Multi-Schlieren CT Measurements of Supersonic Microjets from Circular and Square Micro Nozzles

• 作者: Ahmad Zaid Nazari Fumiya Ito Harumi Kondo Ryoya Yamada Shinichiro Nakao Takanori Motohiro Yojiro Ishino Yoshiaki Miyazato Yuta Ishiko
• 来源期刊: 流量控制、测量及可视化(英文)
• 学科: 物理学
• 关键词: Supersonic Microjet Multi-Directional Quantitative Schlieren Optical System Three-Dimensional (3D) Measurement Computerized Tomography (CT) Circular and Square Micro Laval Nozzles
• 年，卷（期）: llkzcljkshyw_2020,（3）
• 页码范围: 77-101
• 页数: 25页
• 分类号: O35

摘要

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 <em>M</em><em>_j</em> ranging from 1.47 - 1.71, where the design Mach number is <em>M_d</em> = 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<span style="white-space:nowrap;">°</span> 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.