基于非结构网格CFD技术的旋翼气动噪声计算方法研究

将基于非结构网格技术的旋翼流场CFD计算方法与基于FW-H和Kirchhoff方程的声学方法相结合,建立了一套既适合于直升机旋翼厚度、载荷和桨-涡干扰噪声,又适合于跨声速高速脉冲噪声的综合计算模型。为提高旋翼流场及桨叶表面气动载荷计算的精度,主控方程的求解采用了三维可压非定常的N-S方程,网格划分则使用非结构运动嵌套网格方法。在噪声计算中,通过FW-H方法计算旋翼的厚度噪声和载荷噪声,并选取能够包含流场非线性区域的旋转面作为Kirchhoff积分面,由Kirchhoff方法计算包含四极子项的高速脉冲噪声。应用该模型,以AH-1旋翼为算例,计算了不同飞行状态下的旋翼气动噪声,并与可得到的试验结果进行比较,验证了方法的有效性。然后,着重对两种声学方法对计算结果的影响进行了对比研究,并分析了旋翼厚度噪声、载荷噪声和四极子噪声的特性。     

基于FW-Hpds方法的直升机旋翼气动噪声指向性分析

本文使用基于可穿透数据面的Ffowcs Williams-Hawkings方程(FW-Hpds)的预测方法分析了跨声速直升机悬停旋翼气动噪声的指向性。通过求解三维非定常欧拉方程计算了近场噪声,通过延迟时积分方法和求解FW-Hpds方程计算远场噪声。预测了跨声速UH-1H悬停旋翼的高速脉冲噪声(HSI),然后计算了不同观测点处的声压级,并通过声压级在不同方向上的分布分析了HSI噪声的方向性。根据本文研究发现HSI噪声在桨盘平面上最大,在转轴方向上最小,和其它研究者的结论一致。     

基于涡限制法的旋翼气动噪声计算

在直升机旋翼流动的数值模拟中,流动求解精度对旋翼气动噪声的预测有着重要影响.采用中心格式有限体积法求解可压缩Euler方程数值模拟旋翼绕流,并采用基于Ffowcs Williams- Hawkings( FW-H)方程的声类比方法计算旋翼气动噪声.为了抑制中心格式的数值耗散,保持机翼翼尖以及旋翼桨尖的尾涡结构,引入了涡...     

旋翼翼型-桨尖涡干扰的数值模拟

采用Kirchhoff方法计算NACA0012翼型的远场气动噪声,Kirchhoff面为包围整个翼型的一层网格。首先采用欧拉方程计算程序求解得到翼型的Kirchhoff面上在桨尖涡干扰下的近场气动流场解,再根据Kirchhoff方法求解远场声压。从而体现出在计算桨涡干扰噪声时,旋翼CFD技术与Kirchhoff方法相结合的良好效果。      

新型桨尖抑制旋翼跨声速噪声特性的影响机理分析

为研究不同形式的新型桨尖在抑制旋翼跨声速噪声特性方面的作用机理,以UH-1H模型旋翼为基准,开展了多种后掠和前掠桨尖对旋翼高速脉冲噪声特性的数值分析研究。采用积分形式的可压缩雷诺平均NavierStokes(RANS)方程作为旋翼流场求解控制方程,时间推进方法采用高效的隐式LU-SGS格式,空间方向采用高精度的Roe-MUSCL格式,湍流模型选用Baldwin-Lomax模型。在CFD方法验证基础上,采用基于可穿透旋转积分面的鲁棒性较好的FW-H_pds方程来求解旋翼高速脉冲(high-speed impulsive,HSI)噪声,并通过对UH-1H模型旋翼的跨声速噪声的计算,验证了噪声预测方法的有效性。在此基础上,研究了在不同桨尖马赫数下的旋翼桨尖附近的离域化(delocalization)现象以及高速脉冲噪声特性,通过四极子噪声和单极子噪声的对比分析,揭示了旋翼跨声速噪声产生机理。然后,着重研究了不同外形参数的后掠和前掠桨尖旋翼在抑制旋翼跨声速特性方面的影响规律。计算结果表明:随着桨尖马赫数的增加,旋翼高速脉冲噪声辐射愈加强烈,离域化现象愈加明显;后掠和前掠桨尖旋翼均可以不同程度地减弱激波强度,能有效抑制离域化现象的产生,从而降低旋翼跨声速噪声水平;前掠桨尖旋翼还可以驱使激波位置向桨叶内侧移动,减弱其对桨叶外部空间区域的影响,能更有效地抑制离域化现象的产生。     

