I fairly new to LBM and I am trying to wrap my head around the choice of units for LBM. I am using the externalFlowAroundObstacle example case as a starting point but when I change the parameters to fit my case the simulation quickly diverges.
I am trying to simulate the following case:
Domain dimensions (length x width x depth) = 3.135 x 0.486 x 0.326 m
Inlet velocity = 0.183 m/s
Kinematic viscosity = 1.0e-6 (m^2/s) [i.e. Water]
Reynolds Number (based on depth) ~ 60000
Resolution = 98/0.486 = 200 nodes/m
dx = 4.96e-3
By fixing the lattice velocity at 0.01 to keep the mach number low (incompressible)
dt = 2.71e-4
This results in the relaxation parameter being:
tau = 0.500033057
I am assuming that the reason for the simulation diverging is that tau is too close to 0.5 but any any combination that I try to increase it either leaves me with a ridiculously high resolution or a very high Mach number either of which is unacceptable for the case I am trying to simulate.
Also LES modelling is activated with a Smagorinsky constant of 0.2
Any advice will be greatly appreciated.