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

LinkBack  Thread Tools  Display Modes 
October 19, 2009, 08:07 
Please help with implemetation of boundaries conditions for flow in a pipe

#1 
Member
Michail
Join Date: Apr 2009
Location: Lithuania
Posts: 33
Rep Power: 8 
Hello all. Please help with implementation of boundary conditions for fully developed flow in a pipe. I use SIMPLEalgorithm 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(NXmaxC3,J)  P(NXmaxC2,J) )*0.5 U(NXmaxC,j)=U(NXmaxC1,j) But the solution diverged. May be I am wrong? 

October 19, 2009, 09:27 

#2 
New Member
Emre
Join Date: Oct 2009
Location: Ann Arbor, MI
Posts: 12
Rep Power: 8 
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 

October 19, 2009, 09:39 

#3 
Member
Michail
Join Date: Apr 2009
Location: Lithuania
Posts: 33
Rep Power: 8 
Thank You very much for Your suggestion. I'll try immediately and shall answer you today.
But what to do with pressure at inlet? 

October 19, 2009, 09:59 

#4 
New Member
Emre
Join Date: Oct 2009
Location: Ann Arbor, MI
Posts: 12
Rep Power: 8 
I suggest linearly extrapolating the inlet pressure from inside


July 19, 2011, 09:38 
help

#5  
New Member
sadegh
Join Date: Jul 2011
Posts: 2
Rep Power: 0 
Quote:
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. 

July 12, 2012, 05:47 

#6 
Member
Michael Moor
Join Date: May 2012
Location: Ireland
Posts: 30
Rep Power: 5 
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:nYp1)=u(nX1,2:nYp1); % First extrapolate values from the domain u(nX,2:nYp1)=u(nX1,2:nYp1)*sum(u(2,2:nYp1))/sum(u(nX,2:nYp1)); % This multiplier is the mass in divided by the mass out, which ensures continuity. v(nXp,=v(nXp1,; % See Versteeg page 273 p(nXp,2:nYp1)=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 umomentum 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 umomentum 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 

Thread Tools  
Display Modes  


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 