Sweeping jet actuators
Active flow control using fluidic oscillators to increase rudder lift.
Sweeping jet actuators are an active flow control technology that relies on fluidic oscillators to generate sweeping jets. These actuators take the form of slots embedded in an airfoil's control surface, operating on the same principle as blown flaps: blowing air across the airfoil's surface boosts its effective lift. The first demonstration of fluidic oscillators used as sweeping jets for flow control was carried out by Raman and colleagues in 1999.
The motivation for researching sweeping jet actuators comes from the fact that an aircraft's vertical tail is a parasitic surface during level flight. The vertical stabilizer on multi-engine aircraft must be designed to generate enough lift to counter thrust asymmetry from an engine failure during takeoff rotation. However, in non-emergency conditions or when no yaw moment is needed, the vertical stabilizer only adds weight and drag. The actuator's jet nozzles, placed just upstream of the rudder hinge, eject a subsonic air stream over the rudder. This flow helps retain or reattach the boundary layer to the control surface even when the rudder is deflected beyond the angle where natural flow would separate, increasing the rudder's effective lift by up to 30 percent.
As of January 2015, sweeping jet actuators had only been used experimentally and were not a design feature on any known aircraft.
- First demonstration
- Raman et al., 1999
- Lift increase
- 30 percent
- Organizations involved
- ['Boeing', 'NASA', 'University of Arizona Department of Aerospace and Mechanical Engineering', 'Illinois Institute of Technology', 'Advanced Fluidics', 'Technische Universität Berlin']
- Application status as of january 2015
- experimental only, not on any known aircraft
Lore & Background
The impetus behind the research into sweeping jet actuators lies in the realization that any vertical tail structure on an aircraft is a parasitic surface in level flight. The design specification that must be met by the vertical stabilizer of any multi-engined aircraft is that it be able to produce enough lift to counteract any thrust asymmetry that would come as a result of engine failure during rotation (takeoff); but in any condition that is not an emergency or where a yaw moment is not desired the vertical stabilizer will only contribute added weight and drag to the aircraft.
The jet nozzles, located directly upstream of the hinge around which the rudder moves, eject a subsonic stream of air that flows over the rudder and act to retain or reattach the boundary layer to the control surface as it is deflected beyond the incidence angle where natural flow would separate, generating as much as a 30-percent increase in the effective lift produced by the rudder.
As of January 2015 sweeping jet actuators have only seen experimental application and are not included as a design feature of any known aircraft.
Reader's Guide
Sweeping jet actuators represent a notable development in active flow control, addressing the parasitic nature of vertical tail structures in level flight. The article explains that the vertical stabilizer of a multi-engined aircraft is sized to counteract thrust asymmetry from engine failure during takeoff, but otherwise adds only weight and drag. By using fluidic oscillators to produce sweeping jets, these actuators reattach the boundary layer to the rudder when deflected beyond the natural separation angle, increasing effective lift by up to 30 percent. This technology builds on principles similar to blown flaps. The first demonstration was by Raman et al. in 1999, and multiple organizations including Boeing, NASA, and several universities have worked on it. However, as of January 2015, the actuators remained experimental and had not been incorporated into any production aircraft. Their significance lies in the potential to reduce the size or drag of vertical stabilizers, improving aircraft efficiency, though the article does not state that this has been achieved in practice.
Did You Know?
- The first use of fluidic oscillators for sweeping jet flow control was demonstrated by Raman et al. in 1999.
- As of January 2015, sweeping jet actuators had only seen experimental application and were not on any known aircraft.
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