Quote:
Originally Posted by Tesla
There has been a number of threads I've read questioning this idea, I had one a while back and there was at least one more besides this one, then in my travels I came across the discussions about the Don Bur trailers for trucks, some of the threads even had some discussion from a Don Bur rep who signed up to reply. One of the things that stuck in my mind was he said it wasn't just the hump on the trailer as that added frontal area, but it complemented other add ons for an overall reduction. I've seen a number of comments about how people do a number of mods and nothing really changes (I fit that category), then they add another and suddenly the numbers come in. This quote below:
can't remember which thread, but is this what would happen with frontal smoothing mods or the roof cap: airflow & attachment is improved, but the gain is simply transferred to the rear as increased base drag.
I made a bit of a pointed nose cone as the upper grill block to guide air up and to sides, there was a dramatic reduction of wind noise, took it of recently just to confirm the noise factor, but there was no appreciable change in FE, likewise with air dam and front wheel part skirts, improved handling, but no real FE benefits.
Don Bur has put a lot of money into legally protecting their "hump", one would think there must be something in it, particularly if it is part of an overall Aero package.
From what I read their hump was between 300-500mm (12-20"), so scaled back that would be somewhere around 60-100mm (2 1/2-4") for a large wagon or van, anyone ever gone there and tried it, done any tuft tests, anything?
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*The big boys tell us that there are no magic numbers for radii to achieve attached flow in the forebody of the vehicle.
*Very small radii will support attached flow and once achieved,greater rounding pay little further dividends.
*That's at zero-yaw.
*For crosswinds,a bulbous nose is the lowest drag,but once you have attached flow the big boys say go after the back of the vehicle for sumptuous riches.
*The Don Bur 'hump' is part of body camber which helps direct the momentum of air into the wake after it has decelerated to a higher static pressure.
*It's the overall boat-tailing which gives the non-separated flow,deceleration,and pressure regain critical to drag reduction.
*Conventional wisdom is to cut away roof-line to create the hump rather than add frontal area by lofting the roof-line.