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Sunday, October 23, 2011

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 ;-)
    
 
 

20 comments:

  1. Can this be used to prevent airflow separation at the trunk end of an automobile? Your thoughts?

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  2. Anonymous,

    Yes I believe that a plasma actuator like this could work on the back end of an automobile. There would be some considerations because of the high voltage and I don't know how much energy it would require. That would be something to interesting to investigate though.
    Thanks for checking out my blog,

    Otto

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  3. Possibly a electronic aerodynamics could improve the gas milelage like the boattail this fellow put on his Civic.
    http://ecomodder.com/forum/showthread.php/160-000-miles-aeromods-1000s-dollars-fuel-savings-17046.html
    95 mpg

    Van Bushue

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  4. Van Bushue,

    Something like a plasma actuator might get similar results. I imagine that the car would have to be built 'from the ground up' with that in mind though rather than modifications to an existing car. At the very least the outside panels of the car would have to be reconstructed using some insulating material, ideally light weight material.

    - Otto

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  5. great experiment!!!, and I have two questions, what power supply did you use?, DC or AC, and what how expensive is it?, thanks

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    Replies
    1. Anonymous,

      Thanks! Below is a link to the power supply that I used. It is designed for an ozone generator and puts out a pulsed DC voltage around 28KV with the pulses at about 15KHz. You don't have to use that exact power supply of course, there are others out there on the internet that will work.
      If you have trouble finding one, or if you find one and are not sure if it will work let me know and I might be able to help recommend one.

      Thanks again - Otto
      http://www.sonking.com/image/o3110500e.pdf

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    2. But in the description said "Output Voltage 28KVAC PK ± 15%", thats mean is AC?. And thanks for you help. And were you buy it?

      Felipe Pizarro.
      Aeronautical Engineer Student.

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    3. Felipe,

      The spec sheet is a bit misleading isn't it? I measured the output on a scope with a HV probe and it's pulsed DC, doesn't go below ground.
      I would recommend you buy a power supply from someplace like:
      http://www.amazing1.com/hv-dc-power-supplies.htm
      I have bought stuff from them before and their stuff works but it's not the best quality. Be careful!
      What type of experiment are you going to do?
      - Otto

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    4. I want to perform an experiment with EHD (plasma actuators). I read that when the two electrodes are in contact with air is needed DC, and when an electrode is in contact with the air while the other is hidden under an dielectric material is needed AC. So what did you use you, the two electrodes in contact with air, or just one and the other under a dielectric material?

      And Sorry for ask so many things. Thank you.

      Felipe Pizarro.

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    5. Felipe,
      Have a look at the picture I did:

      http://3.bp.blogspot.com/-CH8ne4XD4fo/TqS0BaO_ztI/AAAAAAAAAw4/6SvWesu3QmM/s1600/Plasma+Actuator.jpg

      There is one electrode under the ceramic dielectric and the other is on top. My understanding is you always want one electrode to be more positive than the other so the 'discharge' is going in essentially one direction - with the flow. The pulsed DC is used so that different regions of the electrode can charge and discharge as they reach their discharge potential. I work professionally in a related field designing 'dielectric barrier discharge' ozone generators. Google that phrase, there is a lot of information out there and it is related to the plasma actuator system you are interested in.
      Let me know if I can be of any more help!!!

      - Otto

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  6. i like your experiment and want do this as my final year project.can you give me a detail about this experiment. i really need your help.send to my email kam_naz90@yahoo.com

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    Replies
    1. Anonymous,
      What info do you need specifically? I'm more than happy to help, pretty much everything related to the experiment is on the blog. If you have a specific question I'd be happy to try and answer it.
      - Otto

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    2. can you give me more detail what material need to do this plasma actuator

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    3. can you give me more detail what material need to do this plasma actuator

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    4. can you give me the specific how to create plasma actuator..

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    5. how much the cost to do the plasma actuator?

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    6. nayee,

      Please tell Google that the new interface that they have is a waste of time and idiotic.

      I'll be happy to help you after you do that.

      - Otto

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  7. Nayee,

    Let me know - send me an email at ottobelden@yahoo.com and I'll be happy to let you know what materials I used.

    Otto

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  8. OMG, while surfing for schlieren stuff I end up at your blog and come across this BDB stuff..._OMG_. I want to try this on one of my remote control gliders. Is the power level required practical for this application? Will 1-10 watts work?

    Thanks for your site, Bill

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    Replies
    1. Bill,

      Thanks for checking out my blog. Yes you could probably add this to any wing. I am assuming you mean a RC glider right? You need a really high voltage oscillating at a high frequency for this to work. Keep in mind that moisture and dirt will mess it up.

      Otto

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