低HSI噪声旋翼桨尖外形优化设计方法

建立了一套基于计算流体力学(CFD)/FW-H_pds方程(Ffowcs Williams-Hawkings equations with penetrable data surface)的气动噪声预估技术和组合优化算法的低噪声旋翼桨尖平面外形设计方法。首先,采用积分形式的可压雷诺平均Navier-Stokes(RANS)方程作为旋翼流场求解控制方程,围绕旋翼流场的网格采用嵌套网格方法生成。在优化过程中,桨叶网格生成采用提出的高效参数化的网格自动生成方法。在建立的CFD方法求解基础上,采用基于可穿透旋转积分面的鲁棒性较好的FW-H_pds方程来求解旋翼高速脉冲(HSI)噪声。然后,以降低旋翼HSI噪声为目标,以旋翼悬停气动性能为约束,提出具备前掠-后掠-尖削等组合特征的桨尖外形方案并进行优化分析。将基于拉丁超立方(LHS)方法和径向基函数(RBF)的代理模型方法耦合到遗传算法过程中,建立了一种高效的组合优化算法。在当前的计算状态下,优化后的桨尖外形的负压峰值相比于矩形桨叶降低了58.4%,优化后的桨叶有效地减弱了旋翼桨尖区域的跨声速"离域化"现象,因此可以降低旋翼HSI噪声特性,同时可以减弱旋翼桨尖涡强度达30%,旋翼悬停性能提高了2%~3%。     

悬停状态剪刀式尾桨气动/噪声特性优化分析

建立了一套基于CFD(computational fluid dynamics)方法和FW-H(Ffowcs Williams-Hawkings)方程的剪刀式尾桨气动噪声预估技术和组合优化算法的尾桨外形参数设计方法。基于嵌套网格方法采用雷诺平均Navier-Stokes(RANS)方程作为尾桨流场求解控制方程,采用了一套适用于剪刀式尾桨悬停气动特性模拟的高效CFD方法。在流场分析的基础上,采用FW-H方程预测剪刀式尾桨在典型观察位置处的气动噪声。分别在控制总距以及控制拉力系数不变的情况下,以提高尾桨悬停效率同时降低气动噪声为目标,对剪刀式尾桨的剪刀角和轴间距两个主要外形参数进行优化设计。将基于拉丁超立方(LHS)方法和径向基函数(RBF)的代理模型方法与遗传算法过程相结合,建立了一种有效的组合优化算法。结果表明:剪刀角和轴间距的不同组合可以通过削弱桨-涡干扰现象从而实现降低旋翼桨-涡干扰噪声的目的。在当前的计算状态下,优化得到的剪刀式尾桨的悬停效率比常规尾桨高16%,其平均声压级比常规尾桨降低了2.3 dB。      

