本研究探討雙層氣流渦旋數對預成膜氣衝式噴注器霧化特性的影響。實驗採用雙層同軸流道預成膜氣衝式噴注器，以水及氮氣做為工作流體，水之質量流率定為3 g/s，氣液比固定為7，而內層與外層氣體質量流率分別為7.9 g/s與13.1 g/s，對應軸向速度分別為82.1 m/s與140.8 m/s。內層渦旋數設定為0.39、0.677與1.172，外層渦旋數設定為0.244、0.527與0.912，並進一步比較同向與反向渦旋配置對噴霧特性之影響。研究中利用光學影像量測霧化角，並以粒徑分析儀量測液滴粒徑分布，再透過平面雷射誘導螢光(Planar Laser-Induced Fluorescence, PLIF)建立二維質量機率分布圖，進一步以非均勻度指標(Patternation Index, P.I.)評估噴霧分布均勻性。
實驗結果顯示，內外層渦旋強度皆會顯著影響噴霧之外形、粒徑與空間分布。當渦旋數增加時，霧化角整體呈增加趨勢，平均粒徑則傾向下降，顯示較強之旋流有助於提升液膜與液滴的破碎效果。導流結構之加入可增強氣流對液膜之剪切作用，使液滴粒徑減小，然而其亦可能限制液滴向外徑向擴散，使下游中心區域形成較高液滴濃度。就雙層渦旋方向而言，同向渦旋條件下之噴霧分布較均勻，且噴霧範圍較大，反向渦旋則可提升局部剪切作用並降低平均粒徑(Sauter mean diameter，SMD)，但部分條件下亦可能伴隨較大液滴比例增加，顯示粒徑細化與整體分布均勻性之間仍存在權衡。於高渦旋數條件下，在較下游粒徑分布指標出現回升現象，推測與噴霧核心區液滴濃度增加、液滴碰撞與聚合機率提升有關。PLIF結果進一步顯示，外層渦旋強度增加時，可有效擴大噴霧徑向分布範圍並提升噴霧面積；當內層渦旋數由0.39增加至0.677時，則有助於降低液滴過度集中現象，使噴霧分布趨於均勻。整體而言，外層渦旋對噴霧空間展開之影響較為顯著，而內層渦旋則對近場破碎與中心區分布具有重要作用。

This study investigates the influence of swirl number in dual gas streams on the atomization characteristics of a pre-filming airblast atomizer. A dual-coaxial-flow pre-filming airblast atomizer was employed, using water and nitrogen as the working fluids. The water mass flow rate was fixed at 3 g/s, and the air-to-liquid ratio was maintained at 7. The inner and outer gas mass flow rates were 7.9 g/s and 13.1 g/s, corresponding to axial velocities of 82.1 m/s and 140.8 m/s, respectively. The inner swirl numbers were set at 0.39, 0.677, and 1.172, while the outer swirl numbers were set at 0.244, 0.527, and 0.912. In addition, both co-swirl and counter-swirl configurations were examined to evaluate their effects on spray characteristics. Spray angle was measured using optical imaging, droplet size distribution was obtained using a particle size analyzer, and planar laser-induced fluorescence (PLIF) was employed to establish two-dimensional mass probability distribution maps. Spray distribution uniformity was further evaluated using the Patternation Index (P.I.).
The results show that both the inner and outer swirl intensities significantly affect spray shape, droplet size, and spatial distribution. As the swirl number increases, the spray angle generally increases, while the mean droplet size tends to decrease, indicating that stronger swirl promotes the breakup of the liquid film and droplets. The introduction of the guiding structure enhances the aerodynamic shear acting on the liquid film and leads to smaller droplets; however, it may also restrict outward radial dispersion, resulting in a higher droplet concentration in the downstream central region. For the dual-swirl configurations, co-swirl conditions produce a more uniform spray distribution and a wider spray spread, whereas counter-swirl conditions enhance local shear and reduce the Sauter mean diameter (SMD). However, under some conditions, counter-swirl may also be accompanied by an increased proportion of larger droplets, indicating that a trade-off exists between droplet size reduction and overall spray distribution uniformity. Under high-swirl conditions, an increase in droplet size distribution indicators was observed further downstream, which is inferred to be related to increased droplet concentration in the spray core and a higher probability of droplet collision and coalescence. PLIF results further indicate that increasing the outer swirl intensity effectively enlarges the radial spread and overall area of the spray, while increasing the inner swirl number from 0.39 to 0.677 helps reduce excessive droplet concentration and improves spray uniformity. Overall, the outer swirl plays a more dominant role in controlling the spatial spread of the spray, whereas the inner swirl has an important influence on near-field breakup and droplet distribution in the central region.

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