大宽深比变曲率弯道水动力结构大涡模拟研究
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摘要
弯曲型河流是自然界常见的河流形态,弯曲引起主流、二次流与湍流紊动相互作用,产生复杂的水动力结构,影响河流演变和物质输运。目前相关数值模拟及试验研究多针对小宽深、常曲率弯道,与天然河流大宽深、变曲率形态存在较大差异,为了揭示与天然河流相近的弯道水流运动特性,本文针对大宽深比正弦派生曲线弯道三维水流运动进行大涡数值(LES)模拟研究,结果表明:零曲率断面中心区域二次流沿河宽方向分布最为均匀,回流区范围最大,在大宽深比弯道中,回流区范围最大可达断面面积的15.5%。大宽深比弯道中部流动受到弯曲边界约束较弱,主流区内顺流向流速分布较小宽深比工况更接近于顺直矩形明渠,大宽深比情况下,主流核心区集中在弯道中线附近0.5～1倍水深范围,随着宽深比增大,弯顶附近涡量绝对值增大,对下游的影响范围增大。大宽深比弯道中水流紊动能整体水平较低,紊动能等值线分布和顺流向时均流速等值线一样,均受二次流影响,主流区中心紊动能最小,主流和局部回流区间的剪切层紊动能最大。
The meandering river, one of the most common types in nature, features various bends where the secondary flow is induced by curvature and interacts with turbulences, and usually develops into a complicated flow structure. Secondary flows are crucial to river evolution and nutrition material transport.Most previous numerical simulations and experiments focus on the small width-depth ratios and constant curvature of channel bends, but natural rivers tend to develop into a large width-depth ratio and variable curvature. This study conducts large eddy simulations(LES) of the flows in continuous sine-generated bends, and examines the hydrodynamic structure of large width-depth ratio bends under large Reynolds number conditions. The results show that at the cross-sections of zero curvature in the transition of two bends, the recirculation zone is the largest, and over the core region of these cross sections the secondary flow is transversely distributed most uniform. In the case of large width-depth ratio bends, this region can expand up to 15.5% of the cross-sectional area. The mainstream in this core region, relative to the small width-depth ratio case, is less effected by the curved boundaries, and the cross-sectional distributions of its time-averaged streamwise velocity component is closer to that in a straight, rectangular open channel,with the velocity peak located vertically very close to free surface and transversely within a range of 0.5-1.0 times the flow depth around the channel centerline. With an increasing width-depth ratio, Z-vorticity near the bend apex is increased, and the influence of bend curvature is extended further downstream. The secondary flow also changes the characteristics of flow turbulences in a meandering river. A larger widthdepth ratio leads to less turbulent energy, and turbulent kinetic energy is the lowest in the core of the mainstream while the highest in shear layers.
The meandering river, one of the most common types in nature, features various bends where the secondary flow is induced by curvature and interacts with turbulences, and usually develops into a complicated flow structure. Secondary flows are crucial to river evolution and nutrition material transport.Most previous numerical simulations and experiments focus on the small width-depth ratios and constant curvature of channel bends, but natural rivers tend to develop into a large width-depth ratio and variable curvature. This study conducts large eddy simulations(LES) of the flows in continuous sine-generated bends, and examines the hydrodynamic structure of large width-depth ratio bends under large Reynolds number conditions. The results show that at the cross-sections of zero curvature in the transition of two bends, the recirculation zone is the largest, and over the core region of these cross sections the secondary flow is transversely distributed most uniform. In the case of large width-depth ratio bends, this region can expand up to 15.5% of the cross-sectional area. The mainstream in this core region, relative to the small width-depth ratio case, is less effected by the curved boundaries, and the cross-sectional distributions of its time-averaged streamwise velocity component is closer to that in a straight, rectangular open channel,with the velocity peak located vertically very close to free surface and transversely within a range of 0.5-1.0 times the flow depth around the channel centerline. With an increasing width-depth ratio, Z-vorticity near the bend apex is increased, and the influence of bend curvature is extended further downstream. The secondary flow also changes the characteristics of flow turbulences in a meandering river. A larger widthdepth ratio leads to less turbulent energy, and turbulent kinetic energy is the lowest in the core of the mainstream while the highest in shear layers.
