珠江河口东四口门流场结构与涡流研究

珠江河口东四口门径潮比差异较大,潮优型口门虎门与其他三大河优型口门有明显的涨落潮不一致现象,该现象致使珠江河口东四口门附近流场不同于单一口门流场。根据1978年伶仃洋实测水文资料,结合水动力高分辨率数值模拟,研究了口门附近流场结构与涡度分布,发现口门附近是发生涡流的重点区域。口门之间涨落潮不一致及流场动力相互影响,形成涨落潮流路分异及相互挤压,并在岸线和地形边界的作用下易导致涡流发生。1974—2006年岸线变化较为剧烈区域都是涡流发生的重点区域,这说明涡流对浅滩发育演变可能起到一定作用。

Numerical simulation of friction stir butt-welding of 6061 aluminum alloy

A two-dimensional computational fluid dynamics model was established to simulate the friction stir butt-welding of 6061 aluminum alloy. The dynamic mesh method was applied in this model to make the tool move forward and rotate in a manner similar to a real tool, and the calculated volumetric source of energy was loaded to establish a similar thermal environment to that used in the experiment. Besides, a small piece of zinc stock was embedded into the workpiece as a trace element. Temperature fields and vector plots were determined using a finite volume method, which was indirectly verified by traditional metallography. The simulation result indicated that the temperature distribution was asymmetric but had a similar tendency on the two sides of the welding line. The maximum temperature on the advancing side was approximately 10 K higher than that on the retreating side. Furthermore, the precise process of material flow behavior in combination with streamtraces was demonstrated by contour maps of the phases. Under the shearing force and forward extrusion pressure, material located in front of the tool tended to move along the tangent direction of the rotating tool. Notably, three whirlpools formed under a special pressure environment around the tool, resulting in a uniform composition distribution.

Automatic detection of oceanic mesoscale eddies in the South China Sea

This study focuses on the spatial and temporal distribution characteristics of mesoscale eddies in the South China Sea(SCS). An automatic eddy detection method,based on the geometry of velocity vectors,was adopted to obtain an eddy dataset from 21 years of satellite altimeter data. Analysis revealed that the number of anticyclonic eddies was nearly equal to cyclonic eddies; in the SCS,cyclonic eddies are generally stronger than anticyclonic eddies and anticyclonic eddies are larger and longer-lived than cyclonic eddies. Anticyclonic eddies tend to survive longer in the spring and summer,while cyclonic eddies have longer lifetimes in the autumn and winter. The characteristics and seasonal variations of eddies in the SCS are strongly related to variations in general ocean circulation,in the homogeneity of surface wind stress,and in the unevenness of bottom topography in the SCS. The spatial and temporal variation of mesoscale eddies in the SCS could,therefore,be an important index for understanding local hydrodynamics and regional climate change.

A Mathematical Model for the Velocity Profile Internally to a Conical Diffuser

The use of diffusers around the horizontal-axis wind turbines has been widely studied since the diffuser improves the power coefficient of the turbine and it is often called DAWTs （diffuser augmented wind turbines）.Turbines using diffuser are called DWATs （Diffuser Augmented Turbines）,and have efficiency bigger than the Betz limit （maximum energy flow extracted = 59.26%）. Thus, this study presents a mathematical model describing the behavior of the velocity profile internally to a diffuser according to the characteristics of flow and geometry of a conical diffuser. The results are compared with experimental data and show good agreement.

Laws of Jet Mixing of the Swirled Flows in a Pipe

Results of experimental research of the mixing process of coaxial flows in a pipe with swirled peripheral jet are presented in this paper. Distribution of temperature and concentration of gases on the axis and wall of the channel under the influence of such factors as the regime flow, ratio of density of flows and swirl degree of the peripheral jet are studied. Research of temperature, swirl angle, circulation in cross sections along with the channel have shown that their distributions have the jet-like character and are described by known dependences for the layer of mixture.

Wind Tunnel Study on Wind and Turbulence Intensity Profiles in Wind Turbine Wake

In recent years, there has been a rapid development of the wind farms in Japan. It becomes very important to investigate the wind turbine arrangement in wind farm, in order that the wake of one wind turbine does not to interfere with the flow in other wind turbines. In such a case, in order to achieve the highest possible efficiency from the wind, and to install as many as possible wind turbines within a limited area, it becomes a necessity to study the mutual interference of the wake developed by wind turbines. However, there is no report related to the effect of the turbulence intensity of the external flow on the wake behind a wind turbine generated in the wind tunnel. In this paper, the measurement results of the averaged wind profile and turbulence intensity profile in the wake in the wind tunnel are shown when the turbulence intensity of the external wind was changed. The wind tunnel experiment is performed with 500mm-diameter two-bladed horizontal axis wind turbine and the wind velocity in wake is measured by an I-type hot wire probe. As a result, it is clarified that high turbulence intensities enable to the entrainment of the main flow and the wake and to recover quickly the velocity in the wake.

Reynolds number dependence of flow past a shallow open cavity

Measurements were carried out in a shallow open cavity with particle image velocimetry technique.The cavity has a lengthto-depth ratio of 4:1,and the upstream inflow conditions include laminar,transient,and turbulent regimes at seven different Reynolds numbers.The measured instantaneous velocities were analyzed through ensemble average,vortex extraction,and proper orthogonal decomposition(POD)to investigate overall flow circulations,Reynolds stress distribution,spanwise vortex population,and the characteristics of the POD modes.The results reveal distinctive Reynolds number dependence of the cavity flow,e.g.an increase in Reynolds number results in constant migration of the overall circulation,enhancement of Reynolds stress,reduction of correlation between vortex and Reynolds stress,and decrease of fractional energy of the characteristic POD modes.Finally,a phenomenological model was proposed to describe various features of cavity flow.