Large Eddy Simulation of Unsteady Downburst Outflow Based on Wall Jet Model
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摘要: 为研究边界层风洞中下击暴流大缩尺比试验的可行性，基于冲击射流和壁面射流模型，采用大涡模拟方法，分析了静止和移动下击暴流的风场特性；通过与Wood模型、Oseguera模型、Victory模型以及经典壁面射流实验对比，验证了采用冲击射流和壁面射流模型在模拟稳态下击暴流出流段的一致性和有效性；在壁面射流模型入口处引入3种速度函数，模拟了下击暴流非稳态风速时程. 研究结果表明：与冲击射流一样，无协同流壁面射流能够有效地模拟静止下击暴流的稳态出流段；当冲击射流平移速度为出流速度的15%时，其最大水平风速较静止冲击射流增大了15.8%；协同流速度为射流速度的19.2%时，其最大风速较无协同流壁面射流增大了16.9%，带协同流壁面射流能够有效地模拟移动下击暴流；提出的速度入口函数模型作为壁面射流入流条件，能够较为真实地模拟出Andrews AFB下击暴流非稳态风场.Abstract: The feasibility of a large-scale experiment for downburst in a boundary layer wind tunnel was investigated. Large eddy simulation （LES） was employed to investigate the characteristics of stationary and travelling downburst using the impinging jet and wall jet methods, respectively. The velocity profiles from LES were compared with those obtained from the Wood model, the Oseguera model, the Victory model, and the classical wall jet experiment to verify the reasonableness of the two methods. Then, three time functions of the inlet velocity were used to obtain similar time series of the full-scale data. The results show that the fully-developed velocity profiles of the wall jet cohere with those of the three theoretical models and the classical wall jet experiment. When the translational velocity is 15% of the impinging jet velocity, the maximum horizontal wind speed increased by 15.8% compared to that of the stationary impinging jet, while when the velocity of co-flow is 19.2% of the wall jet velocity, the maximum horizontal wind speed increased by 16.9% compared to that of the wall jet without co-flow. The stationary downburst can be appropriately simulated using the wall jet model without co-flow, while the travelling downburst can be effectively simulated using the wall jet model with co- flow. The results from large eddy simulation （LES） and data obtained from Andrews AFB downburst are in good agreement. The unsteady characteristics of downburst outflow can be perfectly reproduced by the time functions of the velocity inlet.
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Key words:
- downburst /
- wall jet /
- impinging jet /
- numerical simulation /
- wind velocity time series
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图 8 冲击射流距冲击地面点径向距离r = D的速度时程
Figure 8. Time series of imping jet at radial distance r = D
图 10 下击暴流最大平均竖向风剖面对比
Figure 10. Comparison of the maximum vertical velocity profiles of downburst
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