| The change of roadway section form caused by roadway turning,obstacles,sudden expansion,sudden shrinkage,bifurcation,convergence,and existence of wind windows is called abrupt change of roadway section geometric characteristics.Local resistance will occur when the mine air flow passes through the abrupt location of the geometric characteristics of the roadway section.The size of the local resistance is related to the structure and characteristics of the flow field.The structure of the flow field not only affects the size of the local resistance,but also affects the local resistance test.The determination of the location of the local resistance test point and the selection of the test method are the keys to accurately determine the local resistance.In order to determine the reasonable location of local resistance test,the flow field in roadways with different turning angles and obstacles was tested by PIV experiment,and the length of eddy current zone formed under different conditions was found out and its boundary position was determined.Particle image testing technology is a non-contact fluid testing technology,which has the characteristics of wide testing range and high measurement accuracy.In recent years,it has been widely used in the measurement of mine turbulence.In this paper,particle image testing technology is used to test the flow field characteristics of roadway at three typical locations where the geometric characteristics of roadway cross section change suddenly,such as turning,obstacles and roadway sudden expansion.Obstacle flow field,roadway sudden expansion flow field,roadway turning angle(90 degrees,120 degrees,135 degrees)and different wind speed in rectangular straight roadway with different obstruction ratio of obstacles are tested respectively.Flow field of downward turning roadway.The experimental results show that when there are obstacles in rectangular straight roadway,the length of eddy current zone is 1.7 times of the height of roadway section when the blocking ratio is 0.25;when the blocking ratio is 0.5,the length of eddy current zone is 3.38 times of the height of roadway section;and when the blocking ratio is 0.75,the length of eddy current zone is 3.9 times of the height of roadway section.In conclusion,the length of the eddy current zone formed under different blocking ratio is different,the length of the eddy current zone increases with the increase of blocking ratio in roadway,and the ratio between the length of the eddy current zone and the height of roadway cross section also increases.After the sudden change of roadway cross section,two eddy current zones with different sizes will be formed at the upper left corner and the lower left corner,and the velocity streamline will be basically flat before the sudden change of roadway cross section.The length of the eddy current zone in the model is about 690 mm,which is 3.45 times the height of the section after the sudden expansion.After the sudden expansion,the distribution of wind speed in the roadway first transits from "?" to "?" and then returns to "?".PIV tests on model roadways with steering angles of 90,120 and 135 degrees show that the structure of the flow field is relatively stable and the streamline is relatively smooth when the wind flows through the model roadway before turning.Eddy current zones of different sizes will be formed at the upper left corner of the turning roadway and near the lower wall after turning,and the eddy current zones formed at the upper left corner of the turning roadway will follow the turning angle.The length of the eddy current region decreases with the increase of the turning angle,while the length of the eddy current region decreases with the decrease of the turning angle.The paper has 38 pictures,2 tables,and 70 references. |
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