Reynold's number

[fritz_269]

Old PH post (written by fritz_269):

Great post, thanks Texan! I’ve also really enjoyed reading some of your posts on the
http://pub30.ezboard.com/bmclarenshondatechboard

Reynolds number:
Is a dimensionless number that attempts to describe the characteristics of turbulence in fluid flow. Mathematically, it’s stated like this:

Re = p * d * v / u

Where:
Re == Reynolds number (dimensionless)
P == rho == fluid density (kg/m^3)
D == characteristic distance (m)
V == flow rate == average velocity of fluid (m/s)
U == Mu == kinematic viscosity of the fluid (kg/m*s)

For a cylindrical pipe, the characteristic distance is just the diameter.

The magic in Re is that any system with the same Re will behave the same. If you have a laminar flow in a pipe with an Re=10, then you can modify all the variables as much as you want and as long as they still work out to Re=10, you will still have that same laminar flow. For instance, if you make the pipe 10 times smaller, you can make the average velocity 10 times larger (or the viscosity 10 times smaller, or the density 10 times larger), and still have the same characteristic flow.

The metric was first invented to help design boat hulls. A 1:20 scale toy boat hull creates a totally different turbulence pattern in water that that of a 1:1 scale real boat. So we have to increase the water velocity and/or increase its density to correctly model the water turbulence with our toy boat. As long as we keep the Re number the same, the turbulence should scale. Cool!

A low Re indicates laminar flow, a high Re indicates turbulent flow. Generally, for a smooth pipe, an Re of 1000 to 2000 denotes the boundary where laminar changes to turbulent (while briefly passing through a stage of semi-turbulence). Most scientific research is being done on “high Re number systems” and “Re boundaries” (aka semi-turbulence).

There is a brief encyclopedia description here:
http://www.bartleby.com/65/ry/Rynldsnum.html

I did some simple calculations about intake tubes here (long thread, the Re stuff is on the second page):
http://www.purehonda.com/ubb/ubb/For...ML/000359.html
I’ll see if I can get around to doing some simple Re calcs for the headers & exhaust, but my intuition is that they will be very high.

[DemonicAccord]

Outstanding info, THX and bravo!

[fritz_269]

Woha!!! That link to PH still works!!! How cool is that!?!?
:smoker2:

[Moppie]

Whaho!!! looks like you found a back door fritz!
but damn thats an old post!

[delsolguy]

This has no relevance whatsoever but just wanted to say:

I really like the exact-ness of math, and I also enjoy physics, because it teaches me how things work.

However, it really sucks because even though I like them, they are the two hardest subjects for me, and I have a hard time "seeing" the problem...unless we're talking about cars and car related things. I think I need to get someone to teach it to me that way :silly2:. *sigh* Maybe I'll get better at it as I get older.