

| Subject: | Re: aerodynamics, was: 101 MPH Vanagon! |
| From: | Dennis Wood |
| Date: | Tue, 19 Oct 2004 14:37:14 -0400 |
Can anyone decipher the wind speed in the wind tunnel shots? Given the westy shot, perhaps I shouldn't worry about removing my roof racks on the poptop...looks like they are sitting in a vaccuum. For that matter, a few windsurfers on top would probably help. The boundary layer effect has been discussed at length I presume in many disciplines. My understanding is that it helps in situations where flow detachment is an issue. A great example is high end windsurfing fins which are expected to maintain fluid attachment and generate lift at 35 to 50 mph in water. Sanding them in the direction of flow with 600 grit wet/dry paper is customary. In doing so, a thin turbulent water layer is maintained which helps keep non-turbulent flow remain attatched to the fin. It's amazing to see what happens when the fin loses attachment (cavitates)..the board starts sliding sideways at 30mph as if the fin was knocked off. At this point the golfers will chime in with the dimpled golf ball thing... However, with the large difference in density between air and water, I wouldn't run out with 600 grit paper and start scuffing your van .... any volunteers to dimple their vans? Add in some irridescent paint and you've "Pimp'd your ride"
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