基于CFD的扬水曝气器外围流场及曝气室流场模拟
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摘要
扬水曝气器是针对大水深水库富营养化、沉积物内源污染物严重等问题提出的,能实现混合水体、增加水体溶解氧的水质改善设备。它能够通过混合上下水层达到将表层藻类向下迁移使藻类生长受到抑制直至死亡的目的。也可以通过循环混合作用破坏水体分层,促进表层高溶解氧水体向下传递,或者直接向底部水体曝气来改善下层水体的厌氧状态,从而控制沉积物中氮、磷、有机物、铁、锰等污染物释放。
计算流体力学(Computational Fluid Dynamics,简称CFD)是通过计算机数值计算和图像显示,对包含有流体力学和热传导的相关物理量的系统所做的分析。CFD可以看作是在流动基本方程(质量守恒方程、动量守恒方程、能量守恒方程)控制下对流动的数值模拟。通过这种数值模拟,我们可以得到及其复杂的流场内各个位置上的基本物理量(如速度、温度、压力、浓度等)的分布,以及这些物理量随时间的变化情况。FLUENT是目前功能最全面、适用性最广、国内使用最广泛的CFD软件之一。实践证明FLUENT软件具有强大的计算功能,可以处理气、水的传热和运动问题。
本文通过FLUENT软件对扬水曝气器的外围流场以及曝气室流场的模拟得出以下主要结论:
(1)针对不同导流板角度情况下流场的模拟可得出:随着导流板与水平线的角度不同,在流畅中形成的漩涡旋转方向也不同。经模拟计算,37°是漩涡旋转方向发生改变的分界线。当导流板角度从0°变为37°时,由于漩涡旋转方向的改变,模拟区域里除藻区域的比重会明显增加20%,但是从37°再继续增加导流板角度,模拟区域里除藻区域不会有较大变化。而且在相同的出水口流速以及相同的漩涡旋转方向下,导流板角度的改变对流场的混合强度没有明显的影响。
(2)变化出水口流速以及模拟半径可以得出:在相同模拟水域半径的情况下,增加出水口流速对除藻区域的影响不大,但可以加快稳定流场的形成,同时增强流场的混合强度。在出水口流速相同的情况下,水域半径由50m增大到100m后除藻区域面积减小,混合强度也稍有减弱,形成稳定流场所需要的时间大大增加。
(3)曝气室提水量随着气泡直径的增大而增大。气泡直径从1mm增大到5mm时,提水量增加的较为明显,能增大253.69%;从5mm增大到10mm时提水量增大效果不明显,只增大了13.94%。
(4)当气泡直径小于5mm时,有50%以上的气量都随着水流进入到回流室,进而下潜到底部水体,再加上小直径的气泡与水体接触的表面积大,所以气泡直径越小对改善水体溶解氧的状况的效果越好。小直径气泡不利于气水分离,因此生成气弹需要较长的时间。
The Ware-lifting Aerator, aiming at the water quality problems of eutrophication and pollutants' releasing from sediments in deep water source reservoir, is a new water quality improvement device, which can mix water and oxygenate water. Through the way of mixing water, Ware-lifting Aerator can send alga to the lower lay of the water and make it to death by restraining alga's growth. Also it can improvement the anaerobic state in lower water by mixing water or oxygenating water directly. So the pollutants' releasing from sediment in water source is controlled.
Computational Fluid Dynamics, short for CFD, is the analysis on the system which contains the relative physical parameters of fluid dynamics and heat conduction. CFD can be considered a kind of numerical simulations base on flow basic equations (mass conservation equation, momentum conservation equation, energy conservation equation). Through this kind of numerical simulations, we can get the distribution of fundamental physical parameters (such as velocity, temperature, pressure, concentration) in any places of a very complicated flow field and the changing process of these parameters as the time changing. FLUENT is one of the CFD software, which is the most comprehensive, most widely applicability and most widely used CFD software. The practice has proof that FLUENT has powerful computing capabilities and can be used to solve the problems of air and water' motion and heat conduction.
