为实现对圆柱尾流非定常速度场的精确测量,示踪粒子的跟随性与光学散射特性是基于时间解析PIV试验技术的关键问题。为此,选择Laskin-40粒子发生器并匹配粒径1 μm的DEHS作为示踪粒子,并使用热线风速仪专门测试示踪粒子频响特性。高频PI...为实现对圆柱尾流非定常速度场的精确测量,示踪粒子的跟随性与光学散射特性是基于时间解析PIV试验技术的关键问题。为此,选择Laskin-40粒子发生器并匹配粒径1 μm的DEHS作为示踪粒子,并使用热线风速仪专门测试示踪粒子频响特性。高频PIV设备采样频率为1000 Hz,将直径20 mm的金属圆柱尾缘至其后方7.5倍直径、圆柱两侧各3.3倍直径所围成的矩形绕流尾迹区域作为测试区域,重点研究来流风速20 m/s条件下、圆柱特征雷诺数Re = 2.67 × 104下的非定常流场。基于PIV获得的速度场数据,开展流场和频谱特性分析,得到了圆柱绕流尾迹中的瞬态流场特征和旋涡脱落的频率特性。基于时间解析PIV技术能够获得丰富的流场信息,可以准确地识别绕流尾迹中旋涡交替脱落和发展的时空演化过程,在非定常流场测量方面具有普遍推广意义。The tracking characteristics and light scattering properties of tracer particles are the crucial issues of time-resolved Particle Image Velocimetry (PIV) experiment technology for the accurate measurement of the unsteady velocity field in the wake of a cylinder. A Laskin-40 particle generator was chosen with 1-μm-diameter DEHS as the tracer particle, and a hot-wire anemometer was employed to assess its frequency response property. The high frequency PIV device featured a sampling rate of 1000 Hz, for which the test area is the rectangular wake flow region of 7.5 times the diameter of a 20 mm-diameter metal cylinder from its trailing edge and 3.3 times the diameter from both sides. The study focused on the unsteady flow fields at 20 m/s wind speed and the Reynolds number (Re) of 2.67 × 104 for the cylinder. By the flow field and frequency spectrum analysis based on the velocity field data acquired by PIV, the research gained insights into the transient characteristics of flow field and frequency property of vortex shedding in the wake of the cylinder. As the time-resolved PIV technology provides abundant flow field information that allows accurate identification of the vortex shedding and its spatial temporal development in the wake, it is worth spreading in unsteady flow field measurement.展开更多
Application of particle image velocity (PIV) techniques for measuringparticle size distribution and total number in an activation chamber of desulfurization system isintroduced. Watersheld algorithm is used to choose ...Application of particle image velocity (PIV) techniques for measuringparticle size distribution and total number in an activation chamber of desulfurization system isintroduced. Watersheld algorithm is used to choose the suitable initial gray level threshold whichis used to change the gray level images taken by PIV to black and white ones, then every particle inan image is isolated totally. For every isolating particle, its contour is tracked by the edgeenhancement filter function and kept by Freeman s chain code. Based on a set of particle s chincode, its size and size distribution are calculated and sorted. Finally, the experimental data ofcalcium particles and water drops, separately injected into the activation chamber, and the erroranalysis of data are given out.展开更多
文摘为实现对圆柱尾流非定常速度场的精确测量,示踪粒子的跟随性与光学散射特性是基于时间解析PIV试验技术的关键问题。为此,选择Laskin-40粒子发生器并匹配粒径1 μm的DEHS作为示踪粒子,并使用热线风速仪专门测试示踪粒子频响特性。高频PIV设备采样频率为1000 Hz,将直径20 mm的金属圆柱尾缘至其后方7.5倍直径、圆柱两侧各3.3倍直径所围成的矩形绕流尾迹区域作为测试区域,重点研究来流风速20 m/s条件下、圆柱特征雷诺数Re = 2.67 × 104下的非定常流场。基于PIV获得的速度场数据,开展流场和频谱特性分析,得到了圆柱绕流尾迹中的瞬态流场特征和旋涡脱落的频率特性。基于时间解析PIV技术能够获得丰富的流场信息,可以准确地识别绕流尾迹中旋涡交替脱落和发展的时空演化过程,在非定常流场测量方面具有普遍推广意义。The tracking characteristics and light scattering properties of tracer particles are the crucial issues of time-resolved Particle Image Velocimetry (PIV) experiment technology for the accurate measurement of the unsteady velocity field in the wake of a cylinder. A Laskin-40 particle generator was chosen with 1-μm-diameter DEHS as the tracer particle, and a hot-wire anemometer was employed to assess its frequency response property. The high frequency PIV device featured a sampling rate of 1000 Hz, for which the test area is the rectangular wake flow region of 7.5 times the diameter of a 20 mm-diameter metal cylinder from its trailing edge and 3.3 times the diameter from both sides. The study focused on the unsteady flow fields at 20 m/s wind speed and the Reynolds number (Re) of 2.67 × 104 for the cylinder. By the flow field and frequency spectrum analysis based on the velocity field data acquired by PIV, the research gained insights into the transient characteristics of flow field and frequency property of vortex shedding in the wake of the cylinder. As the time-resolved PIV technology provides abundant flow field information that allows accurate identification of the vortex shedding and its spatial temporal development in the wake, it is worth spreading in unsteady flow field measurement.
基金The Special Funds for State Key Projects for Fun- damental Research (G1999022201-04).
文摘Application of particle image velocity (PIV) techniques for measuringparticle size distribution and total number in an activation chamber of desulfurization system isintroduced. Watersheld algorithm is used to choose the suitable initial gray level threshold whichis used to change the gray level images taken by PIV to black and white ones, then every particle inan image is isolated totally. For every isolating particle, its contour is tracked by the edgeenhancement filter function and kept by Freeman s chain code. Based on a set of particle s chincode, its size and size distribution are calculated and sorted. Finally, the experimental data ofcalcium particles and water drops, separately injected into the activation chamber, and the erroranalysis of data are given out.
