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中文核心期刊

SST湍流模型在逆压梯度流动中的改进

IMPROVEMENT OF SST TURBULENCE MODEL IN ADVERSE PRESSURE GRADIENT FLOW

  • 摘要: 逆压梯度和流动分离的正确预测在飞行器设计、发动机设计和机械工程等行业中至关重要。然而,目前在工程界中广泛使用的RANS模型如SA湍流模型等对于逆压梯度的预测往往不尽人意,SST湍流模型虽然引入了Bradshaw假设,考虑了一定的逆压梯度,但是在强逆压梯度下其结果往往也存在一定偏差。本文从SST湍流模型的构造机理和控制方程入手,结合壁面摩擦分解公式,分析模型在逆压梯度下预测分离失准的原因,并指出失准的原因和Bradshaw假设有关,具体表现为Bradshaw假设强制认为湍动能的生成项和耗散项平衡,导致了雷诺应力和湍动能的生成受到限制,流动抵抗分离的能力降低。最后通过局部区域的湍动能的生成项和耗散项之比对结构参数a_1进行一定程度的放缩,提出一种改进的SST湍流模型,利用高斯鼓包、吹吸平板和二维驼峰等案例对改进模型进行了验证。结果表明,针对逆压梯度下的流动分离,改进模型相对原始SST模型在分离、再附点的计算上有更好的预测能力,雷诺应力和湍动能计算也有不同程度的提高。

     

    Abstract: Adverse pressure gradient and flow separation prediction are crucial in industries such as aircraft design, engine design, and mechanical engineering. However, widely used RANS models in the engineering community, such as the SA turbulence model, often perform poorly in predicting adverse pressure gradients. Although the SST turbulence model introduces the Bradshaw assumption, considering a certain degree of adverse pressure gradient, its results are often unsatisfactory under strong adverse pressure gradients. This paper starts from the construction mechanism and control equations of the SST turbulence model, combined with the wall friction decomposition formula, to analyze the reasons for the model's inaccurate prediction of separation under adverse pressure gradients. It points out that the inaccuracy is related to the Bradshaw assumption, specifically manifested in the assumption's forced balance between the production and dissipation terms of turbulent kinetic energy, leading to restrictions on the generation of Reynolds stress and turbulent kinetic energy, and a reduced ability of the flow to resist separation. Finally, by adjusting the structural parameter a_1 based on the ratio of the generation and dissipation terms of turbulent kinetic energy in local regions, an improved SST turbulence model is proposed. The improved model is verified using cases such as Gaussian bumps, blowing/suction plates, and two-dimensional humps. The results show that, for flow separation under adverse pressure gradients, the improved model has better predictive capabilities for separation and reattachment points compared to the original SST model, with varying degrees of improvement in the calculation of Reynolds stress and turbulent kinetic energy.

     

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