Numerical Simulation of Helicopter Rotor Performance Degradation in Natural Rain Encounter

Guozhi Li,Yihua Cao,Jacopo Serafini

doi:10.1155/2021/5533823

Abstract

Sustained flight operation in the rain conditions is still a challenge to a pilot. This problem can be mainly attributed to the aerodynamic performance degradation of aircraft. In this article, in order to quickly understand the influence of rainfall aiming at the engineering application, an approach to predict helicopter rotor performance degradation in heavy rain encounters is presented. Firstly, we develop a computational fluid dynamics- (CFD-) based method of simulation of the blade airfoil under natural rain scenario and different angles of attack in order to obtain a data-driven basis relating to multiple working conditions of the rotating blades for further analysis. Then, these data are studied using a discretization analysis method of rotor aerodynamics. CFD simulations are conducted, including the case of NACA 0012 airfoil with 10 m chord length, and the case of SC1095 airfoil used in a full-scale rotor of UH-60A helicopter. Prediction of helicopter rotor performance degradation is carried out in a thunderstorm heavy rain with the rain rate of 1500 mm/h using this full-scale rotor. The quantitative results indicate that heavy rain dramatically degrades the rotor performance. The maximum percentage decrease in lift coefficient of this full-scale rotor blade airfoil is reached by 12.75%. The maximum percentage increase in drag coefficient of this full-scale rotor blade airfoil is reached by 26.51%. The maximum percentage decrease in averaging lift-to-drag ratio of this full-scale rotor disk is reached by 26.39%.

Highlights

Rainfall has been considered an important meteorological factor, apart from ice accretion, to threat flight safety [1]
(2) The variation of angle of attack (AOA) has a critical influence on the water film flow on the blade airfoil surface
(3) Because the CFD results show that the water film roughness of the SC1095 airfoil with 0.5273 m chord length is about one order of magnitude smaller than that of the NACA0012 airfoil with 10 m chord length, the variation of the chord length of the airfoil might dramatically affect the water film roughness due to craters and the water film roughness due to water waves

Summary

Introduction

Rainfall has been considered an important meteorological factor, apart from ice accretion, to threat flight safety [1]. There are some similarities and differences between helicopter encountering rainfall and ice accretion These main differences are that the thin water film is flowing in the rain conditions and the thin water film forms into an ice layer that adheres to the blade surface due to thermodynamics effect in the icing conditions. Computational fluid dynamics- (CFD-) based techniques might be only applied to conduct in-depth research on the air-raindrop two-phase flow field for a rotor due to the particularity of the rotor structure These lack the ability to thoroughly study the effects of rainfall on the rotor performance including the distribution of the lift-to-drag ratio of a rotor disk, the rotor torque, and required power. Our present work aims at quickly understanding the influence of rainfall from the perspective of engineering application It serves for rotor engineering design especially for analysis of helicopter flight performance, trim, stability, and controllability in rain conditions

CFD-Based Method

NΨ–1 0 1 2

C RL ain

Results and Discussion

Conclusions