I finally got around to putting the wind tunnel together, well actually it's a breeze tunnel. There isn't much of a wind blowing through it! After looking at the performance of the Bladeless Fan I built I decided that it was going to create a higher airflow than I need for the Plasma Actuator experiments that I want to do, so I decided to slow it down a bit and use a small DC fan. The DC fan is easier to use because I can control the speed of the air with a variable power supply and the airflow from the Bladeless fan just dropped off all together when I lowered the input air. This wind tunnel is only to do some experiments with the Schlieren setup I built and High Voltage and a low velocity and variable airflow is what I need. Before I built this wind tunnel I did a lot of reading on line and found some plans from a NASA wind tunnel site describing a small classroom wind tunnel for students to build as well as a lot of very technical information about "real" wind tunnel design. As I mentioned above my wind tunnel is more of a breeze tunnel so I didn't need a lot of the flow control, settling areas and velocity constrictions. I just need something to provide a smooth flow of air past a viewing area. Below is what I came up with.
|Homemade "Suck Down" Wind Tunnel|
In the picture above the airflow is right to left, the fan is on the left, the view area is in the middle where the glass windows are and the inlet air goes into the right side. Because the fan is downstream of the test area this is considered to be a "suck down" tunnel. One advantage of a "suck down" tunnel is the turbulence and chopped up air created by the fan isn't blowing over the test area. Smooth air is sucked past the viewing area. Click below to read more!
The base and the top of the wind tunnel are 2x4's so the width of the test area is 3-1/2 inches. To the left and right of the test area windows there are 4 vertical pieces of plywood (two on the front, two on the back) that support the top 2x4. The 2x4's are overkill for this but I had some spare lumber laying around so I used them. The windows are a couple of picture frames that I picked up at the dollar store and I drilled some clearance holes in the frames for hanger bolts that I screwed into the 2x4's. The straight machine thread of the hanger bolts go through the holes in the picture frames and wing nuts hold the frames in place. This lets me take the windows off for access to whatever it is that I am going to test. I used two windows so that I can put this wind tunnel in front of the parabolic mirror that I use for Schlieren photography. Having two pieces of glass in the optical path will require some adjustments in the setup of the Schlieren but it's not a big problem and painting everything black will help with that.
The bottom 2x4 is longer than the top one on the fan side. In the picture above you can see a piece of thin plywood that I used as a fan mount screwed to the end of the bottom 2x4. Between the test area and the fan I used foam core poster board, hot glue and tape to create a smooth transition and direct the airflow into the fan. The fan itself I scavenged out of something a long time ago and was in a box of fans that I have in my garage (this is a low budget project!) The fan make and model: Xinruilian RDM8025S, there isn't much on the internet about it's performance. I'm going to figure out some kind of anemometer to measure the airflow so it's not that critical but it would have been nice to have some info on the fan.
On the left side in the above picture, on top of the foam core piece there is some blue tape. Hidden underneath the tape is a solid state fan laser that is illuminating the test area. The laser will help show the flow patterns of smoke that I'm going to use in conjunction with my Schlieren setup to see the airflow in the test area. I picked up the fan laser from a garbage can someplace here and I used it in the Vortex Tube smoke experiments I performed last year.
|Wind Tunnel Inlet Diffuser|
To help smooth out the airflow entering the test area I cut some plastic drinking straws and packed them into the inlet side of the tunnel. The straws are about 0.18" I.D. and more or less 4" long. I did some quick tests using incense to make smoke and looking at the flow with the laser it appears to give a nice steady and smooth airflow. I am going to play around with this a bit more to get everything set up the way I want it and then make a plasma actuator. If all looks well put this contraption into the Schlieren setup and turn on the high voltage!
Let me know if this makes sense with a comment or an email and have a look at my Site Index of Projects to see some of the other things that I have built.