Through the Numerical simulations on the periphery flow field of Water-lifting Aerator and the flow field of Aeration room this article can get these conclusions:
(1) The direction of rotation will change because the included angle between hydro-deflector and horizontal plane changes. Through numerical simulations, we know that 37°is the key point at which the direction of rotation inverses. As the included angle changing from 0°to 37°, the direction of rotation also inversing, the alga-removed area will increase by 20%. If we increase the included angle further, bigger than 37°, the alga-removed area will not increase any more.If the inlet velocity condition and the direction of rotation are the same, the changing of the included angle can not affect the mixed strength of the flow field.
(2) If the radiuses of water are the same, increasing the inlet velocity can not expend the alga-removed area, but it can make it faster to form a steady flow field, and at the same time, strengthen the mixed strength.If the inlet velocity are the same, increasing the radius of water from 50m to 100m, the alga-removed area will be reduced, following the mixed strength being weakened and the time which forming a steady flow field needs increasing greatly.
(3) The quantity of lifted water increases as the radius of the air bubble increasing. If the radius of the air bubble increases from 1mm to 5mm, the quantity of lifted water increases by 253.69%. And form 5mm to 10mm, the quantity of lifted water increases by 13.94%.
(4) When the radius of air bubble is smaller than 5mm, there are more than 50% bubbles go into the back-flow room following the water flow, and then being sent into bottom water. And also because the air bubbles which have smaller radius get more effective interaction with water, the smaller air bubbles can oxygenate water better. Small air bubbles are not good for the separation between air and water. So more time will be needed to form an air-bullet.
计算流体力学(Computational Fluid Dynamics,简称CFD)是通过计算机数值计算和图像显示,对包含有流体力学和热传导的相关物理量的系统所做的分析。CFD可以看作是在流动基本方程(质量守恒方程、动量守恒方程、能量守恒方程)控制下对流动的数值模拟。通过这种数值模拟,我们可以得到及其复杂的流场内各个位置上的基本物理量(如速度、温度、压力、浓度等)的分布,以及这些物理量随时间的变化情况。FLUENT是目前功能最全面、适用性最广、国内使用最广泛的CFD软件之一。实践证明FLUENT软件具有强大的计算功能,可以处理气、水的传热和运动问题。
本文通过FLUENT软件对扬水曝气器的外围流场以及曝气室流场的模拟得出以下主要结论:
(1)针对不同导流板角度情况下流场的模拟可得出:随着导流板与水平线的角度不同,在流畅中形成的漩涡旋转方向也不同。经模拟计算,37°是漩涡旋转方向发生改变的分界线。当导流板角度从0°变为37°时,由于漩涡旋转方向的改变,模拟区域里除藻区域的比重会明显增加20%,但是从37°再继续增加导流板角度,模拟区域里除藻区域不会有较大变化。而且在相同的出水口流速以及相同的漩涡旋转方向下,导流板角度的改变对流场的混合强度没有明显的影响。
(2)变化出水口流速以及模拟半径可以得出:在相同模拟水域半径的情况下,增加出水口流速对除藻区域的影响不大,但可以加快稳定流场的形成,同时增强流场的混合强度。在出水口流速相同的情况下,水域半径由50m增大到100m后除藻区域面积减小,混合强度也稍有减弱,形成稳定流场所需要的时间大大增加。
(3)曝气室提水量随着气泡直径的增大而增大。气泡直径从1mm增大到5mm时,提水量增加的较为明显,能增大253.69%;从5mm增大到10mm时提水量增大效果不明显,只增大了13.94%。
(4)当气泡直径小于5mm时,有50%以上的气量都随着水流进入到回流室,进而下潜到底部水体,再加上小直径的气泡与水体接触的表面积大,所以气泡直径越小对改善水体溶解氧的状况的效果越好。小直径气泡不利于气水分离,因此生成气弹需要较长的时间。
The Ware-lifting Aerator, aiming at the water quality problems of eutrophication and pollutants' releasing from sediments in deep water source reservoir, is a new water quality improvement device, which can mix water and oxygenate water. Through the way of mixing water, Ware-lifting Aerator can send alga to the lower lay of the water and make it to death by restraining alga's growth. Also it can improvement the anaerobic state in lower water by mixing water or oxygenating water directly. So the pollutants' releasing from sediment in water source is controlled.
