方形截面弹俯仰振荡对滚转特性的影响

飞行器在大气环境中飞行时,经常受阵风等的干扰,引发非指令的自激振荡,威胁飞行安全.通过建立刚体六自由度运动方程和N-S方程的松耦合求解技术,研究强迫俯仰振荡过程对滚转特性的影响.针对背风区涡流形态及横侧向气动特性复杂的方形截面飞行器,数值模拟研究了其不同攻角下的静态滚转气动特性、自由滚转运动特性,以及俯仰振荡时不同振荡速率对滚转气动和运动特性的影响.结果表明,此飞行器在静态时临界攻角约为13°,当攻角小于临界攻角时,滚转方向是静不稳定的,诱发快速滚转运动;当攻角大于临界攻角时,滚转方向是静稳定,其滚转运动是收敛的.研究发现,俯仰振荡一般会降低飞行器滚转方向静稳定或静不稳定的量值,增强滚转方向的动态稳定性.在俯仰振荡的影响下,即使滚转方向是静不稳定的,如果俯仰振荡的频率足够大,飞行器的滚转运动也可能是收敛的.

NUMERICAL STUDY OF THE EFFECT OF FORCED PITCHING OSCILLATION ON ROLLING CHARACTERISTICS OF VEHICLE 1)

The vehicle may be induced uncommanded oscillation by the disturbance of the gust, this phenomenon would increase the risk of the flight. To study the influence of forced pitching oscillation on rolling characteristics of a square cross section vehicle, the loose couple technique of rigid body dynamic equations and Navier-Stockes equations were developed, and then the steady rolling aerodynamic characteristics, free rolling characteristics and the effect of pitching oscillation at different frequencies on rolling characteristics of the aircraft were studied. The steady results showed that there was a critical attack angle about 13° existing in the free rolling motion, when the attack angle was lower than the critical attack angle, the vehicle was in rapid rolling motion, and when the attack angle was greater than the critical attack angle, the rolling motion was convergent. The results also showed that, the forced pitching oscillation would decrease the level of rolling static instability (stability) as the vehicle was static instable (stable), and increase the level of rolling dynamic stability no matter the vehicle was stable or instable. In the influence of high frequency pitching oscillation, the rolling motion can be convergent even if the vehicle was static instable.