Simulations On The Forcing Effect Of Ununiform Wind Fields To The Hydrodynamic Vortices

Vortex motion as an important part of fluid motion widely exists in the atmosphere, oceans, lakes, and other fluids. Such as the extratropical cyclone, the circumpolar vortex, southwest vortex, the vortices of Meiyu front system, the meso-scale cyclone, typhoons and mesoscale ocean vortex, the vortex in lakes and rivers and so on. The vortex movement not only changes flow field distribution, but also affects the fluid mass and momentum transportation. The generation, maintenance and disappearance of the vortex, the vortex interactions, show up multiscales temporal and spatial status of the general circulation and ocean circulation, and present the characteristics and features of kinematics and dynamics of the atmosphere and ocean, Therefore, to analyze three-dimensional structure of the vortex, to study forcing factor of vortex formation and to investigate the interaction between vortices, and the interaction between vortex and the general circulation are hot topics in dynamic mechanism discussion of the atmosphere, oceans, lakes, and riverThis paper contents come from the project of National Natural Science Foundation of China, focusing on the wind forcing on the water environment, and the interaction between atmosphere and water environment. Using the physical experiments and numerical models to analyze and compare the forcing effects of ununiform wind field on the hydrodynamic vortex, and 3-D dimension structures of the votex driven by wind, and the secondary circulation, and the vortex characteristics of three-dimensional kinematics and dynamics.By Lab experiments, under the forcing of typical ununiform wind field circumstances, the hydrodynamic vortex surface structure, vortex distribution modes and their features.are analysed. The physics experiment can simplify the complex natural environment, highlight the main factors and their functions in nature system, and do linear and non-linear superposition of the factors. In particular, designed typical environment can be repeated for simulation and verification. Therefore, physical experiment is an important way on the vortex. study. During experiment a measurement technique for the surface wind wave and current field is developed, By the video photography measurement method, quantitatively record the surface characteristics of non-uniform wind-driven hydrodynamic vortex. Through the numerical image processing, including a series of procedures, such as image calibration, image recognition, scale calibration etc, and the hydrodynamic vortex surface structure and configuration, and a series of typical vortex circulation modes, driven by ununiform wind can be obtained.Numerical model simulations describ finely and verify in detail the vortex circulation modes, especially in 3-D structure and dynamic characteristics of the vortices and the secondary circulation and The FVCOM regional ocean model with unstructured triangular grids and finite volume method is used to simulate the movement of the vortex under special ununiform wind fields. The three-dimensional (3D)model is based the prediction and primitive equations. Its advantages are in the finite difference method and finite element model. So it can fit shallow and shore coast lines very well, and calculate the original discrete differential dynamic equations easily. And the model can simulate river runoff, which makes it possible to compare the runoff driven vortex with the wind-driven vortex..From comparative analysis of physical experiments and numerical simulation of non-uniform wind-driven hydrodynamic vortex structure and circulation mode, the a few conclusions is followed:(1) The quantitative measurement of physics experiments show that different hydrodynamic vortex modes corresponding to different non-uniform wind-driven. When the non-uniform wind field is stable, the corresponding vortex mode can maintain a long time, and can occur repeatedly in the experiment. When the wind field is strong in the middle and weak in the sides, the water flow show a jet to response to the strong wind zone, and flows reversely back in the weak zone, then forms two vortex. When the wind field have a situation that strong in the edges and weak in the middle, the flow mode has the same direction with wind field in the edge, and the reverse direction weak in the middle, and forms two vortex contrast to the previous. When winds show the alternating distribution of strong and weak, the jet stream appears in wind speed large areas, and flow move back in weak wind speed area, then builds a multiple parallel vortex flow field. The cyclonic and anticyclonic vortex modes are similar to the results of vorticity features of the monsoon on the South China Sea and the meso-eddies in the South China Sea. (2) The surface structure of the hydrodynamic vortex also showed that the flow field is very sensitive to the wind field. The vortex mode transition may occur in the wind field with weak change. The convergence of parallel vortex circulation has the same flow direction, and presents a jet with big speed.. At the both side of the jet stream, the flows show up strong shear. The flow located at divergence zone of parallel vortex circulation is weak, and flow speed and path all weak. It makes intensity differences in different parts of the vortex. The speeds of Water flow and wind speed are with roughly two orders of magnitude difference.(3)The simulation of numerical model shows that the three-dimensional structure of the non-uniform wind-driven hydrodynamic vortex, and match well the physical experimental results. Simulated water surface level decreased at the cyclonic vortex, and increased at the anticyclonic vortex. The convergence and divergence of vortices make the formation of secondary circulation in the vertical direction.(4) Compared with the wind-driven circulation, the runoff-driven circulation is small in scale, and its configuration changes gradually with time. The vortex scale is proportional to the runoff intensity, the surface horizontal component is strong at top levels, and at the lower levels the horizontal component decreased, and the vertical component inceases gradually with height. The difference between the runoff driven vortex and the wind driven vortex is that the runoff vortex happens in uniform density fluids, such as tornado; the wind driven vorteice are results of the interaction between different density fluids, such us cyclonic and anticyclonic circulations and eddies.(5) The surface Circulation quantitative measurement technique is developed during physical experiments, it can be used to quantitatively measurement flow speed for a complex flow surface field with wave and current together. It overcomes the difficult of surface wave scattering when.to measure the random flow field by non-invasive optical measurement technique.