EFFECT ON INLET AND OUTLET BOUNDARY-CONDITIONS ON SWIRLING FLOWS

Numerical simulations are conducted for both three-dimensional, turbul ent flow in a multichannel swirler and axisymmetric, isothermal, turbu lent flow in combustion chambers using the standard kappa-epsilon turb ulence model. Calculations are first carried out for three-dimensional , isothermal and turbulent flow inside the swirler channels in order t o derive the velocity profiles of both air and gas at the swirler outl ets, which are used as inlet boundary conditions of the model combusto r and can also be used in future studies for different combustors with the same type of swirler. In order to study the sensitivity of swirli ng flow inside the chamber to the inlet and outlet boundary conditions , different inlet velocity profiles and outlet boundary conditions are also employed. The results show that in the cases considered, the flo w behaviour in the chamber is not very sensitive to the actual shape o f the inlet velocity profiles provided the averages of the inlet axial , radial and azimuthal velocity components are separately preserved. O ther conditions being equal, we find that the swirling flow performanc e in the combustor depends not only on the inlet swirl number, but als o strongly on the relative magnitude of the radial velocity component at inlet and introduce a new dimensionless number N-r, analogous to th e swirl number, to measure the relative importance of this quantity, O utlet boundary conditions have some influence near the outlet, but nea rly no effect further upstream for the cases investigated. (C) 1998 El sevier Science Ltd.