Computational Fluid Dynamics, short for CFD, is the analysis on the system which contains the relative physical parameters of fluid dynamics and heat conduction. CFD can be considered a kind of numerical simulations base on flow basic equations (mass conservation equation, momentum conservation equation, energy conservation equation). Through this kind of numerical simulations, we can get the distribution of fundamental physical parameters (such as velocity, temperature, pressure, concentration) in any places of a very complicated flow field and the changing process of these parameters as the time changing. FLUENT is one of the CFD software, which is the most comprehensive, most widely applicability and most widely used CFD software. The practice has proof that FLUENT has powerful computing capabilities and can be used to solve the problems of air and water' motion and heat conduction.
Through the Numerical simulations on the periphery flow field of Water-lifting Aerator and the flow field of Aeration room this article can get these conclusions:
(1) The direction of rotation will change because the included angle between hydro-deflector and horizontal plane changes. Through numerical simulations, we know that 37°is the key point at which the direction of rotation inverses. As the included angle changing from 0°to 37°, the direction of rotation also inversing, the alga-removed area will increase by 20%. If we increase the included angle further, bigger than 37°, the alga-removed area will not increase any more.If the inlet velocity condition and the direction of rotation are the same, the changing of the included angle can not affect the mixed strength of the flow field.
(2) If the radiuses of water are the same, increasing the inlet velocity can not expend the alga-removed area, but it can make it faster to form a steady flow field, and at the same time, strengthen the mixed strength.If the inlet velocity are the same, increasing the radius of water from 50m to 100m, the alga-removed area will be reduced, following the mixed strength being weakened and the time which forming a steady flow field needs increasing greatly.
(3) The quantity of lifted water increases as the radius of the air bubble increasing. If the radius of the air bubble increases from 1mm to 5mm, the quantity of lifted water increases by 253.69%. And form 5mm to 10mm, the quantity of lifted water increases by 13.94%.
(4) When the radius of air bubble is smaller than 5mm, there are more than 50% bubbles go into the back-flow room following the water flow, and then being sent into bottom water. And also because the air bubbles which have smaller radius get more effective interaction with water, the smaller air bubbles can oxygenate water better. Small air bubbles are not good for the separation between air and water. So more time will be needed to form an air-bullet.
引文
[1]马经安,李红青.浅谈国内外江河湖库水体富营养化状况[J].长江流域资源与环境,2002,11(6):575-578
[2]朱智,吴江明,周俊杰.滇池污染治理工作若干问题的思考[J].中国给水排水,1999,15(12):27-30
[3]V.H.Chipofya,E.J.Matapa.Destratification of an impounding reservoir using compressed air—case of Mudi reservoir,Blantyre,Malawi[J].Physics and Chemistry of the Earth,2003,28(27):1161-1164.
[4]Klapper H.translated by Bernard Hemmings.Control of eutrophication in inland waters[J].Ellis Horwood,1991
[5]Holdren C,W Jones,J Taggart.Managing Lakes and Reservoirs[M].3rd edition Prep.By N.Am.Lake Manage.Soc.And Terrene Inst.,in coop.with U.S.EPA.,2001
[6]Rohan Stephens,Jrrg Imberger.Reservoir destratification via mechanical mixers[J].Journal of Hydraulic Engineering,1993,119(4):438-457.
[7]Brian Kirke,Ahmed El Gezawy.Design and model tests for an efficient mechanical circulator/aerator for lakes and reservoirs[J].Water Research,1996,31(6):1283-1290.
