James W. Gregory - Research - Plasma Actuators

Plasma actuators are a class of aerodynamic flow control actuators based on the formation of a low-temperature plasma (also known as a dielectric-barrier discharge).  These new actuators hold promise for airfoil lift enhancement, separation delay, drag reduction, and even as an alternative to traditional flight control surfaces such as ailerons or flaps.  The plasma is formed between a pair of asymmetric electrodes when a high-voltage AC signal is applied across the electrodes.  Air molecules are ionized in the vicinity of the encapsulated electrode, and are accelerated through the electric field.  Momentum is then imparted to the flow through the collision of the accelerated ions with neutral particles in the region.  Beyond this basic understanding of plasma generation, there is much to be learned about the force production mechanisms of the plasma actuator.  My experimental work focuses on using advanced diagnostics to further understand the phenomenology of the plasma actuator, thus enabling design modifications that will enhance performance.

(From Enloe, et al., "Mechanisms and Responses of a Single Dielectric Barrier Plasma Actuator: Plasma Morphology," AIAA Journal, v. 42, n. 3, 2004, pp. 589-594.)

Recent studies have evaluated the force production of the plasma actuator under varying pressure conditions.  It was hypothesized that the force production would be strongly coupled to the ambient pressure, which dictates the number of neutral particles available for ionization.  Indeed, experiments demonstrate that the force produced by the plasma actuator scales linearly with the ambient pressure.  This seemingly benign result is actually quite remarkable, considering all the nonlinear interactions that cancel each other to produce this linear relationship.

Plasma-Fluidic Actuators

One significant disadvantage of the plasma actuator is the velocity limitations of the device.  Only low velocities are capable of being produced: typically only a few meters per second.  The plasma-fluidic actuator is a new type of flow control actuator that is being developed to address this limitation.  The plasma-fluidic actuator is a hybrid device (based on plasmas and fluidic oscillators) that uses the imparted momentum from a pair of plasma actuators to switch a bi-stable high-momentum jet.  The output of the actuator is either oscillatory or pulsed flow that is modulated by a plasma actuator.

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