# Turbulent channel flow by LES

 Register Blogs Members List Search Today's Posts Mark Forums Read

 May 11, 2006, 00:51 Turbulent channel flow by LES #1 Paul Guest   Posts: n/a I am testing LES turbulent models by simulating the standard channel flow. But unfortunately, I cannot get to the turblence even after a very long period of computating time. The Reynolds number is 3000, defined by the averaged streamwise velocity and channel half width. Can I ask for any suggestions about it?

 May 11, 2006, 02:47 Re: Turbulent channel flow by LES #2 tom Guest   Posts: n/a Hi, The initial velocity field should have sufficiently large disturbances, fluctuations 10% of the mean, say, and not only random noise but also disturbances with a longer wave length. I just take some random cosine waves.

 May 11, 2006, 03:07 Re: Turbulent channel flow by LES #3 Paul Guest   Posts: n/a Thank you, Tom. Can I have the expressions for the disturbance, or any papers about disturbances? Do your random cosine waves mean that their amplitude and phase angle are random?

 May 11, 2006, 04:43 Re: Turbulent channel flow by LES #4 siri Guest   Posts: n/a Short wave disturbances (random noise) tend to die fast. As tom said, try also with cosine or sine waves (with wavelength of the order of the channel height). Besides, depending on which SGS model you are using, the Re number may be too low to mantain turbulence. I would try with higher Re numbers first.

 May 11, 2006, 04:56 Re: Turbulent channel flow by LES #5 Paul Guest   Posts: n/a Thank you siri. I am testing Smagorinsky model and standard dynamic model. Are these wave disturbances only for initial flow field?

 May 11, 2006, 05:05 Re: Turbulent channel flow by LES #6 Paul Guest   Posts: n/a Sorry, Tom mentioned already that the disturbances were for initial field.

 May 11, 2006, 10:48 Re: Turbulent channel flow by LES #7 agg Guest   Posts: n/a Try this IC u(x,y,z) = C(1-y^8) + E*2*pi*sin(pi*y)*cos(x)*sin(z) v(x,y,z) = -E*(1+cos(pi*y))*sin(x)*sin(z) w(x,y,z) = -E*pi*sin(x)*sin(pi*y)*cos(z) C is the centerline velocity and E=0.1*C

 May 12, 2006, 02:01 Re: Turbulent channel flow by LES #8 diaw (Des_Aubery) Guest   Posts: n/a Agg wrote: Try this IC u(x,y,z) = C(1-y^8) + E*2*pi*sin(pi*y)*cos(x)*sin(z) v(x,y,z) = -E*(1+cos(pi*y))*sin(x)*sin(z) w(x,y,z) = -E*pi*sin(x)*sin(pi*y)*cos(z) C is the centerline velocity and E=0.1*C diaw: Nice standing wave-forms. Wonder what you'll see if you altered the mode numbers a little, or set them moving? diaw... (Des Aubery)

 May 12, 2006, 02:12 Re: Turbulent channel flow by LES *NM* #9 diaw (Des_Aubery) Guest   Posts: n/a

 May 12, 2006, 02:19 Re: Turbulent channel flow by LES #10 Paul Guest   Posts: n/a Thank you, agg! I guess y is in wall normal direction. Am I right?

 May 12, 2006, 02:26 Turbulent channel flow by LES (one more question) #11 Paul Guest   Posts: n/a May I ask the order of the spanwise velocity in this turbulent channel flow? (comparing to mean streamwise velocity)

 May 12, 2006, 03:37 Re: Turbulent channel flow by LES (one more questi #12 diaw (Des_Aubery) Guest   Posts: n/a Paul, Judging from the form of agg's I/C, there is only an initial standing waveform in the y- & z- directions. The x-velocity is given an initial velocity component, the rest is a standing waveform. diaw...

 May 13, 2006, 18:09 Re: Turbulent channel flow by LES (one more questi #13 agg Guest   Posts: n/a I'm sorry i forgot to mention the reference. I don't want to take credit for the IC "Large Eddy simulation of channel flow using finite-difference techniques" D.K. Tafti and S.P. Vanka Report No. CFD-1, Dept. of Mechanical and Industrial Engr. UIUC, March 1990 You could change the value of E to change the fluctuation levels. The paper states "The initial divergence free field satisfies the boundary conditions and consists of a 3D disturbance (wavenumber unity) superimposed on a 2D mean flow." And yes Y is the wall normal direction I have an e-paper (pdf version) that gives IC based on Tollmienn Schlichting (TS) waves. If you need it just ask and i will email it to you.

 May 13, 2006, 23:08 Re: Turbulent channel flow by LES (one more questi #14 diaw Guest   Posts: n/a agg: I have an e-paper (pdf version) that gives IC based on Tollmienn Schlichting (TS) waves. If you need it just ask and i will email it to you. diaw: I would be very grateful if you could e-mail the paper to . Thanks very much. diaw...

July 6, 2009, 04:02
#15
New Member

Li.cy
Join Date: May 2009
Posts: 3
Rep Power: 9
i can't find this paper , what is size of the domain? i guess 2pi*2*pi ,right?
only this size can eliminate jump at periodical boundary in x and z direction

can i adjust the wave number?

Quote:
 Originally Posted by agg ;42615 I'm sorry i forgot to mention the reference. I don't want to take credit for the IC "Large Eddy simulation of channel flow using finite-difference techniques" D.K. Tafti and S.P. Vanka Report No. CFD-1, Dept. of Mechanical and Industrial Engr. UIUC, March 1990 You could change the value of E to change the fluctuation levels. The paper states "The initial divergence free field satisfies the boundary conditions and consists of a 3D disturbance (wavenumber unity) superimposed on a 2D mean flow." And yes Y is the wall normal direction I have an e-paper (pdf version) that gives IC based on Tollmienn Schlichting (TS) waves. If you need it just ask and i will email it to you.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post ElanMorin FLUENT 4 February 25, 2015 17:26 zandi Main CFD Forum 0 January 9, 2010 15:52 pankaj saha Main CFD Forum 0 November 30, 2007 13:04 roberthino OpenFOAM Running, Solving & CFD 5 August 15, 2007 08:35 shiv Main CFD Forum 0 September 21, 2005 00:52

All times are GMT -4. The time now is 09:06.