[8]Heinz G.Stefan,Ruochuan Gu.Efficiency of jet-mixing of temperature-stratified water[J].Journal of Environmental Engineering,1992,118(3):363-379.
[9]Vickie L.Burris,John C.Little.Bubble Dynamics and Oxygen Transfer in Hypolimnetic Aerator[J].Wat.Sci.Tech,1998,37(2):293-300
[10]Clasen J.Raw water quality management at Wahnbach reservoir[J].Water supply,2000,18(1):581-585
[11]Daniel F.McGinnis and John C.little.Bubble dynamics and oxygen Transper in a Speece Cone[J].Wat.Sci.Tech,1998,37(2):285-292
[12]Vickie L.Burris,John C.Little.Bubble Dynamics and Oxygen Transfer in Hypolimnetic Aerator[J].Wat.Sci.Tech,1998,37(2):293-300
[13]Murphy T.P.,Lawson A.,Kumagai M.,Babin J.Review of emerging issue in sediment treatment[J].Aquatic Ecosystem Health and Management,1999,(2):419-434
[14]Holdren C,W Jones,J Taggart.Managing Lakes and Reservoirs[M].3rd edition Prep.By N.Am.Lake Manage.Soc.And Terrene Inst.,in coop.with U.S.EPA.,2001
[15]Klapper H.translated by Bernard Hemmings.Control of eutrophication in inland waters[J].Ellis Horwood,1991
[16]Welch E B,Cooke G D.Effectiveness and longevity of phosphorus inactivation with alum[J].Lake and Reservoir Management,1999,(1):5-27
[17]丛海兵.扬水曝气水源水质改善技术研究[D].西安建筑科技大学.2007
[18]丛海兵,黄廷林,缪晶广等.水体修复装置——扬水曝气器的开发.中国给水排水,2005,21(3):41-45
[19]丛海兵,黄廷林,缪晶广等.扬水曝气器的水质改善功能及提水、充氧性能研究.环境工程学报,2007,1(1):7-13
[20]丛海兵,黄廷林,赵建伟等.扬水曝气器技术在水源水质改善中的应用.环境污染与防治,2006,28(3):215-218
[21]王福军.计算流体力学分析[M].北京:清华大学出版社,2006
[22]韩占忠,王敬,兰小平.FLUENT流体工程仿真计算实例与应用[M].北京:北京理工大学出版社,2006
[23]王霞,金志浩.流体数值模拟中二维、三维模型结果比较研究.沈阳化工学院学报,2007,21(2):121-123
[24]郭烈锦.两相与多相流动力学[M].西安:西安交通大学出版社,2002-12
[25]张军,郑捷庆.气—幂律两相流体流经截面突缩管的数值模拟.石油钻采工艺,2007,29(3):108-113
[26]薛胜伟,尹侠.气升式内环流反应器流场及传质性数值模拟.化学工程,2006,34(5):23-27
[27]Gustavo C.Buscaglia,Fabian A.Bombardelli,Marcelo H.Garcia.Numerical modeling of large-scale bubble plumes accounting for mass transfer effects[J].International Journal of Multiphase Flow,2002,28(11):1763-1785.
[28]王瑞金,张凯,王刚.Fluent技术基础与应用实例[M].北京:清华大学出版社,2007.
[29]Fluent Inc.,FLUENT User's Guide.Fluent Inc.,2003
[30]Fluent Inc.,FLUENT User Defined Function Manual.Fluent Inc.,2003
[2]朱智,吴江明,周俊杰.滇池污染治理工作若干问题的思考[J].中国给水排水,1999,15(12):27-30
[3]V.H.Chipofya,E.J.Matapa.Destratification of an impounding reservoir using compressed air—case of Mudi reservoir,Blantyre,Malawi[J].Physics and Chemistry of the Earth,2003,28(27):1161-1164.
