control over high lift devices; in defense weapons bays for an adjustable flow to reduce damaging noise and reduce the thermal footprint due to flow when opening the bay; and in automotive applications for flow control and aerodynamic flow optimization.