Multi-Schlieren CT Measurements of Supersonic Microjets from Circular and Square Micro Nozzles
Multi-Schlieren CT Measurements of Supersonic Microjets from Circular and Square Micro Nozzles
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DOI：
10.4236/jfcmv.2020.83005
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发表时间：
2020-05
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通讯作者：
A. Nazari;Y. Ishino;Yuta Ishiko;Fumiya Ito;Harumi Kondo;Ryoya Yamada;T. Motohiro;Y. Miyazato;S. Nakao
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文献类型：
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作者：
A. Nazari;Y. Ishino;Yuta Ishiko;Fumiya Ito;Harumi Kondo;Ryoya Yamada;T. Motohiro;Y. Miyazato;S. Nakao
测量了逃逸到周围空间中的完全和不完全膨胀超声速微射流的激波单元结构的瞬时三维（3D）密度分布。为了对超声速微射流进行三维观察，采用了非扫描三维CT技术，利用20个方向的定量纹影光学系统和闪光光源进行同步纹影摄影。采用最大似然-期望最大化法对投影图像进行三维CT重建，得到微射流的三维密度分布数据。本文研究了工作喷管压比为5.0、4.5、4.0、3.67和3.5的轴对称收扩（拉瓦尔）圆形和方形微型喷管。本研究探讨完全扩展，过度膨胀，和欠膨胀的超音速微射流从微喷嘴发出的完全扩展射流马赫数Mj范围从1.47 - 1.71，其中设计马赫数为Md = 1.5。观察到了自由方形微射流的轴向切换现象，并将其分为“十字形”和“直角形”两种类型。在第一冲击单元范围内，初始轴切换为45°。此外，从第一个激波单元的正方形微射流的对称和对角视图中，可以看到两种不同的激波模式。研究并报告了所有喷管压比下的激波单元间距和超音速核心长度。
Instantaneous three-dimensional (3D) density distributions of a shock-cell structure of perfectly and imperfectly expanded supersonic microjets escaping into an ambient space are measured. For the 3D observation of supersonic microjets, non-scanning 3D computerized tomography (CT) technique using a 20-directional quantitative schlieren optical system with flashlight source is employed for simultaneous schlieren photography. The 3D density distributions data of the microjets are obtained by 3D-CT reconstruction of the projection’s images using maximum likelihood-expectation maximization. Axisymmetric convergent-divergent (Laval) circular and square micro nozzles with operating nozzle pressure ratio 5.0, 4.5, 4.0, 3.67, and 3.5 have been studied. This study examines perfectly expanded, overexpanded, and underexpanded supersonic microjets issued from micro nozzles with fully expanded jet Mach numbers Mj ranging from 1.47 - 1.71, where the design Mach number is Md = 1.5. A complex phenomenon for free square microjets called axis switching is clearly observed with two types “upright” and “diagonal” of “cross-shaped”. The initial axis-switching is 45° within the first shock-cell range. In addition, from the symmetry and diagonal views of square microjets for the first shock-cells, two different patterns of shock waves are viewed. The shock-cell spacing and supersonic core length for all nozzle pressure ratios are investigated and reported.