Flutter Boundary Prediction of a Two Dimensional Airfoil in Transonic Flight Regime with the Preset Angles of Attack

考虑初始迎角影响的二维翼型跨声速颤振边界预测

¹ School of Aeronautics, Northwestern Polytechnical University, Xi'an 710072, China
² AVIC Aerodynamics Research Institute, Shenyang 110034, China

Received: 22 April 2017

Abstract

Angle of attack has impact on transonic flow filed and aerodynamic force, but most of current researches on flutter use zero angle hypothesis, which has no consideration about angle of attack. Therefore, we use unsteady Reynold Averaged Navier-Stokes (RANS) equation and structural dynamic equation to establish the time domain aeroelastic analysis method. The solution in time domain is the fourth-order implicit Adams linear multi-step method which is based on prediction-correction method. The numerical simulations were used to analyze the transonic flutter boundary of Isogai Case A Model which was based on zero angle condition and nonzero angle respectively. The simulation results show that the reduced flutter speed decreases as the preset angle of attack decreases between 0.73 and 0.76, which shows a 12.5% decrease of the flutter speed at the farthest. Nonzero angle makes the transonic dip weaker and wider than fully turbulent flow. Changing in angle of attack of 6°, the flutter speed in the deepest position of transonic dip has increased by 124% compared to the flutter speed of 0°. Therefore, when flutter characters of airfoil is analyzed, the effects of the initial angle of attack must be taken into account in order to analyze flutter boundary correctly. In other words, increasing the angle of attack offers a way to control the system in terms of delaying flutter.

摘要

目前大多数颤振问题研究主要采用零迎角条件，并未对迎角影响加以考虑，但是来流迎角对跨声速流场和气动力有一定影响。因此，基于非定常雷诺平均N-S方程（Reynolds-averaged Navier-Stokes，RANS）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。对采用零度条件和考虑迎角影响的Isogai案例A模型的跨声速颤振边界进行研究。对跨声速颤振边界预测的结果表明：当0.73 ≤ Ma ≤ 0.76时，随着初始迎角增加，颤振速度减小，最大可减小12.5%；来流初始迎角增加使得跨声速凹坑程度较零度时有所削弱，凹坑范围扩大，自由来流为6°时，跨声速凹坑最低点的颤振速度较0°时增加了124%。因此，在对翼型开展颤振分析时，必须考虑初始迎角影响，从而准确分析颤振边界。同时，增加初始迎角可以作为一种延迟颤振的控制系统。