Atomization and Sprays, Vol.4, No.3, 303-323, 1994
2-PHASE FLOW CALCULATION OF REACTING AND NONREACTING, NONSWIRLING, AIR-ASSISTED METHANOL SPRAYS
The two-phase axisymmetric flow field present in a methanol fuel spray produced by a nonswirling air-assist atomizer operating in a downfired orientation is studied numerically under both nonreacting and reacting conditions. Fuel issuing out of the atomizer mixes with the surrounding air and burns, resulting in the establishment of the two-phase flow field. Calculations have been performed to characterize both the continuous and dispersed phases present in the spray. The analysis procedure involves the solution of the gas-phase equations in a Eulerian frame of reference. The numerical technique and modeling for the gas phase employs nonorthogonal curvilinear coordinates, the standard k-epsilon turbulence model, and a combustion model made up of an assumed shape probability density function and the conserved scalar formulation. The liquid phase is simulated by using a droplet spray model and by treating the motion of the fuel droplets in a Lagrangian frame of reference. Extensive phase Doppler particle analyzer (PDPA) data for this methanol spray configuration under both reacting and nonreacting conditions has been obtained by McDonell et al. [l, 2]. This includes measurements of the gas-phase velocity together with the droplet size, droplet number count, and droplet velocity distribution information at various downstream axial stations. Numerical calculations of both the nonreacting and reacting flow were performed under the exact inlet and boundary conditions as the experimental measurements. The computed gas-phase velocity field showed excellent agreement with the test data under both nonreacting and reacting conditions. The unique contribution of this work is the formulation of a numerical PDPA scheme for comparing the droplet data. The numerical PDPA scheme essentially converts the Lagrangian droplet phase data to the format of the experimental PDPA. Several sampling volumes were selected within the computational domain. The trajectories of various droplets passing through these volumes were monitored and appropriately integrated. The calculated droplet count and mean droplet velocity distributions were compared with the measurements. The computed nonreacting spray attributes showed good agreement with the data over all drop size ranges; the reacting spray showed good agreement only for the larger drops.