I kept all the turbulence dispersion features off in the DPM settings. I will use them in my final study.

I know that based on the Random walk theory, a u'=\zeta * sqrt (average (u'^2)) term will be added to the flow in which zeta is a normally distributed random number meaning that I will get different DPM results even with the same mesh and settings if I track the particles twice in a row. to avoid that, I kept it off and am still getting different DPM results for different meshes.