机器学习辅助湍流建模在分离流预测中的应用

Application of machine learning assisted turbulence modeling in flow separation prediction

数据驱动湍流建模是近年来发展的提高雷诺平均N-S方程预测精度的有效手段,通过机器学习算法能够从高置信度数据中自动提取特征,建立准确的从平均流动特征到雷诺应力的预测模型。针对高雷诺数下积冰翼型绕流这一类典型的复杂流动分离问题,基于此前研究者提出的机器学习预测框架,从输入输出特征选择和翼型绕流中数据分布特性两个方面出发,对机器学习预测结果的光滑性和准确性进行改善。提出了基于雷诺应力张量分析和流动特征辨识的输入特征选择准则;提出了局部区域建模方法以及基准模型和机器学习预测模型混合的代入计算方法。将改进方法应用于积冰翼型绕流问题之中,结果表明改进的方法能够准确给出训练集和预测集上的雷诺应力结果,并且代入平均流计算可以得到和真实分布更加接近的流动和机翼表面压力分布。

Data-driven turbulence modeling has been considered as an effective method for improving the prediction accuracy of the Reynolds-averaged Navier-Stokes equations.By using machine learning algorithms such as the artificial neural network,features can be automatically extracted from high-fidelity data,and accurate prediction models from the mean flow characteristics to the Reynolds stress can be established.In this study,focused on the ice-accretion airfoil with the typical complex flow separation phenomenon under high Reynolds numbers,efforts are made in two aspects,i.e.,the input and output feature selection and the data distribution characteristics of flow around an airfoil,to improve the smoothness and accuracy of the machine learning assisted prediction results.An input feature selection criterion based on the Reynolds stress tensor analysis and the flow characteristics identification is proposed,and a zonal modeling method together with a hybrid approach of the benchmark model and the machine learning assisted prediction model is also proposed.Results obtained from the improved method show that the Reynolds stress on both the training dataset and the prediction dataset can be accurately predicted,and the flow separation and pressure distribution on the airfoil agree well with the real situation.