Quote:
Originally Posted by freebeard
Assuming a thicker boundary layer, wouldn't bumps be more effective than a dimple?
If that is so, one would do preliminary testing with bubblewrap and duct tape.
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I have no idea
... I do know that dimples do not do the same thing as vortex generators, and I would think that bumps might be closer to something like a vortex generator? I'll link a few German articles, that I have yet to translate, as well as a portion of scientific publishing on the topic of non-smooth surfaces (dimples, divets, pits, grooves) at the end of this post.
My understanding, and that's all it is, doens't mean I *know*... Is that the dimples decrease surface friction by manipulating the boundary layer, and also allow the flow to stay attached on shapes/angles where it would normally detach and create a "wake" (like a spinning golf ball, or the gap between train cars). Vortexes focus on cleaning a wake up, which can reduce drag. So in theory, dimpled surfaces have a smaller "wake" thanks to a prolonged attachment of the flow, so with a smaller "wake" you would also decrease the amount of drag. It's like having two things, that accomplish the same thing, but do it completely differently. The advantage, from what I can tell, is that dimples are less likely to increase surface drag, frontal drag, or pressure drag. Vortex generators have more potential for an increase in drag, or so that's what I have gathered from my readings
They have been experimenting in China and Germany, not sure why we aren't experimenting here in the States
They have tested models of automobiles, trains, and boats. All of which saw a decrease in surface friction, and better .cd values. But none of them have figured out how to implement the idea... All of them say "further research is necessary" at the end of the paper or articles
English:
This one focuses on reduced friction on the hood and roof rather than manipulating flow at the rear of the roofline. Has equations and numbers and all manner of goodies!
http://www.zdrax.de/en/assets/pdf/Bi...d_Surfaces.pdf
German:
http://www.zdrax.de/en/assets/pdf/St...belbildung.pdf
http://www.zdrax.de/en/assets/pdf/Ha...r_und_Luft.pdf
This last one discusses the dimpling of high speed trains
http://www.zdrax.de/en/assets/pdf/Sp...en_im_Dach.pdf
~C