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Numerical simulation of gas dynamics in the high-pressure gas atomization process.

机译：高压气体雾化过程中气体动力学的数值模拟。

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High pressure gas atomization (HPGA) is an effective method for producing high yields of ultrafine metal and alloy powders. The salient gas flow features during such a complicated process must be recognized and understood before full control can be maintained over the process dynamics. In this investigation, the turbulent, compressible Navier-Stokes equations were solved for the gas-only flow in the vicinity of the melt tip within an HPGA atomizer. The influence of operating pressure and melt tip geometry on the HPGA gas flow field and melt aspiration condition were then examined.; The numerical results gained in this study have characterized a recirculation region attached to the melt tip base and a shear layer along the interface between the supersonic expanding flow and subsonic recirculating flow at all operating pressures and a normal shock downstream of the recirculation region at high atomizing pressures. These predominant flow features are in good agreement with published flow visualization results, such as Schlieren photographs and hydraulic analogy with a water table. The recirculation region is seen to experience a transition from an open wake condition to a closed wake condition. During the closed wake operation, the melt tip base center pressure ratio no longer decreases but instead remains relatively constant when the operating pressure is increased.; Different HPGA nozzle and melt tip designs have significant influence on the gas dynamics and melt aspiration in the atomization process as manifested by the numerical results and experimental evidence. As a consequence, a longer tip protrusion, a smaller tip taper angle, a smaller gas jet apex angle and a closer fit of the tip frustum surface to the innermost boundary of the gas jet all encourage a subambient or near-ambient melt tip base pressure, which provides a stable atomization.; A 3-D model was established for a discrete jet HPGA atomizer, which reinforces the axisymmetric results. Generally, the 3-D model predicts lower gas flow field properties, such as the Maximum Mach number within the whole gas flow field and recirculation length, relative to the axisymmetric model.
机译：高压气体雾化（HPGA）是生产高产量超细金属和合金粉末的有效方法。在维持对过程动力学的完全控制之前，必须认识和理解这种复杂过程中的显着气流特征。在这项研究中，对于HPGA雾化器内熔体尖端附近的纯气体流，求解了湍流，可压缩的Navier-Stokes方程。然后检查了操作压力和熔体尖端几何形状对HPGA气流场和熔体抽吸条件的影响。在这项研究中获得的数值结果表明，在所有工作压力下，沿超音速膨胀流与亚音速循环流之间的界面，附着在熔体尖端基部上的回流区域和剪切层以及在高雾化条件下在回流区域下游的法向冲击压力。这些主要的流量特征与已公布的流量可视化结果非常吻合，例如Schlieren的照片和带有地下水位的水力类比。看到再循环区域经历了从打开的唤醒状态到关闭的唤醒状态的转变。在闭合的尾流操作期间，熔体尖端的基础中心压力比不再降低，而是当操作压力增加时保持相对恒定。数值结果和实验证据表明，不同的HPGA喷嘴和熔体尖端设计对雾化过程中的气体动力学和熔体抽吸有重大影响。结果，较长的尖端突起，较小的尖端锥角，较小的气体射流顶角以及尖端的视锥台表面与气体射流的最内边界的更紧密配合都促进了低于或接近环境的熔融尖端基础压力。 ，提供稳定的雾化。针对离散射流HPGA雾化器建立了3-D模型，该模型增强了轴对称结果。通常，相对于轴对称模型，3-D模型预测的气体流场特性较低，例如整个气体流场内的最大马赫数和再循环长度。

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