## turbulence in fluid in a pipe

Kurious:
>Can a pipe exist so that if a bump on its inner surface causes some turbulence in a >passing fluid,other bumps further along the path of the fluid could remove the >turbulence?

Kurious:

I would guess that the answer to this is yes because if enough bumps were put in the pipe in the right places, the pipe would get a smooth surface.
 Can a pipe exist so that if a bump on its inner surface causes some turbulence in a passing fluid,other bumps further along the path of the fluid could remove the turbulence?


kurious wrote: > Can a pipe exist so that if a bump on its inner surface causes some > turbulence in a passing fluid,other bumps further along the path of the > fluid could remove the turbulence? You have to be careful with cause and effect here. Flow patterns are a kind of equilibrium, it is not the right picture that the flow "hits" a bump, becomes turbulent, hits another bump and becomes laminar. Rather, the time scale at which determinism operates in flows is acoustic, ie much faster than the flow itself. So the flow "knows" about downstream bumps as it interacts with the first bump, because pressure waves traveling at the speed of sound have already caused many interactions before the first vortex is formed. Adding bumps can sometimes stabilize a flow and make it laminar. Gerard

## turbulence in fluid in a pipe

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no, scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n&gt;From: kurious alistair@goforit64.fsnet.co.uk\n\n&gt;Can a pipe exist so that if a bump on its inner surface causes some\n&gt;turbulence in a passing fluid,other bumps further along the path of the\n&gt;fluid could remove the turbulence?\n\nWell, sort of. In general, a gently widening or narrowing passage can\nfacilitate the transition from laminar to turbulent flow or back to laminar.\nAn included angle of greater than 14 degrees in an expansion transition almost\ninevitably induces turbulence.\n\nThe radial distribution of the axial velocity component in laminar flow is\nparabolic, peaking in the center of a round pipe. The distribution in turbulent\nflow is more "squared off", more even throughout the pipe. At certain Reynold\'s\nNumbers, one can usually count on the transition, be the flow air or water,\nfluid, liquid or gas.\n\nI\'m sorry, I don\'t have my Fluid Mechanics text here.\n\nWhat constitutes a "bump"?\n\n\nYours,\n\nDoug Goncz ( ftp://users.aol.com/DGoncz/incoming )\nStudent member SAE for one year.\nI love: Dona, Jeff, Kim, Mom, Neelix, Tasha, and Teri, alphabetically.\nI drive: A double-step Thunderbolt with 657% range.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">&nbsp;&nbsp;View this Usenet post in original ASCII form </a></div><P></jabberwocky>>From: kurious alistair@goforit64.fsnet.co.uk

>Can a pipe exist so that if a bump on its inner surface causes some
>turbulence in a passing fluid,other bumps further along the path of the
>fluid could remove the turbulence?

Well, sort of. In general, a gently widening or narrowing passage can
facilitate the transition from laminar to turbulent flow or back to laminar.
An included angle of greater than 14 degrees in an expansion transition almost
inevitably induces turbulence.

The radial distribution of the axial velocity component in laminar flow is
parabolic, peaking in the center of a round pipe. The distribution in turbulent
flow is more "squared off", more even throughout the pipe. At certain Reynold's
Numbers, one can usually count on the transition, be the flow air or water,
fluid, liquid or gas.

I'm sorry, I don't have my Fluid Mechanics text here.

What constitutes a "bump"?

Yours,

Doug Goncz ( ftp://users.aol.com/DGoncz/incoming )
Student member SAE for one year.
I love: Dona, Jeff, Kim, Mom, Neelix, Tasha, and Teri, alphabetically.
I drive: A double-step Thunderbolt with 657% range.


Can a pipe exist so that if a bump on its inner surface causes some > turbulence in a passing fluid,other bumps further along the path of the > fluid could remove the turbulence? Theoretically yes, although this would not require a bump but, as Doug points out, narrowing the pipe. However in normal conditions, a flow that becomes turbulent (sufficiently high above $Ra_crit)$ quickly features a continuous range of length-scales, from the diameter of the pipe to the Kolmogorov lengthscale. The route in which the fluid becomes turbulent is still not fully understood, but Ruelle and Takens picture the instabilities going through two Hopf-bifurcations and then immediately onto a strange higher-dimensional attractor, featuring a range of lengthscales. >From your answer I sense you are thinking in lines of putting the bumps in counter-phase with the turbulence, but as there's a large range of scales involved this is impossible to achieve. Furthermore you would have to have the phases right, which is impossible as this can differ from realisation to realisation. Regards, Maarten van Reeuwijk -- =================================================================== Maarten van Reeuwijk Thermal and Fluids Sciences Phd student dept. of Multiscale Physics www.ws.tn.tudelft.nl Delft University of Technology



Hello, What about putting a grid in the section of the pipe like for tap water for instance before it escapes the pipe. That would reduce the reynold's number and maybe the turbulence. val