Martiqua L. Post

Separation Control on HIgh Angle of Attack Airfoil Using Plasma Actuators

This work involves the documentation and control of leading-edge flow separation that occurs over an airfoil at high angles of attack, well above stall. A generic airfoil shape (NACA 663-018) was used because of its documented leading-edge stall characteristics. It was instrumented for surface-pressure measurements that were used to calculate lift coefficients. Mean-velocity profiles downstream of the airfoil were used to determine the drag coefficient. In addition to these, smoke streakline flow visualization was used to document the state of flow separation. The airfoil was operated over a range of freestream speeds from 10 to 30 m/s, giving chord Reynolds numbers from 77 × 10 3 to 333 × 10 3 .T wo types of plasma actuator designs were investigated. The first produced a spanwise array of streamwise vortices. The second produced a two-dimensional jet in the flow direction along the surface of the airfoil. The plasma actuators were found to lead to reattachment for angles of attack that were 8 deg past the stall angle (the highest investigated). This was accompanied by a full pressure recovery and up to a 400% increase in the lift-to-drag ratio.

Separation control using plasma actuators : Dynamic stall vortex control on oscillating airfoil

A plasma actuator was used to control leading-edge flow separation and dynamic stall vortex on a periodically oscillated NACA 0015 airfoil. The effectiveness of the actuator was documented through phase-conditioned surface pressure measurements and smoke flow visualization records. The airfoil was driven in a periodic cycle corresponding to α = 15 deg+10deg sinwt. The results presented here are for a reduced frequency of k = ωc/2U ∞ = 0.08. Three cases of control with the plasma actuator were investigated: open-loop control with steady plasma actuation, open-loop control with unsteady plasma actuation, and closed-loop control with steady plasma actuation. For closed-loop control, the actuator was activated in selected portions of the oscillatory cycle based on angle-of-attack feedback. All of the cases investigated exhibited an increase in cycle-integrated lift with improvements in the lift-cycle hysteresis. In two cases, the pitch-moment stall angle was delayed and in one of these, the adverse negative moment peak was significantly reduced.

Scaling Effects of an Aerodynamic Plasma Actuator

We present experimental results to yield insight into the scalability and control effectiveness of single-dielectricbarrier-discharge plasma actuators for leading-edge separation control on airfoils. The parameters investigated are chord Reynolds number, Mach number, leading-edge radius, actuator amplitude, and unsteady frequency. This includes chord Reynolds numbers up to 1:0 � 106 and a maximum freestream speed of 60 m=s corresponding to a Mach number of 0.176. The main objective of this work is to examine the voltage requirements for the plasma actuators to reattach the flow at the leading edge of airfoils at poststall angles of attack for a range of flow parameters in order to establish scaling between laboratory and full-flight conditions. For the full range of conditions, an optimum unsteady actuator frequency f is found to minimize the actuator voltage needed to reattach the flow, such that F� � fLsep=U1 � 1. At the optimum frequencies, the minimum voltage required to reattach the flow is weakly dependent on chord Reynolds number and strongly dependent on the poststall angle of attack and leading-edge radius. The results indicate that the voltage required to reattach the flow scales as the square of the leading-edge radius.

Aero-optical environment around a conformal-window turret

This paper presents the aero-optical environment around a generic conformal-window turret formed from a hemisphere on a short cylindrical base. A suite of optical instruments consisting of a Malley probe, a conventional two-dimensional Shack-Hartmann wave-front sensor, and a new high-bandwidth, lower-resolution Hartmann wave-front sensor were used to measure the aberrations on the wave front of a laser beam emanating from the turret at various angles in both the forward and aft direction in the turrets zenith plane. The measurements were made over a range of Mach numbers from 0.35 to 0.45. Complementary steady- and unsteady-pressure measurements over a slightly larger range of Mach numbers were also made, along with a surface-flow-visualization study of the complex flowfield over and around the turret. The use of the suite of sensors allowed for the recognition and separation of the aberrating optical environment into components associated with stationary disturbances and convecting disturbances at the frequency of the turrets separated wake and at order-of-magnitude-higher frequencies associated with structures that form in the separated shear layers, respectively. The optical data separated in this way are valuable because of the implications for adaptive optics.

Single-Dielectric Barrier Discharge Plasma Enhanced Aerodynamics: Concepts, Optimization, and Applications

This paper deals with the physics and design of single dielectric barrier discharge plasma actuators for enhanced aerodynamics in a variety of applications. The actuators consist of two electrodes: one exposed to the air and the other covered by a dielectric material. The electrodes are supplied with an alternating current voltage that, at high enough levels, causes the air over the covered electrode to ionize. The ionized air, in the presence of the electric field produced by the electrode geometry, results in a body force vector that acts on the ambient air. The body force is the mechanism for active aerodynamic control. The plasma generation is a dynamic process within the alternating current cycle. The body force per unit volume of plasma has been derived from first principles and implemented in numerical flow simulations. Models for the time and space dependence of the body force on the input voltage amplitude, frequency, electrode geometry, and dielectric properties have been developed and used along with experiments to optimize actuator performance. This paper presents results that highlight the plasma actuator characteristics and modeling approach. This is followed by overviews of some of the applications that include leading-edge separation control on airfoils, dynamic-stall vortex control on oscillating airfoils, and trailing-edge separation control on simulated turbine blades.

Integrated Experimental and Computational Aerodynamics Education at the U.S. Air Force Academy

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.