Combining flows often occur in open channel networks of drainage systems and river engineering. Open-channel junction flows were analyzed by solving the depth-averaged two-dimensional, elliptic Reynolds-averaged Navie...Combining flows often occur in open channel networks of drainage systems and river engineering. Open-channel junction flows were analyzed by solving the depth-averaged two-dimensional, elliptic Reynolds-averaged Navier-Stokes equations with the Hanjalic-Launder (H-L) modification to the k-ε turbulence model without the free surface “rigid lid” approximation with an efficient finite-volume procedure. The model can also analyze flows with separation. The model was used to analyze the relative importance of various factors and was compared with laboratory measurements. The H-L modification produced much better simulations of the separation zone size with 20% better accuracy than the standard k-ε model. The H-L modification was then used to study the characteristic of junction flows and the separation zones with different discharge ratios. The simulational results show that separation zone size decreases as the discharge ratio of the upstream main channel to the downstream channel increases.展开更多
The 3-dimensional fluid flow in a water model of the continuous casting tundish is simulated with the k-ε two-equation turbulence model. The methods to decide the size of wall-adjacent grids and the effects of resid...The 3-dimensional fluid flow in a water model of the continuous casting tundish is simulated with the k-ε two-equation turbulence model. The methods to decide the size of wall-adjacent grids and the effects of residuals and mesh size on the simulation accuracy are discussed. The current investigation concludes that the following condition should be satisfied to get accurate enough simulation results: (1) If the dimension of the domain is in the order of cubic meters, the average size of cells in the mesh system should be at least smaller than 30 mm; (2) The normalized non-scaled residual should be reached at least smaller than 10-4.展开更多
As it is almost impossible to carry out the prototype hydro-turbine experiment be- fore the power plant is built up, rational prediction of pressure fluctuations in the prototype turbine is very important at the desig...As it is almost impossible to carry out the prototype hydro-turbine experiment be- fore the power plant is built up, rational prediction of pressure fluctuations in the prototype turbine is very important at the design stage. From this viewpoint, we at first treated the unsteady turbulent flow computation based on the modified RNG k-ε turbulence model through the whole flow passage to simulate the pressure fluctuation in a model turbine. Since fair agreement was recognized between the numerical results and the experimental data, this numerical method was applied to simulate the pressure fluctuations in the prototype turbine. From the comparison of them with the model turbine results, it is seen that their qualitative trend of pres- sure fluctuations are similar, but an appreciable difference is observed between the amplitudes of pressure fluctuation of the prototype turbine and that of the model turbine. Though the present findings may be explained by the effect of Reynolds number, further studies are expected for quantitative interpretation. We paid atten- tion to the interaction between the fluid and turbine structure. Adopting a weak fluid-solid coupling method, we studied the pressure fluctuation in the prototype turbine to clarify how the elastic behavior of runner blades influenced the charac- teristics of pressure fluctuation.展开更多
文摘Combining flows often occur in open channel networks of drainage systems and river engineering. Open-channel junction flows were analyzed by solving the depth-averaged two-dimensional, elliptic Reynolds-averaged Navier-Stokes equations with the Hanjalic-Launder (H-L) modification to the k-ε turbulence model without the free surface “rigid lid” approximation with an efficient finite-volume procedure. The model can also analyze flows with separation. The model was used to analyze the relative importance of various factors and was compared with laboratory measurements. The H-L modification produced much better simulations of the separation zone size with 20% better accuracy than the standard k-ε model. The H-L modification was then used to study the characteristic of junction flows and the separation zones with different discharge ratios. The simulational results show that separation zone size decreases as the discharge ratio of the upstream main channel to the downstream channel increases.
文摘The 3-dimensional fluid flow in a water model of the continuous casting tundish is simulated with the k-ε two-equation turbulence model. The methods to decide the size of wall-adjacent grids and the effects of residuals and mesh size on the simulation accuracy are discussed. The current investigation concludes that the following condition should be satisfied to get accurate enough simulation results: (1) If the dimension of the domain is in the order of cubic meters, the average size of cells in the mesh system should be at least smaller than 30 mm; (2) The normalized non-scaled residual should be reached at least smaller than 10-4.
基金Supported by the National Natural Science Foundation of China(Grant No.90410019)
文摘As it is almost impossible to carry out the prototype hydro-turbine experiment be- fore the power plant is built up, rational prediction of pressure fluctuations in the prototype turbine is very important at the design stage. From this viewpoint, we at first treated the unsteady turbulent flow computation based on the modified RNG k-ε turbulence model through the whole flow passage to simulate the pressure fluctuation in a model turbine. Since fair agreement was recognized between the numerical results and the experimental data, this numerical method was applied to simulate the pressure fluctuations in the prototype turbine. From the comparison of them with the model turbine results, it is seen that their qualitative trend of pres- sure fluctuations are similar, but an appreciable difference is observed between the amplitudes of pressure fluctuation of the prototype turbine and that of the model turbine. Though the present findings may be explained by the effect of Reynolds number, further studies are expected for quantitative interpretation. We paid atten- tion to the interaction between the fluid and turbine structure. Adopting a weak fluid-solid coupling method, we studied the pressure fluctuation in the prototype turbine to clarify how the elastic behavior of runner blades influenced the charac- teristics of pressure fluctuation.