引文
[1]BLANCKAERT K.Saturation of curvature-induced secondary flow,energy losses,and turbulence in sharp open-channel bends:Laboratory experiments,analysis,and modeling[J].Journal of Geophysical Research:Earth Surface,2009,114:F03015.
[2]贺莉,陈东,贾亚非,等.弯道推移质同异岸输移的时空演变模拟[J].水力发电学报,2016,35(2):54-60.HE Li,CHEN Dong,JIA Yafei,et al.Modeling bedload transport along river meanders[J]Journal of Hydroelectric Engineering,2016,35(2):54-60.(in Chinese)
[3]BLANCKAERT K,DUARTE A,CHEN Q,et al.Flow processes near smooth and rough(concave)outer banks in curved open channels[J].Journal of Geophysical Research Earth Surface,2012,117:F04020.
[4]WEI M,BLANCKAERT K,HEYMAN J,et al.Aparametrical study on secondary flow in sharp openchannel bends:experiments and theoretical modelling[J].Journal of Hydro-environment Research,2016,13(498):1-13.
[5]KOKEN M,CONSTANTINESCU G,BLANCKAERT K.Hydrodynamic processes,sediment erosion mechanisms,and Reynolds-number-induced scale effects in an open channel bend of strong curvature with flat bathymetry[J].Journal of Geophysical Research Earth Surface,2013,118(4):2308-2324.
[6]童思陈,许光祥,钟亮.弯道水流纵向流速剖面的试验研究[J].水力发电学报,2010,29(4):84-88.TONG Sichen,XU Guangxiang,ZHONG Liang.Experimental study on the vertical profiles of longitudinal velocity of flow in a curved conduit[J].Journal of Hydroelectric Engineering,2010,29(4):84-88.(in Chinese)
[7]BOOIJ R.Measurements and large eddy simulations of the flows in some curved flumes[J].Journal of Turbulence,2003,4(4):N8.
[8]刘月琴,万艳春.弯道水流紊动强度[J].华南理工大学学报(自然科学版),2003,31(12):89-93.LIU Yueqin,WAN Yanchun.Turbulence intensity of bend flow[J].Journal of South China University of Technology(Natural Science Edition),2003,31(12):89-93.(in Chinese)
[9]STOESSER T,RUETHER N,OLSEN N R B.Calculation of primary and secondary flow and boundary shear stresses in a meandering channel[J].Advances in Water Resources,2010,33(2):158-170.
[10]WHITING P J,DIETRICH W E.Experimental studies of bed topography and flow patterns in large-amplitude meanders:1.Observations[J].Water Resources Research,1993,29(11):3605-3614.
[11]SILVA A M F D,EL-TAHAWY T,TAPE W D.Variation of flow pattern with sinuosity in sine-generated meandering streams[J].Journal of Hydraulic Engineering,2006,132(10):1003-1014.
[12]许栋,白玉川,谭艳,等.正弦派生曲线弯道中水沙运动特性动床试验[J].天津大学学报(自然科学与工程技术版),2010,43(9):762-770.XU Dong,BAI Yuchuan,TAN Yan,et al.Experiment on characteristics of flow and sediment movement in sinegenerated meandering channels with movable bed[J]Journal of Tianjin University,2010,43(9):762-770.(in Chinese)
[13]TERMINI D.Experimental observations of flow and bed processes in large-amplitude meandering flume[J].JHydraul Eng-ASCE,2009,135(7):575-87.
[14]KANG S,SOTIROPOULOS F.Assessing the predictive capabilities of isotropic,eddy viscosity Reynoldsaveraged turbulence models in a natural-like meandering channel[J].Water Resources Research,2012,48(6):6505.
[15]MONCHO-ESTEVE I J,PALAU-SALVADOR G,GARCíA-VILLALBA M,et al.A Numerical Study of the Complex Flow Structure in a Compound Meandering Channel[J].Advances in Water Resources,2018,116:95-116.
[16]魏炳乾,裴传康,龚秀秀,等.缓变曲线改善120°弯道水沙运动的三维数值模拟[J].水力发电学报,2018,37(3):78-87.WEI Bingqian,PEI Chuankang,LONG Xiuxiu,et al.Improvement on flow and sediment transport by transition curves in 120°channel bend and its 3-D numerical simulations[J].Journal of Hydroelectric Engineering,2018,37(3):78-87.(in Chinese)
[17]假冬冬,邵学军,肖毅,等.不同来水条件下弯道摆动的三维数值模拟[J].水力发电学报,2010,29(5):190-196.JIA Dongdong,SHAO Xuedong,XIAO Yi,et al.3-Dnumerical simulation of meander migration under different flow conditions[J].Journal of Hydroelectric Engineering,2010,29(5):190-196.(in Chinese)
[18]RAMAMURTHY A S,HAN S S,BIRON P M.Threedimensional simulation parameters for 90°open channel bend flows[J].Journal of Computing in Civil Engineering,2013,27(3):282-291.
