Doubts Regarding externalFlowAroundObstacle example

Hello Everyone,

I am trying to simulate flow over an airfoil and I think the example ‘externalFlowAroundObstacle’ would be the best for this task. I am very new to LBM and palabos both and I have little understanding of these topics, mainly the basics. I have a few doubts regarding this example. Currently, I have a STL file for the airfoil(which is of roughly of the same dimension as the original obstacle specified in the example) and I have edited the ‘.xml’ file and replaced the original obstacle with this airfoil.

Now, I have these doubts,

  1. What physical units have been used to specify the domain dimensions/velocity/viscosity etc.? In the ‘.xml’ these are only specified as some numerical quantity in physical units, but which physical unit has not been mentioned

  2. The Inlet Velocity has been specified as 0.1 in the original example. But is this quantity, the inlet velocity(in physical units eg m/s) or is it the Mach number? According to my understanding, an inlet velocity of 0.1 m/s doesn’t make sense. I just want to confirm if I am thinking correctly or not.

  3. I am confused about how can I specify my own conditions? Let’s say I want to do a simulation with standard sea level conditions (Pressure= 1.013x10^5 Pa, density=1.225 kg/m^3) and flow velocity=60m/s, then should I specify the following qunatities to the code in the ‘.xml’ file


0.00001412 60

where nu=0.00001412  is calculated as kinematic viscosity = dynamic viscosity/density.

4. For the values given in the original example(inlet velocity = 0.1, kinematic viscosity = 0.01, sphere radius=0.05) the Reynolds number comes out to be Re = 1. But what should I do if I want to change the Reynolds number to 1000?

Basically, I want to know how I should change the values in the original xml file so that I can simulate flow over an airfoil at sea level conditions? or instead what values should I specify in the code to get the desired simulation.

Any help would be appreciated, my understanding of LBM and palabos is not very good. :-/

Thanks in advance and sorry for my band English and such a long post

I suppose you have a very small nu. Your nu (kinematic viscosity) in lattice units should be not less than 0.01, and it had better be around 0.1. Velocity in lattice units should be not higher than 0.3. See this.