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Old   May 13, 2011, 09:16
Default Negative pressure
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Hi
I'm modeling blood flow in bifurcation by using steady flow rate at inlet and constant flow distribution at outlets. the flow is Newtonian and incompressible.Inflow was calculated based on the physiological velocity known in at inlet section area. My problem is I'm getting negative pressure at the apex of bifurcation and I don't know how to explain it. I tried to set up the reference pressure as an atmosphere pressure but it didn't change. The problem convergenced with residual 10-5, but this negative pressure means that it didn't converge properly or is there something else.

I will appreciate if anyone can help me.
Thanks
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Old   May 14, 2011, 06:19
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Negative pressures are normal in incompressible simulations. If the reference pressure is atmospheric it simply means the pressure is less than atmospheric. Why do you think this is not correct?
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Old   May 14, 2011, 07:50
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Thanks Glenn, in terms of physiology how I can explain the negative pressure in artery, is that mean there is suction on the wall?
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Old   May 14, 2011, 08:08
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Yes, correct.
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Old   May 14, 2011, 08:33
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but it's not what I expected from our model. I was calculating energy loss of system based on Eloss=Ein- Eout1-Eout2 and for each term,from Bernoullii equation I calculated E= Sum(P+0.5*Ro* v^2 )i (i is all element of section area ) but this negative pressure leads me to negative Eloss (Ein<Eout) which is not correct. Could you please tell me how can I get the positive pressure. My mind goes to increase of inflow( there is a limitation because it's a doppler measurement) or somhow set up the reference pressure( I chose 10^5 Pa but still the same results). Any idea??

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Old   May 14, 2011, 08:45
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Bernoulli applies along a streamline. You will probably find the low pressure region is in a recirculation and not on a main streamline at all. Also Bernoulli is inviscid, you obviously have viscosity.

http://en.wikipedia.org/wiki/Bernoulli%27s_principle
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