| Popis: |
One of the most important processes in a gas turbine combustor, influencing to a large extent the efficiency of the entire combustion process, is the mixing between a swirling annular jet (primary air) and the non-swirling inner jet (fuel). To study this fundamental flow geometry an experimental facility has been built which allows independent flow rate adjustment of the central (mean stream) and coaxial jet flow Vc/Vm and furthermore, good optical access for laser-based flow measurement techniques. Further important flow parameters include the Reynolds number (Rem), the swirl intensity (S) and the combustor confinement, expressed in terms of an expansion ratio (ER). The work presented focuses on the features of the swirling flow in the concentric annuli being the part of the inlet system. The laser Doppler technique has been used to measure the velocity profile and the gradient of the velocity in the annular cross section. The circumferential velocity profile follows the so-called free-vortex flow type, being characterized by an increase in the mean angular momentum by radius of curvature. The outcome of the experiment is that the axial velocity profile becomes increasingly asymmetric with increased swirl intensity. The velocity increases from the inside to the outside of the annular flow (with a decreasing gradient) corresponding to an intensified radial movement towards the outer wall due to imposed swirl. The numerical investigations, especially those accounting for the complete swirl generator system and using a second-moment closure reproduced all important mean flow and turbulent features in good agreement with available experimental data. Both the modelling and the Large Eddy Simulations of an equilibrium, fully developed swirling flow, performed with the method for the swirling inflow data generation due to Pierce and Moin (1998), revealed some interesting departures with respect to the opposite sign of the axial velocity gradient. |
