rarefied gas

I’m new to Palabos and BGK methods in general. I would like to simulate a gas expanding into vacuum. The gas originates at a surface where the density and flow speed is known.

My questions are:
(1) Can Palabos deal with rarefied gases?
(2) How do I set up a vacuum boundary condition? This should be a boundary where molecules can leave the domain while there is no flow inwards. The pressure is not necessarily zero.

Thank you for any feedback.

Dear BenaZuba,

I now read yours post, and have the same question. Do yout have the answer?, Today, I have been to read isoThermalDynamics’ file where says … it cuts out the modes at higher Knudsen numbers and therefore can not be used in the regime of rarefied gases … …

My question is, Cannot I to use the regime of rarefied gases at all cases with Palabos library ?.

Thanks for your time and your response