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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-Re_(θt)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。
Laminar flutter flutter in the low Reynolds number range is accompanied by strong aerodynamic nonlinearities and complex viscous effects. Therefore, it is very difficult to predict and analyze this phenomenon. Laminar separation flutter will significantly affect the flight stability of some flying creatures and micro-aircraft, so it is necessary to explore the mechanism of triggering and maintaining vibration so that the occurrence of flutter of this type can be suppressed or even avoided in flight. The unsteady Reynolds averaged Navier-Stokes (RANS) equation and the γ-Reθ (θt) transition model were used to simulate the complex viscous flow over the airfoil surface. A time-domain aeroelastic analysis method was established through the coupled structure motion equation. The structural equation of motion is solved in time domain using the fourth-order implicit Adams linear multi-step method based on the estimation-correction technique. Aeroelastic analysis is used to simulate the laminar flutter flutter response of NACA0012 airfoil. The results show that this method can accurately simulate the laminar flutter flutter phenomenon. The flutter characteristics of laminar flow under different turbulence degrees are compared. Combined with the analysis of instantaneous flow field results, it is found that laminar flow separation is the main factor that triggers and maintains the laminar flutter separation flutter, and the tail vortex shedding at high frequency only increases the aerodynamic Of the nonlinear, and turbulence to such limit ring oscillation (LCO) has a certain degree of inhibition. Comparing the laminar-flow flutter response of airfoils with different thickness and camber, we find that reducing the airfoil thickness or increasing the airfoil camber can restrain laminar flutter flutter.