[GSMacLean]

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Retro Winger wrote:

My question would be what effect it has on gas mileage (up or down, I would think up creating more of a slipstream), and how does it affect rain riding?

Turbulence = drag. Less turbulence = less drag = better fuel mileage. I would expect mileage to increase.

 

[GSMacLean]

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Bagzzz wrote:

Not necessarily... fluid dynamics is more of an art than a science. They put dimples on golf balls to decrease drag by increasing turbulence. Depends on the reynolds number. I would say in this case the number is low enough that more turbulanceshould equal more drag, but by no means does turbulence = drag. The best way to find out is to wait till we get the actual milage results after it is installed.

sorry to jump all over you like a grammar school teacher. My wife often says I should work on my diplomatic skills. Really thought you might be interested in the golf ball thing cause that is the case that blew me away in fluids class. Before that, I thought like you that turbulence=drag.

OK, that is true - in that case, the dimples on the golf ball set up a very thin boundary layer of turbulent air, which is more "slippery" than the otherwise smooth layer of the golf ball. Similarly, vortex generators on an aircraft wing create small vortices of turbulent air, which prevent the airflow from separating from the wing at low speeds, decreasing stall speed.

However, when you're talking about large amounts of turbulence, involving large volumes of air, where the volume of the directly affected turbulent air is approaching the size of the object creating the turbulence, there is considerable drag produced.