Investigation on effects of time-frequency characteristics of ship airwake on helicopter flight characteristics

Jinghui Deng

doi:10.1051/jnwpu/20213951087

Abstract

A conventional helicopter flight dynamics model, which can be coupled with ship airwake date, is developed in this study. In the method, the ship airwake data is obtained by the high-accuracy DES model, and a strategy which can transmit CFD data to the flight dynamics model is established based on the "one-way" coupling idea. Then, the SFS2 ship model and UH-60A helicopter are chosen as a combination to investigate the influences of the spatial and temporal characteristics of ship airwake from the aspects of control margins and unsteady level. The time-averaged simulation results show that for the counterclockwise-rotor helicopter, although pilot could have more collective pitch margin under crosswind condition compared to the headwind condition, he might possess much less pedal margin due to the sidewash in the airflow. The unsteady results indicate that the unsteady loading level of the helicopter would increase significantly under the crosswind condition compared to the headwind condition due to the increase of turbulent density in the airwake. Furthermore, for the conventional helicopter, the disturbances on the forces and moments which along the rotor hub (i.e., thrust and yaw moment) are the critical factors that increasing the pilot workload during the landing procedure.

Highlights

A conventional helicopter flight dynamics model, which can be coupled with ship airwake date, is devel⁃ oped in this study
The ship airwake data is obtained by the high⁃accuracy DES model, and a strate⁃ gy which can transmit CFD data to the flight dynamics model is established based on the " one⁃way" coupling idea
The SFS2 ship model and UH⁃60A helicopter are chosen as a combination to investigate the influences of the spatial and temporal characteristics of ship airwake from the aspects of control margins and unsteady level

Summary

Introduction

式中, TbR ,TRH ,THB ,TBE ,TEC 分别为矩阵 TRb ,THR , TBH,TEB 以及 TCE 的逆矩阵。为 7× 106。计算过程中,首先采用 RANS 方法求解定常流场以缩短计算时间,然后继续采用 DES 方法计算非定常舰船流场,5 s 后流场拓扑结构基本稳定,继续计算 30 s 并输出非定常流场数据。将获得的艉流场数据导入到飞行力学模型中,初始的总距、纵 / 横向周期变距值分别为 15.25°,2.36° 和- 2.56°, 计算结果如图 3 所示。可以看到,本文计算得到的旋翼时均拉力变化趋势与 Kääriä 等[16] 的计算结果基本一致。进一步分析时均拉力可以看出,在移动至着舰域中心( y / B = 0.0) 过程中,旋翼拉力减小了 10%,这也与实际着舰飞行试验相符。这充分说明了本文所建立的直升机 / 舰船动态界面数值方法的有效性。量要明显小于 0 WOD 情形,这表明在该情形下,直升机能够具有更多的总距操纵余量。值得注意的是,在 G30 WOD 情形下,流场中的侧洗分量会导致尾桨拉力降低,从而使得该过程中的脚蹬余量大幅降低( 见图 7d) ) 。由于 UH⁃60A 直升机尾桨有 20° 的侧倾角,尾桨拉力的迅速下降( -0.5≤y / B≤0.0) 还会导致低头力矩显著减小,飞行员需要施加向前的纵向操纵杆量使得桨盘前倾以抵消此影响。因此,从图 7c)可以看到,在此范围内直升机配平的纵向杆量迅速减小。

Results

Conclusion