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Adaptive Vorticity Control Enabled Flight (AVOCET)

The unsteady interaction between trailing edge aerodynamic flow control and airfoil motion in pitch and plunge is investigated in wind tunnel experiments using a two degree-of-freedom traverse which enables application of time-dependent external torque and forces by servo motors. The global aerodynamic forces and moments are regulated by controlling vorticity generation and accumulation near the trailing edge of the airfoil using hybrid synthetic jet actuators.  Figure 1 shows time-averaged maps of spanwise vorticity with overlaid streamlines for (a) full suction-side actuation, (b) no actuation, and (c) full pressure-side actuation.  The dynamic coupling between the actuation and the time-dependent flow field is characterized using simultaneous force and particle image velocimetry (PIV) measurements that are taken phase-locked to the commanded actuation waveform. The effect of the unsteady motion on the model-embedded flow control is assessed in both trajectory tracking and disturbance rejection maneuvers.

 

The time-varying aerodynamic lift and pitching moment are estimated from a PIV wake survey using a reduced order model based on classical unsteady aerodynamic theory. These measurements suggest that the entire flow over the airfoil readjusts within 2-3 convective time scales, which is about two orders of magnitude shorter than the characteristic time associated with the controlled maneuver of the wind tunnel model.  This illustrates that flow-control actuation can be typically effected on time scales that are commensurate with the flow’s convective time scale, and that the maneuver response is primarily limited by the inertia of the platform.  Figure 2 shows the time histories of (a) plunge, (b) angle of attack, and (c) actuation command when the controller is commanded to track the square wave trajectory (black) in plunge with the flow control actuators.

Supported by AFOSR

 

 
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