Results from experimental studies on the performance of plasma and synthetic jet actuators for active control
of flow over a circular cylinder in subcritical flow conditions ranging from a Reynolds Number of 2.5 x 104 to
7.3x104 are presented. The experiments were conducted at the NASA Langley Research Center in the 20" x 28"
Shear Flow Wind Tunnel and the results provide an indication of the effectiveness of, as well as the similarities
and differences between these two active flow control (AFC) methods for reducing pressure drag on a bluff body
shape. Flows over a cylinder are well understood and in particular flow separation characteristics for cylinders
are well documented both experimentally and theoretically. The effect of the flow control devices is quantified by
measuring the pressure distribution around the bluff bodies using a multi-port piezoelectric pressure scanner and
integrating the distribution for drag analysis. This comparison consists of operating the two types of actuators in
the same range of Reynolds Numbers (Re) over the cylinder and for the same actuator angular positions on the
cylinder. The applied voltages and frequencies to the actuators varies based on the individual actuator operating
conditions. At low Re, the plasma actuators have a strong effect on the pressure distribution reducing the drag
up to 32% relative to the drag with no actuators on the surface. The synthetic jet reduces drag up to 25% but
with lower voltage and frequency. For both actuator cases, the actuator is the most effective 5° to 10° upstream
of the baseline separation point.
Alloys of iron and non-magnetic gallium (of the form Fe1-xGax where x ranges from 13 to 30) exhibit large magnetostrictions of over 300 ppm at room temperature that are produced by saturation magnetic fields of approximately 600 Oe. While not producing magnetostrictions of the degree achievable with giant magnetostrictives, large magnetostrictive alloys of iron and gallium, called Galfenol, have much more desirable mechanical characteristics, such as non-brittleness and in-plane auxetic behavior. Additionally, Galfenol requires a much smaller saturation magnetic field than the giant magnetostrictives Terfenol and Terfenol-D (alloys of Iron and non-metallic Terbium and Dysprosium). Beginning from the body of knowledge gained from Terfenol and Terfenol-D dynamic research transducer designs is a good starting point for designing a Galfenol dynamic research transducer. However, several modifications are being made to adapt the transducer to some of Galfenol's unique properties. Any measured value uncertainty will quickly propagate through the calculated material properties. While not completely successful at addressing all the unique aspects Galfenol in this transducer design, the data presented will assist in future design attempts.