Dear all.
this is my first quastion in openlb forum. i think iti svery usefull for lBM reserchers.
Im investigating turbulence flow with lattice boltzmann method, but i have sereious problem. first of them is when i choose Re number near 10^4 and N=30 and U=.1 then :
Re=(U*N)/nu then nu=.0003
so ta=3nu+.5 then ta=.5009
this ta is near .5 and we know that this cannot bo converg
so what can i do for solving it.
one that i can do is increase N. but i think it take memory and maybe cause unstablity.
whats your idea for my problem.
i will make two remarks on you simulation. The first one is that i guess that you wnat to simulate an incompressible fluid. The LBM is a weakly compressible solver. And in order to simulate “incompressible” flows you have to be in the small Mach number regime. The maximum U you take should therefore be around 0.02.
The second remark which is probably more important is that you are trying to solve a problem with a very unresolved grid. So your simulation should not converge, since you are not resolving the dissipative scale of your system. In order to resolve it you should have N ~ Re^(3/4) grid points per physical direction.
dear malaspin
thanks for your answer, you are right,if i dont use turbulent modeling my grid cant resolve small eddy, so i use LES for solve small eddy with smagorisky model, but i have a serios problem, i choose d2q9 and my domail consist 300*60 lattice, asn a obstacle with 30 lattic is mounted in chanel,
i use uinform flow aa inlet and zerogradian in oulet,and no slip condition for surfaces, but my problem is after some iteration the error function come in order 10^-4 and it will come constant and dosnt reduce. so my hidrodynamic parameter always change and they never converg. i want toknow is it tru for nature of lES. if yes sowhat can i do for exit my data. i want to say how can i compare my result to existing one (LARGE-EDDY SIMULATIONS WITH A
MULTIPLE-RELAXATION-TIME LBE MODEL by li shi lou)
if not what is my mistake. please help me, im realy confused
dear malaspin
thanks for your answer, you are right,if i dont use turbulent modeling my grid cant resolve small eddy, so i use LES for solve small eddy with smagorisky model, but i have a serios problem, i choose d2q9 and my domail consist 300*60 lattice, asn a obstacle with 30 lattic is mounted in chanel,
i use uinform flow aa inlet and zerogradian in oulet,and no slip condition for surfaces, but my problem is after some iteration the error function come in order 10^-4 and it will come constant and dosnt reduce. so my hidrodynamic parameter always change and they never converg. i want toknow is it tru for nature of lES. if yes sowhat can i do for exit my data. i want to say how can i compare my result to existing one (LARGE-EDDY SIMULATIONS WITH A
MULTIPLE-RELAXATION-TIME LBE MODEL by li shi lou)
if not what is my mistake. please help me, im realy confused
Are your hydrodynamic parameters really changing, or is your implemented error function wrong?
I do not see any reason why your parameters should change with a constant rate at large times, when anything else is constant. Maybe your boundary conditions are not properly implemented?
Please recheck your code.