dsmcFoam with a partially-reflecting patch

vapormonger · August 5, 2016, 16:23

I'd like to use dsmcFoam to model a system with walls that evaporate particles -- like a box with vacuum or low pressure inside, but the walls are coated with water held at a constant temperature.

From my understanding, a FreeStream boundary emits a Maxwellian distribution of particles, so the emission from evaporating surface could be modelled by FreeStream boundary with U=(0,0,0).

But, FreeStream absorbs all particles that hit it. I'd like to have walls/patches that emit particles like FreeStream, but have some chance of absorption and some chance of a wall interaction, for example MixedDiffuseSpecular.

Would be possible? How might I modify the code to allow this new boundary condition? I was thinking that DsmcParcel would be the main place to modify, by overriding one of the hitPatch functions of Particle to be similar to the hitWallPatch function.

Even better would be for different patches to have different probabilities of absorption vs bouncing, based on some dict.

ehsan · August 6, 2016, 00:52

Dear Jacob,

Have a look at the paper below, it suggest a simple but an efficient method:

citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.50.8229

So, create a new wall sub-model which inherits some features from free stream but injects particles from a different distribution function, like that in the paper, and then some part of the particles reflect from this wall with a probability of 1-S_e, and other particles absorb this wall with a probability of S_e.

Regards
Ehsan

August 5, 2016, 16:23	dsmcFoam with a partially-reflecting patch	#1
vapormonger New Member Jacob Schwartz Join Date: Aug 2016 Posts: 1 Rep Power: 0	I'd like to use dsmcFoam to model a system with walls that evaporate particles -- like a box with vacuum or low pressure inside, but the walls are coated with water held at a constant temperature. From my understanding, a FreeStream boundary emits a Maxwellian distribution of particles, so the emission from evaporating surface could be modelled by FreeStream boundary with U=(0,0,0). But, FreeStream absorbs all particles that hit it. I'd like to have walls/patches that emit particles like FreeStream, but have some chance of absorption and some chance of a wall interaction, for example MixedDiffuseSpecular. Would be possible? How might I modify the code to allow this new boundary condition? I was thinking that DsmcParcel would be the main place to modify, by overriding one of the hitPatch functions of Particle to be similar to the hitWallPatch function. Even better would be for different patches to have different probabilities of absorption vs bouncing, based on some dict.

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August 6, 2016, 00:52		#2
ehsan Senior Member Ehsan Join Date: Mar 2009 Posts: 112 Rep Power: 17	Dear Jacob, Have a look at the paper below, it suggest a simple but an efficient method: citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.50.8229 So, create a new wall sub-model which inherits some features from free stream but injects particles from a different distribution function, like that in the paper, and then some part of the particles reflect from this wall with a probability of 1-S_e, and other particles absorb this wall with a probability of S_e. Regards Ehsan