This paper presents a computational study of entrainment characteristics in the near-field of gas jets under atmospheric and Diesel conditions and sprays under Diesel conditions. Computed flowfield information is used to estimate the rate of mass entrainment in the jet and derive the entrainment rate constant. The value of the entrainment rate constant is compared to experimental results in the literature. It is found that the computed values of the constant in the near-field are less than the values in the self-similar region of the jet with the values increasing monotonically from the orifice to the self-similar region. These results are consistent with experimental results. In the case of sprays, it is found that it is difficult to arrive at firm conclusions because the results are sensitive to several parameters that are not well known and to the numerics. The computed results for sprays are also discussed relative to measurements in sprays quoted in the literature. [S0098-2202(00)00802-6]
Results from numerical computations performed to represent the transient behavior of axisymmetric non-vaporizing and vaporizing sprays injected into a constant volume chamber are presented. These results are compared with those from vaporizing spray experiments where, for the same mass and momentum flow rates, the effect of chamber density on spray penetration and dispersion angle was studied. It is shown that with the practical numerical resolution employed here, which appears to be inadequate, the results do not agree. Higher resolution is impractical from a numerical point of view for sprays. Hence, the present work further explores whether gas jets, which may be computed with a high resolution, are comparable to the sprays in terms of penetration and dispersion angle. For each gas jet computation, the injected mass and momentum flow rates and the chamber density in the corresponding gas jet computations are maintained the same as those in the spray experiments. Comparisons show that the gas jet penetration and angles are in agreement with the trends of the spray measurements. In both cases. the penetration decreases with increasing chamber density and the dispersion angle increases.
A two fluid Eulerian-liquid Eulerian-gas (ELEG) model for diesel sprays is developed. It is employed to carry out computations for diesel sprays under a wide range of ambient and injection conditions. Computed and measured results are compared to assess the accuracy of the model in the far field, i.e., at axial distances greater than 300 orifice diameters, and in the near field, i.e., at axial distances less than 100 orifice diameters. In the far field, the comparisons are of drop mean velocities and drop fluctuation velocities and in the near field they are of entrainment velocities and entrainment constants. Adequate agreement is obtained quantitatively, within 30 percent, and qualitatively as parameters are changed. Unlike in traditional Lagrangian-drop Eulerian-fluid (LDEF) approaches that are employed for diesel spray computations, adequate resolution can be employed in the near field to achieve numerical grid independence when the two-fluid model is employed. A major source of uncertainty in the near field is in the modeling of liquid jet breakup and atomization.
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