The Rule 28 data that Dan posted shows the same Cd-Re characteristics, not surprisingly perhaps, as the characteristics of a cylinder or sphere with roughness that is often illustrated in fluid mechanics text books. For example:
http://brennen.caltech.edu/fluidbook/externalflows/drag/dragonasphere.pdf[/url]
This shows, if it wasn’t already obvious, that these aerostripe fabrics are working by tripping the boundary layer, and that you’d want to choose a fabric with protuberances that are just large enough to cause transition for the Reynolds number of interest, but not larger than is necessary (otherwise that’ll just overly thicken the turbulent boundary layer).
I have a couple of thoughts and questions, having just read the posts on this thread from the last few months about speed dependence on CdA (and possibly Crr):
1) Many of the things that people would want to test with the Chung method will affect in some way the points of flow separation on the bike or rider (e.g. socks, skinsuits, torso angles). Should the protocol recommended in this thread suggest that the person targets the speed range that is relevant to their race/event/discipline? That might affect the location that somebody chooses for testing. For example (a real example for me), if I want to check the benefit of trip socks, and my usual event is a flat-ish TT done at 40-45 kph, doing a VE test where half of the lap is uphill at 25kph may introduce uncertainties about whether the trips are working at the low speed sections. A velodrome would be a better choice. Of course, our choice of test location is usually a compromise, with several considerations.
2) For the Tom Compton Challenge, I’ve always wondered whether a sphere is a good object to use, in view of it’s Reynolds sensitivity. Personally, I’ve never found the time to do the test. However, the polystyrene ball, that has been patiently sitting in my garage for a few years, does not have a smooth surface. I’m not sure which side of the drag crisis it would sit. I wonder if it would be better to instead use an object that is less Reynolds-sensitive, such as a flat disc perpendicular to the flow.