| Swirl injectors are widely used in liquid rocket engine, aero-engine and non-combustion industrial equipment. A comprehensive understanding of the spray characteristic and atomization mechanism of the swirl injector is crucial for engineering application and technical breakthrough. A spray test rig with an ambient pressure chamber was developed for the open-end swirl injector. Combined with a variety of optical measurement and numerical simulation, the spray evolution process, spray pattern, macroscopic atomization parameters,influence law of the key factors and engineering applications were systematically investigated.The main research works and obtained conclusions in this dissertation are as follow:(1) A spray test device was developed, which was suitable to wide flow rate range, a variety of optical measurement and ambient pressure experiment.An ambient pressure spray device was successfully developed, which could support a maximum air flow rate of 600g/s and a maximum liquid flow of 500g/s. Moreover, a lot of optical measuring methods could be adopted on it, such as PDPA (phase Doppler particle analyzer), PIV (particle image velocimetry), high-speed shadowgraph and high-speed backlight. A vertical displacement device was installed at the top of the chamber to adjust the position of the injector.(2) The flow characteristic and evolution process of an open-end swirl injector were investigated by means of experiment and numerical simulation.High precision optical measurement method of high-speed backlight and good interface tracking methods VOF (Volumn of fluid) model were combined to capture the formation of air core, the liquid film filling and breaking process of an open-end injector. The main achievements are as follows: In the filling process, the spray pattern of the cross-sectional at the tangential inlets was also changing. It changed from a square shape to a petal shape, and finally to a circle shape. After the liquid sheet left the injector exit, it would not break up immediately. At first, it must experience thinning. Then the liquid sheet would break up when the wave amplitude reached half-wavelength. The liquid sheet repeated thinning, deforming,shedding, breaking and coalescence during the formation and breakup process. With the increased injection pressure drop, the spray pattern would experience distorted pencil stage,onion stage, tulip stage and fully developed stage in turn in the opening process. Increased ambient pressure transformed the spray structure from a wide hollow cone to a narrow contracting bell,and a higher ambient pressure would result in an earlier transformation. When the ambient pressure reached 0.6 MPa, a vortex was indicated by upward droplets outside of the liquid sheet. The contracting bell continued to appear under the ambient pressure of 1.6 MPa. And the entire bell appeared at a high ambient pressure of 2.1 MPa.(3) The influences of operating parameters and geometrical parameters on the steady flow and spray characteristics of an open-end swirl injector were systematically studied.High precision optical measurement method of high-speed shadows and VOF model were combined to capture the image of the steady flow. Considering the true shape of the tangential inlets, the distributions of the pressure and velocity were not completely uniform at the interface between the tangential hole and the swirl chamber. The flow field in the central area of the injector was irregular. And the axial velocity had a peak between the two tangential holes. As the injection pressure drop increased from 0.002MPa to 0.8MPa, the spray field experienced pencil-shaped, onion-shaped, tulip-shaped and fully open-shaped in turn. The breakup time was shortened while the particle number in the spray region increased. At the same injection pressure drop, with the increased ambient pressure, the spray region, breakup length, spray angle decreased while the particles number increased under the same injection pressure drop.High-speed shadow and PDPA were combined to obtain the performance parameters,including discharge coefficient, spray angle, breakup length, velocity distribution and droplet size distribution. At a high ambient pressure of 2.1 MPa, the discharge coefficient increased significantly when the injection pressure drop increased from 0.1 MPa to 0.2MPa. At a low ambient pressure of 0.1 MPa, the discharge coefficient kept constant as the injection pressure drop increased. When the injection pressure drop increased to a critical value of 0.4MPa, the discharge coefficient slightly reduced with the increased ambient pressure. At the same injection pressure drop, the spray angle decreased as the ambient pressure increased. With increased injection pressure drop and geometric characteristic parameters, the liquid film thickness and breakup length reduced. With the increased ratio of injector length to injector orifice diameter, the fluid momentum loss and the breakup length increased. As the tangential inlet diameter or the ratio of injector length to injector orifice diameter increased, the swirl strength would be weakened. As a result, the spray angle decreased while the discharge coefficient increased.Finally, the empirical formulas of discharge coefficient, spray angle and breakup length were obtained by considering the important factors, such as ambient pressure, injection pressure drop, ratio of injector length to injector orifice diameter and geometric characteristic parameter A. The wider application range and smaller fitting error would be more suitable for engineering reference.(4) Combined with engineering applications, the evolution process and spray characteristics of a gas-liquid coaxial injector were carried out. And the combustion heater was designed and ignited with the selected gas-liquid coaxial injector.Considering the wide application of gas-liquid coaxial swirl injectors in the combustion equipment, the spray evolution process and the structure of the flow field were investigated. As the development of the liquid film was limited by the wall of the outer injector, the spray angle of the gas-liquid coaxial injector was smaller than swirl injector. And it appeared in the form of a Christmas tree. The velocity of the droplets was significantly increased. As a result, the droplet distribution was improved. And the droplet diameter decreased. The Gas-liquid coaxial injector with an open-end swirl injector was adopted in the high-temperature wind tunnel combustion heater. The combustion heater could achieve rapid ignition and efficient combustion over a wide range with good combustion stability and well flow filed uniformity.The spray evolution process, spray pattern, macroscopic atomization parameters, and the influence law of key factors under different ambient pressure were systematically investigated.And after comprehensively considering the effect of geometric parameters (tangential inlet diameter and injector length) and operating parameters (ambient pressure and injection pressure drop), empirical formulas of discharge coefficient and spray cone angle were proposed. Moreover, it was verified that the gas-liquid coaxial injector with an open-end swirl injcetor was suitable to the combustion heater, which would expand the application scope of the open-end swirl injector. |
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