Influence of the Haizhou Open Pit Coal Mine on the atmospheric flow over Fuxin,China

Journul of Environmental Sciences Vol 16. No 6, pp. 978-980, 2004CNi1-2697XInfluence of the Haizhou Open Pit Coal Mine on the atmospheric flow overFuxin, ChinaCHEN He, YANG Zhi-feng WANG Xuan( State Key Laboratory of Environment Simulation and Pollution Control, School of Environment, Beijing Normal University, Beijing 100875, China.E-Abstract: The influence of the Haizhou Open Pit Mine on the atmospheric flow in nearby Fuxin City in China was analyzed with the aid ofthe steady-state Navier- Stokes equations, The finite element method was used to obtain numerical solutions to these equations. Theresults showed that the Haizhou Open Pit Coal Mine contributes to the turbulent flow in the Fuxin City and its surroundings. Howevewhen compared with the climatic effects, the open pit mine has a relatively small impact on the atmospheric flow over FuxinKeywords: numerical simulation; turbulence; finite element method: open pit coal mineIntroductionpurpose and is suited to problems with complicatedboundaries in multi-connected regions. It also has the abilityFuxin is a city in Liaoning Province of northeast China, to remove difficulties of transformation within regions and thewith a large open pit coal mine located nearby. Strong windsdefinition of the grid is easily formulatedblow over the city almost continuously. On those occasions 1.1 Mathematical modelwhen the winds are gentle the air over the city is stagnant. AtWe consider the atmosphere as a steady incompressibluch times atmospheric pollutants usually accumulate in the viscous fluid, the flow of which can be described with theproblemsNavier-Stokes equations. Atmospheric flow differs fromin China, is located to the south of Fuxin. The pit is a huge fluid flows in channels, and the unne. restrictedThe Haizhou Open Pit Coal Mine, the largest such mine general fluid flow in that the scale of eddies is restricted whenexcavation whose dimensions are four kilometers in length, atmospheric flow does not exist( Chen, 1998two kilometers in width, and about 300 m in depth. Williams, 1980 ). The Reynolds number in the solutionResearchers have been uncertain about the degree to which domain is larger than 3000( the critical number )so thethe Haizhou Pit influences the atmospheric flow over Fuxin atmospheric flow is a turbulent flow obeying the followingand its surroundings. If the mechanisms influencing theequations( Shi, 1994)atmospheric flow over the Haizhou Pit were understoodContinuity equationould have a solid theory for understanding the wayaUh atmospheric pollutants are diffused in the region(1)This theory would also assist planners in making decisions Reynolds equationsconcerning the location of factories and other types of civicacilities in the area surrounding the haizhou Pitx(U)=f-1P)(U)a(U>To study this problem we employed atmosphericboundary layer theory. The Navier-Stokes equations wereused to model fluid flows. We solved the Navier-Stokes k-e modelequations with the aid of numerical simulation methods, Afew other researchers have reported on studies that are relatedto our work. Mountain and valley winds in Japan wereax|-e,(3)studied by Mannouji( Mannouji, 1982), and San and ReiterCka(San, 1983 )examined atmospheric: flows in a large-scaleCiPamountain valley with the aid of numerical models. GrangeC,Eand Meroney( Grainger, 1993)used a physical model to(4)study the dispersion in an open pit coal mine under the〈u',u〉=a(U〉a(Uondition of a stably stratified flow. Zhu( Zhu, 1997)hadk.(5)studied fluid now past concave topographies, but his worka(U.was largely theoretical and did not address practical Where, P. =-(u'u,)applications anaturbulent kinetic energy, e is the dissipation rate of turbulent1 Numerical simulation and resultskinetic energy, R,=-(u, u,) is Reynolds number,x,isIn our study of the mechanisms influencing theatmospheric flow over Fuxin, the Navier-Stokes equations that中国煤化工 -onstants appearing in theImodel fluid flows were used. It is not possible to obtain turbuCNMH0.09,a=1.3,C=analytical solutions to these partial differential equations. 1. 45,L2=1.y4, 0.=UU/, C=U.09(Chen, 1984)Therefore it is necessary to employ numerical methods. TheFrom the above equations we can get the finite elementfinite element method is appropriate and effective for this equationsFoundatinheNationalHi-TechR&DProgram(973)ofChina(No.G1999043605):*Correspondingauthor:E-mail:ryang@bnu.edu.cnInfluenee of the Haizhou Open Pit Coal Mine on the atmospheric flow over Fuxin, China1.2 Boundary conditions and meshingBecause the width of the pit is small compared to thelength, we consider a two-dimensional flow across the pitBased on meteorological data, the northwest wind is thecardinal wind in Fuxin. Furthernore, the Haizhou Open PitMine is located to the southeast of fuxin therefore southwestwinds and northeast winds flowing over the pit have littleimpact on the city. The velocity boundary conditions showrin Fig. I indicate the condition that the north wind nowsacross the pit. The influence of the open pit coal mine on theg 3 Pressure contoursmospheric flow far above the ground is small and can beeglected. We suppose that the velocity of the air on theupper and left-hand and right-hand sides is equal to therelocity of the wind, which is 1 m/s in the x-directionelocity gradient near the groundbecause the air is considered as a viscous fluid. Hence thevelocity of the atmospheric flow there is assumed to he zerolms↑yUx-I m/s, U,+0Fig 4 Pressure contours around the pitFig. I Simulation domain anu boundary conditionsWhat concerns human beings most is the atmospherflow near the ground, therefore the grid density near theound is finer than that far above the ground. The mesh usedis shown in Fig. 2Hig. 5 CotmpariMan of prssure cuntour to north and south sidesFig 2 Mesh1. 