Quote:
Originally Posted by Pooft Lee
As far as whats practical, a flat undertray will reduce drag. This thread is packed with hypotheticals and theories, so being confused is totally normal.
For practicality, a flat pan will cut drag even if it isn't perfect. An air dam is a much less time consuming place to start, with similar benefits
One reason dimpling isn't common is cost. Flat is way easier. The other big one, is that without the steep transitions that cause flow separation, you don't need it. The golf ball is fighting flow separation as best it can to shrink its wake.
Its been explored a little previously, but size is the biggest issue. A large object like a car will inevitably have turbulent flow anyways. You can use vortex generators to help, but those are adding drag upstream to hopefully ease it downstream, and not ideal
If you wanted more on why people are talking about rough surfaces to streamline, they're concerned about the boundary layer. Attached airflow has a greater influence on the vehicle. Metal intake manifolds leave the casting roughness to avoid attached airflow and keep velocity high, and boats use it as well. Ford tried it on the probe iv with difficult to measure results.
To be honest, I'm not quite sure when turbulent attached and laminar attached airflow are best. I don't think there is a "right" answer
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*you always want attached laminar outer flow (sometimes referred to as inviscid flow).
*you cannot have attached laminar outer flow on the vehicle's afterbody unless you have a full turbulent boundary layer.
*and unless the afterbody is very much like the template,you lose both.