turbulence in fluid in a pipe

*kurious*

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.

*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?

Gerard Westendorp

<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>\nkurious wrote:\n\n> Can a pipe exist so that if a bump on its inner surface causes some\n> turbulence in a passing fluid,other bumps further along the path of the\n> fluid could remove the turbulence?\n\n\nYou have to be careful with cause and effect here. Flow patterns are\na kind of equilibrium, it is not the right picture that the flow "hits"\na bump, becomes\nturbulent, hits another bump and becomes laminar. Rather, the time scale\nat which determinism operates in flows is acoustic, ie much faster than\nthe flow itself. So the flow "knows" about downstream bumps as it\ninteracts with the first bump, because pressure waves traveling at the\nspeed of sound have already caused many interactions before the first\nvortex is formed.\n\nAdding bumps can sometimes stabilize a flow and make it laminar.\n\nGerard\n\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">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>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

Doug Goncz

<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>From: kurious alistair@goforit64.fsnet.co.uk\n\n>Can a pipe exist so that if a bump on its inner surface causes some\n>turbulence in a passing fluid,other bumps further along the path of the\n>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">  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.

Maarten van Reeuwijk

<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> Can a pipe exist so that if a bump on its inner surface causes some\n> turbulence in a passing fluid,other bumps further along the path of the\n> fluid could remove the turbulence?\n\nTheoretically yes, although this would not require a bump but, as Doug\npoints out, narrowing the pipe. However in normal conditions, a flow that\nbecomes turbulent (sufficiently high above Ra_crit) quickly features a\ncontinuous range of length-scales, from the diameter of the pipe to the\nKolmogorov lengthscale. The route in which the fluid becomes turbulent is\nstill not fully understood, but Ruelle and Takens picture the instabilities\ngoing through two Hopf-bifurcations and then immediately onto a strange\nhigher-dimensional attractor, featuring a range of lengthscales.\n\n>From your answer I sense you are thinking in lines of putting the bumps in\ncounter-phase with the turbulence, but as there\'s a large range of scales\ninvolved this is impossible to achieve. Furthermore you would have to have\nthe phases right, which is impossible as this can differ from realisation\nto realisation.\n\nRegards,\n\nMaarten van Reeuwijk\n\n--\n===================================================================\n Maarten van Reeuwijk Thermal and Fluids Sciences\nPhd student dept. of Multiscale Physics\nwww.ws.tn.tudelft.nl Delft University of Technology\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">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>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 [itex]Ra_crit)[/itex] 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

val

<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\nHello,\nWhat about putting a grid in the section of the pipe like for tap\nwater for instance before it escapes the pipe. That would reduce the\nreynold\'s number and maybe the turbulence.\nval\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">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>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

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kurious	turbulence in fluid in a pipe Tweet 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.