Breakdown of Low-Speed Tests
Since we wanted to have most of our infinite airfoil testing to be at a Reynolds number we could replicate and compare to the upcoming finite airfoil tests, we have a lot more data to look at here. Unfortunately, we also experimented with different angle of attack sweeps, making it difficult to compare all of the data at once.
Though most of the tests follow the same trend in the Lift-Drag polar, there are a few oddities:
Two of the reattachment tests showed significant deviation from the rest of the data, while the third did not. The weird thing here is that we expected all of them to show a difference from the tests with ascending angle of attack. I really don’t know why, but the third test’s drag coefficient actually does correlate well with the other two test. The only significant difference occurs in the lift coefficient plot where it deviates from the other two tests, and oddly is even farther away from the increasing angle of attack tests.
Just like the reattachment tests, there was one normal test that was just weird. For clarity, I added little triangles to this plot. In all three plots, this test almost exactly followed the odd reattachment test for a majority of the tested angles of attack. I went in and checked the numbers to make sure there wasn’t something going wrong with the variables, but it all checked out and the two problem tests were actually different (very slightly).
The very last normal test, labeled “LS 13~20 3,” had a few odd data points near 15° (expected stall). This test saw a little increase in both lift and drag in this region, but was otherwise normal.
I honestly have no explanations for the first two bullet there. I first made these plots on Friday and have since mulled it over, but I can’t figure it out.
The last point though, we have a well recorded source of error. During the last two tests listed in the legend, we conducted a little bit of flow visualization with smoke. We wanted to take a look at how flow was behaving around the airfoil, and also the rake. The results of that are a whole nother post, but it’s possible that having one of our group members standing directly in front of the tunnel inlet affected our data.










