Wake flow and angular oscillation behavior of two cylinders in tandem arrangement forming a van der Pol oscillator

Data result from careful measurements with hot wires and a high-speed camera in an aerodynamic channel with a rectangular cross-section of 0.146 m x 0.193 m (height × width), 2.29 m long, to study the wake behavior and the oscillating pattern of two cylinders in tandem arrangement assembled on a free-to-oscillate table. The cylinders were made from commercial PVC (PolyVinyl Chloride) with 25.1 mm diameter and pitch-to-diameter ratio p/d = 1.26. One of the cylinders is aligned with the table axis, while the second one is placed eccentrically. The table is coupled on the upper and lower channel walls using low wear bearings. The blockage ratio is 13% when the set is perfectly aligned with the flow. The airflow, from a 0.75 kW centrifugal blower, passes through a diffuser, two honeycombs, and two screens, to reduce the flow turbulence intensity to about 1. Upstream of the test section, a Pitot tube measures the free stream velocity, used for the calculation of the Reynolds number. The Reynolds numbers (Re) of the experiments were 8.47 × 10³, 12.7 × 104, and 16.6 × 104, based on the cylinder diameter and a flow velocity of respectively 5, 7.5, and 10 m/s. The axial component of the wake flow velocity behind the cylinder set and its fluctuations is measured with a DANTEC StreamLine constant hot-wire anemometry, with a DANTEC 55P11 single wire probe. The sampling frequency was 1 kHz, low pass filter at 300 Hz, and time acquisition of 32.768 s. Data acquisition was performed by a USB 16-bit NI USB-9162 A/D board. The oscillation of the cylinder set was studied using a high-speed Phantom V411 – Ametek camera with a 50 mm AF-S VR Micro-Nikkor lens, with a resolution of 640 × 480 pixels and 1000 frames per second, corresponding to the 1 kHz sampling frequency of the hot-wire signal. The camera was triggered and synchronized with the CTA via an Ethernet cable. A mirror inclined 45° was mounted at the top of the channel to track the position of a pointer, which indicated the angle between the cylinders and the main flow. The free software Tracker© (https://physlets.org/tracker/) was used to analyze the digital movies to generate time series of the angular displacement of the cylinders. The mean error for this analysis is 0.0239 rad. The experimental procedure was as follows: data acquisition and video recording started while the air blower was turned on. After the setup achieved an apparent stabilization, a disturbance device was inserted from downstream the cylinders, tangent to the walls up to be aligned with the cylinder’s setup and immediately removed. The overall perturbation lasts about 2.4 seconds. Velocity and angular position files for each Reynolds number: time (s), wake flow velocity (m/s), angular displacement (rad). Re8470_time_u_theta.txt Re12700_time_u_theta.txt Re16600_ time_u_theta.txt Digital movies of the cylinder set for each Reynolds number: upper and side view: Re8470_Ang_displ.mp4 Re12700_Ang_displ.mp4 Re16650_Ang_displ.mp4本数据集基于在截面尺寸为0.146 m × 0.193 m（高×宽）、长度2.29 m的矩形截面气动通道中，采用热线（hot-wire）与高速相机（high-speed camera）开展的精准测量实验所得，实验旨在研究组装于可自由振动平台（free-to-oscillate table）上的串联布置双圆柱的尾流特性与振动模式。实验所用圆柱采用商用聚氯乙烯（PolyVinyl Chloride, PVC）加工，直径为25.1 mm，节径比（pitch-to-diameter ratio）p/d=1.26。其中一根圆柱与平台轴线对齐，另一根则呈偏心布置。该平台通过低磨损轴承与风洞上下壁面相连。当圆柱组与来流完全对准时，堵塞比（blockage ratio）为13%。 实验气流由功率0.75 kW的离心鼓风机（centrifugal blower）提供，经扩压器、两组蜂窝整流器与两组筛网整流，将流动湍流强度降至约1。在试验段上游，采用皮托管（Pitot tube）测量来流速度，用于雷诺数（Reynolds number, Re）的计算。本实验的雷诺数基于圆柱直径与对应来流速度（分别为5、7.5、10 m/s）计算得到，取值依次为8.47×10³、12.7×10⁴与16.6×10⁴。 采用DANTEC StreamLine型恒温热线风速仪（Constant Hot-Wire Anemometry）搭配DANTEC 55P11型单丝探头，测量圆柱组后方尾流流速的轴向分量及其脉动。实验采样频率为1 kHz，低通滤波截止频率为300 Hz，单次采集时长为32.768 s。数据采集通过NI USB-9162型16位USB模数转换（Analog-to-Digital, A/D）板完成。 针对圆柱组的振动行为，采用Ametek公司Phantom V411型高速相机搭配50 mm AF-S VR Micro-Nikkor镜头开展观测，相机分辨率为640×480像素，拍摄帧率为1000帧每秒，与热线信号的1 kHz采样频率相匹配。相机通过以太网线缆与恒温热线风速仪实现触发同步。风洞顶部安装有45°倾角反射镜，用于追踪指示圆柱与来流夹角的指针位置。采用开源软件Tracker©（https://physlets.org/tracker/）对数字影片进行分析，以提取圆柱角位移的时间序列。该分析的平均误差为0.0239 rad。 实验流程如下：开启鼓风机后启动数据采集与视频录制，待实验装置达到表观稳定状态后，从圆柱组下游插入扰动装置，使其贴合壁面直至与圆柱组对齐，随后立即移除该扰动装置。整体扰动持续时长约为2.4秒。 各雷诺数下的流速与角位移数据文件格式为：时间（s）、尾流流速（m/s）、角位移（rad），对应文件如下： Re8470_time_u_theta.txt Re12700_time_u_theta.txt Re16600_time_u_theta.txt 各雷诺数下的圆柱组数字影片（包含顶面与侧面视角）如下： Re8470_Ang_displ.mp4 Re12700_Ang_displ.mp4 Re16650_Ang_displ.mp4