I asked the cap owner if he saw any improvement. (He seems to know who MetroMPG is, even though I asked using the EcoModder account - mysterious!)
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Originally Posted by EcoModderDOTcom ... (21 hours ago)
Were you able to measure any fuel economy change after making the aero cap?
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Quote:
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Originally Posted by NickSuch21 ... (9 minutes ago)
Hey MetroMPG! I need to build an MPGuino so I can get some better data. I saw about a 2mpg improvement, but that was within the noise of my per-tank fuel measurement method. This was mostly for testing the attachment method at speed and the robustness of the construction. Definitely a lot of room for improvement.
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Also, some screen grabs of the tuft testing:
Top image shows what you want to see: attached flow (tufts streaming aft) on the top & sides, right to the end of the cap.
Middle image shows evidence of the separation bubble behind the cab. Not a huge deal, but interesting to catch. The lower tuft reversed direction / swirled around a lot more often than the next one up.
Lower image is interesting because it captures what to my eye looked like a tendency of the uppermost tufts on the side of the cap to angle slightly upward on average. I think this indicates flow moving upward toward the lower pressure on the top surface. And it underscores why we should aim for curved transitions where possible instead of sharp corners, so flow moving from one surface to another doesn't have the chance to "trip" or separate going past the corner. (The exception being trailing edges, where it's OK to chop off and leave a sharp angle.)
Just nitpicking. Perfect is the enemy of good. I think it's fair to say the cap probably works as intended.