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Description
The pseudo (1D) approximation for computing the structure of premixed stagnation flames is evaluated through comparison to two-dimensional (2D) computations and experiments. OPPDIF and commercial ANSYS Fluent is used to solve pseudo 1D and 2D reacting flow governing equations, respectively. The pseudo 1D formulation solves the 2D axisymmetric flow by assuming that the radial velocity increases linearly with radial position and all other variables are not a function of radial position. This simplification is useful for faster computations if the solution is accurate. New experimental flame images are used to interpret the accuracy of the current flame computational modeling. Four flame conditions are studied with an emphasis on agreement on radial velocity predictions between the models. A range of flame aspect ratio, inlet velocity, and strain rate is examined. The pseudo 1D formulation is known to perform best when the aspect ratio of the stagnation flow is wide, meaning that the inlet nozzle is wide and distance to the stagnation surface is short. Flame 10 matches this criterion and, as expected, the agreement in radial velocity is best between OPPDIF and ANSYS solutions for Flame 10. The radial velocity contour predicted by the pseudo 1D model agrees with the 2D computations for all four flame conditions within a narrow range close to the centerline. Away from the centerline, the pseudo 1D model diverges from the 2D radial velocity prediction because the loss of radial momentum is not accounted for. Based on the four flame conditions studied, the radial velocity predicted by the pseudo 1D is reasonable within 1.5x the nozzle radius. Other key factors that affected flame simulations were the aspect ratios of the flame domain and strain rate of the flow. The limitations found between both the 1D and 2D solutions are great avenues for future computations in understanding how strain and aspect ratios can effect nano-particle production. The results are important for designing stagnation flame processes for nano- material synthesis.
