Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.
Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Laminar flow with periodic inlet
Posted 15 apr 2011, 02:07 GMT-4 Fluid & Heat, Geometry, Studies & Solvers Version 4.1 1 Reply
Please login with a confirmed email address before reporting spam
Hi,
I redraw the graph which is simpler, domain 1 is fluid domain, others 2-5 are used later for plane strain.
my boundary conditions are (because it is the valve in our body, so the entrance velocity is periodic)
1. entrance
assume a fully developed parabolic axial velocity u(0,y,t) and v (0, y, t) at the tube entrance, the axial velocity is assumed to be periodic
u(0,y,t)=Um(r(0,t)-y)(r(0,t)+y)
UM=U_max*sin(2*pi*t/Tc) (n-1)Tc<t<(n-0.5)Tc Tc is the period=3s
=0 (n-0.5)Tc<t<n*Tc
u_max is the maximum axial centerline velocity and Tc is the time between opening and closing of the leaflet(domain 3)
2. Exit prescribed pressure condition Pd=1000pa
3. Internal boundary of the tube wall
assumed to be the same as the rate of the displacement of internal tube wall in the respective directions.
For here I just assume they are no slip wall to see if the model can work or not.
4. centerline
Symmetric boundary conditions are assumed.
These are the right conditions that after I discussed with my professor. But I really don't know how to put periodic boundary conditions in the model, and I am not sure other boundaries are right or not. so would you please check it for me?
how can I define like 0<t<1.5, UM=U_max*sin(2*pi*t/Tc), when 1.5<t<3, UM=0, should I use the wave function?
I will run this model first and then add the moving mesh in 2-5
Thank you for all your help to help me and walk together with me on this difficult comsol road!
Give my bigggest thanks first!
I redraw the graph which is simpler, domain 1 is fluid domain, others 2-5 are used later for plane strain.
my boundary conditions are (because it is the valve in our body, so the entrance velocity is periodic)
1. entrance
assume a fully developed parabolic axial velocity u(0,y,t) and v (0, y, t) at the tube entrance, the axial velocity is assumed to be periodic
u(0,y,t)=Um(r(0,t)-y)(r(0,t)+y)
UM=U_max*sin(2*pi*t/Tc) (n-1)Tc<t<(n-0.5)Tc Tc is the period=3s
=0 (n-0.5)Tc<t<n*Tc
u_max is the maximum axial centerline velocity and Tc is the time between opening and closing of the leaflet(domain 3)
2. Exit prescribed pressure condition Pd=1000pa
3. Internal boundary of the tube wall
assumed to be the same as the rate of the displacement of internal tube wall in the respective directions.
For here I just assume they are no slip wall to see if the model can work or not.
4. centerline
Symmetric boundary conditions are assumed.
These are the right conditions that after I discussed with my professor. But I really don't know how to put periodic boundary conditions in the model, and I am not sure other boundaries are right or not. so would you please check it for me?
how can I define like 0<t<1.5, UM=U_max*sin(2*pi*t/Tc), when 1.5<t<3, UM=0, should I use the wave function?
I will run this model first and then add the moving mesh in 2-5
Thank you for all your help to help me and walk together with me on this difficult comsol road!
Give my bigggest thanks first!
Attachments:
1 Reply Last Post 15 apr 2011, 03:53 GMT-4
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Hi
Yes this looks cleaner ;)
by the way a small remark, you have several constant already defined in V4 such as g_const = 9.81 the gravity acceleration, for the other see the doc, all names end with the suffix "_const"
You symmetry condition means I beleive this is the middle of the tube ? if so the velocity should be max along this border. Now you are using the correct formula for (UM*(1+s)*(1-s)) a single boundary entry so you should rather use the following one: UM*(1-s)^2
Your outlet is defined but not applied to any border, I assume it's for #12. But if you set the outlet pressure
to "1000", then you are more or less sure the inlet pressure and initial conditions should be at least that high. So it's wisely, to help the solver, to set the initial pressure also to "1000" or even to "1000[Pa]+Po*(0.180-x[1/m])/0.180" (where 0.180 is you total fluid length) the latter gives a small pressure drop along the tube to be decided what to use for Po[Pa], I usually look up the Poiseuille law, as initial conditions. By the way do not forget the initial pressure conditions for the gravity effects "g_const*rho*1[m]*(0.180-x[1/m])" taking into account your gravity direction and the fact that you are in 2D, hence everything is expressed "per meter" depth (Z out of paper direction)
You can also apply the same thinking to the initial velocity, you start with a time series and "0" so we can leave it as default if it solves OK.
The volume force is along -X so I assume wee see the tube rotated by 90 w.r.t. "reality"
I see you use a stationary solver to set the initial conditions for the time series, always wise when it solves. To be able to easily check the model you might want to run just the stationary solver, if you disable the time series, AND add a parameter "t = 0[s]" then you can run it alone, even using "t=0.1[s]" would help to see if the flow "goes on", when you then turn on the time series again, the value of t will be adjusted automatically by COMSOL so it does not hurt to leave the parameter
And to see what is happening, particularly in fluid flow cases, it is useful to turn on the Solver "Plot While Solving"
Then you might turn on the time series
--
Good luck
Ivar
Yes this looks cleaner ;)
by the way a small remark, you have several constant already defined in V4 such as g_const = 9.81 the gravity acceleration, for the other see the doc, all names end with the suffix "_const"
You symmetry condition means I beleive this is the middle of the tube ? if so the velocity should be max along this border. Now you are using the correct formula for (UM*(1+s)*(1-s)) a single boundary entry so you should rather use the following one: UM*(1-s)^2
Your outlet is defined but not applied to any border, I assume it's for #12. But if you set the outlet pressure
to "1000", then you are more or less sure the inlet pressure and initial conditions should be at least that high. So it's wisely, to help the solver, to set the initial pressure also to "1000" or even to "1000[Pa]+Po*(0.180-x[1/m])/0.180" (where 0.180 is you total fluid length) the latter gives a small pressure drop along the tube to be decided what to use for Po[Pa], I usually look up the Poiseuille law, as initial conditions. By the way do not forget the initial pressure conditions for the gravity effects "g_const*rho*1[m]*(0.180-x[1/m])" taking into account your gravity direction and the fact that you are in 2D, hence everything is expressed "per meter" depth (Z out of paper direction)
You can also apply the same thinking to the initial velocity, you start with a time series and "0" so we can leave it as default if it solves OK.
The volume force is along -X so I assume wee see the tube rotated by 90 w.r.t. "reality"
I see you use a stationary solver to set the initial conditions for the time series, always wise when it solves. To be able to easily check the model you might want to run just the stationary solver, if you disable the time series, AND add a parameter "t = 0[s]" then you can run it alone, even using "t=0.1[s]" would help to see if the flow "goes on", when you then turn on the time series again, the value of t will be adjusted automatically by COMSOL so it does not hurt to leave the parameter
And to see what is happening, particularly in fluid flow cases, it is useful to turn on the Solver "Plot While Solving"
Then you might turn on the time series
--
Good luck
Ivar