低雷诺数下二维翼型层流分离颤振特性

摘要

低雷诺数范围内的层流分离颤振现象伴随着强气动非线性和复杂的黏性效应,因此对该现象进行预测和分析具有很高的难度.层流分离颤振会显著地影响部分飞行生物和微型飞行器的飞行稳定性,所以有必要探究其触发和维持振动的机制,以便可以在飞行中抑制甚至避免该类型颤振的发生.采用非定常雷诺平均Navier-Stokes(RANS)方程和γ-Reθt转捩模型对翼型表面的复杂黏性流动现象进行数值模拟,通过耦合结构运动方程,建立时域气动弹性分析方法,其中结构运动方程采用基于预估-校正技术的四阶隐式Adams线性多步法进行时域推进求解.采用该气动弹性分析方法对NACA0012翼型的层流分离颤振响应进行数值模拟,结果表明,该方法可以准确地模拟层流分离颤振现象.对不同湍流度下的层流分离颤振特性进行对比研究,结合瞬时流场结果分析,发现层流分离是触发和维持层流分离颤振的主要因素,高频的尾涡脱落仅增加了气动的非线性,而湍流对此类极限环振荡(LCO)具有一定程度的抑制作用.对比具有不同厚度和弯度的翼型的层流分离颤振响应,发现适当地减小翼型厚度或者增大翼型弯度可以抑制层流分离颤振.%Highly nonlinear and complex viscous effects occur in laminar separation flutter at low Reynolds numbers ,so it is very difficult to predict and analyze this phenomenon .However ,this phenomenon can affect the flight stability of some flying animals and micro-air vehicles significantly .Therefore ,it is essential for us to investigate the mechanisms of triggering and sustaining oscillations ,in order to suppress and even avoid this type of flutter during flight .The unsteady Reynolds Averaged Navier-Stokes (RANS) equation andγ-Reθt transition model are used to simulate the complex viscous flow phenomena ,and are coupled with the structure motion equation to establish the time domain aeroelastic analysis method .The solution for the time domain is the fourth order implicit Adams linear multi-step method ,which is based on the prediction-correction method . This aeroelastic analysis method is used to simulate the laminar separation flutter responses of the NACA 0012 airfoil .The re-sults indicate that this method can simulate laminar separation flutter accurately .The characteristics of laminar separation flutter at different turbulence intensities have been compared and analyzed .It can be found from transient flow results that laminar separation plays a critical role in initiating and sustaining pitching oscillations ,and the shedding vortex with high fre-quencies enhance only nonlinearity of aerodynamics .Turbulence can inhibit Limit Cycle Oscillation (LCO) to some extent .A comparison of the responses of laminar separation flutter of the airfoils of different thicknesses and cambers shows that lami-nar separation flutter can be suppressed when the thickness of the airfoil decreases or the camber of the airfoil increases properly .