Numerical Research on Performance Prediction for Centrifugal Pumps

Performance prediction for centrifugal pumps is now mainly based on numerical calculation and most of the studies merely focus on one model. Therefore, the research results are not representative. To make an improvement of numerical calculation method and performance prediction for centrifugal pumps, performance of six centrifugal pump models at design flow rate and off design flow rates, whose specific speed are different, were simulated by using commercial code FLUENT. The standard k-t turbulence model and SIMPLEC algorithm were chosen in FLUENT. The simulation was steady and moving reference frame was used to consider the impeller-volute interaction. Also, how to dispose the gap between impeller and volute was presented and the effect of grid number was considered. The characteristic prediction model for centrifugal pumps is established according to the simulation results. The head and efficiency of the six models at different flow rates are predicted and the prediction results are compared with the experiment results in detail. The comparison indicates that the precision of head and efficiency prediction are all less than 5%. The flow analysis indicates that flow change has an important effect on the location and area of low pressure region behind the blade inlet and the direction of velocity at impeller inlet. The study shows that using FLUENT simulation results to predict performance of centrifugal pumps is feasible and accurate. The method can be applied in engineering practice.

Research of the CICC Stability by the Numerical Code Gandalf

The basic approach to computer analysis of the CICC in superconducting Tokamak HT-7U is given and discussed. We will apply a 1-D mathematical model (Gandalf) to investigate the stability of CICC at real operating modes of Tokamak. 1-D model can be directly adopted to follow the evolution of the zone when the energy input is large enough and the coil quenches. In this report, we will analyze the stability of typical CICC (including pure copper) and discuss effect of copper on the stability of CICC.

A Numerical Research on the Influences of the Diurnal Variation of Solar Radiation on the Medium-Range Weather Processes

In this paper, we use a spectral model for the medium-range numerical weather forecast to discuss the impact of the diurnal variation of solar radiation on the medium-range weather processes. Under the tests of two typical winter and summer cases, we find that the influences of the diurnal variation of solar radiation on summer weather are really important, especially on its rainfall, surface heat transport and 500 hPa height field. On winter weather, however, the influences are very weak.

Physical Model of Drying Shrinkage of Recycled Aggregate Concrete

We prepared concretes（RC0, RC30, and RC100） with three different mixes. The poresize distribution parameters of RAC were examined by high-precision mercury intrusion method（MIM） and nuclear magnetic resonance（NMR） imaging. A capillary-bundle physical model with random-distribution pores（improved model, IM） was established according to the parameters, and dry-shrinkage strain values were calculated and verified. Results show that in all pore types, capillary pores, and gel pores have the greatest impacts on concrete shrinkage, especially for pores 2.5-50 and 50-100 nm in size. The median radii are 34.2, 31, and 34 nm for RC0, RC30, and RC100, respectively. Moreover, the internal micropore size distribution of RC0 differs from that of RC30 and RC100, and the pore descriptions of MIM and NMR are consistent both in theory and in practice. Compared with the traditional capillary-bundle model, the calculated results of IM have higher accuracy as demonstrated by experimental verifi cation.

复合材料表面加强时冰层的应力应变状态研究

Ice crossings have been used for several reasons.First,due to the active development of the Arctic shelf,supplies and minerals are provided and transferred on special transports on the surface of ice covers.Second,ice crossings across rivers are used to reduce the length of transport routes.Traditional methods of increasing the load bearing capacity of ice are ice freezing from above,ice freezing from below,and ice strengthening through a wooden copepod flooring.Practical experience shows that the physical and mechanical properties of ice covers are unreliable and changeable in time and strongly depend on various external factors.Therefore,ice covers should be strengthened through alternative methods.Thus,predicting the bearing capacity of ice crossings and exploring methods for their strengthening are important.In this study,we consider the results of experimental and numerical studies on the bearing and deformation capacity of ice beams upon destruction from pure bending.Under pure bending,ice breaks down in the ice crossing when transports move along it.Tests were carried out with a specified reinforcement scheme.The results of the model experiments were compared with numerical calculations in the ANSYS software package.Experiments on ice beams reinforced with various composite materials were also performed.Destruction of samples in all cases occurred as a result of the formation of extensive cracks in the ice caused by the bending moment in the middle of the beam span.Based on the experimental and numerical research results,the use of a surface reinforcement in ice with various materials can increase the bearing capacity from 65%to 99%for this reinforcement scheme.

Numerical research on the mechanism of contaminant release through the porous sediment-overlying water interface

After the pollutant discharged into the river or lake has been reduced, the release of the contaminant from the sediment to the overlying water may cause the river and lake be contaminated again. On the condition that the overlying water flow does not lead to sediment suspension, numerical researches are carried out for the mechanism of contaminant release through the sedimentoverlying water interface. The overlying water flow is calculated as turbulence. The sediment is regarded as isotropic homogeneous porous medium, therefore the seepage field in the porous sediment layer is obtained by solving Darcy＇s equations. Coupled two dimensional steady flows of the overlying water and the pore water in the sediment are calculated. Based on the flow fields obtained, the unsteady contaminant solute transportation process in the pore water in the sediment and the overlying water is numerically simulated, as the shapes of the sediment-overlying water interface are flat or periodic triangular respectively. Numerical results show that the exchange of the pore water and the overlying water is an important factor which decides the release flux of the contaminant from the sediment to the overlying water. The pressure distribution produced by the overlying water flow along the sedimentoverlying water interface, as it is not flat, may induce the seepage of the pore water in the sediment and through the sedimentoverlying water interface, which may increase the release flux of the contaminant from the sediment to the overlying water.

A NUMERICAL RESEARCH OF NONLINEAR BODY-WAVE INTERACTIONS

This paper presents numerical research results of nonlinear body-wave interactions. The body-wave interac- tion is treated as a transient problem with known initial conditions. The development of the flow can be obtained by a time-stepping procedure, in which the velocity potential of the flow at any instant is obtained by utilizing a source density distribution on all boundary surfaces. The Orlanski's method is used to implement the boundary con- dition at the open boundary. The position of intersection points are determined by a direct method. The contents of this paper are: (1) A study of the nonlinear radiation problem of a floating body; (2) A study of nonlinear wave diffraction problem around large structures; (3) Interaction of nonlinear waves with a free floating body; (4) An attempt in generating a numerical wave tank. Pretty good agreement is met between the numerical results and the analytical solution.