[emadsiadati]

Hi all.

Since we define parcels as a number of particles, why do we have to define clouds?

Thanks
Emad

[emadsiadati]

Also
- In discrete phase method (DPM) the forces are solved for parcels or particles or cloud in dpmfoam?
- if nParticle=1 are dpm and dem exactly the same?

[emadsiadati]

And anothe question:
I have defined stick parameter between the particles and the wall. When a particle sticks to a wall the whole cloud stickes or the parcel including that particle or just the individual particle?

[joshwilliams]

Originally Posted by emadsiadati

Hi all.

Since we define parcels as a number of particles, why do we have to define clouds?

Thanks
Emad

A cloud is a collection of parcels/particles. A parcel is a collection of particles. If number of particles in a parcel is one, then a cloud is simply a collection of particles.
Yes, if number of particles in parcel is one, then DPM = DEM. Otherwise, it is same as 'coarse DEM'.

[emadsiadati]

Originally Posted by joshwilliams

A cloud is a collection of parcels/particles. A parcel is a collection of particles. If number of particles in a parcel is one, then a cloud is simply a collection of particles.
Yes, if number of particles in parcel is one, then DPM = DEM. Otherwise, it is same as 'coarse DEM'.

Thanks for your reply.

How the diameter of the cloud is defined?
And do parcels leave a cloud?

[joshwilliams]

Originally Posted by emadsiadati

Thanks for your reply.

How the diameter of the cloud is defined?
And do parcels leave a cloud?

A cloud does not have a diameter. A particle has a diameter. I am not sure if a parcel has a diameter.

Parcels do not leave a cloud. Particles do not leave a parcel (I think).

[emadsiadati]

Originally Posted by joshwilliams

A cloud does not have a diameter. A particle has a diameter. I am not sure if a parcel has a diameter.

Parcels do not leave a cloud. Particles do not leave a parcel (I think).

Then what is the criterion for assigning the particles to a parcel and the parcels to a cloud?


If a cloud does not have a diameter then the forces like drag force which is a function of diameter is calculated for each parcel if it has a diameter, otherwise calculation is conducted over each particle!

What is the rationale behind defining clouds and parcels then?! We are just doing dem imo!

[joshwilliams]

Originally Posted by emadsiadati

If a cloud does not have a diameter then the forces like drag force which is a function of diameter is calculated for each parcel if it has a diameter, otherwise calculation is conducted over each particle!

You are not getting what a cloud is. A cloud is just the collective term for the particles or parcels in your simulation. The term cloud is pretty much meaningless. It is just openfoam terminology. Not sure how else to explain it.... Think of a cloud in the sky, made of, lets say, billions of water droplets. The motion of the cloud is not determined by calculating the drag force based on the diameter of a cloud (it would be ludicrious, the cloud to particle size ratio is probably like 1e20 metres, also at a macro-scale I guess you would consider it a highly porous medium, but that is not relevant). You calculate forces on each particle.

In OpenFOAM, you define the diameter of one particle. You define how many particles are in one parcel. You can calculate the forces using the particle diameter. Lets say you use parcel approach like MPPIC, you calculate drag based on particle diameter (p.d() in the source code). Then you apply some collision kernel (like Harris-Crighton in tutorials), which is based on the number of parcels in each cell, the number of particles in a parcel, and the individual particle diameter.


If you have further difficulty, I suggest you review the source code

cd $FOAM_SRC/lagrangian/intermediate/parcels/Templates/KinematicCloud

and source code for calculating drag

 cd $FOAM_SRC/lagrangian/intermediate/submodels/Kinematic/ParticleForces/Drag/SphereDrag

[emadsiadati]

Thanks!
This was very illustrative.