长江河口北槽弯道横向次生流、混合与层化:资料分析与数学模似

发布时间：2019-05-19 07:01

【摘要】：为了认识长江河口北槽弯道横向次生流、混合与层化的时空变化及其物理机制,本文采用了现场观测资料分析和数学模拟的方法对其进行研究。首先,2013年2月25至26日(枯季/大潮)、7月23至24日(洪季/大潮)分别在长江河口北槽弯道沿着3条横向测线CS6、CSW和CS3(每条测线上有北、中、南3个站位)测得水位、流速、盐度和含沙量的时间序列资料。其次,通过这些资料的定量计算、分析,结果显示:(i)3条横向测线均存在横向次生流,且横向测线CS3还出现横向次生环流;(ii)枯、洪季,仅在横向测线CS6、CS3出现环状欧拉余流;(iii)枯、洪季,沿着横向测线CS3,3个站位的横向斜压梯度比离心加速度和科氏加速度都大1~2个数量级,而后两项大小接近且数量级都是10-4,罗斯贝数在1左右。这些表明:横向次生流受横向斜压梯度、离心加速度和科氏加速度共同驱动,前一项相对于后两项更加重要。再次,通过这些资料的进一步定量计算、分析,结果显示:(i)枯、洪季大潮,沿着3条横向测线,平均势能差异分别约为54.23、66.56 J·m-3,枯季层化弱于洪季;(ii)枯季,涨潮时平均势能差异普遍小于落潮;而洪季,涨潮时平均势能差异普遍大于落潮,湍流混合存在潮汐不对称性;(iii)枯季,由横向、纵向水深平均应变(ΦS-y、ΦS-x)引起的势能差异变化率的范围分别是-67~37×10-3、-7~11×10-3 W·m-3;而洪季,相应的范围分别是-45~30×10-3、-14~13×10-3 W·m-3,ΦS-y均大于ΦS-x,对水体混合与层化的影响更大;(iv)枯季大潮,纵向平流(ΦA-x)、横向平流(ΦA-y)、纵向水深平均应变(ΦS-x)和横向水深平均应变(ΦS-y)的潮汐平均绝对值占四项总和之比例分别为26%、33%、18%和23%;而洪季大潮,相应的值的比例分别为13%、9%、22%和56%;枯季,平流项(ΦA-y最大)对混合与层化的控制可能占主导地位;洪季,应变项(ΦS-y最大)可能占主导地位。最后,采用三维有限元TELEMAC-3D水动力模型进行数值模拟。模拟结果显示:(i)弯道横向次生流存在;(ii)层化在涨潮时弱于落潮时,并且从横向测线CS6到CS3依次减弱;(iii)枯季大潮,横向斜压梯度和fA-y分别在横向次生流、混合与层化的物理机制中占主导地位。模拟的结果与实测资料的计算结果一致。
[Abstract]:In order to understand the temporal and spatial variation and physical mechanism of lateral secondary flow, mixing and stratification in the bend of the north trough of the Yangtze River Estuary, the field observation data analysis and mathematical simulation are used to study it. First of all, from 25 to 26 February 2013 (dry season / high tide) and from 23 to 24 July 2013 (flood season / tide), respectively, along three transverse lines CS6,CSW and CS3 (each line is north, medium, respectively) in the north trough bend of the Yangtze River Estuary. The time series data of water level, velocity, salinity and sediment concentration were measured. Secondly, through the quantitative calculation and analysis of these data, the results show that the transverse secondary current exists in all three transverse lines of: (i), and the transverse secondary circulation exists in the transverse line CS3. (ii) withered, flood season, only in the transverse line CS6,CS3 appeared annular Euler residual current; In the dry and flood season of (iii), the transverse baroclinic gradient of CS3,3 stations along the transverse measuring line is 1 鈮，

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