[19]GHOBADIAN R,MOHAMMADI K.Simulation of subcritical flow pattern in 180°uniform and convergent open-channel bends using SSIIM 3-D model[J].Water Science and Engineering,2011,4(3):270-283.
[20]VAN BALEN W,UIJTTEWAAL W S J,BLANCKAERTK.Large-eddy simulation of a mildly curved openchannel flow[J].Journal of Fluid Mechanics,2009,630:413-442.
[21]张兆顺.湍流大涡数值模拟的理论和应用[M].北京:清华大学出版社,2008.ZHANG Zhaoshun.Theory and application of turbulent large eddy numerical simulation[M].Beijing:Tsinghua University Press,2008.(in Chinese)
[22]JI C,MUNJIZA A,WILLIAMS J J R.A novel iterative direct-forcing immersed boundary method and its finite volume applications[J].Journal of Computational Physics,2012,231(4):1797-1821.
[23]JI C,MUNJIZA A,AVITAL E,et al.Direct numerical simulation of sediment entrainment in turbulent channel flow[J].Physics of Fluids,2013,25(5):531-560
[24]及春宁,陈威霖,宋晓阳,等.明渠紊流中泥沙颗粒输移的大涡模拟研究[J].泥沙研究,2014(4):1-9.JI Chunning,CHEN Weilin,SONG Xiaoyang,et al.Large eddy simulation of sediment particles transport in turbulent open channel flow[J].Journal of Sediment Research,2014(4):1-9.(in Chinese)
[25]FADLUN E A,VERZICCO R,ORLANDI P,et al.Combined immersed-boundary finite-difference methods for three-dimensional complex flow simulations[J].Journal of Computational Physics,2000,161(1):35-60.
[26]WERNER H,WENGLE H.Large-eddy simulation of turbulent flow over and around a cube in a plate channel[M].Berlin:Springer Berlin Heidelberg,1993.
[27]LANGBEIN W B,LEOPOLD L B.River meanders and the theory of minimum variance[M].Rivers and River Terraces.Palgrave Macmillan UK,1970.
[28]高术仙.河流典型弯段水流结构及动力特性研究[D].天津:天津大学,2017.GAO Shuxian.Flow structure and dynamic characteristics in typical river bends[D].Tianjin:Tianjin University,2017.(in Chinese)
[29]FARHADI A,SINDELAR C,TRITTHART M,et al.An investigation on the outer bank cell of secondary flow in channel bends[J].Journal of Hydro-Environment Research,2018(18):1-11.
[30]BLANCKAERT K,KLEINHANS M G,MCLELLANDS J,et al.Flow separation at the inner(convex)and outer(concave)banks of constant-width and widening openchannel bends[J].Earth Surface Processes&Landforms,2013,38:696-716.
[31]TERMINI D,PIRAINO M.Experimental analysis of cross-sectional flow motion in a large amplitude meandering bend[J].Earth Surface Processes&Landforms,2011,36(2):244-256.
[32]JOHANNESSON H,PARKER G.Velocity redistribution in meandering rivers[J].Journal of Hydraulic Engineering,1989,115(8):1019-1039.
[33]WILSON C A M E,BOXALL J B,GUYMER I,et al.Validation of a three-dimensional numerical code in the simulation of pseudo-natural meandering flows[J].Journal of Hydraulic Engineering,2003,129(10):758-768.
[34]王虹,王连接,邵学军,等.连续弯道水流紊动特性试验研究[J].力学学报,2013,45(4):525-533.WANG Hong,WANG Lianjie,SHAO Xuejun,et al.Turbulence characteristics in consecutive bends[J].Chinese Journal of Theoretical and Applied Mechanics,2013,45(4):525-533.(in Chinese)
[35]ROCA M,BLANCKAERT K,MARTíNVIDE J P.Reduction of bend scour by an outer bank footing:flow field and turbulence[J].Journal of Hydraulic Engineering,2009,135(5):361-368.
