斜压作用对河口落潮水流剖面的影响
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摘要
在咸淡水混合的河口由于水体密度在空间不均匀分布,水流受到斜压影响,其流速分布经常会偏离传统的对数分布。而常用的密度流分布基于常涡黏系数假定,无法用于瞬时流速剖面的拟合。基于水动力方程,得出考虑斜压影响下的湍流切应力分布,分析发现在斜压影响下的湍流切应力呈抛物线分布。在此基础上应用Prandtl混合长理论,提出考虑河口斜压影响的落潮水流流速剖面。通过比较数值模拟结果与实测资料,发现本文公式能很好地校正斜压引起流速剖面对于传统对数分布的偏差,提高拟合精度,得到更趋于合理的拟合参数。
Due to the uneven distribution of water density in space,the flow is affected by baroclinic force,and the velocity profile often deviates from the traditional logarithmic profile in saline-freshwater mixed estuaries. The well-known density flow profile, which is assumed constant eddy viscosity, cannot fit the instantaneous velocity profile. Based on the hydrodynamic equations, we obtain the profile of the turbulent shear stress,which indicates that the distribution of the shear stress is parabolic under the effect of baroclinic force. Then we derive the velocity profile of ebb flow influenced by the baroclinic force through Prandtl's mixing theory. By comparison with numerical simulation results and experimental data,the proposed equation can correct the deviation between the classical logarithmic and the measurements, improve the fitting accuracy,and obtain the more reasonable fitting parameters.
Due to the uneven distribution of water density in space,the flow is affected by baroclinic force,and the velocity profile often deviates from the traditional logarithmic profile in saline-freshwater mixed estuaries. The well-known density flow profile, which is assumed constant eddy viscosity, cannot fit the instantaneous velocity profile. Based on the hydrodynamic equations, we obtain the profile of the turbulent shear stress,which indicates that the distribution of the shear stress is parabolic under the effect of baroclinic force. Then we derive the velocity profile of ebb flow influenced by the baroclinic force through Prandtl's mixing theory. By comparison with numerical simulation results and experimental data,the proposed equation can correct the deviation between the classical logarithmic and the measurements, improve the fitting accuracy,and obtain the more reasonable fitting parameters.
引文
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[2]周济福,刘青泉,李家春.河口混合过程的研究[J].中国科学(A辑),1999,29(9):835-843.
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[5]HANSEN D V,RATTRAY M.Gravitational circulation in straits and estuaries[J].Journal of marine research,1966,23:104-122.
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[8]STACEY M T,BURAU J R,MONISMITH S G.Creation of residual flows in a partially stratified estuary[J].Journal of geophysical research oceans,2001,106(8):17013-17037.
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[11]SCULLY M E,FRIEDRICHS C,BRUBAKER J.Control of estuarine stratification and mixing by windinduced straining of the estuarine density field[J].Estuaries,2005,28(3):321-326.
[12]CHANT R J.Secondary circulation in a region of flow curvature:relationship with tidal forcing and river discharge[J].Journal of geophysical research oceans,2002,107(9):1-11.
[13]LERCZAK J A,ROCKWELL G W.Modeling the lateral circulation in straight,stratified estuaries[J].Journal of physical oceanography,2004,34(6):1410-1428.
[14]VALLE-LEVINSON A.Density-driven exchange flow in terms of the Kelvin and Ekman numbers[J].Journal of geophysical research atmospheres,2008,113(4):1-10.
[15]郝嘉凌,宋志尧,严以新.河口海岸近底层潮流速分布模式初步研究[J].泥沙研究,2006(1):25-31.
[16]李文祥,张静怡,徐小明.长江口潮流速垂线分布规律研究[J].水文,2010,30(3):68-70+76.
[17]BURCHARD H,HETLAND R D.Quantifying the contributions of tidal straining and gravitational circulation to residual circulation in periodically stratified tidal estuaries[J].Journal of physical oceanography,2010,40(6):1243-1262.
[18]MELLOR G L,YAMADA T.Development of a turbulence closure model for geophysical fluid problems[J].Reviews of geophysics and space physics,1982,20(4):851-875.
