To understand the behavior of gas escaping a rapidly decompressed particle bed, an experimental study is performed in a cylindrical (D = 41 mm) glass vertical shock tube containing a densely packed particle bed. The bed is comprised of spherical glass beads. Two sets of beads are used, with median diameters of 67.5 and 254.5 $$\mu$$ m. The volume fraction of the glass beads is approximately 60%. High-speed pressure sensors capture the shock wave and expansion wave fronts. Optical measurements based on particle image velocimetry (PIV) are developed to examine the velocity of gas initially above the bed as well as gas initially within the interstices of the particle bed using both quantitative and qualitative visualization techniques. For above-bed gas flow analysis, passive tracer particles are seeded above the bed, whereas for interstitial gas measurements, lightweight but non-passive particles are mixed into the upper layers of the bed itself. Development of this technique to optically measure interstitial escape flow is utilized herein to measure the gas rise velocity in response to variation in bead diameter, with faster gas velocities observed as bead diameter increases. For the experiments performed herein, an initial acceleration of the gas velocity is observed at the earliest stages of particle bed decompression, whereas the gas velocity begins to decelerate between 1.25 and 2.25 ms of the estimated arrival of the expansion wave at the particle bed.

中文翻译：

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冲击驱动膨胀过程中气体逸出颗粒床的速度测量

为了了解气体从快速减压的颗粒床中逸出的行为，在包含密集颗粒床的圆柱形 (D = 41 mm) 玻璃垂直激波管中进行了一项实验研究。床由球形玻璃珠组成。使用了两组珠子，中值直径分别为 67.5 和 254.5 $$\mu$$ m。玻璃珠的体积分数约为 60%。高速压力传感器捕捉冲击波和膨胀波阵面。开发了基于粒子图像测速 (PIV) 的光学测量，以使用定量和定性可视化技术检查最初在床上方的气体以及最初在粒子床间隙内的气体的速度。对于床上气流分析，被动示踪粒子在床上方播种，而对于间隙气体测量，轻质但非被动的粒子被混合到床本身的上层。这种光学测量间隙逸出流的技术的发展在本文中被用来测量响应于珠直径变化的气体上升速度，随着珠直径增加观察到更快的气体速度。对于本文进行的实验，在颗粒床减压的最早阶段观察到气体速度的初始加速，而气体速度在膨胀波到达颗粒床的估计到达的 1.25 到 2.25 毫秒之间开始减速。这种光学测量间隙逸出流的技术的发展在本文中被用来测量响应于珠直径变化的气体上升速度，随着珠直径增加观察到更快的气体速度。对于本文进行的实验，在颗粒床减压的最早阶段观察到气体速度的初始加速，而气体速度在膨胀波到达颗粒床的估计到达的 1.25 到 2.25 毫秒之间开始减速。这种光学测量间隙逸出流的技术的发展在本文中被用来测量响应于珠直径变化的气体上升速度，随着珠直径增加观察到更快的气体速度。对于本文进行的实验，在颗粒床减压的最早阶段观察到气体速度的初始加速，而气体速度在膨胀波到达颗粒床的估计到达的 1.25 到 2.25 毫秒之间开始减速。