In this study, free-flight tests of a sphere for Reynolds numbers between 3.9 × 103 and 3.8 × 105 and free-flight Mach numbers between 0.9 and 1.6 were conducted using a ballistic range, and compressible low-Reynolds-number flows over an isolated sphere were investigated with the schlieren technique. The flow visualization was carried out under low-pressure conditions with a small sphere (minimum diameter of 1.5 mm) to produce compressible low-Reynolds-number flow. Also, time-averaged images of the flow near the sphere were obtained and compared to previous numerical results for Reynolds numbers between 50 and 1000. The experimental results clarified the structure of shock waves, recirculation region, and wake structures at the Reynolds number of 103–105 under transonic and supersonic flows. As a result, the following characteristics were clarified: (1) the amplitude of the wake oscillation was attenuated as the free-flight Mach number increased; (2) use of singular value decomposition permitted extraction of the mode of the wake structure even when schlieren images were unclear due to severe condition, and different modes in the wake structure were identified; (3) the Reynolds number had little effect on the separation point, but the length of the recirculation region increased as the Reynolds number decreased; and (4) the wake diameter at the end of the recirculation region decreased as the Mach number increased.

中文翻译：

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通过带纹影可视化的自由飞行测试，对雷诺数为 103-105 的球体上的跨音速和超音速流动进行实验研究

在这项研究中，使用弹道范围对雷诺数介于 3.9 × 103 和 3.8 × 105 之间和自由飞行马赫数介于 0.9 和 1.6 之间的球体进行自由飞行测试，并且可压缩的低雷诺数流过孤立的用纹影技术研究球体。流动可视化是在低压条件下用小球体（最小直径为 1.5 毫米）进行的，以产生可压缩的低雷诺数流动。此外，还获得了球体附近流动的时间平均图像，并与之前雷诺数在 50 到 1000 之间的数值结果进行了比较。实验结果阐明了雷诺数为 103 时的冲击波、再循环区域和尾流结构的结构–105 在跨音速和超音速流动下。因此，明确了以下特点：(1)尾流振荡的幅度随着自由飞行马赫数的增加而衰减；(2)使用奇异值分解允许提取尾迹结构的模态，即使由于条件恶劣，纹影图像不清晰，并且识别了尾迹结构中的不同模态；(3)雷诺数对分离点影响不大，但回流区长度随着雷诺数的减小而增加；(4) 再循环区末端的尾流直径随着马赫数的增加而减小。(2)使用奇异值分解允许提取尾迹结构的模态，即使由于条件恶劣，纹影图像不清晰，并且识别了尾迹结构中的不同模态；(3)雷诺数对分离点影响不大，但回流区长度随着雷诺数的减小而增加；(4) 再循环区末端的尾流直径随着马赫数的增加而减小。(2)使用奇异值分解允许提取尾迹结构的模态，即使由于条件恶劣，纹影图像不清晰，并且识别了尾迹结构中的不同模态；(3)雷诺数对分离点影响不大，但回流区长度随着雷诺数的减小而增加；(4) 再循环区末端的尾流直径随着马赫数的增加而减小。