Abstract
Control of a turbulent boundary layer separating on a half-cylinder mounted on a flat plate has been investigated using a Dielectric Barrier Discharge (DBD) plasma actuator placed along the apex of a cylinder. The main focus of the study has been to evaluate if the control ability of the actuator can be improved through pulsed actuation compared to its steady counterpart. Investigations of the electric wind induced by the DBD plasma actuator in still air, when mounted on the flat plate, revealed that while the steady actuation produces an electric wind similar to a wall jet, the pulsed actuation creates a train of co-rotating vortices. The vortices are the result of a starting vortex produced by the actuator at each actuation pulse. A parametric study showed a dependence of the size, shape and propagation velocity of the vortices on the pulse frequency and duty cycle. With the actuator mounted along the apex of the cylinder, Particle Image Velocimetry measurements of the uncontrolled and controlled flow with a free-stream velocity of 5 m/s showed a clear reduction of the recirculation region downstream the cylinder when using plasma actuation. An even higher control effect could be achieved with pulsed actuation compared to the steady actuation. Phase-locked measurements of the unsteady actuation showed that pulsed actuation periodically shifted the flow separation location resulting in the propagation of vortical structures in the recirculation region. The size of the vortical structures showed a dependence on the pulsed actuation timing parameters.
Highlights
Separation of boundary layers on an object moving through a fluid, such as an aircraft or a vehicle, typically means an increase in drag
In almost all cases separation is detrimental to performance
For technical applications measures are usually taken to fully avoid or at least limit the extent of separation
Summary
Separation of boundary layers on an object moving through a fluid, such as an aircraft or a vehicle, typically means an increase in drag. For technical applications measures are usually taken to fully avoid or at least limit the extent of separation Such measures can be taken through a suitable geometrical design of the body, as for instance shaping an airplane wing in such a way that separation is avoided at high angles of attack or by using some type of flow control, either passive or active. With passive control we refer to methods that do not require external power input, whereas active methods need such an input. In the latter case it could be reactive control, i.e. the amount of control employed is based on information from a sensing system
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