[2]贺莉,陈东,贾亚非,等.弯道推移质同异岸输移的时空演变模拟[J].水力发电学报,2016,35(2):54-60.HE Li,CHEN Dong,JIA Yafei,et al.Modeling bedload transport along river meanders[J]Journal of Hydroelectric Engineering,2016,35(2):54-60.(in Chinese)
[3]BLANCKAERT K,DUARTE A,CHEN Q,et al.Flow processes near smooth and rough(concave)outer banks in curved open channels[J].Journal of Geophysical Research Earth Surface,2012,117:F04020.
[4]WEI M,BLANCKAERT K,HEYMAN J,et al.Aparametrical study on secondary flow in sharp openchannel bends:experiments and theoretical modelling[J].Journal of Hydro-environment Research,2016,13(498):1-13.
[5]KOKEN M,CONSTANTINESCU G,BLANCKAERT K.Hydrodynamic processes,sediment erosion mechanisms,and Reynolds-number-induced scale effects in an open channel bend of strong curvature with flat bathymetry[J].Journal of Geophysical Research Earth Surface,2013,118(4):2308-2324.
[6]童思陈,许光祥,钟亮.弯道水流纵向流速剖面的试验研究[J].水力发电学报,2010,29(4):84-88.TONG Sichen,XU Guangxiang,ZHONG Liang.Experimental study on the vertical profiles of longitudinal velocity of flow in a curved conduit[J].Journal of Hydroelectric Engineering,2010,29(4):84-88.(in Chinese)
[7]BOOIJ R.Measurements and large eddy simulations of the flows in some curved flumes[J].Journal of Turbulence,2003,4(4):N8.
[8]刘月琴,万艳春.弯道水流紊动强度[J].华南理工大学学报(自然科学版),2003,31(12):89-93.LIU Yueqin,WAN Yanchun.Turbulence intensity of bend flow[J].Journal of South China University of Technology(Natural Science Edition),2003,31(12):89-93.(in Chinese)
[9]STOESSER T,RUETHER N,OLSEN N R B.Calculation of primary and secondary flow and boundary shear stresses in a meandering channel[J].Advances in Water Resources,2010,33(2):158-170.
[10]WHITING P J,DIETRICH W E.Experimental studies of bed topography and flow patterns in large-amplitude meanders:1.Observations[J].Water Resources Research,1993,29(11):3605-3614.
[11]SILVA A M F D,EL-TAHAWY T,TAPE W D.Variation of flow pattern with sinuosity in sine-generated meandering streams[J].Journal of Hydraulic Engineering,2006,132(10):1003-1014.
[12]许栋,白玉川,谭艳,等.正弦派生曲线弯道中水沙运动特性动床试验[J].天津大学学报(自然科学与工程技术版),2010,43(9):762-770.XU Dong,BAI Yuchuan,TAN Yan,et al.Experiment on characteristics of flow and sediment movement in sinegenerated meandering channels with movable bed[J]Journal of Tianjin University,2010,43(9):762-770.(in Chinese)
[13]TERMINI D.Experimental observations of flow and bed processes in large-amplitude meandering flume[J].JHydraul Eng-ASCE,2009,135(7):575-87.
[14]KANG S,SOTIROPOULOS F.Assessing the predictive capabilities of isotropic,eddy viscosity Reynoldsaveraged turbulence models in a natural-like meandering channel[J].Water Resources Research,2012,48(6):6505.
[15]MONCHO-ESTEVE I J,PALAU-SALVADOR G,GARCíA-VILLALBA M,et al.A Numerical Study of the Complex Flow Structure in a Compound Meandering Channel[J].Advances in Water Resources,2018,116:95-116.
[16]魏炳乾,裴传康,龚秀秀,等.缓变曲线改善120°弯道水沙运动的三维数值模拟[J].水力发电学报,2018,37(3):78-87.WEI Bingqian,PEI Chuankang,LONG Xiuxiu,et al.Improvement on flow and sediment transport by transition curves in 120°channel bend and its 3-D numerical simulations[J].Journal of Hydroelectric Engineering,2018,37(3):78-87.(in Chinese)
[17]假冬冬,邵学军,肖毅,等.不同来水条件下弯道摆动的三维数值模拟[J].水力发电学报,2010,29(5):190-196.JIA Dongdong,SHAO Xuedong,XIAO Yi,et al.3-Dnumerical simulation of meander migration under different flow conditions[J].Journal of Hydroelectric Engineering,2010,29(5):190-196.(in Chinese)
[18]RAMAMURTHY A S,HAN S S,BIRON P M.Threedimensional simulation parameters for 90°open channel bend flows[J].Journal of Computing in Civil Engineering,2013,27(3):282-291.
