直升机/加油机耦合流场数值模拟

Numerical simulation of coupled flow field of helicopter/tanker

  • 摘要: 为了研究空中加油过程中加油机尾流对受油直升机的气动干扰,发展了基于RANS方程的直升机/加油机耦合流场数值模拟方法。以A400M运输机和UH-60A直升机为研究对象,分析了孤立加油机尾流场特征、直升机/加油机耦合流场特征以及尾流干扰下直升机气动特性变化,研究表明:加油机尾流场呈现出类螺旋翼尖涡、内螺旋桨滑流、机身尾流和平尾尾流等4类流动特征,在机身后方形成高度非定常的强垂向速度场,通过横向偏移可有效减弱尾流干扰强度;受尾流非定常干扰影响旋翼拉力系数增大约2.5%至4.4%,并伴随明显振荡,旋翼/尾桨操纵力矩波动加剧;对接位置处旋翼尾迹结构变化显著,机身和尾桨对周围流场结构影响有限;尾流在直升机机头附近区域产生的高压强区使得机身俯仰力矩减小约60%且出现强烈振荡;受油管所受的纵横向力矩分别减小约95%和88%,力矩的周期交变特征及垂向力矩的增大(约20%)会加剧其疲劳与变形风险。

     

    Abstract: To investigate the aerodynamic interference caused by tanker wake on helicopter during aerial refueling, a numerical simulation method for the coupled flow field of tanker and helicopter based on the Reynolds-Averaged Navier-Stokes (RANS) equations is developed. The A400M transport aircraft and UH-60A helicopter are used as research subjects to analyze the characteristics of the isolated tanker wake and the coupled helicopter/tanker flow field. Results show that The tanker wake primarily consists of rotating tip vortex, inner propeller slipstreams, fuselage wake, and horizontal tail wake, forming a highly unsteady and strong vertical velocity field behind the tanker fuselage. Notably, lateral offset maneuvers can effectively reduce the turbulence intensity of the wake. The wake-induced upwash leads to an overall increase in the rotor thrust coefficient by approximately 2.5% to 4.4%, accompanied by pronounced fluctuations compared to baseline conditions. Meanwhile, the moment of rotor and tail rotor increase markedly.As the rotor moves laterally toward the docking position, the unsteady disturbances intensify, resulting in more significant tension oscillations. During the standard aerial refueling procedure, the helicopter can generally avoid the strong wake interference area during the traverse phase, with minimal changes observed in both the thrust coefficient amplitude and the rotor thrust distribution. However, at the docking position the influence of wake amplifies vortex energy within the tip vortex, causing a notable enlargement of the vortex structures. Within the rotor disk region, the tip vortex tubes become increasingly deformed and broken. Furthermore, the vortex distribution between the front and rear rotor blades shows asymmetry, with the front blade vortex slightly stronger and tending to spread downward. Under full-configuration simulation condition, the large rotor tilt angle limits the fuselage’s effect on the surrounding flow field. Meanwhile, the presence of tail rotor vortex increases turbulence beneath and behind the fuselage. Compared to the baseline state, the rotor thrust distribution changes significantly: thrust on the forward side of the rotor blades increases sharply, and the tip vortex deformation leads to negative thrust zones appearing near the blade tips. Wake-induced turbulence generates high pressure around the helicopter nose, reducing the fore fuselage pitching moment by about 60% and causing pronounced high-frequency oscillations. This dynamic behavior can adversely affect the helicopter pitch stability during docking maneuvers. The wake decreases structural loads on the receiver hose by roughly 95% and 88% in the longitudinal and lateral directions. However, the cyclically alternating torque fluctuation may accelerate fatigue damage. Simultaneously, the wake increases the vertical torque amplitude on the receiver hose by approximately 20%, which may raise the risk of oscillatory deformation along this direction.

     

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