| Simplex atomizers (pressure-swirl atomizers) are widely used in air-breathing gas turbine engines as they have good atomization characteristics and are relatively simple and inexpensive to manufacture. To reduce emissions, it is critical to design fuel atomizers that can produce spray with a predetermined droplet size distribution at the desired combustor location (small mean droplet diameters and uniform local air/fuel ratios). Manufacturing methods are now available where complex atomizer geometries can be easily obtained. However to use such methods, the influence of atomizer geometry on its performance must be well understood.; In this dissertation, a two-dimensional axi-symmetric computational fluid dynamics (CFD) model based on the Arbitrary-Lagrangian-Eulerian (ALE) method to predict the flow in pressure-swirl atomizers was developed. The Arbitrary-Lagrangian-Eulerian method was applied so that the free interface between gas and liquid could be tracked sharply and accurately. The developed code was validated by comparison of predictions with experimental data for large scale prototype and with semi-empirical correlations at small scale. The computational predictions agreed well with experimental data for the film thickness at the exit, spray cone angle, and the pressure drop across the atomizer as well as velocity field in the swirl chamber.; Using the validated code, a comprehensive parametric study on simplex atomizer performance was conducted. The geometric parameters of atomizer covered in this study include: atomizer constant (K), the ratio of length to diameter in swirl chamber (Ls/Ds), the ratio of length to diameter in orifice (lo/do), the swirl chamber to orifice diameter ratio (Ds/do), inlet slot angle (beta), trumpet angle (thetat), trumpet length (lt), and swirl chamber convergent angle (thetac). The effects of these geometric parameters on the atomizer performance were studied for a fixed mass flow rate through the atomizer as well as for a fixed pressure drop across the atomizer. The atomizer performance was described in term of dimensionless film thickness at the exit (t*), discharge coefficient (Cd) and spray cone half angle (theta).; To address applications in pharmaceutical and food processing industry, flow of non-Newtonian power-law fluids through pressure-swirl atomizers was considered. Detailed flow patterns inside the atomizer for shear-thinning, Newtonian and shear-thickening fluids were investigated. A range of power law index from 0.7 to 1.3 was considered. With a fixed flow rate through the atomizer, the shear-thickening fluids exhibit higher film thickness at exit, lower spray angle, and higher discharge coefficient compared to Newtonian fluids. For the range of power law index considered in this study, the atomizer performance parameters for shear-thinning fluids show small change from Newtonian fluids. The variation of atomizer performance with the atomizer constant was delineated for different power-law index. |
