I am having some doubts about in which routine of my code I must write my velocity and density outputs in order to have realistic results. Does anybody know how when do I have to write it in a generic way or do I need to be specific on my code?
Anyway I use basic bounceback in a channel flow. 2DQ9, and I want to visualize correctly my vortex shedding.
The real purpose of my question is no to find the exact timestep which I do have to get my outputs, but to know in which routine of my program I should have my file written. I mean if I have a loop scheme like:
inlet outlet boundary conditions treatment
Comput Macroscopic properties
second order Boundary treatment (Mei et al. 32,33)
As far as I remember it should be like this:
Advection and collision are (physically) instantaneous.
This is not the case in LBM, therefore some people save the output at half timesteps.
This is achieved by averaging of pre and post-collision data.
A quick search and skimming Nguyen and Ladd 2002 (DOI: 10.1103/PhysRevE.66.046708) indicates that this is used for force coupling, but I don’t see why e.g. density shouldn’t be just as instantaneous.
By coincidence I’m just reading the Ladd and Verberg 2001(DOI:10.1023/A:1010414013942) paper, that shows the difference in error of before,after and midway, as compared to the analytical solution. This paper then is the answer to your question. The velocity field should be measured in the middle of each time step.
you are welcome.
The second paper really was a lucky coincidence. I was curious before, how much this improves the result and if it really is worth the overhead.
Apparently it is.
No, sadly I’m not at the ICMMES conference. Hopefully next time.