# Negative pressure

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 May 13, 2011, 10:16 Negative pressure #1 Member   Join Date: Mar 2009 Posts: 48 Rep Power: 15 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

 May 14, 2011, 07:19 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,234 Rep Power: 135 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?

 May 14, 2011, 08:50 #3 Member   Join Date: Mar 2009 Posts: 48 Rep Power: 15 Thanks Glenn, in terms of physiology how I can explain the negative pressure in artery, is that mean there is suction on the wall?

 May 14, 2011, 09:08 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,234 Rep Power: 135 Yes, correct.

 May 14, 2011, 09:33 #5 Member   Join Date: Mar 2009 Posts: 48 Rep Power: 15 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

 May 14, 2011, 09:45 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,234 Rep Power: 135 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 HappyS5 likes this.