[4]Klapper H.translated by Bernard Hemmings.Control of eutrophication in inland waters[J].Ellis Horwood,1991
[5]Holdren C,W Jones,J Taggart.Managing Lakes and Reservoirs[M].3rd edition Prep.By N.Am.Lake Manage.Soc.And Terrene Inst.,in coop.with U.S.EPA.,2001
[6]Rohan Stephens,Jrrg Imberger.Reservoir destratification via mechanical mixers[J].Journal of Hydraulic Engineering,1993,119(4):438-457.
[7]Brian Kirke,Ahmed El Gezawy.Design and model tests for an efficient mechanical circulator/aerator for lakes and reservoirs[J].Water Research,1996,31(6):1283-1290.
[8]Heinz G.Stefan,Ruochuan Gu.Efficiency of jet-mixing of temperature-stratified water[J].Journal of Environmental Engineering,1992,118(3):363-379.
[9]Vickie L.Burris,John C.Little.Bubble Dynamics and Oxygen Transfer in Hypolimnetic Aerator[J].Wat.Sci.Tech,1998,37(2):293-300
[10]Clasen J.Raw water quality management at Wahnbach reservoir[J].Water supply,2000,18(1):581-585
[11]Daniel F.McGinnis and John C.little.Bubble dynamics and oxygen Transper in a Speece Cone[J].Wat.Sci.Tech,1998,37(2):285-292
[12]Vickie L.Burris,John C.Little.Bubble Dynamics and Oxygen Transfer in Hypolimnetic Aerator[J].Wat.Sci.Tech,1998,37(2):293-300
[13]Murphy T.P.,Lawson A.,Kumagai M.,Babin J.Review of emerging issue in sediment treatment[J].Aquatic Ecosystem Health and Management,1999,(2):419-434
[14]Holdren C,W Jones,J Taggart.Managing Lakes and Reservoirs[M].3rd edition Prep.By N.Am.Lake Manage.Soc.And Terrene Inst.,in coop.with U.S.EPA.,2001
[15]Klapper H.translated by Bernard Hemmings.Control of eutrophication in inland waters[J].Ellis Horwood,1991
[16]Welch E B,Cooke G D.Effectiveness and longevity of phosphorus inactivation with alum[J].Lake and Reservoir Management,1999,(1):5-27
[17]丛海兵.扬水曝气水源水质改善技术研究[D].西安建筑科技大学.2007
[18]丛海兵,黄廷林,缪晶广等.水体修复装置——扬水曝气器的开发.中国给水排水,2005,21(3):41-45
[19]丛海兵,黄廷林,缪晶广等.扬水曝气器的水质改善功能及提水、充氧性能研究.环境工程学报,2007,1(1):7-13
[20]丛海兵,黄廷林,赵建伟等.扬水曝气器技术在水源水质改善中的应用.环境污染与防治,2006,28(3):215-218
[21]王福军.计算流体力学分析[M].北京:清华大学出版社,2006
[22]韩占忠,王敬,兰小平.FLUENT流体工程仿真计算实例与应用[M].北京:北京理工大学出版社,2006
[23]王霞,金志浩.流体数值模拟中二维、三维模型结果比较研究.沈阳化工学院学报,2007,21(2):121-123
[24]郭烈锦.两相与多相流动力学[M].西安:西安交通大学出版社,2002-12
[25]张军,郑捷庆.气—幂律两相流体流经截面突缩管的数值模拟.石油钻采工艺,2007,29(3):108-113
[26]薛胜伟,尹侠.气升式内环流反应器流场及传质性数值模拟.化学工程,2006,34(5):23-27
[27]Gustavo C.Buscaglia,Fabian A.Bombardelli,Marcelo H.Garcia.Numerical modeling of large-scale bubble plumes accounting for mass transfer effects[J].International Journal of Multiphase Flow,2002,28(11):1763-1785.
[28]王瑞金,张凯,王刚.Fluent技术基础与应用实例[M].北京:清华大学出版社,2007.
[29]Fluent Inc.,FLUENT User's Guide.Fluent Inc.,2003
[30]Fluent Inc.,FLUENT User Defined Function Manual.Fluent Inc.,2003
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