Quote:
Originally Posted by freebeard
You keep busy. And that's not even counting the speaker enclosures. 
I only found the time for the third one. There exists a picture that aerohead posts occasionally (that I can't find via Search). His friend in the 1980s had a VW camper that he drove to Mexico one a year that had a conduit and boat wrap open-ended boat tail — a bigger cavity than the one you tested. There was some claim associated with it. |
I was surprised by a couple of things with box cavities.
1. How low the gain was in the wind tunnel tech presentation that people quote - just 2.3 per cent on the Audi A2. I had assumed from people's comments that it would be higher.
2. That I could actually measure a change (improvement) in wake base pressure with the very large box cavity I trialled on the Insight. But that change, as I described in the video, is very small in terms of drag force - so the small reduction in Cd with the A2 (even with its much bigger wake area) makes sense.
But for vehicles with really large wakes, it could be beneficial. Otherwise, separation edges are easy and cheap to add.