冲击射流火焰流场的LDV实验研究

搭建了基于激光多普勒测速仪（LDV）的冲击射流火焰流场实验平台，开发了固态粒子发生器、粒子回收装置和精密位移机构等装置，对单孔喷嘴（功率200W）、同轴喷嘴（功率1200W）的自由射流火焰流场和冲击射流火焰流场进行高精度测量，测量数据具有较高的准确性和可重复性。在冲击射流模式下，利用多个位置点的平均速度分量测量值进行流场重构，获得了冲击射流火焰流场基本特征。实验发现:在靠近冲击壁面区域距中心滞止点约1倍喷嘴直径处出现水平方向速度峰值，该点处可能会形成短冲击距离下换热强度的第二次峰值。在同轴射流工况中，外环同轴射流和中心射流间存在一个内部剪切混合层:在自由射流火焰模式下，该混合层随着射流的发展而耗散；在冲击射流火焰模式下，由于受到滞止区的作用，混合层向外扩张。

Experimental study of the flow fields of the impinging jet flames using Laser Doppler Velocimetry (LDV)

A Laser Doppler Velocimetry system containing a particle generator, a particle collector and a motorized precision translation stage is built to diagnose the fluid fields of a vertical flow burner. The free jet flame and impinging jet flame are investigated, both for a single nozzle (200W power) and a coaxial dual-nozzle (1200W power). An adaptable signal to noise ratio (SNR) threshold is analyzed and employed for post-processing. The experimental data shows high repeatability and accuracy in multiple measurements. For impinging jet cases, the Reynolds numbers (Re) of low power and high power flame are 1200 and 7200, respectively. The mean velocity vectors and contours are sketched from the measurements at different axial and radial positions, displaying the main characteristics of the impinging jet flame. Meanwhile, a peak of the horizontal velocity occurs roughly at one-nozzle-diameter distance departed from the nozzle axis in the near-wall region. This feature possibly provides an explanation for the mechanism of the secondary peak of the heat transfer captured in previous literatures. For the cases of coaxial jet, a mixing region exists between the outer annular jet and the core jet:the mixing zone is gradually damped with the development of the free jet flame, whereas radially expanding in the impinging flame driven by the high-pressure stagnation region.