Relations between lagrangian particle concentration and mesh size

Jasper Z · June 8, 2022, 22:51

Dear Foamers,

I am wondering that if the lagrangian particle concentration varies with mesh grid size? In openfoam, the particle concentration theta was defined as:

Code:

 theta[celli] += p.nParticle()*p.volume();
theta.primitiveFieldRef() /= mesh_.V();

If we decrease the mesh size, shouldn't the particle concentration increase? If that is the case, how can we validate the concentration with experiment?

Any point is welcome!

joshwilliams · June 10, 2022, 05:06

Hi Huan,
Yes the concentration will naturally change with mesh size.

Regarding your point "how can we validate the concentration with experiment?": Could you give some information on the experimental data you are trying to validate against? It is unlikely that experimental data would give as detailed measurement as local particle concentration (at a similar length scale as a computational cell). It is more likely that the experiment may provide some domain-averaged concentration statistics (mean, std dev, etc).

Alternatively, if there is some local information provided, then you may need to resample your particle cloud in post-processing to match the length scale used for to quantify 'concentration' in the experimental data. E.g. in the paper below by Marchioli et al, several laboratories performed simulations of particle-laden channel flow on varying meshes. Then they all sample instantaneous particle concentrations following the same protocol (which is therefore mesh independent).

Marchioli, Ch, A. Soldati, J. G. M. Kuerten, B. Arcen, A. Taniere, G. Goldensoph, K. D. Squires, M. F. Cargnelutti, and L. M. Portela. "Statistics of particle dispersion in direct numerical simulations of wall-bounded turbulence: Results of an international collaborative benchmark test." International Journal of Multiphase Flow 34, no. 9 (2008): 879-893.

June 8, 2022, 22:51	Relations between lagrangian particle concentration and mesh size	#1
Jasper Z Member Huan Zhang Join Date: Nov 2020 Posts: 55 Rep Power: 6	Dear Foamers, I am wondering that if the lagrangian particle concentration varies with mesh grid size? In openfoam, the particle concentration theta was defined as: Code: theta[celli] += p.nParticle()*p.volume(); theta.primitiveFieldRef() /= mesh_.V(); If we decrease the mesh size, shouldn't the particle concentration increase? If that is the case, how can we validate the concentration with experiment? Any point is welcome!

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June 10, 2022, 05:06		#2
joshwilliams Senior Member Josh Williams Join Date: Feb 2021 Location: Scotland Posts: 113 Rep Power: 5	Hi Huan, Yes the concentration will naturally change with mesh size. Regarding your point "how can we validate the concentration with experiment?": Could you give some information on the experimental data you are trying to validate against? It is unlikely that experimental data would give as detailed measurement as local particle concentration (at a similar length scale as a computational cell). It is more likely that the experiment may provide some domain-averaged concentration statistics (mean, std dev, etc). Alternatively, if there is some local information provided, then you may need to resample your particle cloud in post-processing to match the length scale used for to quantify 'concentration' in the experimental data. E.g. in the paper below by Marchioli et al, several laboratories performed simulations of particle-laden channel flow on varying meshes. Then they all sample instantaneous particle concentrations following the same protocol (which is therefore mesh independent). Marchioli, Ch, A. Soldati, J. G. M. Kuerten, B. Arcen, A. Taniere, G. Goldensoph, K. D. Squires, M. F. Cargnelutti, and L. M. Portela. "Statistics of particle dispersion in direct numerical simulations of wall-bounded turbulence: Results of an international collaborative benchmark test." International Journal of Multiphase Flow 34, no. 9 (2008): 879-893.