| China has the longest wind-sand disaster railway line in the world.The railway lengthunder this threat reaches nearly10000kilometres,which distribute in more than30railway linesin desert area. Aiming at various wind-sand railway disaster types in different regions, thedomestic scholars have conducted a lot of research, summed up the characteristics of railwaywind-sand disaster, put forward a number of control measures,applied to the engineeringpractice successfully, and achieved remarkable results. But restricted by natural environment,study of the wind-blown sand flow field around embankment is still inadequate, which leads tosome certain irrationality exsiting in design of wind-sand disaster control system, and can’t everlive up to its full potential.Therefore,in order to cure railway wind-sand disaster,it is necessaryto do further research on the characteristics of flow field around the embankment,optimize thedesign parameters of retaining sand wall,make the control system more perfect and save theproject cost.On base of the two-fluid unsteady model in FLENT Eulerian, this thesis calculates thewind-blown sand flow field around the embankment and the oblique inserting plate retainingsand wall with different parameters,and analyse the sand wall response rule of wind-blown sandflow field to the railway embankment and the oblique inserting plate retaining sand wall.As aresult,the paper provides reliable theoretical and technological basis for the embankment wind-sand disaster control and design parameters of the oblique inserting plate retaining sand wall.It optimizes sand control engineering measures furtherly and ensures the safety of railway. Theresearches have quite important practical significance to the safe operation of the railway.Themain contents include:(1) Through the force analysis of a single grain of sand, the paper deduces motiondifferential equation and establishes the basic equation of wind-sand two phase flow.It also usesthe standard k-ε model to calculate the air turbulence, and uses wall function method to treatthe flow field near the wall.(2) Motion characteristic of wind-sand around embankment is simulated when the netwind or sand-carrying wind is perpendicular to embankment.The results show that:comparedwith the net wind conditions,turbulent area in leeward slope and low velocity zone on the topsurface are bigger when sand-carrying wind pass through embankment;speed surge zoneappears near the leeward slope toe at the same time.Airflow horizontal velocity componentdistributes as the shape of "W" similarly and vertical velocity component distributes as theshape of "M" similarly around embankment. Airflow velocity outline of sand-carrying winddistribute as the shape of logarithm increase with height at the foot of the windward slope,airflow velocity outline distribute as"trunk effect"with height at windward slope shoulder,and the wind outline of leeward slope shoulder and leeward slope toe distribute similarlyas theshape of "S".When the wind direction was single, the aeolian sand amount in windward slopetoe decreases with the increase of wind speed gradually, the aeolian sand amount changes inleeward slope toe unobviously,the aeolian sand amount has increasing trendon the topsurfaceof embankment,the aeolian sand amount of leeward slope sand are greater than windward slopeat the same time，the aeolian sand amount distributes similar as the "normal" on the top surfaceof embankment,the middle are more than both sides.The numerical simulation is in conformitywith the field investigation,the model can simulate the motion characteristics of wind-blownsand flow around the embankment well.(3)Wind-sand flow field around the oblique inserting plate retaining sand wall aresimulated with different parameters,results show that:flow velocities around the sand retainingwall change obviously,horizontal velocity components distribute similarly as the shape of "V"below the sand retaining wall height region, vertical velocity components distribute similarlyas the shape of "M" above the sand retaining wall height region,the wind outlines of leewardslope distribute similarly as the shape of "S" within a certain height.Airflow changes can bedivided into three parts：the low velocity zone, vortex area and accelerating region，the windoutlines of windward side also distribute similarly as the shape of "S",but the change tendencyis gentle compared with the leeward side.If the the porosity is smaller, the effect of windreduction is better,and the eolian-sand amount are greater.And if the sedimentary sand is closerto the retaining sand wall, it will be easier to be buried，causing that the function of windprevention and sand resistance are earlier to lost.It is an suitable advise to take the porosity at25%~40%.If the angle of inserting plate is less than90°, the deposition sand area of theleeward side is close to the retaining sand wall, if the angle is larger than90°,there will be acertain distance between the deposition sand area and the retaining sand wall, if the angle isbetween90°and135°, most of the deposition sand will be blocked around the retaining sandwall, which has the best effect of sand preventing. Combined with the engineering costs, theangle should be taken between110°and135°.The retaining sand wall height has two sideson the effect of controlling sand：on the one hand, airflow velocity of low velocity zone andvortex area gradually increases with increase of the retaining sand wall height,so the sanddeposit on the surface of bed more easily; on the other hand,flow velocity and scope of highspeed area gradually increase with increase of the retaining sand wall height,it not only causesa part of sand from saltation movement to suspension movement but also makes the suspensionmovement sand get more energy to transport further distance.Sand deposition will come intobeingwind-sand disaster when meeting the deposition conditions. The scope of sand depositionarea gradually increases with the increase of the retaining sand walll height，sand deposition area will become a new source of sand under multi wind direction.Based on comprehensiveconsideration of the project cost and wind-sand prevention effect, the retaining sand wall heightis recommended as1.5m~2.0m.(4)The design parameters of the retaining sand wall determines not only the sand controlsystem work efficiency but also the cost of the project. In order to improve efficiency and savethe project cost, before the design of the retaining sand wall,we should investigate the localcharacteristics of wind-sand flow structure in detail, and design the parameters combined withtopography around embankment reasonablely. |
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