基于FLOW3D的浊流数值模拟研究

NUMERICAL SIMULATION OF TURBIDITY CURRENTS BASED ON FLOW3D

杨宇平

11849410

硕士

物理学

徐景平

2020-05-29

2020-07-08

哈尔滨工业大学

深圳

海底浊流是将陆源泥沙物质输送到深海沉积的重要载体，是沉积物“源到汇”的重要研究对象。由于浊流的随机性和强大破坏性，导致了实际观测资料的匮乏，因此目前对浊流的流动和沉积特性认识还不是很充足，实验室尺度的浊流研究耗时耗资同时又受时空限制，故而运用数值模拟手段进行浊流理论的研究具有重要的科学意义及一定的经济价值。本研究利用CFD（Computational Fluid Dynamics）软件FLOW3D探究了不同粒径、不同坡度、不同入流机制（突然释放型、连续入流型）条件下的浊流在地形上流动特性和沉积特征。不同粒径条件下浊流流动及沉积数值模拟研究结果表明：不同粒径及含量对突然释放型浊流的形态演化和沉积特征具有重要的影响。由于泥沙颗粒的不同沉降速度，混合粒径大小的改变会大大影响浊流的水动力学特性。在沉积方面，随着时间增加，底床沉积物的总质量增多，离浊流释放较近的位置沉积物量堆积最多且随着距离增加沉积物质量逐渐减少，直至全部沉积完毕，沉积物质量不再变化。由于浊流粗细颗粒的含量比例不同，导致最后浊流完全沉积的位置也会有所差异。在浊流释放初期，地形高程会因浊流头部较大流速的夹带作用，将本该沉积于此位置的沉积物携带向前，地形上形成一个“∽”型，且颗粒越粗，此现象越明显。不同粒径条件下的浊流对地形塑造作用有重要影响。不同坡度条件下浊流流动及沉积数值模拟研究结果表明：在动力方面，实验坡度与浊流的最大流速呈正相关关系。到达平坡时流速更大的浊流在后续运动中衰减更快。在沉积方面，三种坡度浊流流经之后的平坡地形高程变化总体趋势一致，随着距离增加，地形高程逐渐减少，在坡折处坡度较小的泥沙沉积量较多。不同入流机制（突然释放型、连续入流型）条件下浊流流动及沉积数值模拟研究结果表明：在动力方面，突然释放型浊流平均流速大于连续入流型浊流平均流速。连续入流型浊流最大密度主要集中在离入口不远处的位置，且在斜坡上呈现出较稳定均一的状态。突然释放型浊流的底剪切流速最大值出现在前缘部分，然而连续入流型浊流的底剪切流速最大值出现在离入口不远处的位置。在沉积方面，两者在水平地形高程的变化趋势上一致，随着距离增加，地形高程逐渐减小，最终突然释放型浊流沉积距离相较于持续入流型浊流沉积距离更远一些。

Turbidity currents is an important carrier to transport the continental sediment to the deep-sea. It’s also an important research object of sediment "source to sink". Due to the lack of turbidity current actual observation data, the understanding of flow characteristics and sedimentary characteristics of turbidity current also is still not well understood, laboratory scale turbidity current research takes cost, and also has certain limitations. So by means of numerical simulation of turbidity current theory research has important scientific significance and economic value. In this study, CFD (Computational Fluid Dynamics) software FLOW3D was used to explore the flow characteristics and deposition characteristics of turbidity flow under different particle sizes, slopes and inflow mechanisms (sudden-release flow, sustained-inflow).The model results of turbidity currents and deposition under different particle sizes show that particle sizes and contents have important influences on the morphological evolution and sedimentary characteristics of sudden-release turbidity currents. In terms of dynamics, due to the different settling velocity of sediment particles, the change of mixing particle size will greatly affect the hydrodynamic characteristics of turbidity flow. In terms of deposition, with the increase of time, the total mass of sediments in the bottom bed increases, and the sediments near the release of turbidity current accumulate the most, and the sediment mass decreases gradually with the increase of distance, until all the sediments are deposited, the sediment quality will not change any more. Due to the different proportion of coarse and fine particles in turbidity currents, the final position of the complete deposition of the turbidity current will also be different. At the early stage of turbidity current release, the elevation of the topography will be carried forward by the entrapment of the turbidity current with a large velocity at the head of the turbidity current, and the sediment that should have been deposited at this position will form "∽" type on the terrain, and the coarser particles, the more obvious this phenomenon is, which has an important impact on the topography shaping.The model results of turbidity currents and deposition under different slope conditions show that, in terms of dynamics, there is a positive correlation between the experimental gradient and the maximum velocity of turbidity current. The turbidity current with higher velocity decays faster in the subsequent motion when it reaches the flat slope. In terms of sedimentation, the change trend of the elevation of the flat slope after the turbidity currents of the three slopes flows through is consistent, and the elevation of the topography gradually decreases with the increase of the distance. At the slope break, the sediment amount with a small slope is more.The model results of turbidity currents and deposition under different inflow mechanisms (sudden-release flow, sustained-inflow) show that, in terms of dynamics, the advance distance of sudden-release turbidity currents at the same time is always greater than that of sustained-inflow turbidity currents. The maximum density of sustained-inflow turbidity currents is concentrated not far from the entrance and presents a stable and uniform state on the slope. The maximum of the bottom shear velocity of the sudden-release turbidity currents appears in the front of head, while the maximum of the bottom shear velocity of the sustained-inflow turbidity currents appears not far from the entrance. In terms of deposition, both of them are consistent in the change trend of horizontal topographic elevation. As the distance increases, the topographic elevation gradually decreases. Finally, the sudden-release turbidity currents deposition distance is longer than the sustained-inflow turbidity currents deposition distance.

浊流 数值模拟 计算流体力学 FLOW3D 流动特性 沉积特征

turbidity currents numerical modelling Computational Fluid Dynamics FLOW3D flow characteristics sedimentary characteristics

中文

联合培养

南方科技大学

杨宇平. 基于FLOW3D的浊流数值模拟研究[D]. 深圳. 哈尔滨工业大学,2020.