Hello,nthanks for your answer, During this time i figured out, that the main problem is in inflation itself, anytime I suppress this option the results look fine. So my solution was to delete the inflation and use more precise decomposition. Picture below.n Then i used edge sizing to define boundary layer meshing. picture below.nand then more edge sizings on the interior fluid itself. picture below.nplus Face Meshing and multizone quad/tri method set to all quad and the result is in the picture. the picture shows the middle part where the pipe is narrowing. it is Venturi´s nozzle.nI really do not know why the inflation was making such a mess but with this mesh the result looks good. picture.nI thank you very much for your proposal @Kremella , but i am not sure what you mean. I never used streamwise periodic simulation and i am not really sure how to do it. I am sorry but since the problem is resolved, I am not sure i have the energy to go through the necessary tutorials to use streamwise p. sim. I hope you wont be angry if I won´t try your solution. Also, the PRESTO and QUICK will be necessary in the later stages where i will use RSM optimization to maximize cavitation and minimize pressure losses. the geometry can get a pretty wild when spline is applied on the narrowing part instead of two lines. Since i am using Latin hypercube to create my DoE in some design points the diameter in the most narrow part can get to 1mm.nnThanks a lot again and if the problem returns i know what should i try next.n