圆自由射流多尺度涡结构迁移特性的实验研究

The experimental study of convection characteristics of the multi-scale eddy structure in turbulent jet flow

在流场背景湍流度比较大或流场中涡结构的尺度范围比较宽的情况下,为了研究湍流场中不同尺度涡结构的迁移速度,用IFA300双通道恒温热线风速计和两个热线探针测量圆自由射流中心线上距离一定的空间两点同一时刻的流向速度分量,用子波分析提取了每一个探针输出的不同尺度的脉动速度信号,计算了两个探针输出的同一尺度脉动速度信号的互相关函数,利用互相关函数达到最大值对应的延迟时间研究了湍流多尺度涡结构的迁移特性。实验结果表明:不同尺度涡结构具有不同的迁移速度,小尺度涡的迁移速度较大,大尺度涡的迁移速度较小。其中,一部分尺度的涡结构是湍流中的主要结构,该尺度涡结构对湍流的贡献也是主要的,其迁移速度与实验测得的湍流平均速度较为接近。

In order to study the convection velocity of multi-scale eddy structures in turbulent flow field with the background of high turbulent intensity and wide range of eddy scales, velocity measurements are carried out at different places on the center line of turbulent jet flow with circular nozzle with IFA300 double-channel anemometer and two hot-wire probes. The simultaneous velocity signals are transformed by wavelet analysis and decomposed into individual scale eddy structures. Correlation functions are calculated for individual scale velocity signals output from two hot-wires. The time delay corresponding with the maximum of the correlation functions are used to study the convection characters of the multi-scale eddy structures of turbulent flow. According to the investigation, the following conclusions have been drawn: 1. The convection velocities of small scale eddies are higher while the large scale's are lower. 2. The eddy structures with specific scales whose convection velocities are very similar to the mean velocities measured in experiments are the main structures of the turbulent flow. The contributions of these specific scale eddies are also the most important to turbulent flow.