二维激光多普勒测速系统用于测量湍流分离流动

 为解决具有回流区的高湍流度分离流动的二维测量问题,研制了一种偏振分离型二维激光测速系统;测量了非对称阶跃扩张管道中湍流分离区的平均速度向量分布;得到了回流中心位置和回流区长度等参数;部分实验结果同数值模拟结果作了比较。

MEASUREMENTS OF TURBULENT SEPARATED FLOWS WITH A TWO-DIMENSIONAL LDV SYSTEM

A polarized separated type of 2-D LDV system has been constructed by authors and applied to measuring highly turbulent recirculating flow in a two-dimensional duct.The optical system has three Bragg cells in order to obtain three different frequency shifts about the central frequency 40 MHz. In result the electronic mixer is unnecessary to cancel the central frequency, and only low frequency response photomultipliers are used. Two frequency trackers are adopted to deliver both the analog and frequency outputs. Because the accuracy of the analog output is lower than that of frequency output, the Doppler frequencies are recorded by two digital counters and averaged over a long time to obtain the mean velocities. As the intermediate frequencies are measured very attentively, the mean velocity measurements give an accuracy of better than 0.2%. Therefore, it is possible to determine the mean velocity vectors in the flow field and to locate the zero velocity center and reattachment point more accurately. But both the nondi-mensionalized turbulent intensity and Reynolds stress are transformed from the analog output.The experiments have been completed at two Reynolds numbers, ReH -5900 and 8340. The difference between the axial and vertical mean velocities in main flow region is of about two orders of magnitude, but both the axial and vertical turbulent intensities in the separated flow region are of the same order. Comparison between the experimental data and the calculated results for axial mean velocity and turbulent kinetic energy distributions at ReH = 5588 is in good agreement in general.