Thank you, Kostya for your helpful comment . nYes, I can see that there is a backflow too but I am still not clear about why the particles are getting trapped in that reason(recirculation zone ). Is there some wrong with the boundary condition on the wall which I had setup a trap and made the wall rotating? Is there something wrong with the meshing? Is there something wrong with the design of the nozzle? Is there any suggestion you guys can help me to overcome this problem?n I will appreciate your helpn