Unclassified 20. Security Classif.

No abstract

No abstract

Computations arc reported on the detailed structures of unconfined turbulent combusting sprays. Favre-averaged gas-phase equations and a k-e-g turbulence closure model are utilized. Using a conserved scalar approach and assuming the form of probability density function to be a clipped Gaussian, the thermodynamic scalar variables are calculated from a partial equilibrium model. The major features of the liquid-phase model are that a stochastic random-walk approach is used to represent the effect of gas-phase turbulence on droplet trajectories and vaporization. variable-property effects are considered in a comprehensive manner, and a conduction-limit model is employed to represent the transient liquid-phase processes. This two-phase model is used to study the structure of an unconfined methanol spray flame. An important observation is that the turbulent spray flame structure is significantly different, both quantitatively and qualitatively, from that of the corresponding gaseous diffusion flame. In addition. the spray flame exhibits a strong sensitively to transient liquid-phase processes. The latter result is interesting since, in an earlier computational study for an evaporating spray, the vaporization behavior for the same liquid fuel indicated only a weak sensitivity to these processes.

A computational study of turbulent evaporating sprays is reported. The major focus is to study the structure of turbulent evaporating sprays and to examine the sensitivity of their vaporization behavior to transient liquid-phase processes. Three models considered to represent these processes are the thin-skin, infinite-diffusion, and diffusionlimit models. Favre-averaged equations with a k-s-g turbulence model are employed for the gas phase. The Lagrangian approach with a stochastic separated-flow method is used for the liquid phase where the effects of gas turbulence on droplet trajectories and interphase transport rates are considered using random-walk computations. Variable-property effects are also considered in a comprehensive manner. Results indicate that, depending upon the boiling temperature and heat of vaporization of the fuel considered, the vaporization behavior of turbulent sprays may be quite sensitive to the modeling of transient liquid-phase processes. Thus, it is important that for most hydrocarbon fuels these processes be adequately represented in comprehensive spray computations. The present results also provide further support to the conclusions of earlier studies which have been based on simplified spray configurations.

Computations are reported on the detailed structures of unconfined turbulent combusting sprays. Favre-averaged gas-phase equations are used and a k-ε-g turbulence closure model is utilized. Using a conserved scalar approach and assuming the form of probability density function to be a clipped Gaussian, the thermodynamic scalar variables are calculated from a partial equilibrium model. The major features of the liquid-phase model are that a stochastic random-walk approach is used to represent the effect of gas-phase turbulence on droplet trajectory and vaporization, the variable-property effects are considered in a comprehensive manner, and a conduction-limit mode is employed to represent the transient liquid-phase processes. This two-phase model is used to study the structure of an unconfined methanol spray flame. Important observation is that the turbulent spray flame structure is significantly different, both quantitatively and qualitatively, from that of the corresponding gaseous diffusion flame. In addition, the spray flame exhibits a strong sensitively to the transient liquid-phase processes. The latter result is interesting since, in an earlier computational study for an evaporating spray, the vaporization behavior for the same liquid fuel indicated only a weak sensitivity to these processes.