Spatial and temporal variation of water mass mixing characteristic in the East China Sea

On the basis of the observation data of Kuroshio since 1984 and relative historical data in the East China Sea, spatial and temporal variation of water mass mixing characteristic in the observation area is analysed. The main results are as follows.

Pollutant mixing and transport process via diverse transverse release positions in a multi-anabranch river with three braid bars

A multi-anabranch river with three braid bars is a typical river pattern in nature, but no studies have been conducted to describe mixing characteristics of pollutants in the river. In this study, a physical model of a typical multi-anabranch river with three braid bars was established to explore the pollutant mixing characteristics in different branches. The multi-anabranch reach was separated into seven branches, B1, B2, B3, B4, B5, B6, and BT, by three braid bars. Five tracer release positions located 2.9 m upstream from the inlet section of the multi-anabranch reach were adopted, and the distances from the five positions to the left bank of the upstream main channel were 1/6B, 1/3B, 1/2B, 2/3B, and 5/6B （B is the width of the upstream main channel）, respectively. The longitudinal velocities and pollutant concentrations in the seven branches were measured. The planar flow field and mixing characteristics of pollutants from the bottom to the surface in the multi-anabranch river were obtained and analyzed. The results show that the pollutant release positions are the main influencing factors in the pollutant transport process, and the diversion points and pollutant release positions jointly influence the percentage ratios of the pollutant fluxes in branches B 1, B2, and B3 to the pollutant flux in the upstream main channel.

Large eddy simulation on the flow characteristics of an argon thermal plasma jet

Large eddy simulations based on the CFD software Open FOAM have been used to study the effect of Reynolds number and turbulence intensity on the flow and mixing characteristics of an argon thermal plasma jet.Detailed analysis was carried out with respect to four aspects:the average flow field,the instantaneous flow field,turbulence statistical characteristics and the selfsimilarity.It was shown that for the argon thermal plasma jet with low Reynolds number,increasing the turbulence intensity will increase the turbulent transport mechanism in the mixing layer rather than in the jet axis,leading to the faster development of turbulence.The effect of the turbulent transport mechanism increases with increasing Reynolds number.However,the characteristics of flow and mixing are not affected by turbulence intensity for high Reynolds number situations.It was also found that the mean axial velocity and mean temperature in the axis of the turbulent thermal plasma jet satisfy the self-similarity aspects downstream.In addition,decay constant K is 1.25,which is much smaller than that(5.7-6.1)of the turbulent cold gas jet and has nothing to do with the Reynolds number or turbulence intensity in the jet inlet.

Discrete element simulation of the grain mixing law in brown rice germination device

The discrete element method(DEM)was used in this study to numerically simulate the mixing process and motion law of particles in brown rice germination device.And the reliability of simulation experiments was verified through physical experiments.In the discrete element simulation experiment,there were three mixing stages in the mixing process of the particles.The particle motion conditions at different rotational speeds were rolling,cascading,cataracting and centrifuging.The lower the filling degree,the higher the particle mixing efficiency.The radial trajectory of the particles was approximated as an elliptical helix that continuously shrank towards the axis.The research results indicated that under the same speed and filling conditions,the motion of brown rice particles in both the simulated and physical test environments is rolling and the drop height is the same.

Numerical study of the effect of coflow argon jet on a laminar argon thermal plasma jet

The effects of the velocity and width in coflow argon jet inlet on the flow characteristics of laminar argon thermal plasma jet flowing into the cold air have been studied by the large eddy simulation methods. The Kelvin–Helmholtz instability between argon thermal plasma jet and coflow argon jet causes the transition from a laminar jet to a turbulent jet in the presence of coflow argon jet. Moreover, increasing the velocity and width in coflow argon jet inlet can enhance turbulent transport and provoke coherent structure in the downstream of thermal plasma jet. And the mixing characteristics between argon thermal plasma, coflow argon and ambient air are strengthened. In addition, the width in coflow argon jet inlet has a significant effect on the distribution of temperature in the upstream of thermal plasma jet. It was also found that the transition occurs in advance with the increase of velocity and width in coflow argon jet inlet.

