强旋翼尾迹涡干扰对直升机空速测量的影响

Effects of strong rotor wake vortex interference on helicopter airspeed measurement

准确的空速测量对于直升机飞行安全至关重要。本文建立了基于非定常动量源理论的旋翼/机身气动干扰流场数值模拟方法,研究了旋翼尾迹涡干扰对直升机空速测量的影响。以某参考直升机为例,分析了不同旋翼拉力下,空速管布置区在全速度范围内空速值的变化特性。由于旋翼桨叶运动、机身阻滞等影响,不同位置空速管的静压相位和峰值存在差异,其中相位差异受到桨叶激励时刻影响、峰值差异受桨盘载荷与机身阻滞影响。研究也发现并解释了在特定速度段存在的由于旋翼桨尖涡通过空速管区域引起的“空速迟滞”现象。空速管的空速变化可分为下洗流主导区、迟滞区、来流主导区3个区域,对于常规构型直升机迟滞区仅在中低速度段。进一步的参数研究表明:空速管的位置越靠近机身前部、旋翼拉力越小,迟滞区的速度区间越靠前;当靠近机头时空速管并无明显的“迟滞”。最后,本文从气动干扰的角度给出了空速管的布置建议。

Accurate airspeed measurement is crucial for helicopter flight safety.This article establishes a numerical simulation method for the rotor/fuselage aerodynamic interference flow field based on the unsteady momentum source theory and investigates the influence of rotor wake vortex interference on helicopter airspeed measurement.Using a reference helicopter as an example,we analyze the variation characteristics of airspeed values within the entire speed range for different rotor thrusts and airspeed probe locations.Due to factors such as rotor blade motion and fuselage blockage,there are differences in the static pressure phase and peak values at different airspeed probe locations.The phase difference is influenced by the impact of rotor blades,while the peak value difference is affected by the rotor disc load and fuselage blockage.The study also identifies and explains the“airspeed hysteresis”phenomenon caused by rotor tip vortices passing through the airspeed probe area within specific speed ranges.The variation of airspeed in the airspeed probe area can be divided into three regions:the downwash-dominated region,the hysteresis region,and the incoming-flow-dominated region.For conventional configuration helicopters,the hysteresis region occurs only at medium to low speeds.Further analysis of parameter effects suggests that the closer the airspeed probe is to the front of the fuselage and the smaller the rotor thrust,the further forward the speed range of the hysteresis region.When the airspeed probe is positioned near the nose,no significant hysteresis appears.Finally,the article provides recommendations for the placement of airspeed probes from the perspective of aerodynamical interference.