CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

Please help with implemetation of boundaries conditions for flow in a pipe

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 19, 2009, 08:07
Default Please help with implemetation of boundaries conditions for flow in a pipe
  #1
Member
 
Michail's Avatar
 
Michail
Join Date: Apr 2009
Location: Lithuania
Posts: 32
Rep Power: 8
Michail is on a distinguished road
Hello all. Please help with implementation of boundary conditions for fully developed flow in a pipe. I use SIMPLE-algorithm on collocated grid. The enumerating of CV is below. I implemented dp/dx = constant and dU/dx=0 as:

-------------------------
For inlet :


P(1,J)= P(2,J)-( P(3,J) - P(2,J) )*0.5

U(1,J) = U_inlet

-------------------------
For outlet:

P(NXmaxC,J)= P(NXmaxC,J)-( P(NXmaxC-3,J) - P(NXmaxC-2,J) )*0.5

U(NXmaxC,j)=U(NXmaxC-1,j)



But the solution diverged. May be I am wrong?
Michail is offline   Reply With Quote

Old   October 19, 2009, 09:27
Default
  #2
New Member
 
Emre
Join Date: Oct 2009
Location: Ann Arbor, MI
Posts: 12
Rep Power: 7
esozer is on a distinguished road
dp/dx=0 is not a good idea for pipe flow. Fix the pressure at the outlet and velocity or mass flow rate (or pressure) at the inlet.
-------------------------

For inlet :


U(1,J) = U_inlet

-------------------------
For outlet:

P(NXmaxC,J)= P_outlet

__________________
Free CFD developer
www.freecfd.com
esozer is offline   Reply With Quote

Old   October 19, 2009, 09:39
Default
  #3
Member
 
Michail's Avatar
 
Michail
Join Date: Apr 2009
Location: Lithuania
Posts: 32
Rep Power: 8
Michail is on a distinguished road
Thank You very much for Your suggestion. I'll try immediately and shall answer you today.

But what to do with pressure at inlet?
Michail is offline   Reply With Quote

Old   October 19, 2009, 09:59
Default
  #4
New Member
 
Emre
Join Date: Oct 2009
Location: Ann Arbor, MI
Posts: 12
Rep Power: 7
esozer is on a distinguished road
I suggest linearly extrapolating the inlet pressure from inside
__________________
Free CFD developer
www.freecfd.com
esozer is offline   Reply With Quote

Old   July 19, 2011, 09:38
Default help
  #5
New Member
 
sadegh
Join Date: Jul 2011
Posts: 2
Rep Power: 0
parsad is on a distinguished road
Quote:
Originally Posted by Michail View Post
Hello all. Please help with implementation of boundary conditions for fully developed flow in a pipe. I use SIMPLE-algorithm on collocated grid. The enumerating of CV is below. I implemented dp/dx = constant and dU/dx=0 as:

-------------------------
For inlet :


P(1,J)= P(2,J)-( P(3,J) - P(2,J) )*0.5

U(1,J) = U_inlet

-------------------------
For outlet:

P(NXmaxC,J)= P(NXmaxC,J)-( P(NXmaxC-3,J) - P(NXmaxC-2,J) )*0.5

U(NXmaxC,j)=U(NXmaxC-1,j)



But the solution diverged. May be I am wrong?
hello mr
i have problem i want a solve turbulence flows of air on a flat plate in two dimensional with matlab but i dont know what starting from where i request help me,can u help me?
my method is control volume and my algorithm is simplec.
parsad is offline   Reply With Quote

Old   July 12, 2012, 05:47
Default
  #6
Member
 
Michael Moor
Join Date: May 2012
Location: Ireland
Posts: 30
Rep Power: 5
michaelmoor.aero is on a distinguished road
Hello everyone, I am trying to solve for steady Poiseulle flow on a backward staggered grid using FVM and SIMPLE, these are the initial boundary conditions that I set...
%% Wall 1,The inlet
u(2,=uin; % U values are stored at i=2
v(1,=vin; % V values are stored at I=1
p(1:2,=pstaticin; % Pressure is stored at I=1, and using dp/dx=0 enters the domain at I=2

%% Wall 2, The top plate
%For Poiseulle flow; No slip boundary condition:
u(:,nYp)=0;
v(:,nY)=0;
p(:,nYp)=0;

%% Wall 3, Outlet
u(nX,2:nYp-1)=u(nX-1,2:nYp-1); % First extrapolate values from the domain
u(nX,2:nYp-1)=u(nX-1,2:nYp-1)*sum(u(2,2:nYp-1))/sum(u(nX,2:nYp-1)); % This multiplier is the mass in divided by the mass out, which ensures continuity.
v(nXp,=v(nXp-1,; % See Versteeg page 273
p(nXp,2:nYp-1)=0; % Constant static pressure value of '0' set at the outlet (I = NI)

%% Wall 4, Plate
%For Poiseulle flow; No slip boundary condition:
u(:,1)=0;
v(:,2)=0;
p(:,1)=0;

From here, I solve for the momentum equations, noting that the source term is the pressure gradient, as well as the source terms in appendix C of Versteeg. The wall shear stress also enters the u-momentum equations in the central coefficient, Versteeg: Sp = -(mu/delta yp)*Acell ... eqn 9.11 pg 275. Since I am using a backward staggered grid, there is no need to incorporate the inlet and outlet boundary conditions as source terms (right hand side of equation), since the hybrid differencing scheme ustilizes the already stored inlet value of uin at i=2, and the u-momentum equations are calculated from i=3.

Once u* and v* are calculated, solve for the pressure correction equaiton, being sure to cut the coefficients to the inlet (aW), outlet (aE), and the top and bottom plates (aN and aS), noting also that the coefficients are simply the central coeficients of the u- & v- momentum equations, multiplied by the density and the cellface area (rho*d*a)i,J etc... and that the source term is the continuity imbalance accross a pressure volume, i.e West face - East face + south face -north face.

I am using the MATLAB function BICGSTAB to solve the sets of equations... can anyone point out something wrong?
REgards, 0565113@gmail.com
michaelmoor.aero is offline   Reply With Quote

Reply

Thread Tools
Display Modes

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 Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
pipe with buoyantFoam buoyancy, boundary conditions Thomas Baumann OpenFOAM 0 June 15, 2009 08:58
Boundary Conditions for Stratified Pipe Flow Zhang FLUENT 0 June 30, 2008 13:33
Terrible Mistake In Fluid Dynamics History Abhi Main CFD Forum 12 July 8, 2002 09:11
Pipe Flow Boundary conditions Kunal Jain Main CFD Forum 0 September 4, 2001 20:52
fluid flow fundas ram Main CFD Forum 5 June 17, 2000 21:31


All times are GMT -4. The time now is 06:53.