The flow characteristics in the bellmouth region of a circular pipe have been numerically studied for Reynolds numbers, Re, ranging from 1000 to 4000. Until now, the axial veocity has been assumed to be uniform at the bell mouth outlet both experiemntally and theoretically. The calculation results, however, reveal that it develops a profile somewhat towards the Posiseuille's parabolic profile. Next, it was found that the pressure on the wall of the bellmouth is lower than in the central core. this result contradicts both bernoulli's law and Prandtl's boundary-layer assumption. Moreover, a feasible reason for the increases in critical Reynodlds number when suing bellmouths was identified. i.e., if the belmouth region is replaced by the pipe one, it was observed that the equivalent Re decreases from the original Re value.
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