Evaluation of three-dimensional droplet shape for analysis of the crossflow-type atomization

Abstract

The development of a numerical analysis of fuel atomization is important for engine design but has the problem that the required resolutions for the gas phase and atomized droplets are significantly different. To solve this, an Euler-Lagrange coupling numerical analysis for fuel atomization has been developed. For the improvement of this analysis by including the shape effect of atomized droplets and increasing the number of droplets that can be replaced by Lagrange particles, a new droplet shape representation method using five shape parameters — Sphericity, Bentness, Slenderness, Flatness and Complexity — are proposed. These parameters are defined based on indices that reflect the overall scale of droplets, such as volume and area, and the local distribution of shape features within a droplet. First, a test case with ideal geometries showed how well these parameters qualitatively and quantitatively represent the characteristics of droplet shapes. Then, the distribution of droplet shapes in a crossflow computed by a detailed numerical analysis using the S-CLSVOF method was analyzed by the proposed shape representation method. As a result, it was shown that the parameters expressed the characteristics of actual droplets sampled from the analysis. In addition, it was confirmed that the shape distributions expressed by the proposed five parameters differed depending on the density ratio of gas and liquid and/or the Weber number, and that the analysis result is consistent with the theories of surface tension and linear instability.