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 alimea April 16, 2018 04:40

Lift amplitude error in viscoelastic Fluid

Dear Foamers

I'm simulating the shedding flow around a circular cylinder in viscoelastic fluid with rheoFoam.
At first I was working with viscoelasticFluidFoam that is just allow me to use upwind scheme for div(phi,tau) that gave me 30% error in CL amplitude. If I use any other scheme insted of that, the solution would be diverged!
I reduced Courant number to 0.01 and ​the grid became smaller. but again with upwind scheme I couldn't get appropriate result and I had 25% error in CL amplitude!

So I installed openFOAM v 4.0 and compile rheoFoam and read the related part of user manual. Then I tried to get results of Fig. 4 of Oliviera [1] with this condition:
FENE-CR, Re=100 , De=80 , L2=100
ddt: CN 1 - div(phi,U) , div(phi,tau) , div(phi,A) : GaussDefCmpw cubista
SIMPLE algorithm - URF=1 - nInIter=1 - Courant Number = 0.01

But the results are very strange: CLmax=0.4 (Oliviera: 0.15) .
Also there are some strange fluctuations that I don't knw what they are!
1- Could you please tell me what is wrong in my simulation?

Note: To calculate CL and CD I have written this function:
F= - stress & A[i]
Drag=F.x();
Lift=F.y();
CD=Drag/ (0.5*rho*U_inf^2*Aref)
CL=Lift/ (0.5*rho*U_inf^2*Aref)

3- what is difference between FENE-CR and FENE-CRlog?

Validating this problem has been my problem for a long period of time.

I appreciate if any answers me.
--------------------------------------------
[1] Method for time-dependent simulations of viscoelastic flows: vortex shedding behind cylinder, Paulo J. Oliveira, J. Non-Newtonian Fluid Mech. 101 (2001) 113–137

 alimea April 17, 2018 04:26

Quote:
 Originally Posted by alimea (Post 689024) Dear Foamers I'm simulating the shedding flow around a circular cylinder in viscoelastic fluid with rheoFoam. At first I was working with viscoelasticFluidFoam that is just allow me to use upwind scheme for div(phi,tau) that gave me 30% error in CL amplitude. If I use any other scheme insted of that, the solution would be diverged! I reduced Courant number to 0.01 and ​the grid became smaller. but again with upwind scheme I couldn't get appropriate result and I had 25% error in CL amplitude! So I installed openFOAM v 4.0 and compile rheoFoam and read the related part of user manual. Then I tried to get results of Fig. 4 of Oliviera [1] with this condition: FENE-CR, Re=100 , De=80 , L2=100 ddt: CN 1 - div(phi,U) , div(phi,tau) , div(phi,A) : GaussDefCmpw cubista SIMPLE algorithm - URF=1 - nInIter=1 - Courant Number = 0.01 But the results are very strange: CLmax=0.4 (Oliviera: 0.15) . Also there are some strange fluctuations that I don't knw what they are! 1- Could you please tell me what is wrong in my simulation? http://uupload.ir/files/01gm_screens...6_04_27_59.png Note: To calculate CL and CD I have written this function: stress = tau+etta_S*(grad(U)+gradT(U)) - p F= - stress & A[i] Drag=F.x(); Lift=F.y(); CD=Drag/ (0.5*rho*U_inf^2*Aref) CL=Lift/ (0.5*rho*U_inf^2*Aref) 3- what is difference between FENE-CR and FENE-CRlog? Validating this problem has been my problem for a long period of time. I appreciate if any answers me. -------------------------------------------- [1] Method for time-dependent simulations of viscoelastic flows: vortex shedding behind cylinder, Paulo J. Oliveira, J. Non-Newtonian Fluid Mech. 101 (2001) 113–137