Inviscid evolution of incompressible swirling flows in pipes: The dependence of the flow structure upon the inlet velocity field

This paper analyses the influence of the inlet swirl on the structure of in compressible inviscid flows in pipes. To that end, the inviscid evolution a long a pipe of varying radius with a central body situated inside the pipe is studied for three different inlet swirling flows by solving the Bragg-Ha wthorne equation both asymptotically and numerically. The downstream struct ure of the flow changes abruptly above certain threshold values of the swir l parameter (L). In particular, there exist a value L-r above which a near- wall region of flow reversal is formed downstream, and a critical value L-f above which the axial vortex flow breaks down. It is shown that the depend ence upon the pipe geometry of these critical values of the swirl parameter varies strongly with the inlet azimuthal velocity profile considered. An e xcellent agreement between asymptotic and numerical results is found. (C) 1 999 Editions scientifiques et medicales Elsevier SAS.