zshi6193
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zshi6193Participant
Dear Aurelio,
Thanks for your suggestion, I am just wondering about how to set the state of fluid in OpenLb for example if I am using single or two component ShanChen model.Best regards,
SimonOctober 17, 2019 at 12:54 am in reply to: add gravity leads to instability, bifurcation 3D, multiphase, particles #4600zshi6193ParticipantDear Max,
You mention the force field in OpenLB is actually a force over reference density. For multiphase flow, I have two phases (liquid and vapor via using single component ShanChen model). If I define a force field (an acceleration) into the whole domain, will this method still works?
I am just thinking that vapor tends to have very small acceleration because of very small density. Or this method can only be used twocomponent ShanChen model.Thanks for your help.
Simonzshi6193ParticipantDear Dr. Mathias,
Thanks for your quick response. I think that I find a way to solve the problem but want to doublecheck with you.
In two compartment ShanChen model(oil with rho=0.8 inside the water with rho=1), I try different g. When g is 3.5, the simulation can converged in around 40000 steps (the simulation domain is 100*100*60, the initial oil drop size is 40*40*40, periodic boundary in x and y, the top and bottom is set up to be bounceback solid wall with a density (0.6 for latticeOil, 0.4 for latticeWater)). I increase g for larger repulsive force because I find that there are significant miscibility if g is 3 or less. When g is 3, the volume of formed droplet tends to decrease with the fixed contact angle and it takes very long time to converge. In that case, if the initial volume of droplet is small, the droplet tends to disappear after many iterations.To be concluded, It is very hard to achieve the mass conservation if g is 3 or less. Choosing g of 3.5 may works for setting up the contact angle in 3D.
Thanks for your response.
Best regards,
SimonSeptember 25, 2019 at 3:28 pm in reply to: "WARNING: no discreteNormal is found " in the free energy model #4572zshi6193ParticipantDear Dr Mathias,
Thanks for your reply and suggestion. After I increase the mesh size, the problems are partly solved.
Best regards,
SimonSeptember 23, 2019 at 6:46 pm in reply to: "WARNING: no discreteNormal is found " in the free energy model #4566zshi6193ParticipantDear Mathias,
Sorry I have difficulty in uploading the image.
Here are the dropbox links of of my geometry. Thanks for your time. The highlight is the another boundary problem when two particles are close to each other. The multiphase model that I used is the free energy one.
Thanks for your help.Best regards,
Simon.
https://www.dropbox.com/s/cjftfooi4i85qbn/1.PNG?dl=0
https://www.dropbox.com/s/k6k4v8csgskjmrr/2.PNG?dl=0 This reply was modified 4 years, 8 months ago by zshi6193.
September 23, 2019 at 6:34 pm in reply to: "WARNING: no discreteNormal is found " in the free energy model #4564September 23, 2019 at 6:27 pm in reply to: "WARNING: no discreteNormal is found " in the free energy model #4560zshi6193Participantzshi6193ParticipantDear Sam,
Thanks for your time to look into the problem. Appreciate.
I propose a new way for this problem. If the ShanChen model allows three components, one of components could be the boundary. A new G can be introduced to define the interaction between the boundary and the fluid. In this way, the contact angle can be achieved. Compared to define the contact angle via virtual wall density, the new proposed way can yield numerical stable results. Would you think that it can work in OpenLB?Many thanks
Best regards,
Simon.September 23, 2019 at 8:13 am in reply to: "WARNING: no discreteNormal is found " in the free energy model #4550zshi6193ParticipantDear Sam,
Thanks for your reply. I try to use “superGeometry.clean” and superGeometry.innerClean”. The same error comes out. But in fact, it seems this error doesn’t affect the results.
Thanks
Best regards,
Simon.zshi6193ParticipantBased on the paper (Proposed approximation for contact angles in ShanandChentype multicomponent multiphase lattice Boltzmann models, 2007), is it possible to add the adhesion force between fluid and solid for the consideration of contact angle by using “sLatticephase1.addLatticeCoupling”?
Thanks
Best regards,
Simonzshi6193ParticipantHi Max and Aurelio,
Really thanks for your help. It helps me a lot.
I will try Max’s suggestion and see how it goes. So Can I say that there is no way to set the pressure boundary for both inlet and outlet in ShanChen multiphase model?
Best regards,
Simonzshi6193ParticipantDear Max,
Sorry that I didn’t express myself clearly. I would like to test whether the system can reach equilibrium without gravity. So the middle of the domain is filled with oil and the rest part of the domain is filled with water. I set the same density for oil and water. If I use the following code, the system should reach the equilibrium but unfortunately, it didn’t. Would you think that the following codes are correct for the constant pressure boundary at both inlet and outlet?
Also, a very small question, do we need add ” sLatticeWater.addLatticeCoupling(superGeometrytest, 3(inlet), couplingtest, sLatticeOil ) for the inlet and outlet.Thank you.
Code:
slatticeWater.defineRho(supergeometry,3(inlet),rhowater)
slatticeOil.defineRho(supergeometry,3(inlet),zero) (not sure whether we need to set the pressure for oil is zero)
slatticeWater.defineRho(supergeometry,4(outlet),rhowater)
slatticeOil.defineRho(supergeometry,4(outlet),zero).
(applied in each step)zshi6193ParticipantDear Max,
Thanks for your reply. Much appreciated.
I am sorry that I have one more question regarding the pressure boundary used in ShanChen two compartment multiphase model. To set the pressure inlet and pressure outlet, I used the following methods:
slatticeWater.defineRho(supergeometry,3(inlet),rhowater)
slatticeOil.defineRho(supergeometry,3(inlet),zero)
slatticeWater.defineRho(supergeometry,4(outlet),rhowater)
slatticeOil.defineRho(supergeometry,4(outlet),zero).
(I applied above four codes every iteraction to keep the constant pressure)
Alternatively, I also try:
Bcwater.addPressureBoundary(supergeometry,3(inlet),omega)
BcWater.addPressureBoundary(supergeometry,4(outlet),omega)
slatticeOil.defineRho(supergeometry,3(inlet),zero).
slatticeOil.defineRho(supergeometry,4(outlet),zero).The middle part of the domain is filled with oil and the rest is filled with water. But under above set up, the equilibrium state can not be achieved. The prefilled oil layer moves downwards.
I am not sure that I set up the boundary conditions correctly or not? .Could you help me to check it? Ideally, at the same pressure at the top and bottom (no pressure gradient), the oil in the middle part should be stable.Thank you very much.
Simon 
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