Applied Mechanics and Materials Vols. 444-445

Abstract: This paper presents numerical simulation of the vortex flow field with anisotropy turbulence in cyclone dust collector using modified K-ε model and IMPLE algorithm. The axial, radial, tangential velocity field, turbulence kinetic energy K field and turbulent dissipation rate ε field were analyzed in this paper. The calculation results on the order of magnitude and the trend are agreement with the experimental results. The results show that the modified K-ε model for calculating the anisotropy turbulence is suitable.

Abstract: A numerical study using computational fluid dynamics (CFD) under air/water two-phase flow condition without thermal transmission is carried out utilizing the commercial CFD code CFX. A detailed geometry of 5×5 rod bundles with two grid spacers in the Pressurized Water Reactor (PWR) is set up for analyzing. The Multiple Size Group (MUSIG) model based on the population balance equation is employed to describe the characteristic of flow field in which the dispersed phase has a large variation in size, and the breakup and coalescence interaction among different sizes of the bubbles. The effects of the size fraction at inlet, the size group quantities, the breakup and coalescence coefficients, the momentum transfer model, and so on, are studied. The results demonstrate that various parameters and two-phase model have different impacts on the analysis results. The detailed CFD modeling methodology for two-phase flow conditions in PWR fuel assemblies is developed according to the above-mentioned investigations. The flow field patterns and air/water phase distributions in the computational results shows that the two-phase modeling methodology in the present work is reasonable.

Abstract: A robust and practical CFD code has been developed. The numerical framework, so-called VSIAM3 (Volume/Surface Integrated Average based Multi-Moment Method) makes use of two kinds of integrated moments of physical field, i.e. the volume integrated average (VIA) and the surface integrated average (SIA), which are treated as the computational variables and separately updated in time. VSIAM3 formulation is essentially different from conventional finite volume method and provides a convenient and robust framework to accommodate many existing numerical techniques for simulating various complex flows. In this paper, we will present the underlying idea of VSIAM3 and the extensions to make it applicable to various practical problems. Efforts toward high computational performance on hard wares with distributed memory and GPGPU will be also reported.

Abstract: The backtracking of flow occurs easily in cavity of aeration step in spillway tunnel with a gentle bottom slope and ultra-low Frounde number, and this influences the intake of air, so combined with the spillway tunnel of Chang heba Hydropower Station, four bodily form of aeration steps are chosen to be studied by both numerical simulation and model test based on κ-ε turbulence model, they are continuous aeration step, U-type aeration step + local steep slope, continuous aeration step + circular arc type steep slope and continuous aeration step + ogee curve steep slope, the results show that, the downstream bottom slope of aeration step with suitable ogee curve or circular arcs can efficiently inhibit the backtracking of flow in continuous aeration step, and can efficiently eliminate hydrops in cavity and in the same time can improve the efficiency of aeration. Usually, the results of bottom slope with an ogee curve are better than that with a circular arc.

Abstract: A 3D numerical model for incompressible multi-fluid flows has been developed by using a multi-moment finite volume method and an accurate and efficient VOF type scheme for capturing moving interfaces of multi-fluids. The numerical model is validated with the theoretical and experimental results of the benchmark tests of solitary wave and dam break flow, which indicates the adequate numerical accuracy of the model as a practical tool to assess and predict offshore waves and their impacts on coastal structures. Numerical experiments have been systematically conducted to investigate wave breaking phenomena and the impacts on seawalls.

Abstract: It is important for the research of flight characteristics to master the distribution of wind field and the character of turbulence intensity in a complex-terrain mountain. Based on the potential flow theories in fluid dynamics, a numerical simulation method of complex terrain including asymmetrical and symmetrical mountains has been developed in this paper. In particular, asymmetrical mountains are simulated by the combination of two transformed quarter-semiellipsoids. Furthermore, mountain-induced airflow is calculated based on potential flow theory, which could reflect the characteristic of wind field. As an example, the wind field near Dingling airport in Beijing has been simulated and analyzed by this method. The results demonstrate that this method is suitable and accurate for engineering practice, and also applicable for flight dynamics characteristics analysis of aircrafts.

Abstract: In order to investigate the characteristics of unsteady flow in a mixed flow pump guide vane under the small flow conditions, several indicator points in a mixed flow pump guide vane was set, the three-dimensional unsteady turbulence numerical value of the mixed flow pump which is in the whole flow field will be calculated by means of the large eddy simulation (LES), sub-grid scale model and sliding mesh technology. The experimental results suggest that the large eddy simulation can estimate the positive slope characteristic of head & capacity curve. And the calculation results show that the pressure fluctuation coefficients of the middle section in guide vane inlet will decrease firstly and then increase. In guide vane outlet, the pressure fluctuation coefficients of section will be approximately axially symmetrical distribution. The pressure fluctuation minimum of section in guide vane inlet is above the middle location of the guide vane suction surface, and the pressure fluctuation minimum of section in which located the middle and outlet of guide vane. When it is under the small flow operating condition, the eddy scale of guide vane is larger, and the pressure fluctuation of the channel in guide vane being cyclical fluctuations obviously which leads to the area of eddy expanding to the whole channel from the suction side. The middle of the guide vane suction surface of the minimum amplitude pressure fluctuation to which the vortex core of eddy scale whose direction of fluids rotation is the same to impeller in the guide vane adhere.

Abstract: We designed a kind of swirler to produce strong vortex which was inspired by tornado . Focusing on the velocity and pressure distribution of inlet flow within the swirler, we also conducted a series of numerical simulations on the swirler when we set geometric inlet conditions at the bottom ,middle and top of the swirler. The simulation results showed :1 When the geometric inlet condition was set in the middle of the swirler, it would produce the strongest magnitude of vorticity and the highest vacuum degree in the center of vortex compared with other two places.2When we set the geometric inlet condition at the middle of the swirler, it would create reversed swirl flow. We discovered that such kind of reversed swirl flow would enhance the magnitude of main swirl flow vorticity.

Abstract: Because micro-channel has the advantages of small volume, low flow velocity and high efficiency, with the rapid development of miniaturization industry, micro heat sink is widely used. Previous studies have shown that the micro-channel heat transfer performance is mainly determined on its geometric and flow condition, and compared with triangle and trapezoid shape, rectangle structure has better heat transfer performance.Based on the finite element software ANSYS Workbench, micro-channel heat sink with the length of 40mm and different cross-sectional dimension are analyzed numerically, the dimension of micro-channel with smaller pressure drop and high heat transfer is gained. For the optimized model, when a given initial temperature 298K, flow rate of 1.5×10^-4kg/s, the substrate give heat flux as 187500 W/m². The heat flux of 5532W/m² can be dissipated, the pressure drop is reduced to 230.2Pa, and the heat transfer rate is 5.254W, so this micro-channel heat sink has good working performance.

Abstract: A numerical simulation method for the wind field over complex terrain is developed in this paper. The complex terrain is represented by a surface, which is established by the surface spline method basing on the contour line of the map. Then it is divided into panels containing vortex ring singularities. The singularity distribution is solved by combining with the potential flow theory and the boundary condition of terrain surface. Finally, the wind field is simulated by linear superposition of the uniform stream and the induced velocity of vortex rings. A numerical example is studied, and the result indicates that the method proposed in this paper could describe the terrain much more accurately and provide a reasonable result of wind field distribution, but has a simple and efficient procedure, which is suitable for the engineering use in flight dynamics.