Experimental Study On Characteristics Of The Airflow In The Roadway Based On LDA And PIV

Wind speed distribution is the fundamental basis for calculating the migration of gas,gas fire,dust,temperature,humidity,heat and mass transfer processes within the underground tunnel.It also plays a great significance in the arrangement of wind speed sensors and the research of wind instruments.This research is supported by the National Science Foundation of China under the project No.51574142 that is "Study on the mechanism of uncertainty for mine ventilation resistance measure with non-interference".In view of "the uncertainty problem" that the value of wind instruments appears irregular fluctuations in the mine ventilation test,non-contact measurement technology of the Laser Doppler Anemometer(LDA)and Particle Image Velocimetry(PIV)are used to test the velocity of the airflow field in the roadway,and overcoming the limitations of traditional contact instantaneous velocity measurement methods.So the variation characteristics of underground airflow are revealed from the angle of turbulence random pulsation based on the turbulent statistical analysis method.The experimental results show that,the magnitude and direction of instantaneous velocity of airflow particles show extreme turbulence pulsation under the full development of steady flow in the straight roadway,but the wind velocity and wind direction of the measuring point obey the normal Gaussian distribution,then the time-averaged wind method of a single point's instantaneous wind speed has been proposed;Instantaneous wind speed of roadway section presents an irregular and dynamic form distribution,and it don't exist the distribution curve that is used for characterization of the average wind speed of the roadway section,only in the concept of time-averaged wind speed,there is an average wind speed equivalent ring,and the time-averaged speed of the particle is equal to the average wind speed of the section;Time-averaged wind speed distribution approximately accords with exponential function from the side wall to the axial direction of the roadway section(except viscous sublayer);A certain point's time-averaged wind speed(<vi>)is proportional to the average wind speed of the cross section(v)in the rectangular,and the ratio k is constant under the common wind speed range of the underground,so the approximate constant theory of the non dimensional velocity field structure of the roadway section has been presented,and then the mathematical model of single point time-averaged statistical measurement of the average wind speed is also established in the cross section based on the above.Velocity distribution structure of the flow field space is more comprehensively reflected by the combined application of the PIV and LDA measurement technique in the sudden enlarged roadway.The distribution characteristic of the airflow field is obtained by PIV technology in the longitudinal section of the sudden enlarged roadway.The transient distribution presents"changing",but the streamline of the time-averaged wind speed is basically a smooth line in the straight roadway,and the large vortices exist in the corner of the sudden extension with asymmetric distribution,where the wind direction is very unstable,and the wind speed is very low relative to the main wind speed.The time-averaged wind speed fluctuates at about-0.6 m/s?0.6 m/s,which indicates that the vortex area can be neglected conditionally when measuring wind in the coal mine.The distribution characteristic of the airflow field is obtained by LDA technology in the cross-sectional.Wind speed distribution is basically the same as the PIV test on the vertical axis of roadway section.The wind speed of the cross section shows the"?" type distribution trend in the backflow zone,while the wind speed distribution is symmetrical on the horizontal axis.The wind speed distribution presents a slightly protruding form at the corners of the cross section in the sudden enlarged roadway.The time-averaged wind speed contours show a ring-like distribution in the full section,and the curve form is related to the shape of the roadway section.