[19]GHOBADIAN R,MOHAMMADI K.Simulation of subcritical flow pattern in 180°uniform and convergent open-channel bends using SSIIM 3-D model[J].Water Science and Engineering,2011,4(3):270-283.
[20]VAN BALEN W,UIJTTEWAAL W S J,BLANCKAERTK.Large-eddy simulation of a mildly curved openchannel flow[J].Journal of Fluid Mechanics,2009,630:413-442.
[21]张兆顺.湍流大涡数值模拟的理论和应用[M].北京:清华大学出版社,2008.ZHANG Zhaoshun.Theory and application of turbulent large eddy numerical simulation[M].Beijing:Tsinghua University Press,2008.(in Chinese)
[22]JI C,MUNJIZA A,WILLIAMS J J R.A novel iterative direct-forcing immersed boundary method and its finite volume applications[J].Journal of Computational Physics,2012,231(4):1797-1821.
[23]JI C,MUNJIZA A,AVITAL E,et al.Direct numerical simulation of sediment entrainment in turbulent channel flow[J].Physics of Fluids,2013,25(5):531-560
[24]及春宁,陈威霖,宋晓阳,等.明渠紊流中泥沙颗粒输移的大涡模拟研究[J].泥沙研究,2014(4):1-9.JI Chunning,CHEN Weilin,SONG Xiaoyang,et al.Large eddy simulation of sediment particles transport in turbulent open channel flow[J].Journal of Sediment Research,2014(4):1-9.(in Chinese)
[25]FADLUN E A,VERZICCO R,ORLANDI P,et al.Combined immersed-boundary finite-difference methods for three-dimensional complex flow simulations[J].Journal of Computational Physics,2000,161(1):35-60.
[26]WERNER H,WENGLE H.Large-eddy simulation of turbulent flow over and around a cube in a plate channel[M].Berlin:Springer Berlin Heidelberg,1993.
[27]LANGBEIN W B,LEOPOLD L B.River meanders and the theory of minimum variance[M].Rivers and River Terraces.Palgrave Macmillan UK,1970.
[28]高术仙.河流典型弯段水流结构及动力特性研究[D].天津:天津大学,2017.GAO Shuxian.Flow structure and dynamic characteristics in typical river bends[D].Tianjin:Tianjin University,2017.(in Chinese)
[29]FARHADI A,SINDELAR C,TRITTHART M,et al.An investigation on the outer bank cell of secondary flow in channel bends[J].Journal of Hydro-Environment Research,2018(18):1-11.
[30]BLANCKAERT K,KLEINHANS M G,MCLELLANDS J,et al.Flow separation at the inner(convex)and outer(concave)banks of constant-width and widening openchannel bends[J].Earth Surface Processes&Landforms,2013,38:696-716.
[31]TERMINI D,PIRAINO M.Experimental analysis of cross-sectional flow motion in a large amplitude meandering bend[J].Earth Surface Processes&Landforms,2011,36(2):244-256.
[32]JOHANNESSON H,PARKER G.Velocity redistribution in meandering rivers[J].Journal of Hydraulic Engineering,1989,115(8):1019-1039.
[33]WILSON C A M E,BOXALL J B,GUYMER I,et al.Validation of a three-dimensional numerical code in the simulation of pseudo-natural meandering flows[J].Journal of Hydraulic Engineering,2003,129(10):758-768.
[34]王虹,王连接,邵学军,等.连续弯道水流紊动特性试验研究[J].力学学报,2013,45(4):525-533.WANG Hong,WANG Lianjie,SHAO Xuejun,et al.Turbulence characteristics in consecutive bends[J].Chinese Journal of Theoretical and Applied Mechanics,2013,45(4):525-533.(in Chinese)
[35]ROCA M,BLANCKAERT K,MARTíNVIDE J P.Reduction of bend scour by an outer bank footing:flow field and turbulence[J].Journal of Hydraulic Engineering,2009,135(5):361-368.