Charged gas in neutral gas

[kolotinsky]

Dear Mathias,
is it possible to simulate the following situation with OpenLB? The ion gas, which is affected by an external electric field, is in a neutral gas. The ion gas itself, in our approximation, is collisionless, and only collides with a neutral gas. In my last post, I represented just such a situation and therefore wrote that speed would come to a constant value.

[kolotinsky]

If I add viscosity to external force term to describe collisions with neutral gas can I set zero relaxation frequency in MRT operator or simply use BGK operator with zero relaxation frequency?

[mathias]

Dear Kolotinsky,

that is a two component system. You may use a simular apporach to

https://www.researchgate.net/publication/299371751_Inertial_Dilute_Particulate_Fluid_Flow_Simulations_with_an_Euler-Euler_Lattice_Boltzmann_Method?_sg=I7CmprSSToWRHj8LcX29DzfYWgADQLhDWHKa8FHwQNP37uyhET1xk2CYQ-PT9mFH6GOfeQHIXpFEl6LntWDHOzrM0qML-tqlGh7nC-gs.k5Iqm9Yn5P2L6ARUK-Q_NXjT1Ks9GWY9WBUg44O6xmBEE0JtDGOD78n3Ol4vxmEEEHK4d60FJd0htgxmJCyJKw

The test case in available by means of the bifiurcatiuon example.

Using only convection and zero difussion is not possible. You need a stabilization simular to the one proposed in the paper.

We will discuss that apporach in our spring school in the LBM theory part as well as in the practical part.

Best
MJ

[kolotinsky]

So, if I understand correctly, then using OpenLB it is not possible to simulate a collisionless gas, isn’t it?

[mathias]

We have a model for that scenario (see paper) and a test case in OpenLB that is very simular to it.

Best
MJ

[kolotinsky]

My aim is to simulate the following equation
df/dt + v*df/dr + (F/m)*df/dv = w*(f-f0)
As I understand in OpenLb algorithm for this case f0 is shifted maxwell distribution.
I suppose to simulate collisionless ion gas in neutral gas it is enough to replace shifted maxwell distribution function of ions with maxwell distribution function of neutral gas. How can I apply my idea using OpenLB? Is it possible to change some source file to implement my idea?

[mathias]

You may change any source file – that is the idea of sharing open source code.

Best
Mathias

[kolotinsky]

I understand this. I mean, could you advice me which file should I rewrite to change equilibrium distribution function for MRT or BGK forced dynamic?

[mathias]

You can use our dogygen html Version https://www.openlb.net/DoxyGen/html/index.html to find and work with the code. It is in core/dynamics.*

Best
Mathias

[kolotinsky]

I have found interesting method named “staticCollide” in doxygen. I suppose it can help me for my purpose. But I do not really understand what this method do. Could you explain it for me?

[mathias]

No, static collide will not help you. It collides without updating u. You can look at ConstRhoBRK, that is the one you need.

Best
Mathias

[kolotinsky]

What does “collides without updating u” mean? Does it mean that equilibrium distribution function in collision BGK operator which is f0 = f0(u) does not change during a simulation. And for example I can set u to zero?

[mathias]

Please have a look in the source code.

[Author]

Posts