横向射流动态流场特征的高帧频实验研究

Experimental study on high frame rate characteristics of dynamic flow field of jet in crossflow

在横向射流流场中,各种涡结构运动对射流轨迹变化和标量混合有着决定性影响,但目前仍然缺乏输运过程中剪切层涡高频动态特性的相关研究。本文基于40 kHz高频粒子图像测速(Particle Image Velocimetry,PIV)技术和20 kHz丙酮平面激光诱导荧光(Acetone Planar Laser Induced Fluorescence,Acetone PLIF)技术研究了不同直径喷嘴、不同速度比下的横向射流高频动态流场特征和标量场浓度分布规律,以及湍流细微结构的形成和破碎过程。速度场和标量场的实验测量表明增大速度比对回流区的生长起促进作用;通过拟合得到了射流轨迹、速度分布及剪切层涡运动轨迹方程,射流速度沿轨迹呈指数下降,剪切层涡强度与涡运动频率也呈下降趋势,且迎风侧剪切层涡运动频率略低于背风侧;随着射流速度增大,剪切层涡运动频率逐渐增大,斯特劳哈尔数降低。

Despite the decisive influence of various vortex structures of a jet in crossflow on the jet trajectory and scalar mixing,there are few studies related to the high-frequency dynamic characteristics of shear-layer vortexes during transportation.This paper focuses on the high-frequency flow field characteristic,the scalar concentration distribution and the formation and collapse process of the turbulent microstructure of the jet in crossflow with different nozzle diameters and velocity ratios using 40 kHz Particle Image Velocimetry(PIV)and 20 kHz Acetone Planar Laser Induced Fluorescence(Acetone PLIF).The experimental measurements of the velocity and scalar field show that:increasing the velocity ratio promotes the expansion of the circulation zone behind the jet;in the near field of the jet trajectory,power law fitted velocity distribution and shear-layer vortex trajectory shows an exponentially decrease of the jet velocity,the shear-layer vortex strength and vortex motion frequency also show a downward trend,with the frequency of the shear-layer vortex on the windward side slightly lower than that on the leeward side;as the jet velocity increases,the frequency of the shear-layer vortex increases gradually,but the Strouhal number decreases.