Aeronautics Research Center

Sun City Center, United States

Aeronautics Research Center

Sun City Center, United States
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Seidel J.,U.S. Air force | Siegel S.,U.S. Air force | McLaughlin T.,U.S. Air force | McLaughlin T.,Aeronautics Research Center | Fagley C.,University of Wyoming
5th Flow Control Conference | Year: 2010

Computations using the compressible Navier-Stokes equations were used to investigate feedback flow control for a shear layer behind a backward facing step. The controller was built based on a reduced order model (ROM), designed using Wavelet Neural Nets (WNN) for the Proper Orthogonal Decomposition (POD) mode amplitudes of unforced and open-loop forced data. Results of the model simulations indicate that a 35% reduction in the optical aberrations is possible when feedback flow control is applied. While the CFD results show a similar OPD reduction, modifications to the controller parameters based on the CFD results improved the performance and revealed a more effective mechanism to reduce the optical aberrations.


Post M.L.,U.S. Air force | Cummings R.M.,U.S. Air force | McLaughlin T.E.,U.S. Air force | McLaughlin T.E.,Aeronautics Research Center
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition | Year: 2012

The Aeronautical Engineering program at the U.S. Air Force Academy over the past decade has focused on integrating experimental and computational experiences in all Aerodynamic sequence courses. The required courses in the Aerodynamic Discipline include Aeronautical Fluid Dynamics, Computational Aerodynamics, and Advanced Aerodynamics. The experiences in these courses prepare cadets for capstone-like experiences in the Experimental/Computational Discipline of the required Aeronautical Laboratory and the elective Advanced Computation Aerodynamics. The paper highlights the experiences in each of these courses and summarizes how these contribute to success in the program.


Font G.I.,U.S. Air force | Font G.I.,Stanford University | Enloe C.L.,U.S. Air force | Enloe C.L.,Stanford University | And 8 more authors.
AIAA Journal | Year: 2011

Atmospheric pressure dielectric barrier discharge plasma actuators are experimentally investigated. The temporal force characteristics and dielectric surface charging are determined using interferometry and split electrode techniques. The experiments are conducted at atmospheric pressure in diminishing levels of oxygen content to investigate the effects of oxygen ions. The results show that the force production is dominated by oxygen ions down to a level of 2-5% oxygen content. Temporal force measurements show that the plasma accelerates the air twice during the bias cycle for all oxygen levels, including pure nitrogen. Surface charging measurements show that, for oxygen content levels above 5%, a positive voltage region builds up on the dielectric downstream of the actuator. In the absence of oxygen, no such buildup is observed. The temporal force production characteristics in the pure nitrogen discharge appear to be greatly affected by the dielectric surface charging. Finally, at a 20% oxygen content level, the majority of the force is produced by the actuator while the exposed electrode is negative. When all of the oxygen is removed, the majority of the force is produced while the exposed electrode is positive.


Seidel J.,U.S. Air force | Fagley C.,U.S. Air force | McLaughlin T.,U.S. Air force | McLaughlin T.,Aeronautics Research Center
33rd AIAA Applied Aerodynamics Conference | Year: 2015

Fully coupled CFD-CSD simulations are used to characterize the dynamic aeroelastic behavior of a torsionally flexible, finite aspect ratio NACA0018 wing. The main aeroelastic instability, which is also known as stall flutter, is a cycle from increasing angle of attack, large lift, then flow separation and a reduction of the angle of attack due to the elastic forces in the wing. The same sequence of events happens for negative angles of attack. This dynamic instability is a very periodic limit cycle oscillation. A single blowing port was integrated in the wing to control the lift oscillation. Constant blowing at various amplitudes had significant impact, reducing the limit cycle amplitude. The data was used to develop a simple model of the damping added to the structural dynamics due to the forcing. The model showed that the response to forcing is highly nonlinear and that a optimum blowing strength exists. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All Rights Reserved.


