Quote:
Originally Posted by John_H
The article you cite reaffirms what I know: dimpling does not set up a laminar airflow layer, it specifically changes the laminar flow to turbulent flow. This allows the flow to stick to the back surface of the golf ball longer, pushing the ball forward more effectively than the laminar case which separates from the back of the ball too quickly, losing that push.
In a hose, there's no pressure loss from "separation of flow" so the only benefit from tripping the flow from laminar to turbulent would be the added friction and, therefor, added pressure with a resulting reduced flow.
John_H
... Degreed [non-practicing] Aerospace Engineer ...
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Ah, Grasshopper, don't make me dust off my FD book and come over there and quote you chapter and verse. I haven't used some of these brain cells since I had acne, and I might get a charlie horse!
This is waaay off topic, but no more so than ribbed tubes requiring KY. So, let's peel off a layer or two of that onion and see what is going on.
I said that the dimples on a golf ball “could -- and I mean could, not will -- set up a laminar airflow layer that might actually improve airflow.” If I would have actually read the article I referenced, instead of simply glancing at it to verify that it had the information I thought it should, I would have been more precise in my language. I previously confessed than it has been a while since I took and Fluid Dynamics, so forgive me in my poor selection of words.
There is in fact a very thin layer of turbulent flow that acts as a boundary layer for the fluid (air in this case) flow. The resulting flow looks laminar-ish from the 40,000 foot level Bottom line is that the all important wake is reduced and drag is reduced.
Which was my point.
I can also tell you that for rocket engines under certain conditions we will burn fuel to cool down the injectors and the nozzle's throat. And for an orbiting object we speed up to slow down. Sounds counter-intuitive, but there you have it.
While it is true that the dimpled sphere example doesn't extend very well to flow in a tube, there is some carry over. I'm going off of memory here, and as my son likes to tell me, "memory is the first thing to go, Dad," but I'm sticking to my guns regarding to what I said previously. For shorter tubes, dimples have the potential to improve flow. I doubt very much, though, that it would be valid for tubes longer than about two, three, maybe four times the diameter. Longer than that, then yes, dimples would restrict flow.
If you can find something rigorous to dispute the above, I'm only too happy to say "I was wrong!" If not, we'll simply have to agree to disagree.
Sorry to veer off topic, but, hey, we weren't too on topic when I veered off anyway.
geo "degreed, but there ain't no air in the aerospace I practice" synch
I've heard of seeing dead people, now we see smoother air flow. What's next, Electric superturbo chargers!!!
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