Abstract: The flow field of a submerged impinging stream mixer with two opposite nozzles was measured by non-intrusive planar laser induced fluorescence and two-dimensional high-speed particle image velocimetry techniques, and the flow field under different momentum ratios (M) and nozzle spacings (L/d) was decomposed further using proper orthogonal decomposition analysis for extracting the large scale structure in the flow. The results show that the energy of instantaneous flow field in the impinging stream is concentrated in the first order model, in which the momentum ratio of two jet outlets at M=1 accounts for 50% in the total turbulent kinetic energy, which is the highest proportion. 2%~5% in the total turbulent kinetic energy belongs to the second order model, 2% to the third order model, and there is almost no difference in the fourth order model. The highest proportion is about 38.6% at L/d=3. Obvious coherent structure that is located in the region near the non-stable radial jet exists in impinging stream low order intrinsic mode and large scale flow structure is directly related to the energy distribution of flow field, and the higher order intrinsic mode represents the flow of small scale structure. The large scale coherent structure is directly related to the liquid phase mixing behavior of the impinging stream, the larger scale coherent structure in the flow field helps achieve greater energy, which benefits the fast mixing of liquid phase.

Key words: impinging stream, planar laser induced fluorescence, two-dimensional high-speed particle image velocimetry, proper orthogonal decomposition, coherent structure, liquid mixing

摘要： 利用平面激光诱导荧光技术和二维高速粒子图像测速技术对浸没对置撞击流的湍流场进行了测量，利用本征正交分解方法对所测两喷嘴出口流体不同动量比(M)和不同喷嘴间距(L/d)下的流场进行分解，提取流场中含能大尺度结构. 结果表明，撞击流瞬时流场的能量基本集中在1阶模态，M=1工况下，1阶模态的能量占总湍动能的比例最高，约为50%，2阶模态约占总湍动能的2%~5%，3阶模态约占2%，与4阶模态差异甚微；在L/d=3时前4阶模态能量占比最大，约为38.6%；低阶本征模态中存在明显的相干结构，主要位于非稳定径向射流附近区域，且大尺度的流动结构与撞击流的液相混合行为直接相关，流场中相干结构尺度越大，能量越大，越有利于快速均匀混合.

关键词: 撞击流, 平面激光诱导荧光技术, 二维高速粒子图像测速技术, 本征正交分解, 相干结构, 液相混合