Thanks for the Input! I recently found some paper, where they did a LES of a ripped pipe wiht only on rib, here a example: https://web.stanford.edu/group/ctr/Summer/SP14/09_Large-eddy_simulation/10_zhu.pdf The author also showed in this PHD thesis that the influence on the pressure loss, which I am intrested in, is nearly the same for a longer streamwise geometry. So I am wondering because I thought that should not work.