[19]倪志辉,宋志尧.近底层潮流速分布模式比较[J].水科学进展,2010,21(1):89-94.
[20]FRIEDRICHS C T,WRIGHT L D.Sensitivity of bottom stress and bottom roughness estimates to density stratification,Eckernf?rde Bay,Southern Baltic Sea[J].Journal of geophysical research oceans,1997,102(3):5721-5732.
[21]乔红杰,张静怡,徐小明.长江口潮流摩阻流速和粗糙长度计算方法探讨[J].水文,2010,30(4):23-27+96.
[2]周济福,刘青泉,李家春.河口混合过程的研究[J].中国科学(A辑),1999,29(9):835-843.
[3]钱宁,张仁,周志德.河床演变学[M].北京:科学出版社,1987.
[4]周济福,李家春.河口混合与泥沙输运[J].力学学报,2000,32(5):523-531.
[5]HANSEN D V,RATTRAY M.Gravitational circulation in straits and estuaries[J].Journal of marine research,1966,23:104-122.
[6]SIMPSON J H,BROWN J,MATTHEWS J,et al.Tidal straining,density currents,and stirring in the control of estuarine stratification[J].Estuaries,1990,13(2):125-132.
[7]BURCHARD H,BAUMERT H Z.The formation of estuarine turbidity maxima due to density effects in the salt wedge.A hydrodynamic process study[J].Journal of physical oceanography,1998,28(2):309-321.
[8]STACEY M T,BURAU J R,MONISMITH S G.Creation of residual flows in a partially stratified estuary[J].Journal of geophysical research oceans,2001,106(8):17013-17037.
[9]STACEY M T,FRAM J P,CHOW FK.Role of tidally periodic density stratification in the creation of estuarine subtidal circulation[J].Journal of geophysical research oceans,2008,113(8):1-13.
[10]ZHANG Z,SONG Z,CHEN C,et al.The effect of density gradient on boundary flow[J].Estuarine,coastal and shelf science,2016,183:163-178.
[11]SCULLY M E,FRIEDRICHS C,BRUBAKER J.Control of estuarine stratification and mixing by windinduced straining of the estuarine density field[J].Estuaries,2005,28(3):321-326.
[12]CHANT R J.Secondary circulation in a region of flow curvature:relationship with tidal forcing and river discharge[J].Journal of geophysical research oceans,2002,107(9):1-11.
[13]LERCZAK J A,ROCKWELL G W.Modeling the lateral circulation in straight,stratified estuaries[J].Journal of physical oceanography,2004,34(6):1410-1428.
[14]VALLE-LEVINSON A.Density-driven exchange flow in terms of the Kelvin and Ekman numbers[J].Journal of geophysical research atmospheres,2008,113(4):1-10.
[15]郝嘉凌,宋志尧,严以新.河口海岸近底层潮流速分布模式初步研究[J].泥沙研究,2006(1):25-31.
[16]李文祥,张静怡,徐小明.长江口潮流速垂线分布规律研究[J].水文,2010,30(3):68-70+76.
[17]BURCHARD H,HETLAND R D.Quantifying the contributions of tidal straining and gravitational circulation to residual circulation in periodically stratified tidal estuaries[J].Journal of physical oceanography,2010,40(6):1243-1262.
[18]MELLOR G L,YAMADA T.Development of a turbulence closure model for geophysical fluid problems[J].Reviews of geophysics and space physics,1982,20(4):851-875.
[19]倪志辉,宋志尧.近底层潮流速分布模式比较[J].水科学进展,2010,21(1):89-94.
[20]FRIEDRICHS C T,WRIGHT L D.Sensitivity of bottom stress and bottom roughness estimates to density stratification,Eckernf?rde Bay,Southern Baltic Sea[J].Journal of geophysical research oceans,1997,102(3):5721-5732.
[21]乔红杰,张静怡,徐小明.长江口潮流摩阻流速和粗糙长度计算方法探讨[J].水文,2010,30(4):23-27+96.