Reply To: Validation of HLBM

[avrachan]

Hi Stephan,

Thank you for your reply.

I have tried various combination of parameters.

For example, I have fixed the packing fraction to be 0.3, and applied a very small forcing field ~ 10^{-10} and varied the relaxation time tau.

I find a strong dependence on the value of the drag coefficient on the value of tau. F/v * [6 pi et a]^(-1), is supposed to be independent of tau. This has been reported in [1] section 3, where they looked at a packing fraction below 0.1. [1] is the only comparative study of partially saturated method (as implemented in OpenLB) with Momentum exchange method as discussed in Ladd [2] where drag force on periodic array of spheres in calculated. At the packing fraction they have considered, the calculated value from OpenLB agrees with analytical calculation. The disagreement between analytical values and values calculated from my code increases at higher packing fractions, where I have found that I have to chose very small tau (close to 0.5) to get values close to the analytical one.

As shown in the previous post, the Re, Ma and Kn are all very small. I find the strongest dependence on Kn, due to dependence on tau.

Analytical value of the drag coefficient have been reproduced by [3] (Table 1) for the TRT dynamics and momentum exchange method.

This makes me wonder, if the issue is related to the HLBM and the BGK dynamics.

PS: I have linked the code in the very first post.

[1] Rettinger, C.; Rüde, U. A Comparative Study of Fluid-Particle Coupling Methods for Fully Resolved Lattice Boltzmann Simulations. Computers & Fluids 2017, 154, 74–89. https://doi.org/10.1016/j.compfluid.2017.05.033.

[2] Ladd, A. J. C. Numerical Simulations of Particulate Suspensions via a Discretized Boltzmann Equation. Part 2. Numerical Results. J. Fluid Mech. 1994, 271, 311–339. https://doi.org/10.1017/S0022112094001783.

[3] Bogner, S.; Mohanty, S.; Rüde, U. Drag Correlation for Dilute and Moderately Dense Fluid-Particle Systems Using the Lattice Boltzmann Method. International Journal of Multiphase Flow 2015, 68, 71–79. https://doi.org/10.1016/j.ijmultiphaseflow.2014.10.001.

• This reply was modified 3 weeks, 6 days ago by avrachan.