دانلود رایگان مقاله جفت 1D-3D برای شبیه سازی سیستم هیدرولیک گذرا

Abstract

This work describes a coupling between the 1D method of characteristics (MOC) and the 3D finite volume method of computational fluid dynamics (CFD). The coupling method is applied to compressible flow in hydraulic systems. The MOC code is implemented as a set of boundary conditions in the OpenFOAM open source CFD software. The coupling is realized by two linear equations originating from the characteristics equation and the Riemann constant equation, respectively. The coupling method is validated using three simple water hammer cases and several coupling configurations. The accuracy and robustness are investigated with respect to the mesh size ratio across the interface, and 3D flow features close to the interface. The method is finally applied to the transient flow caused by the closing and opening of a knife valve (gate) in a pipe, where the flow is driven by the difference in free surface elevation between two tanks. A small region surrounding the moving gate is resolved by CFD, using a dynamic mesh library, while the rest of the system is modeled by MOC. Minor losses are included in the 1D region, corresponding to the contraction of the flow from the upstream tank into the pipe, a separate stationary flow regulation valve, and a pipe bend. The results are validated with experimental data. A 1D solution is provided for comparison, using the static gate characteristics obtained from steady-state CFD simulations.

5. Conclusion

A 1D–3D coupling method is implemented with the aim of simulating compressible water hammer in hydraulic systems,taking advantage of the benefits of both the 1D and 3D approaches. The 1D region is simulated using MOC and the 3D region is simulated using the finite volume method implemented in an extended version of the sonicLiquidFoam solver of the OpenFOAM open source CFD software. The coupling and the entire MOC code are implemented as a set of boundary conditions in OpenFOAM. The coupling does not require any iterations, and is based on a set of linear equations that can be solved easily. The accuracy and robustness of the coupling are verified by three water hammer cases in a straight constant-area duct, a straight variable-area duct and a bent duct. The coupling is finally applied to a hydraulic system in which the flow is controlled by the difference in elevation between two free surfaces and a closing and opening gate. The results are similar as both the experimental data and 1D MOC results where the gate is included using its numerically determined static characteristics. The main outcomes are as follows: (1) The method accurately captures and transmits the pressure surge at the coupling interface, both from 1D to 3D and from 3D to 1D. The same holds for an interface that couples two 3D regions with a built-in intermediate 1D MOC region. (2) The results are independent of the ratio of mesh size across the coupled interface. (3) The coupling is successfully applied to a hydraulic system where a closing and opening gate is resolved with a dynamic mesh. (4) The coupling interface should be placed at some distance to regions with 3D flow features. For reducing the 3D zone, the interface should be close to the geometrically non-1D region. However, if the interface is too close to the 3D region, the flow at the interface may be non-1D feature that will affect coupling of different scales. We recommend the distance between the coupling interface and the geometrically non-1D region is not less than 5 times of the cross sectional dimension at the interface.