Discussion Forum

Hi

I have noticed, that often it's better to set up some initial conditions on velocity and pressure drop (i.e. linear pressure drop and parabolic velocity profile), check the Forum it has been discussed many times

Check that you are in laminar (or respective turbulent) flow conditions and that your mesh is related (Reynolds mesh number see the doc

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Good luck
Ivar

Hi

I have noticed, that often it's better to set up some initial conditions on velocity and pressure drop (i.e. linear pressure drop and parabolic velocity profile), check the Forum it has been discussed many times

Check that you are in laminar (or respective turbulent) flow conditions and that your mesh is related (Reynolds mesh number see the doc

--
Good luck
Ivar

Dear Ivar,

Thank you so much for your response. I still don't understand how to start post processing since I'm really new to COMSOL. I need to plot Flow rate vs viscosity and flow rate vs Radius. How do I find flow rate and plot these? Is it possible to plot Velocity vs Radius and Velocity vs viscosity too?


Thank you very much for your time.

I'm attaching what I have so far. Please take a look at it.

How do I set the velocity profile to be parabolic if I apply a pressure difference across inlet and outlet. I know that the inlet velocity should be parabolic, but how do I specify that I I don know the flow speed? The flow speeds is what I am calculating.

Hi

that looks good ;) Not that it matters but to be closer to a more realistic initial condition, as you impose 400[Pa] on the inlet at Z=0, and 0[Pa] pressure at the outlet at z=0.05, is to use something like initial pressure = 400[Pa]*(1-z/0.05[m])


To plot the radial veloyity, right click the "Data Set" and add a 3D cut line from 0,0,0 to 0,0.001,0 and or add a line higher up at Z=0.025 and 0.05 (these wil lshow up as small red lines. Then add a 1D plot node that points to the new data set "cut line 3D", and add a line plot with spf.U the velocity norm.

T get the response fr varying the dynamic viscuosity, you must rerun the model with different values, the easiest is to use a solver continuation sweep: 1) adda Global Parameter Param = 0, then change your viscosity nu0 to nu0*Param, thengo the the stationary solver node, and open the lower tab "continuation" add + Param and define a range i.e.
range(0.25,0.25,4)
This will add your nu0 from 25% to 400%. The resulting data set will now be an array, that you might plot per t value

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Good luck
Ivar

I AM WORKING ON LAMINAR FLOW. ALL MY INITIAL CONDITIONS ARE ZERO. I HAVE SET INLET VELOCITY CONDOTIONS AND OUTLET PRESSURE CONDITIONS & CALCULATING PRESSURE DROP FROM THE PRESSURE CONTOUR IN RESULTS . THIS PRESSURE DROP SHOULD FOLLOW HEGAN POISEUILLES LAW. BUT IT IS NOWHERE NEAR THAT. WHAT AM I DOING WRONG.