Plasma Dynamics and Flow Control

A dielectric barrier discharge (DBD), operating at KHz and KV conditions, can generate largely isothermal surface plasma and induce wall jet-like fluid flow. The discharge gaps usually range from less than a millimeter to a few centimeters depending on the application. The most interesting property of these discharges is that, at about atmospheric pressure, the breakdown is initiated in the form of a large number of independent current filaments which are known as microdischarges that operate on very small time-scales on the order of tens of nano-seconds. These are characterized by weakly ionized plasma channels that resemble those at high pressures. They are very attractive for industrial applications as they can provide non-equilibrium plasma conditions at atmospheric pressure with little arc formation and temperature rise. The exact mechanism of induced flow generation is not sufficiently understood although the concept behind the force generation is widely perceived to be that of Lorentzian collisions and the effect of the plasma on the fluid is like a localized body force.

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Actuator schematic illustration

Such a device can serve as an aerodynamic actuator, and has advantages of no moving parts. In order to better understand the mechanism of the momentum coupling between the plasma and the fluid flow, computational modeling is necessary. In particular, the focus is on the operating mechanism and thermo-fluid effects of the discharge plasma actuator which generates efficient surface plasma using a dielectric barrier arrangement.
The plasma and fluid species are treated as a two-fluid system exhibiting decades of length and time scale disparities. The time scale ratios between convection, diffusion, and reaction/ionization mechanisms are about O(107), allowing the effect of plasma on the fluid dynamics modeled via a body force treatment.Also, the plasma and the neutral fluid display three-dimensional characteristics as reported from experimental observations which when coupled with the plasma chemistry considerations would motivate a compromise between necessary physics and computational cost. To minimize computational cost, the plasma model at a phenomenological level is established using a linearized force distribution to approximate the discharge structure. A high fidelity approach using a first principle-based hydrodynamic plasma model is also developed with focus on the numerical techniques to handle the computational stiffness.

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Particle density evolution using Hydrodynamic DBD simulation

The present research is restricted to the low Mach number, essentially incompressible flow regime where the plasma dynamics is mainly shaped by the electromagnetic effects and is little influenced by the surrounding fluid flow. The actuators typically operate on low power consumption (2-40 W/ft of wing span) with the capability to be operated either in a steady or unsteady fashion. Typical examples of plasma-based flow control have been to enhance lift, excite 3-D boundary layer instabilities, control separation for low-pressure turbine blades and wings, control dynamic stall on oscillating airfoils control acoustic effects in subsonic cavity flows, etc.

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Plasma-On

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Re=60000, 15-degrees angle of attack with actuator at 1% chord

Surrogate models and dielectric barrier discharge (DBD) flow actuator performance

The DBD flow actuator, has various parameters of importance – geometry of electrodes, insulator material, magnitude and waveform of excitation voltage, etc – that determine the performance and efficiency of the actuator. Using surrogate models one can deduce an idea about the correlation between variables as well as information about the optimal conditions.

Researchers: Balaji Jayaraman , Young-Chang Cho

References:

  1. Shyy, W., Jayaraman, B. and Andersson, A., "Modeling of Glow Discharge-Induced Fluid Dynamics", Journal of Applied Physics, Vol. 92-11, (2002), pp. 6434-6443.
  2. Jayaraman, B. and Shyy, W., "Flow Control and Thermal Management Using Dielectric Glow Discharge Concepts", 33rd AIAA Fluid Dynamics Conference and Exhibit, Orlando, June 25-28, AIAA Paper No. 2003-3712, 2003
  3. Jayaraman, B., Thakur, S. and Shyy, W., "Modeling of Dielectric Barrier Discharge and Resulting Fluid Dynamics", 44th Aerospace Sciences Meeting & Exhibit, Paper No. 2006-0686, 2006
  4. Jayaraman, B., Shyy, W. and Thakur, S., "Modeling of Fluid Dynamics and Heat Transfer Induced by Dielectric Barrier Plasma Actuator", Journal of Heat Transfer 129-4 (2007) 571-525
  5. Jayaraman, B., Cho, Y. and Shyy, W., "Modeling of Dielectric Barrier Discharge Plasma Actuator", 38th AIAA Plasmadynamics and Lasers Conference, 25-28 June 2007, Miami, Florida, Paper No. AIAA-2007-4531
  6. Jayaraman, B., Lian, Y. and Shyy, W., "Low-Reynolds Number Flow Control Using Dielectric Barrier Discharge Actuators", 37th AIAA Fluid Dynamics Conference and Exhibit, Miami, FL, Jun 25-28, AIAA paper 2007-3974, 2007