3 Results and discussionWe compared the atmfow of the south side tohat of the north side in onler to inv estigate the influence ofthe Haizhou Open Pit Mine on the atmospheric flow in FuxinIn a general way, the heating power action and the dynamicaction determine the turbulence in the almosphere. When theof temperature drop is high. the heating power action isdominant effect. On the other hand, the dynamic action Fig.6 Comparison of veloeity vectors in the same area when the pit exists anddominant when the rate of temperature drop is low( Liu1998). The simulation described below was done with thcondition that the wind flows across the open pit mine and the The dimensions of the simulation domain are forty kilometersheating power action is neglectedin length, one kilometer in height. The city is al waysFig 3 and Fig, 4 show the pressure contours when the disturbed by winds with a speed of about 10ws acrossthe pit. As can be seen from these figuressuppose that the velocity of the air on the upper and left-handthe pit greatly impacts the atmospheric nlow in nearby areand right-hand sides is equal to the velocity of the windAs shown in Fig. 5, the pressure contours slope gradually which is 10 m/s in the x-direction. The velocity of theupward from the left side to the right side, therefore we cantmospheric now near the ground is assumed to be zero. Theconclude that the pit has a greater impact on the south side velocity vectors of natural wind with a speed of 10 m/sthan on the north side. Furthernore, in Fig. 5 this difference without the Open Pit Coal Mine is shown in Fig.7.Theis even more appareIatmospheric flow is more turbulent in Fig. 7 than that inThe boundary conditions for the first solution( assuming Fig. 6the presence of the pit)are the same as those for the secondIn中国煤化工 nat a degree the Opensolution( assuming the pit is absent). In Fig. 6, a comparison Pit CoalCNMHflow of Fuxin.weof the velocity vectors clearly indicates that the pit contributes employedqunu a at nuicates the human senseto the turbulent flowof disturbing winds. f is determined in the followingIn order to analyze the main fact that influences theatmospheric flow of Fuxin, we simulated the atmospheric flow￡=(u'u'2)数贴 h the city without Open Pit Coal MiWe set a point 5 meters above the ground in the centerChen He et alFig 7 Velocity verturs of natural wind(10m/s)Fig 9 Comparison of velocity vectors in the spots 5 kn from the north andof the city and respectively calculated the i of this point in south sidesthree conditions. In the first condition that the wind speed is China. As can be seen from these results, the Haizhou OpenI m/s and there exists the Open Pit Coal Mine the f is equal Pit Mine influences the atmospheric flow over Fuxin becauseto 0. 32. In the second condition that the wind speed is I m/ the pit has the effect of strengthening abnormal flows over thes and there does not exist the Open Pit Coal Mine the i is city. The dominant influence on atmospheric now in Fuxin isequal to 0. 13. In the third condition that the wind speedderived from the eccentric climate. Because the Open Pit10 m/s and there does not exist the Open Pit Coal Mine the Coal Mine has a greater influence on the leeward side than onf is equal to 0. 85. As can be seen from the above results, the windward side, south winds have a greater influence onthe pit is not the dominant cause because the pit plays a the city than winds from other directions. When winds aresmaller role in abnormal atmospheric flow over Fuxin than strong and the atmospheric flow is abnormal, the pit has aeccentric climatic factors do. Fuxin lies in the North negative influence on the atmospheric flow. On the otherTemperate Zone where the winds are determined mainly by hand, the pit has a positive influence derived from its abilityclimatic factors( strong winds caused by atmospherie to diffuse air pollutantspressure), A continental climate has an impact upon Fuxin Acknowledgement: The authors wish to thank Professorwhen northwest winds prevail. During such times the Robert Wenger from the University of Wisconsin-Green Bay inpheric pressure gradient is high, which accounts for Green Bay, wisconsin, USA, for providing advice that led tostrong and abnormal winds in the cityimprovements in the manuscriptcomparison of velocity vectors, as shown in Fig 8 and9, indicates that the pit has a greater influence on thReferencesleeward side than on the windward side. This reveals that the Chen C J. 1984. Prediction of turbulent flow[ M]. Iowa City: The University ofpit is a factor that results in turbulent flows. In additionsolar energy assimilated by the air can cause a change in theChen S F. Sun B N, Tang J C. 1998. An extended k-e model for numericalsimulation of wind flow around buildings[ J]. Applied Mathematics andair density. A redistribution of density will give rise to localMechanics, 19(1): 95-100atmospheric circulation, which canstratified flow[Ji. Boundary-layer Meteorology. 63: 117-140atmospheric nlowHood P, Taylor C, 1974. Navier-stokes equations using mixed interpolation M]Finite element methods in flow probiems, Mexico City: CAM Press, 121-Liu YJ, 1998, SIon of unsteady now in plane sudden expansion by LFSJ]. Chinese Journal ofMechanics,15(2);186-191982. A numermountain and valley winds J.Journal60:1085-1105San jG, Reiter E R, 1983[C]. Proceelings of the firsts-Sino-American workshop on mountaineteorology.9--30Shi X G, 1994. Turbulence[ M]. Tianjin: Tianjin University IrexWilliams B R, 1980. The finite +lement method for subsonic compressible flowFig 8 Comparison of velocity vectors in the spots 3 km from the north andwund multiple aero foils( M;. Numerical methols in applied fluidsouth sideZhu Y, 1997. Resonant flow of a fluid past a concave topography[J]. Appliedathe mutics and Mechanics. 18(5): 447-4502 ConclusionsReceived for review December 19, 2003. Accepted February 20. 2004)In this paper we have shown the results from asimulation of the atmospheric flow over the city of Fuxin in中国煤化工CNMHG