Fagley C.,U.S. Air force | Porter C.,U.S. Air force | Porter C.,National Research Council Italy | McLaughlin T.,U.S. Air force | McLaughlin T.,Aeronautics Research Center
AIAA Journal | Year: 2014

The asymmetric vortex regime of a von Kármán ogive with a fineness ratio of 3.5 is experimentally studied at a Reynolds number of 156,000. The wake of an axisymmetric bluff body is an ideal candidate for active feedback flow control because minute fluidic disturbances and geometry perturbations near the tip of the ogive get amplified through the flow's convective instability. The resulting disturbance interacts with the quasi-steady vortex location and produces a deterministic port or starboard asymmetric vortex state (i.e., side force). Accurate control or manipulation of this asymmetric vortex state holds the potential for increased maneuverability and stability characteristics of slender flight vehicles. For implementation of an active feedback flow-control system, plasma actuators at the tip of the ogive are used as the flow effector, and surface-mounted pressure sensors are used to estimate the vortex configuration in real time. A linear time invariant model developed from open-loop experimental tests and a proportional-integral control law are used to close the loop in the experimental setting. Closed-loop experimentation shows the ability to arbitrarily track a side force set point while also suppressing low-frequency fluctuations. Thus, the adopted model-based feedback flow-control approach is validated experimentally for a complex, three-dimensional flow. Copyright © 2014 by the American Institute of Aeronautics and Astronautics, Inc.


Farnsworth J.,U.S. Air force | Fagley C.,U.S. Air force | Porter C.,U.S. Air force | McLaughlin T.,U.S. Air force | McLaughlin T.,Aeronautics Research Center
52nd AIAA Aerospace Sciences Meeting - AIAA Science and Technology Forum and Exposition, SciTech 2014 | Year: 2014

To improve the robustness of close-loop controllers at off-design operating conditions the open-loop estimated side force response of an asymmetric vortex state on a von Ḱarḿan ogive forebody was experimentally investigated for a range of angles of attack and Reynolds number. The estimated side force was utilized as a monitor of the vortex state and was calculated from four time-resolved surface pressure measurements on the forebody. Both single dielectric barrier discharge plasma actuators and steady-blowing jets were used to augment the vortex state and the estimated side force response was presented. The momentum coefficient provided a modest normalization for the steady-blowing control input with variations in Reynolds number, however it did not completely collapse the results, suggesting some unforseen uncertainty in the quantification of the blowing strength exists. Changes in angle of attack displayed the sharp transition of the vortex system from a proportional response at α = 42.5° to a clearly bistable system by α = 57.5°.


Font G.I.,U.S. Air force | Font G.I.,Stanford University | Enloe C.L.,U.S. Air force | Enloe C.L.,Stanford University | And 2 more authors.
AIAA Journal | Year: 2010

Dielectric barrier discharge plasma actuators are examined experimentally and computationally. Experimental temporal force measurements show that the plasma actuator produces two positive (accelerating) forces per ac cycle. While the plasma is ignited, the actuator experiences an accelerating force, and, when the plasma is extinguished, a decelerating force appears. This occurs twice during each ac bias cycle. In addition, while the accelerating force is approximately equal in magnitude and direction during each half of the ac cycle, the decelerating force is not. Navier-Stokes simulations of the neutral air flow with a prescribed plasma force reveal that the variation in the decelerating actuator force is consistent with structural changes in the plasma itself. These plasma structural changes alter the volume over which the plasma forceis imparted to the air and, in turn, change the amount of air drag in curred by the wall jet created by the plasma. During each a ctuator bias cycle, 70-90% of the momentum supplied by the plasma actuator is destroyed by drag with the wall immediately after the plasma extinguishes.


Porter C.,U.S. Air force | Seidel J.,U.S. Air force | Fagley C.,U.S. Air force | Farnsworth J.,U.S. Air force | And 2 more authors.
6th AIAA Flow Control Conference 2012 | Year: 2012

The flowfield around an axisymmetric forebody at a moderate angle of attack (40° < α < 60°) can produce a significant side force as the result of an asymmetric pressure distribution around the body. The asymmetry of the pressure distribution results from a steady, asymmetric vortex configuration around the body even though the body is axisymmetric. Unsteady laminar simulations were performed on a von Kármán tangent ogive forebody with a fineness ratio of 3.5, angle of attack of 50 degrees, and a diameter based Reynolds number of 220,000. As a first step towards feedback flow control of the asymmetric vortex state, open-loop disturbances similar to those produced by a Dielectric Barrier Discharge (DBD) plasma actuator near the tip of the model were simulated. The resulting side force from the open-loop simulations are compared to the unforced simulations. In the unforced case, a large side force was observed with maximum amplitudes similar to those observed in a companion experiment. However, the side force fluctuates between the port and starboard sides, in contrast to experimental observation where the side force is relatively steady. When forcing is turned on, the resultant asymmetric vortex state locks into one position where the magnitude of the side force is proportional to the strength of the applied forcing. These simulations, both forced and unforced, are used to develop a flow state database through Proper Orthogonal Decomposition (POD) for the development of reduced order models. It is shown that the second POD mode (including the mean) captures the asymmetry of the different vortex states tested.

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