Effect of turbulence intensity and gradient of turbulence intensity on airfoil aerodynamic characteristics at low Reynolds number

低雷诺数条件下湍流度及湍流梯度对翼型气动特性的影响

School of Aeronautics, Northwestern Polytechnical University, Xi’an 710072, China

Received: 29 September 2020

Abstract

Based on the complex flow field of vertical takeoff and landing (VTOL) aircraft with distributed propulsion, the influence of the turbulence intensity and gradient of turbulence intensity on the aerodynamic characteristics of two-dimensional airfoil under low Reynolds number was studied by solving the unsteady Reynolds averaged Navier-Stokes (URANS) Equation based on the c-type structural mesh and γ-Re_θt transition model. The aerodynamic characteristics of NACA0012 airfoil at different turbulence intensities and Reynolds numbers are simulated and compared with the experimental data, which verifies the reliability of the low Reynolds number calculation method. Meanwhile, the effects of the different low Reynolds number and gradient of turbulence intensity on the aero-dynamic characteristics of airfoil are studied, and the effect mechanism of the turbulence on the flow field around airfoil is analyzed. It shows that the flow characteristics of the airfoil with high turbulence or Reynolds number are more stable, the separation bubble size is smaller, the flow separation is delayed, and the stall angle of attack is larger, but the effect of the two mechanisms on the earlier transition is different. The influence of the turbulence gradient on the airfoil is limited by the Reynolds number, and the flow separation, transition and reattachment of the airfoil with high turbulence gradient are advance. The generation and evolution of the laminar separation bubble are closely related to the turbulence intensity and Reynolds number, and its scale and location also affect the aerodynamic characteristics of the airfoil.

摘要

以分布式动力垂直起降（VTOL）飞行器起降时的复杂流场研究为背景，对低雷诺数条件下来流湍流度/湍流梯度对翼型的气动特性影响进行了研究。采用C型结构网格及γ-Re_θt转捩模型求解非定常雷诺平均Navier-Stokes（URANS）方程的方法，对NACA0012翼型在不同湍流度/雷诺数下的气动特性进行了研究，并与实验值进行对比，验证了计算方法的可靠性。研究了不同湍流度、雷诺数及湍流度梯度对翼型气动特性的影响，分析了其对翼型绕流转捩过程产生影响的机理。研究表明，处于较高湍流度或雷诺数的翼型绕流流动特征更加稳定，分离泡尺度更小，流动分离有所推迟，失速迎角更大，但是二者对转捩提前作用的机理不同；湍流度梯度对翼型的气动影响受到雷诺数及湍流度大小的限制，处于较高湍流度梯度的翼型绕流在流动分离、转捩及再附方面均得到了提前；层流分离泡的产生和演化与湍流度及雷诺数大小密切相关，其尺度与位置也影响着翼型的气动特性。