Plasma Actuator Airfoil Wind Tunnel Testing

This week I built a Plasma Actuator in the shape of a crude airfoil and tested it in my Homemade Wind Tunnel. Plasma Actuators are research devices that use an electric field to change the characteristics of gas flow near a surface. In this experiment I was trying to get the airflow over the top of the airfoil (wing) to adhere to the surface of the airfoil when it normally wouldn't. Separation of the airflow over the top of a wing causes the lift generated by the wing to be reduced resulting in a stall. Before I talk more about what I built let me put a couple of pictures that I took from my experiment to help explain what I'm writing about.

   

Airfoil in Wind Tunnel Plasma Actuator Off

   

Airfoil in Wind Tunnel Plasma Actuator On

   

The above pictures were taken one after the other with the same airflow, the only difference between the two is in the lower picture the Plasma Actuator is turned on. In the lower picture the flow over the top of the wing is much smoother than in the top picture and is adhering to the top of the wing. Read more below for some details about the Plasma Actuator that I built and a video of it running.

The airfoil wing that I made is a simple wedge shape based around a 0.437" round dowel at the leading edge and is 3.0" wide. The top surface of the wing is a 0.040" thick alumina ceramic plate (that I had in my garage) and acts as the dielectric for the Plasma Actuator. The bottom surface of the wing and the sides are made from thin white paperboard. There are layers of Kapton tape on the top surface ceramic that progressively get thicker (by layering) toward the round dowel.

 

Plasma Actuator (click on the picture for a bigger view)

    

On the underside of the ceramic dielectric there is a copper foil 0.69" long, 0.0014" thick and 1.87" wide centered on the wing that is the negative electrode. On the leading edge of the wing is another foil of same width and thickness 0.32" long. The ceramic and the Kapton tape are acting as a dielectric with the Kapton getting progressively thinner (because of layering) toward the trailing edge of the wing. I decided to make the electrodes different sizes because of the Biefeld-Brown effect, whether that makes a difference or not will be left up to later experiments. In whole this makes up a Dielectric Barrier Discharge Actuator.

    

The two electrodes are powered by a 28,000 volt power supply pulsed at 15KHz when the Plasma Actuator is turned on. The ceramic and the Kapton tape prevent cascade arcing of the power supply and because the Kapton tape is layered the electric field between the electrodes is gradually increased toward the trailing edge of the wing. The electric field or Plasma Field is what is 'pulling down' the airflow on the top of the wing.

      

Plasma Actuator on stand

    

Plasma Actuator in my homemade wind tunnel

         

Above is a picture of the wing in the wind tunnel. The wires on the upper left side of the picture are for a fan laser that I mounted in the top of the wind tunnel to illuminate the wing and the smoke trail. There is another fan laser mounted off to the right in front of the fan. Both fan lasers are aligned with each other and the smoke trail. Have a look at THIS post for details about the construction of the wind tunnel.

   

What I was trying to do here is get something to work and establish it as a baseline so that I have some reference for further experiments. I wrote this post rather rapidly and will come back with some details about not only the Plasma Actuator but also the wind tunnel that I built. There are several more things that I want to write about regarding this experiment and will get to them later. One thing in particular is the speed of the airflow in the tunnel. In the meantime if you have any questions email me or leave a comment (or both) and I'll get back to you!

     

In the meantime have a look at this video of the Plasma Actuator in the wind tunnel that I built.

   

    

   

I'll post details of this experiment in the future. Below is a picture of the setup in my garage that needs a through cleaning after a breach in the smoke generator hose and an accumulation of miscellaneous junk!

   

Garage Wind Tunnel Plasma Actuator Experiment Setup

This is a initial experiment with homemade gear and I have several ideas regarding improvements to all of this. the first thing is I need to know the speed of the airflow in the tunnel for any of this to make sense. I also have to build an accumulator tank for the smoke so I have a continuous flow rather than a sporadic 'off and on' that I have now. The smoke generator gets hot and it blew out the hose that I was using because of the heat and ended the experiment early - heat resistant tubing is in the future.
     
I also want to try different shapes and sizes of electrodes, different tapering of the dielectric material, different voltages and air flows, alternative airfoil shapes and a few other things. All in all I think this was a success and a lot of work fun to build ;-)