旋翼跨音速噪声发声机理分析及控制方法研究

The rotor high-speed impulsive (HSI) noise is one of the most important helicopter noise sources in high-speed forward flight. The investigations on rotor noise mechanism in forward flight are conducted by analyzing hovering rotor with larger blade-tip Mach number, which is obviously different from the noise mechanism in unsteady environment. Therefore, the transonic noise mechanism of rotor will be revealed and the noise control method will be proposed in the unsteady transonic environment in high-speed flight by numerical simulations in this project. The key and difficult points are as follows: (1) Considering the elastic effect of blade, based on grid self-adaptive strategy, the high-resolution and low-dissipation numerical simulation method which can accurately capture the details of the shock wave / boundary layer interaction and the strong vortex in forward flight will be established. (2) A high-accuracy numerical method for simulating flowfield and sound field of rotor will be established for analyzing the distortion characteristics when the acoustic wave passes through shock wave and other strongly nonlinear regions. The noise mechanism and the propagation properties of the rotor transonic noise will be revealed, and the character parameters reflecting the delocalization phenomena will be presented, as a result, the reliable analysis theory of rotor transonic noise will be established. (3) The action laws of different parameters of blade on reducing transonic noise will be explored, and some noise control methods which are partly verified by experiment will be proposed. As a result, the theoretical foundation t for accurately calculating the transonic rotor noise characteristics and designing low-noise rotor will be established, and the applications of the CFD method and acoustics in aeronautical field will be enlarged.

大速度前飞状态下，旋翼跨音速高速脉冲噪声是直升机主要噪声源之一。关于旋翼前飞非定常跨音速噪声机理研究是采用大桨尖马赫数的悬停旋翼作为研究对象，与实际不符。为此，本项目直接针对直升机前飞状态，通过数值方法，揭示旋翼非定常跨音速噪声发声机理和建立噪声控制方法，涉及的关键点和难点是：(1)考虑桨叶弹性影响，并采用自适应网格技术，建立精确捕捉前飞流场中激波/附面层干扰、强烈漩涡等的高分辨率、低耗散数值模拟方法；(2)发展高精度流场与声场混合计算方法，分析声波穿越激波等强非线性区域的畸变特性，提出旋翼跨音速离域化现象的表征参数，掌握跨音速噪声发声机理和传播特性，形成可靠的旋翼跨音速噪声分析理论；(3)探索桨叶外形参数对降低旋翼跨音速噪声的作用规律，并提出经部分试验验证的旋翼噪声控制方法。为准确计算旋翼跨音速噪声特性及直升机降噪设计打下理论基础，同时扩大计算流体力学和气动声学在航空领域的应用范围。

本项目开展了旋翼跨音速噪声发声机理分析及控制方法研究，针对直升机前飞状态下跨音速高速脉冲噪声传播和辐射的复杂性，在流场数值模拟方法、噪声预估方法、高速脉冲噪声发声机理及噪声抑制方法等方面进行研究，建立了一套适合旋翼高速脉冲噪声的高精度预估分析方法，在此基础上，着重揭示前飞状态下高速脉冲噪声发声机理，依此发展旋翼跨音速噪声抑制方法，并进行了原理性验证试验。.课题为了模拟旋翼非定常跨音速流场的流动细节，建立了一套旋翼非定常跨音速流场的高效高精度数值模拟方法。考虑桨叶弹性变形的影响，并结合自适应网格技术，建立适合旋翼跨音速流场激波/边界层干扰和尾迹涡量模拟的高分辨率、低耗散数值方法。在旋翼跨音速流场的数值模拟基础上，为了获得典型的旋翼流场结构特征，建立了旋翼高速脉冲噪声的高精度预估方法，揭示了旋翼高速脉冲噪声在其复杂流场中的传播规律和畸变特性。进一步通过对旋翼高速脉冲噪声特性的数值模拟，分析了前飞状态非定常流动影响下前行桨叶附近的离域化现象，包括跨音速流动中的激波强度、位置和范围等，探索与噪声传播特性（辐射强度、方向和相位等）之间的关系，揭示了旋翼高速脉冲噪声发声机理。在此基础上，采用建立的数值模拟方法，基于揭示的非定常流动影响下旋翼高速脉冲噪声发声机理，分析了桨尖外形参数（后掠角、下反角、尖削等）对旋翼附近离域化现象发生程度的控制规律，从噪声的辐射强度、方向、频率和相位分析上，提出了旋翼高速脉冲噪声的抑制方法，并进行了初步试验验证研究。