NUMERICAL COMPUTATION AND VALIDATION OF 2-PHASE FLOW DOWNSTREAM OF A GAS-TURBINE COMBUSTOR DOME SWIRL CUP

The two-phase axisymmetric flow field downstream of the swirl cup of a n advanced gas turbine combustor is studied numerically and validated against experimental Phase-Doppler Particle Analyzer (PDPA) data. The swirl cup analyzed is that of a single annular GE/SNECMA CFM56 turbofa n engine that is comprised of a pair of coaxial counterswirling air st reams together with a fuel atomizer. The atomized fuel mixes with the swirling air stream, resulting in the establishment of a complex two-p hase flow field within the swirl chamber. The analysis procedure invol ves the solution of the gas phase equations in an Eulerian frame of re ference using the code CONCERT. CONCERT has been developed and used ex tensively in the past and represents a fully elliptic body-fitted comp utational fluid dynamics code to predict flow fields in practical full -scale combustors. The flow in this study is assumed to be nonreacting and isothermal. The liquid phase is simulated by using a droplet spra y model and by treating the motion of the fuel droplets in a Lagrangia n frame of reference. Extensive PDPA data for the CFM56 engine swirl c up have been obtained at atmospheric pressure by using water as the fu el (Wang et al., 1992a). The PDPA system makes pointwise measurements that are fundamentally Eulerian. Measurements have been made of the co ntinuous gas phase velocity together with discrete phase attributes su ch as droplet size, droplet number count, and droplet velocity distrib ution at various axial stations downstream of the injector Numerical c alculations were performed under the exact inlet and boundary conditio ns as the experimental measurements The computed gas phase velocity fi eld showed good agreement with the rest data. The agreement was found to be best at the stations close to the primary venturi of the swirler and to be reasonable at later stations. The unique contribution of th is work is the formulation of a numerical PDPA scheme for comparing dr oplet data. The numerical PDPA scheme essentially converts the Lagrang ian droplet phase data to the format of the experimental PDPA. Several sampling volumes (bins) were selected within the computational domain . The trajectories of various droplets passing through these volumes w ere monitored and appropriately integrated to obtain the distribution of the droplet characteristics in space. The calculated droplet count and mean droplet velocity distributions were compared with the measure ments and showed very good agreement in the case of larger size drople ts and fair agreement for smaller size droplets.