Active Flow Control by Using Plasma Actuators

Abstract

Active flow control has recently received an increasing attention since it allows to directly manipulate the flow-field around a surface only when it is effectively requested. Aerodynamic plasma actuators supplied by a dielectric barrier discharge (DBD) can be used for this purpose. Usually, sinusoidal voltages in the range 5-50 kV peak and frequencies between 1 and 100 kHz are utilized to ignite this plasma typology. The surface discharge produced by these devices is able to tangentially accelerate the flow field by means of the electrohydrodynamic (EHD) interaction. DBDs generate non-thermal plasmas characterized by low input energies and limited temperature increments. Plasma actuators can be easily designed by following the shape of the aerodynamic body and can be used over heat-sensitive surfaces. These aerodynamic devices have demonstrated to produce boundary layer modifications with induced speeds up to 10 m/s. Their use over airfoils, flaps, and blades have shown the possibility to delay the transition between laminar to turbulent regime, to prevent flow separation enhancing lift and reducing drag. Moreover, the adoption of these actuators over landing gears and trailing edges may induce a noise reduction effect. Dielectric materials, electrodes configuration, and supplying waveforms are most relevant parameters to be considered to enhance actuator performance. On a parallel plane, on/off actuation strategy is a key point in the use of these devices when utilized over aerodynamic surfaces impinged within an external flow.

Separation drag reduction through a spanwise oscillating pressure gradient

“…The actuator was located at two positions upstream of the separation point and led to a reduction of the reattachment length, similar to that obtained with vortex generators in the same configuration. The main drawback of plasma actuators is the energy used for their activation, causing a low efficiency at high Reynolds numbers (Neretti 2016).…”

Investigation of a Dielectric Barrier Discharge Plasma Actuator to Control Turbulent Boundary Layer Separation

“…The applied voltage frequency used for the DBD plasma actuator was 3 kHz. As at this frequency, the DBD actuator could vary from 1-10 kHz [2], the analysis was done to understand the significance of the applied voltage frequency in the plasma body force. It should be noted that the plasma body force was proportional to the applied voltage frequency, and hence, an increase in frequency would increase the body force.…”

“…A common definition of boundary layer flow control was given by Flatt [1]: "Boundary layer control includes any mechanism or process through which the boundary layer of a fluid flow is caused to behave differently than it normally would were the flow developing naturally along a smooth straight surface". Due to the increase of computational resources and the development of sensor and actuator technology, the numerical and experimental implementation of advanced flow actuation has accelerated rapidly during the past 15 years [2]. The ability to control unwanted fluid flow occurrences is motivated by the desire to improve the aerodynamic performance of air vehicles.…”

Improved performance of polyimide Cirlex‐based dielectric barrier discharge plasma actuators for flow control

“…These effects will lead to optimized fuel consumption and heat transfer improvement. Flow control is typically achieved by introducing disturbances into the flow field allowing the manipulation of the original flow around a specific surface, when requested 1,2 . In this context, dielectric barrier discharge (DBD) plasma actuators appear as suitable electrohydrodynamic devices for effective aerodynamic control.…”