基于模式匹配法的明渠紊流涡结构分析

Analysis of vortex structure in open channel turbulence based on model matching

对涡结构进行识别是紊流涡动力学研究的难题,为了降低涡识别方法对流速测量空间分辨率的要求,消除阈值对涡识别结果可能产生的影响,提出了基于二维平面流场的涡结构模式匹配方法。应用该方法对明渠紊流中涡结构的密度、涡量、半径和强度等特征参数和涡动力学特征进行了分析。结果表明,涡结构的密度和涡量沿水深逐渐减小,涡半径沿水深逐渐增大,涡结构的环量在近壁区迅速增大而随后基本维持稳定;在相同水深处,顺向涡密度大于逆向涡且具有更强的旋转运动;顺向涡的平均流场具有典型的发夹涡群特征,部分逆向涡与顺向涡在空间上具有相关关系。

A novel scheme was proposed for identifying and extracting vortex structures from two-dimensional velocity fields. The new scheme involves no threshold values and requires a lower spatial resolution than velocity-gradient based methods. The scheme was used to analyze the characteristics of vortex structures based on two-dimensional ve- locity data measured with particle image velocimetry in a turbulent open channel flow. The educed parameters show that population density and vorticity of spanwise vortex decrease along the wall-normal direction while the radius tend to increase all the way. In addition, vortex strength represented by the circulation stabilizes after a quick increase in the inner region, Comparison demonstrates that population density of the prograde vortex is larger than that of the ret- rograde one and the prograde vortices exhibit stronger swirl motion. Conditionally averaged velocity fields of vortical structures statistically verify the existence of hairpin vortex packets and the spatial correlation of retrograde-prograde vortices in open channel turbulence.