Method for air velocity measurement with single-point under the influence of turbulent fluctuation

LI Xuebing; LIU Jian; QIN Hongyan; WANG Haidong; HU Yang

doi:10.3969/j.issn.1672-7169.2018.02.001

Abstract：Air velocities over the roadway section vary from point to point, and instantaneous velocities are all pulsing at the same time, so it's a technical problem in field of mine ventilation to measure air velocity of a point and convert it to the mean velocity accurately. Statistical measurement models for a certain point velocity (u) and means (V) are described, according to the characteristics of turbulent roadway flow, and also conversion mechanism between u and V is investigated theoretically and experimentally in this paper. The theoretical study of fully developed turbulent in circular tunnel indicates that non-linear relationships are shown between u and V, which can be approximated as linear ones over a broad range of velocity changes. The experimental results show that, dimensional flow field structure of non-fully-developed turbulent in non-circular tunnel is nearly constant, and proportional relationship is still remain between u and V, and the ratio k is constant. In other words, the value and distribution of the ration are fixed when the flow field structure is constant. The k values are independent on velocity and are only relevant to boundary conditions such as direction, shape basal area and support pattern of the roadway. Once time-averaged velocity and k value of any point on the roadway section are obtained, the mean velocity can be get. Furthermore, a method for k value calibration under constant flow field structure is provided, and the time-averaged principle of instantaneous velocity is put forward that the time-average-scale should greater than ergodic hypothesis. Thus, new sensors should improve the data acquisition-frequency to satisfy the time-averaged requests.