突扩巷道模型风流态的LDA与PIV联合测试

针对传统的接触式瞬时速度测量方法的局限性,采用非接触测量技术激光多普勒测速仪(LDA)及粒子成像测速仪(PIV)对平直巷道及断面突扩后风流状态进行试验测试。在巷道试验模型条件下,PIV技术可以瞬时获得巷道突扩流场信息,平直巷道速度流线基本呈平滑直线,突扩隅角有大涡存在,并且涡流区测风方向极不稳定,而且风速很低,风速平均值在0.1~0.2 m/s波动,表明在煤矿井下测风时可以有条件地忽略涡流区。LDA技术测试得到巷道断面各点统计平均流速,由于受突扩涡流及二次流的影响,平直巷道断面风速从壁面以跃迁方式"突变"达到均值,断面风速分布呈近似均等的动态波浪线分布而非准抛物线型分布。结果表明,LDA与PIV测量技术联合应用可以测试以湍流为特征的巷道流场风流变化情况。

LDA/PIV joint experimental investigation for the airflow situation in-situ in the instantly extended roadway model

The paper is aimed to introduce a non-contact measurement technology vit the Laser Doppler Anemometer(LDA) and Particle Image Velocimetry (PIV) instead of the traditionally used contact instantaneous velocity measurements in hoping to overcome the limitations of the airflow status in the straight roadway and the suddenly expanded cross-section.For the said purpose,we have managed to determine the measuring and testing areas of the pre-and-post sudden enlarged interface of the roadway.As the result of the measurement via LDA,we have found that the wind speed of the 10 cross-sectigns should be equal to 100 mm with the interval distance between the cross-sections being 100 mm.Since the moving step is 10 mm in the horizontal and vertical directions,each testing section should be divided into 289 measuring points before the enlargement but into 561 points after that.However,due to the limitation of the maximally observable range of the CCD camera,it wouldn't be possible for PIV to collect at once all the longitudinal data pre-and-post the sudden enlargement interface,which makes it necessary to divide the enlargement into two steps:in the first step,that is before the sudden enlargement,the test area can be made to reach 100 mm × 160 mm,while in the second step,that is,after the enlargement,the test area can be made to reach 220 mm× 320 mm.The experiment results have thus shown that all the information of the flow field in the sudden enlargement roadway has been obtained by PIV in a moment.Therefore,the velocity vector streamline in the straight roadway can be said smooth and straight in general,though large eddies may appear in the comer of such sudden enlarged areas with the velocity being unstable in the turning areas and small in magnitude (the mean velocity fluctuating between 0.1 m/s and 0.2 m/s,which indicates that the eddy zone can be conditionally neglected when the wind speed in the coal mine is measured to meet the needs of the projects.The statistical mean velocities of each point in the roadway cross-section measured by LDA tend to show that the velocity can directly increase to the mean value of the main stream when the points are just out of the wall,and the distribution of the wind speed in the cross-section has been shown as equal dynamic wavy lines rather than the quasi parabolic distribution,which is likely to be affected by the vortex in the sudden enlargement and the secondary flow.Furthermore,our study also proves that the LDA measurement technology in combination with PIV can be said qualified enough for testing the airflow change of the flow field characterized by the turbulence in the roadway.