Re: Setting Boundary Values • OpenLB - Open source lattice Boltzmann code

January 25, 2017 at 10:33 am #2526

Keymaster

Hi Sumit,

in this example yes the physical velocity is charU * latticeL. Usually setting latticeU will give you charU as physical velocity (for a scaling factor of 1), however in this example the scaling factor in the CirclePoiseuille is chosen to be latticeL.
This scaling is not necessary if you replace
CirclePoiseuille3D<T> poiseuilleU(superGeometry, 3, converter.getLatticeU(), converter.getLatticeL());
by
CirclePoiseuille3D<T> poiseuilleU(superGeometry, 3, converter.getLatticeU(), 1.);
or
CirclePoiseuille3D<T> poiseuilleU(superGeometry, 3, converter.getLatticeU());
you will get a inlet velocity of 100m/s for charU=100m/s.

To learn more about the transformations (e.g. what is effected by latticeU) you could have a look at the doxygen of the unit converter:
http://optilb.com/DoxyGen/html/d1/d25/classolb_1_1LBconverter.html

The influence of compressibility should be related to the Mach number, to find more detailed information I can recommend e.g.
T. Krüger, H. Kusumaatmaja, A. Kuzmin, O. Shardt, G. Silva, E.M. Viggen. The Lattice Boltzmann Method – Principles and Practice

Best
Robin