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Equation in Comsol

Posted Sep 21, 2010, 4:26 a.m. EDT 2 Replies

Xsu
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Hi,

I am doing simulation on nozzle and diffuser and I need to find the pressure loss coefficient,which the formula will be:
kd=(vb/va)
where vb is inlet velocity and va is outlet velocity

The Vb and Va is the variable calculated form comsol.

may i ask is it possible to insert (vb/va) function in comsol and to calculate for Kd?

Thanks.
2 Replies Last Post Sep 23, 2010, 8:37 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Sep 21, 2010, 6:04 a.m. EDT
Hi

You define your new variable kd as Vb/Va and then you plot the value kd over the region you want

--
Good luck
Ivar
Hi You define your new variable kd as Vb/Va and then you plot the value kd over the region you want -- Good luck Ivar
Xsu
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Posted: 1 decade ago Sep 23, 2010, 8:37 a.m. EDT
Thanks Ivar,
but my problem is Va is velocity at the entrance(inlet boundary) while Vb is velocity at exit (outlet boundary).

I have tried to go for boundary expression,where i select
inlet boundary=Va
outlet boundary=Vb

then go to gloabl expression ,kd= (Vb/Va)
but when I plot using cross section plot, I type in Kd at expression,
It give me blank graph.

Issit possible to have mean velocity at Va and Vb as the velocity value varies along the vertical line. (laminar flow)

thanks.
Thanks Ivar, but my problem is Va is velocity at the entrance(inlet boundary) while Vb is velocity at exit (outlet boundary). I have tried to go for boundary expression,where i select inlet boundary=Va outlet boundary=Vb then go to gloabl expression ,kd= (Vb/Va) but when I plot using cross section plot, I type in Kd at expression, It give me blank graph. Issit possible to have mean velocity at Va and Vb as the velocity value varies along the vertical line. (laminar flow) thanks.

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