方形截面飞行器上仰机动对滚转特性影响的数值模拟

飞行器从中小迎角至大迎角范围内，由于背风区流动分离形态的演化，静态气动特性特别是横侧向气动特性也随迎角显著变化，可能诱发复杂的滚转运动。但飞行器一般是上仰机动时，才从平飞状态快速拉起至大迎角，此机动过程对横侧向气动特性和滚转运动可能产生较大影响。本文发展了刚体动力学方程和Navier-Stokes方程的松耦合求解技术，并通过数值模拟航天飞机脱落碎片的六自由度运动轨迹进行了验证。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迎角下的静态滚转气动特性、自由滚转运动特性，以及上仰机动时不同拉起速率对滚转运动特性的影响。结果表明，对于此飞行器，静态时存在临界迎角约为13°，当迎角小于临界迎角时，滚转方向是静不稳定的，诱发快速滚转运动；当迎角大于临界迎角时，滚转方向是静稳定的，其滚转运动是收敛的。但上仰机动时，滚转运动的形态还与拉起速率相关，即使拉起的终止迎角大于临界迎角，如果拉起速率较慢，也可能出现快速滚转运动。

Numerical simulation of rolling characteristics in nose-up process of square cross section vehicle

The vortex of the flow separation at the leeward site is varying momently as the vehicle pulls up to high angles of attack, which may induce strong unsteady effect of aerodynamics and additional lateral aerodynamics. The vehicle is pulled up rapidly from level-off to high angle of attack flight in the nose-up process, which may has prominent effect on the lateral aerodynamics and the rolling motion. To study the unsteady effect of aerodynamics and its influence to rolling characteristics, the loose couple technique of rigid body dynamic equations and Navier-Stockes equations was developed. The established loose couple technique was then validated by simulating the 6-degree of freedom trajectory of debris shedding from the space shuttle. Taking the square cross section vehicle as example, the steady rolling aerodynamic characteristics, free rolling characteristics and the effect of nose-up process at different speeds to rolling characteristics of the aircraft were studied. The results showed that there was a critical attack angle about 13° existing in the free rolling motion, when the attack angle was greater than the critical attack angle, the vehicle was in rapid rolling motion, and when the attack angle was lower than the critical attack angle, the rolling motion was stable. While in the nose-up process, the rolling characteristics were also affected by the pulling velocity, the vehicle could be in rapid rolling motion under the slow pulling speed even the final attack angle was greater than the critical attack angle.