Research on combustion characteristics of scramjet combustor with different flight dynamic pressure conditions

Combustion characteristics in a scramjet combustor equipped with a thin strut were observed and discussed in this paper.A series of numerical simulations were carried out under different flight dynamic pressure conditions.The parameters of cold flow field and combustion field were used to analyze the combustion characteristics.Based on the basic data,the mixing efficiency,characteristics of flame establishment and propagation as well as combustion field characteristics were discussed in this paper.The influence laws of lower dynamic pressure conditions were further revealed to optimize combustor performance.Results indicated that properly reducing the flight dynamic pressure can enhance the mixing of kerosene.The diffusion of kerosene determined the distribution of combustion zone and heat release.Then,the influencing factor that affected the chemical reaction rate was revealed to shorten chemical reaction time.And the higher flight Mach number made the flame propagation velocity faster and the combustion stability stronger.The fuel mixing became the main factor and low dynamic pressure had little effect on laminar flame propagation velocity under high Mach number conditions.The investigations in this paper are helpful for understanding the combustion characteristics under low dynamic pressure conditions.

AN EXPANDED CHARACTERISTIC-MIXED FINITE ELEMENT METHOD FOR A CONVECTION-DOMINATED TRANSPORT PROBLEM

In this paper, we propose an Expanded Characteristic-mixed Finite Element Method for approximating the solution to a convection dominated transport problem. The method is a combination of characteristic approximation to handle the convection part in time and an expanded mixed finite element spatial approximation to deal with the diffusion part. The scheme is stable since fluid is transported along the approximate characteristics on the discrete level. At the same time it expands the standard mixed finite element method in the sense that three variables are explicitly treated： the scalar unknown, its gradient, and its flux. Our analysis shows the method approximates the scalar unknown, its gradient, and its flux optimally and simultaneously. We also show this scheme has much smaller time-truncation errors than those of standard methods. A numerical example is presented to show that the scheme is of high performance.

Effects of Driver Response Time Under Take‑Over Control Based on CAR‑ToC Model in Human–Machine Mixed Traffic Flow

The take-over control(ToC)of human–machine interaction is a hotspot.From automatic driving to manual driving,some factors affecting driver response time have not been considered in existing models,and little attention has been paid to its effects on mixed traffic flow.This study establishes a ToC model of response based on adaptive control of thought-rational cognitive architecture(CAR-ToC)to investigate the effects of driver response time on traffic flow.A quantification method of driver’s situation cognition uncertainty is also proposed.This method can directly describe the cognitive effect of drivers with different cognitive characteristics on vehicle cluster situations.The results show that when driver response time in ToC is 4.2 s,the traffic state is the best.The greater the response time is,the more obvious the stop-and-go waves exhibit.Besides,crashes happen when manual vehicles hit other types of vehicles in ToC.Effects of driver response time on traffic are illustrated and verified from various aspects.Experiments are designed to verify that road efficiency and safety are increased by using a dynamic take-over strategy.Further,internal causes of effects are revealed and suggestions are discussed for the safety and efficiency of autonomous vehicles.

Multi-Component Model of Diesel Sprays Under High Injection Pressure

The combustion efficiency of a diesel engine depends not only on spray characteristics but also on fuel-air mixing characteristics. Based on the original spray model, a new spray model is established in this paper to accurately predict the diesel spray, and then a multi-component evaporation model is added into it. The model takes the influence of component concentration gradient and species on its evaporation rate in the liquid phase into account. This paper studies the spray characteristics(spray penetration, spray angle and spray morphology) and fuel-air mixing characteristics(spray area, spray volume and air entrainment mass) using the spray model, and the results are compared with the experimental results. The comparison shows that the simulated spray penetration and spray angle are close to the experimental results with the average deviations less than 3%. Moreover, this paper studies the spray area, spray volume and air entrainment using empirical formula under different conditions. And the maximum deviations of the spray volume, spray area and air entrainment mass are less than 5% as compared with the test values. Overall, this spray model can predict the diesel spray characteristics and fuel-air mixing characteristics under high injection pressure accurately.

Effect of methane-hydrogen mixtures on flow and combustion of coherent jets

Coherent jets are widely used in electric are furnace （EAF） steelmaking to increase the oxygen utilization and chemical reaction rates. However, the influence of fuel gas combustion on jet behavior is not fully understood yet. The flow and combustion characteristics of a coherent jet were thus investigated at steelmaking temperature using Fluent software, and a detailed chemical kinetic reaction mecha- nism was used in the combustion reaction model. The axial velocity and total temperature of the supersonic jet were measured via hot state experiments. The simulation results were compared with the experimental data and the empirical jet model proposed by Ito and Muchi and good consistency was obtained. The research results indicated that the potential core length of the coherent jet can be prolonged by optimizing the combustion effect of the fuel gas. Besides, the behavior of the supersonic jet in the subsonic section was also investigated, as it is an important factor for controlling the position of the oxygen lance. The investigation indicated that the attenuation of the coherent jet is more notable than that of the conventional jet in the subsonic section.