Investigation On The Characteristics Of Large Scale Coherent Vortex Structures In A Shallow Homogeneous Flow

Large-scale coherent vortex structure is a kind of large-scale specialflow structure originating from a certain momentum resources. Jetsproduced by propellers and cooling water let of underwater vehicles arejust a sort of momentum resources which can evolve into a large-scalestructure with a horizontal scale about1to200km and a duration time ofseveral weeks. Moreover, such momentum resources could be captured byocean remote sensing satellite. Therefore, investigation on the formationand evolution characteristics of such large scale coherent vortex structuresis of great significance in academics and military.On the basis of reviewing and summarizing the recent researchprogresses of this subject, the formation mechanism and evolutioncharacteristics for such large scale coherent vortex structures due tosubmerged round jets are considered. The following work has been carriedout:In Chapter II，numerical simulation and analysis are conducted forthe formation mechanism of a submerged laminar round jet and theevolution characteristics of the mushroom-like vortex structure in adeep-water fluid are investigated based on the incompressibleNavier-Stokes equation. Results show that there exist three distinct stagesin the formation and evolution procedures of such a mushroom-like vortexstructure, including the starting, developing and decaying stages. Inparticular, such a mushroom-like vortex structure has considerableself-similarity in developing stage, and L*, R*and d*display the sameproportional relationship to t*1/2with the non-dimensional time t* regardless of the variations of Reynolds number and injection duration,where three non-dimensional parameters for the mushroom-like vortexstructure, including the length of the jet L*, the radius of themushroom-like vortex R*and the length of vortex circulation d*, areintroduced.In Chapter III, numerical simulation and analysis are conducted forthe formation mechanism of a submerged laminar round jet and theevolution characteristics of the large-scale vortex structure in a shallowwater fluid by use of the numerical method presented in Chapter II. Resultsshow that there occur the collapse and spiral rising of the submerged jet inthe case of the shallow water, and the vortex structure has a good stability,which mainly shows three-dimensional (3D) vortex structure in the case oflow Reynolds numbers. Moreover, the vortex structure losses its stability,which primarily shows quasi two-dimensional (Q2D) features in the caseof high Reynolds numbers, and the length of the jet L*and the radius of thevortex structure R*show the same proportional relationship to t*2/3regardless of the variations of injection duration.In Chapter IV, numerical simulation and analysis are conducted forthe formation mechanism of a submerged turbulent round jet and theevolution characteristics of the large-scale vortex structure in a shallowwater fluid, where the jet procedure of such a turbulent round jet isnumerically simulated by use of the RANS method, while the evolutionprocedure of such a turbulent round jet is numerically simulated by use ofthe LES method with the flow field calculated from the RANS step set asits initial one. Results show that the evolution of the shallow turbulent jetflow has randomness which will weaken for longer jet duration time.Moreover, the quasi two-dimensional (Q2D) features of the large-scalevortex structure will become more remarkable for longer jet duration time,and the longitudinal component is proportional to t*2/3, while the transversecomponent is proportional to t*for the geometry center for the vortexstructure.