Discussion Forum

Hi

you are in 3D so you need a Data Sets - Cut Line 3D (and not 1D), then you make a 1D plot from the Cut Line source and it should go

Another comment, particularly in cfd its important to have initial conditions close to the results, to help the solver. You haved all initial conditions at default "0". But you could as well set the parabolic velocity field here too and a first pressure drop along your pipe (using Poiseuille law)

--
Good luck
Ivar

Thanks Ivar .......both for the solution on how to plot and for the tip about initial conditions.

Sirisha

Hi

for the solution right click Data set selelct 3D cut line (and define your 2 points)

in result plot, right click and select 1D plot, in the 1D plot window, , top, select solution 3D cut line. Right click 1D plot and select line plot

for the initial conditions, copy your inflow velocity profile of the type
(note Q [m^3/s]=v0[m/s]/SectionArea[m^2])=v0[m/s]/(pi*(R[m])^2)

v0[m/s]*2*(1-(x^2+y^2)/R_tube[m]^2)

or define a cylindrical (i.e.sys2) coordinate system along the tube and use the formula

v0[m/s]*2*(1-(sys2.r/R_tube[m])^2)

Where R_tube is the interiour tube radius, defined either as a parameter , or calculated with a line integration

check the output you should have about 2*v0 on axis, 0 on the non slip walls (this works also approx. for an elliptical tube shape, or you elaborate the formula further)

Then for the Poiseille law pressure drop it states (see i.e. wiki en.wikipedia.org/wiki/Poiseuille) for the visuosity "mu"

Dp[Pa] = 8*mu[Pa*s]*V0[m/s]/(Radius[m])^2*Length[m]

carefull with the max and average velocity, but even if you are a factor 2 off, it's mostly better than all "0" (except if you inverse the sign ;)

Then you need to replace , in the initial conditions "Length" by (for a pipe of axis aong Z, change if different)

Dp[Pa](z) = 1*8*mu[Pa*s]*V0[m/s]/(Radius[m])^2*Length[m]*(1-z/Total_length)

And get the sign, correct.
For that it's always good to start to ask COMSOL to "get the initial values" by a right-click on Solver - Dependent variable - Compute to selected. Then you can make the plots of the initial conditions

But all this is plain Physics, it's not my jo to train your for that, or ?.
For me that is the main reason of using COMSOL ...

PS: pls check carefully my formulas, as typos are quickly done

Have fun Comsoling

Ivar

Ivar,

I mentioned thanks for letting me know about how to plot the 3D velocity and also for giving me the tip of setting the initial values = inlet condition:)

I am not sure why you explained it in so much detail. I am sorry if my earlier reply was a bit confusing. I was just conveying my thanks!

Anyway .... thanks once again
sirisha

Hi

well with the details, you, and other can probably better understand the idea, no ?

--
Good luck
Ivar