發(fā)布時間：2019-05-19 07:01

【摘要】：為了認識長江河口北槽彎道橫向次生流、混合與層化的時空變化及其物理機制,本文采用了現(xiàn)場觀測資料分析和數(shù)學模擬的方法對其進行研究。首先,2013年2月25至26日(枯季/大潮)、7月23至24日(洪季/大潮)分別在長江河口北槽彎道沿著3條橫向測線CS6、CSW和CS3(每條測線上有北、中、南3個站位)測得水位、流速、鹽度和含沙量的時間序列資料。其次,通過這些資料的定量計算、分析,結(jié)果顯示:(i)3條橫向測線均存在橫向次生流,且橫向測線CS3還出現(xiàn)橫向次生環(huán)流;(ii)枯、洪季,僅在橫向測線CS6、CS3出現(xiàn)環(huán)狀歐拉余流;(iii)枯、洪季,沿著橫向測線CS3,3個站位的橫向斜壓梯度比離心加速度和科氏加速度都大1~2個數(shù)量級,而后兩項大小接近且數(shù)量級都是10-4,羅斯貝數(shù)在1左右。這些表明:橫向次生流受橫向斜壓梯度、離心加速度和科氏加速度共同驅(qū)動,前一項相對于后兩項更加重要。再次,通過這些資料的進一步定量計算、分析,結(jié)果顯示:(i)枯、洪季大潮,沿著3條橫向測線,平均勢能差異分別約為54.23、66.56 J·m-3,枯季層化弱于洪季;(ii)枯季,漲潮時平均勢能差異普遍小于落潮;而洪季,漲潮時平均勢能差異普遍大于落潮,湍流混合存在潮汐不對稱性;(iii)枯季,由橫向、縱向水深平均應變(ΦS-y、ΦS-x)引起的勢能差異變化率的范圍分別是-67~37×10-3、-7~11×10-3 W·m-3;而洪季,相應的范圍分別是-45~30×10-3、-14~13×10-3 W·m-3,ΦS-y均大于ΦS-x,對水體混合與層化的影響更大;(iv)枯季大潮,縱向平流(ΦA-x)、橫向平流(ΦA-y)、縱向水深平均應變(ΦS-x)和橫向水深平均應變(ΦS-y)的潮汐平均絕對值占四項總和之比例分別為26%、33%、18%和23%;而洪季大潮,相應的值的比例分別為13%、9%、22%和56%;枯季,平流項(ΦA-y最大)對混合與層化的控制可能占主導地位;洪季,應變項(ΦS-y最大)可能占主導地位。最后,采用三維有限元TELEMAC-3D水動力模型進行數(shù)值模擬。模擬結(jié)果顯示:(i)彎道橫向次生流存在;(ii)層化在漲潮時弱于落潮時,并且從橫向測線CS6到CS3依次減弱;(iii)枯季大潮,橫向斜壓梯度和fA-y分別在橫向次生流、混合與層化的物理機制中占主導地位。模擬的結(jié)果與實測資料的計算結(jié)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，

本文編號：2480497