Abstract
For large eddy simulation, it is critical to choose the suitable turbulent inlet boundary condition as it significantly affects the calculated flow field. In this paper, the effect of different inlet boundary conditions, including random method (RAND), Lund method, and divergence-free synthetic eddies method (DFSEM), on the flow in a channel with a hump are investigated through large-eddy simulation. The simulation results are further compared with experimental data. It has been found that turbulence is nearly fully developed in the case based on the Lund method, not fully developed in the case based on DFSEM, and not developed in the case based on the RAND method. In the flow region before the hump, mean velocity profiles in the case applying the Lund method gradually fit the law of the wall as the main flow moves towards the hump, but the simulation results based on the RAND and DFSEM methods cannot fit the wall function. In the flow region after the hump, cases applying Lund and DFSEM methods could relative precisely predict the size of turbulent bubble and turbulent statistics profiles. Meanwhile, the case based on the RAND method cannot capture the positions of flow separation and re-attachment point and overestimates the turbulent bubble size. From this research, it could be found that different turbulent inflow generation methods have a manifested impact on the flow separation and re-attachment after the hump. If the coherent turbulence is maintained in the approach flow, even though turbulent intensity is not large enough, the simulation can still predict the flow separation and turbulent bubble size relative precisely.
Highlights
Atmospheric wind is almost always turbulent and has a strong impact on the aerodynamic loads for objects in the atmospheric boundary layer (ABL), such as wind turbines, ground transportation, high-rise buildings, and many other engineering applications
At the position x/c = 0.65, there is a slight drop of the peak values of u u /Uin f 2 in cases based on the random method (RAND) method, Lund method, and divergence-free synthetic eddies method (DFSEM), respectively, and all peak values from simulations are larger than the experimental data
The results of simulation based on the Lund method and DFSEM are closer to the experimental data than the results of simulation based on the Lund and RAND methods, but the deviation is still large at x/c = 0.65
Summary
Atmospheric wind is almost always turbulent and has a strong impact on the aerodynamic loads for objects in the atmospheric boundary layer (ABL), such as wind turbines, ground transportation, high-rise buildings, and many other engineering applications. Besides the Fourier approach, the synthetic eddies method (SEM) [22] is used to generate inflow turbulence as well This method was based on a three-dimensional correlation of fluctuations with a predefined shape function and demonstrated an improved downstream development compared to other formulations. Xie et al [25] developed the digital method on the basis of the Klein’s work, and this method allows spatially varying turbulence scales on non-uniform grids to be imposed at the inlet based on exponential (rather than Gaussian) velocity correlation functions. This method is used only for the generation of spatially correlated two-dimensional slices of data with a two-dimensional filter [26]. The work provides potential strategies for implementation of IBC methods on the flat plate boundary layer, complex terrain problems and the ABL when using LES as the simulation method [32]
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