| Lanzhou-Xinjiang Railway through the zone along the Tianshan Gobi, Under the effect of strong airflow movement, Serious instability of gobi surface and frequent sandstorm disaster easily result in harm of train overturning and accumulating sand in the line,transportation are often forced to stop, due to the sand disasters, every year's direct economic loss is up to several billion yuan. Construction of retaining walls and sand wall wind through investigation and research along the windward side of the railway is an important measure for railway safety operations, in order to reduce the overturning force of train and achieve the purpose of purifying the sand flow. At present, the research of windbreak wall is mainly studied from the train overturning perspective, and research on Accumulating sand problem in the line caused by the wind wall is less, the facts show that the wall while providing security for the operation stability of locomotive, also will cause the line blown sand. At present, the main railway retaining wall of sand laid on experience, there is no uniform standard, often caused the sand retaining effect is not ideal or the waste of sand material.This article is based on the FLUENT software to simulate the flow field changes that is wind-blown-sand two phase flow passing by different types on the Leeward side of wind break wall, and route accumulating sand in the leeward side of the wind break wall is studied,which provide the basis for railway windproof and Sediment Control; To simulate the flow field changes around embankment that is wind-blown-sand two phase flow passing by retaining sand wall, and to study the form of line accumulation of sand on the top surface of sub-grade, which is to achieve optimization of design parameters, improve the efficiency of sand prevention. The main content are:(1)Wind profile change are in three stages on the Leeward side in the position of 2m of wind break wall: Between the 0~0.5M show an exponential growth trend, and with the increase of wind break wall height, the wind speed increases larger; In the height range of0.5m to its own wind wall height the change is more complex, show a trend of first increase and then decrease; In the above 0.5m part is an accelerator, and law curve is a sharp increase in exponential growth trend. Near-surface airflow changes are in three stages on the Leeward side of wind break wall: Less than 10 m from the wind break wall, the wind speed increases along the direction opposite to the initial air velocity, and with the increase of wind break wall height, the wind speed increases larger; From the leeward side of 10m~20m, the maximum wind speed decreases from reverse to zero and return to the original speed sharply; After 20 m wind gradually restore to its original speed.(2) When the height of wind break wall is certain, with the increase of wind speed, the scroll vertical velocity of the air is becoming more complicated on the Leeward side of windbreak wall, from the bed above 4m, the wind speed increase linearly; Near-surface wind speed is maintained at the maximum rate of increase of about 50% on the Leeward side of wind break wall, the greater the wind speed, the more obvious the weakening effect of the airflow.Near-surface airflow velocity on the Leeward side of wind break wall reversal increases along the direction of the initial velocity is reduced to 0 and continue to increase the initial velocity,And at the same distance from the Leeward side of wind break wall, lee side of wind the velocity of on the Leeward side of embankment type wind break wall is always greater than the column plate wind break wall.(3) When the initial velocity is 10m/s and 20m/s, less sand is on the line, most of sand accumulate at the corner on the Leeward side of wind break wall; With the increase of wind speed, when the initial air velocity is 30m/s and 40m/s, grains of sand passing by wind break wall are more per unit time, since the flow cross-section is reduced, leading to air flow diffusion, more sand is deposited on the line. When the initial velocity is 10m/s, the majority of sand accumulation is on the leeward side at the corner; As the wind speed increased to20m/s, the majority of sand accumulation is on the leeward side at the corner of the embankment type windbreak wall, and there are a lot of wind blown sand on the plate cylinder wall leeward side on the line, resulting in sand accumulation on the route.(4) When the embankment height is 5m and there is no sand retaining wall, the air flow forms a low velocity turbulent zone on the near surface of the subgrade, sand is easily deposited here, causing the line to accumulate sand; After laying retaining sand wall on the upwind side of the line, will be form a relatively high speed zone near surface at the top of the subgrade, sand is hard to deposit here, in order to achieve the sand preventing effect. When the embankment height is 5m, after air flow passing by the retaining sand wall of 2.0m and2.5m height, the top surface of the subgrade is relatively clean, in the near surface at the top of subgrade air velocity is basic keep in more than 10 m/s and the direction of the wind and the initial airflow speed is in the same direction. Considering that the higher the sand retaining wall, the greater the lateral wind pressure, the greater the depth of the buried depth, the greater the cost of the project, considering the effect of sand fixation, 2.0m height is appropriate.Gobi wind-sand railway roadbed is appropriate to the embankment, and the embankment height should not be less than 3 m, the height of embankment in Gobi area is below 6m, and the height of retaining sand wall is suitable for 1.5m to 2.0m, when the height of embankment is larger than that of carrying sand, the retaining sand wall can not be distributed.(5) Sand flow is a dynamic process, the wind speed and direction should be considered according to the local wind speed of 80% more than a year, when setting the retaining sand wall. When the embankment height is 5m, the sand carrying wind speed is 10m/s to 20m/s,retaining sand wall should be distributed in the windward side of the line between 15 m to20m; When the sand carrying wind speed is 20m/s to 30m/s, the retaining sand wall should be distributed in the windward side of the line between 20 m to 25m; When the sand carrying wind is more than 30m/s, it is recommended to lay a multi row resistance sand fence. With the decrease of embankment height, location of sand retaining wall should be far away from the line, to achieve the best effect of sand. In the strong wind area, wind break wall layout to meet anti overturning moment conditions, not recommended for heightening the wind, and should examine the situation on the line of surface in upwind area, Rich sources of sand should use blocking sand, high vertical, neutral type retaining sand wall combining with engineering of sand control measures to reduce the wind sand flow density, to achieve the purpose of sand. |
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