#lab hack

To deal with the gap between the debris screen and the fan housing we decided to cut blue foam inserts to smooth the transition between the  test section octagon and the fan housing.

Using the cad model of the tunnel we created inserts that continued the polycarbonate inserts that we used to blend the corners of the tunnel. The small extrapolation of the inserts were then used to create a file that the CNC machine can convert into g-code.  For this project  we decided that if we had the CNC hotwire available , then we should use it accordingly.

With the help of Kurt from DBF we completed the inserts in about two hours, which was for 10-12am of this Thursday. The hotwire snapped once so that was a delay that ended up costing about 30 minutes of reassembly and re-zeroing. All in all, it’s a fantastic machine that was fun to watch as it worked on our parts.

The parts turned out great, the finish along the curve was excellent and much better and faster than anything we could have done by hand. The edges did get messed up but nonetheless, the parts looked great. The finished forms were twice as thick as needed so I was volunteered to cut the pieces down in the hangar as I was the only one wearing pants that day. The others in my group finished installing the diffuser plastic inserts. they turned out great. 

The foam inserts that I cut were installed shortly afterward with gorilla glue 5 minute epoxy that was found in the tunnel. After the cure, the pieces were sanded down to ensure the proper fit in the tunnel. To install these, the tunnel diffuser had to be moved. Which was no problem, the getting it back in was the challenging part. It was annoying because we spent nearly all the time that we intended to test trying to get the diffuser section back in the tunnel.

The weird thing was that we removed and put back the tunnel so many times last  Friday with more ease, you would think that this would be a snap! We don’t know why it was giving us so much trouble. Either way, the tunnel was installed properly, and then we began our tests, except the dynamic pressure  readout was not working.

I was looking forward to this day when we would get an answer whether all that we did was in vain or for triumph . Oh well, all thing in time, I was just looking forward to the satisfaction of something that I helped make and design working.  Sometimes I feel that is a feeling that I haven't had in a long time.

Today in the lab we  learned that we have an in house option for the  plastic inserts that would be placed in the tunnel. It’s a material called mackrolon made by bayer plastics and it is essentially a polycarbonate sheet that is stiff enough to hold its own in the tunnel and flexible enough to be placed in the tunnel and be a smooth transition between the plastic and the fan inlet/ outlet

Harrison and Eric cut down the plastic that we had marked on and we were able to place the triangle in the wind tunnel and test the fit. With two wood screws in each, and possibly some silicon caulking , the plastic should work beautifully.

One thing that we did notice that there is a gap between the fan and the debris screen in the rear of the tunnel. We are wondering if that will be a problem with the insert as the insert on the test section do not sit flush with the fan housing. What I'm worrying about is if we need to have a continuous blend into the fan, we need to make sure that it doesn’t  freaking fall into the fan. That would be bad.

Today, we went over packing or efficiency of packing the triangular inserts, unfortunately the polycarbonate sheet is at odds with the dimensions that we need and that means that we will unfortunately have some unusable plastic left over after we make all of our inserts. We also need more plastic because of this fact, in total we will be able to squeeze 10 triangle inserts out of the entire sheet. So if you ask me that's pretty good.

During the last hour of lab we performed a simple test of the tunnel diffuser using tufts. WE wanted to see the actual recirculation or any other strange aerodynamic effects in the diffuser. The video documents these problems in the tunnel and confirms our theory of recirculation within those very small pockets.

we tested at multiple speeds the first being  15 m/s  approximately. We then tested at a range of speeds, however, as we expected the pocket of recirculation was formed even at 15 m/s. This Test confirms that our project will have an effect although the exact performance metric and magnitude is not known. If all goes well, this simple modification will produce a result that increases the  speed of the flow for a given rpm.

One of the worries that I have about this project is the aesthetics that will come out of it, I hope that we aren't too rushed come finals week and we are able to make the inserts look nice. WE might have to discuss painting or other installation considerations to make sure that our project is something that makes the wind tunnel not only perform better, but also look better.