Control of Transitional and Turbulent Flows Using Plasma-Based Actuators
36th AIAA Fluid Dynamics Conference and Exhibit
An exploratory numerical study of the control of transitional and turbulent separated flows by means of asymmetric dielectric-barrier-discharge (DBD) actuators is presented. The flow fields are simulated employing an extensively validated high-fidelity Navier-Stokes solver which is augmented with both phenomenological and first-principles models representing the plasma-induced body forces imparted by the actuator on the fluid. Several applications are considered, including suppression of wing
... ppression of wing stall, control of boundary layer transition on a plate, control of laminar separation over a ramp, and turbulent separation over a wall-mounted hump. Effective suppression of stall over a NACA 0015 airfoil at moderate Reynolds numbers is demonstrated using either co-flow or counter-flow pulsed actuators with sufficiently high frequency. By contrast, continuous actuation (simulated by a steady body force in the phenomenological model) is found to provide little control of separation. For continuous actuator operation, the first-priciples approach is needed in order to reproduce the benefits of the inherently unsteady force induced by the plasma actuator. The pulsed-modulated unsteady plasma force is found to be more effective than a monochromatic radio-frequency forcing. These results highlight the greater importance of transition and turbulence enhancement mechanisms rather than pure wall-jet momentum injection for the effective use of DBD devices. As a consequence, meaningful computations require the use of three-dimensional large-eddy simulation approaches capable of capturing the effects of unsteady forcing on the transitional/turbulent flow structure. For a laminar boundary layer developing along a flat plate, a counter-flow DBD actuator is shown to provide an effective on-demand tripping device . This property is exploited for the suppression of laminar separation over a ramp. It is demonstrated that tripping of the laminar boundary layer upstream of the adverse pressure gradient is more effective than forcing of the separated shear layer. This behavior may be beneficial in the control of laminar flow wings and low-pressure turbines. Control of turbulent boundary-layer separation over a wall-mounted hump suggests that once the flow is turbulent, control effectiveness is only achieved provided the actuator strength exceeds a certain threshold. This finding has implications for the scalability of DBD devices to higher freestream velocities encountered in practical applications. Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.