井巷断面内单点风速与平均风速转换机制

准确测量一点风速并将其转换为断面平均风速是矿井通风领域的一项技术难题。对其中涉及的单点风速测不准问题和单点风速与平均风速的转换机制进行了研究。结果表明,湍流充分发展的圆管断面上任一点(黏性底层除外)风速与平均风速为非线性关系,但在井下常见风速0.25~15 m/s,两者可近似为正比关系。为验证这一结论的普适性,在实验室采用激光多普勒测速仪对矩形非充分发展湍流断面上单点风速与平均风速的关系进行了测试。结果表明:当平均风速在0.78~6.2 m/s变化时,单点风速与平均风速仍表现为正比关系,比值k可作为该点风速与平均风速间的无因次转换系数;k的空间分布反映了断面速度场结构,当断面速度场结构变化时转换系数失效。在单点风速测不准问题上提出,测试传感器在提高数据采集频率的基础上应对速度信号进行时间平均处理,且时间平均尺度要大于湍流各态遍历假设。

On the conversion between the mean airflow velocity and that of the individual point in the underground mine tunnels

This paper is to focus itself on the exploration for a conversion method and the low accuracy in the measurement of the point air velocity in the underground mine tunnels,for it is indeed a technological challenge to measure the point air velocities and convert them to the mean air velocities of the section under mining.It is just for the said purpose that we have done a theoretical analysis in a circular tube with the fully developed turbulence under way.The theoretical results we have gained have indicated that a non-linear relationship should be exiting between the mean and the point air velocities (boundary layers rejected) at the same section of the tunnel under the general scenario.However,it would be possible for the said nonlinear relationship to be approximated as if it were a linear one on the condition when the two mean air velocities is in a range of 0.25 m/s to 15 m/s.As is known,the underground tunnels are generally supposed to be taken as non-circular sections which are different from the circular tube flow.What's more,the airflow in the tunnels remains usually under the non-fully developed turbulence which is different from the fully developed one in the theoretical analysis meaning.Therefore,to verify such a kind of theoretical analysis,we have done experiments in a rectangular duct with the non-fully developed turbulence to test the mean and the individual point air velocity in the same section.The results of our analysis prove that,when the mean air velocity is within a range of 0.78 m/s to 6.2 m/s,the point air velocity would be positively proportional to the mean velocity.Thus,the ratio between the mean velocity and the point air velocity can be defined as the conversion coefficient of the both sides.Furthermore,it can also be noticed that the ratios in the full-section are in a position to reflect a velocity field structure that can influence the changes of the conversion coefficients.And,finally,with the help of the time-average approach to the velocity signals,it would be possible to heighten the accuracy of the velocity monitoring in a point.Under such a case,the window size of average air velocity should be greater or longer than the ergodic hypothesis of turbulence.