基于HHC方法的旋翼噪声抑制机理及参数影响

旋翼桨-涡干扰(BVI)噪声是旋翼气动噪声抑制的主要对象之一。其中,高阶谐波控制(HHC)是一种较为有效的噪声主动抑制方法。为探究HHC方法的降噪效果、降噪机理及参数影响规律,基于嵌套网格生成方法,采用可压雷诺Navier-Stokes方程对流场进行求解,建立了适合于模拟旋翼桨-涡干扰流场的计算流体力学(CFD)数值方法。在流场CFD分析的基础上,采用FW-H(Ffowcs Williams-Hawking)方程预测桨-涡干扰状态下的旋翼噪声,通过对施加高阶谐波控制后的BO-105模型旋翼BVI噪声进行算例验证,得到了一套可以应用于高阶谐波控制下旋翼BVI噪声估算的CFD/FW-H方法。通过对不同HHC方案的数值模拟,发现在直升机斜下降状态下,施加高阶谐波控制后的旋翼BVI噪声能够降低多达4~7dB。进一步,细致分析了HHC方案的控制频率、输入相位以及输入幅值3个参数对旋翼BVI噪声抑制效果的影响,得到了相关参数的影响规律。并且,基于输入幅值对HHC降噪效果的影响规律,对高阶谐波控制方法的降噪机理做出了进一步的说明。     

悬停状态倾转旋翼噪声试验及数值计算

结合消声室试验和数值计算研究了悬停状态倾转旋翼气动噪声特性。消声室试验采用孤立倾转旋翼模型,测试了不同总距角和桨尖马赫数状态的气动噪声数据。数值计算基于CFD(computational fluid dynamic)结合FW-H(Ffowcs Williams-Hawkings)声学方程的方法,采用试验数据验证了计算模型的可靠性。分析了倾转旋翼的噪声传播特点以及拉力系数和桨尖马赫数对噪声总声压级的影响,并对比了孤立旋翼和双旋翼状态的气动噪声特性。结果表明:倾转旋翼噪声随着拉力系数和桨尖马赫数的增加均有所增加,维持旋翼拉力不变时降低桨尖马赫数虽然使得拉力系数增加,旋翼噪声水平仍然降低;倾转双旋翼噪声相对纵向平面对称分布,在多个方位角区域存在着局部最大值,这和双旋翼噪声传播时的相互叠加以及双旋翼间气动干扰相关。      

旋翼桨叶翼型流场和跨音速翼涡干扰噪声研究

基于桨涡干扰流动的噪声场分析了NACA0012翼型的远场气动噪声.采用Euler方程计算了NACA0012、NACA23012、OA207三种翼型的绕流场,选取Kirchhoff面选为包围整个翼型的一层网格,通过得到NACA0012翼型的Kirchhoff面上在桨尖涡干扰流动下的近场解,根据Kirchhoff方法求解远场声压.样例计算分析体现出:在计算桨涡干扰噪声时,旋翼CFD技术与Kirchhoff方法相结合的良好效果.     

Kirchhoff方法在旋翼前飞噪声预测中的应用研究

将CFD(计算流体力学)技术与噪声预测的Kirchhoff方法相结合,发展了前飞状态下直升机旋翼远场气动噪声的定量预测方法,得到了旋翼噪声的时域解。先用具有解析解的“点源”流动代替旋翼流动,通过比较计算值与理论值,验证了该预测方法的可行性和可靠性;尔后针对AH—1／OLS旋翼模型的两种前飞状态进行计算,通过比较计算值与实验值,进一步验证了本文方法及其所发展的程序的正确性。     

Aeroacoustic integral methods,formulation and efficient numerical implementation

The paper makes a contribution to the clearer understanding of the physical meaning and domain of applicability of the Ffowcs Williams–Hawkings (FW-H) and Kirchhoff aeroacoustic integral methods. The analytical relationship between the two approaches, and the physical implications involved in the use of the Kirchhoff approach are discussed. In particular, where the Kirchhoff surface cuts into a domain where non-negligible volume sources of Lighthill's Acoustic Analogy are present (domain crossed by a shock, non-uniform flow or vortices for instance), the Kirchhoff integral must be complemented by additional surface integrals to recover the FW-H surface integral. The paper goes on to describe a fast, robust integration technique for computing FW-H or Kirchhoff surface integrals. This integration technique starts from emission time, and treats each integration surface element as non-compact. It obviates the need to build retarded acoustic surfaces and avoids some of the drawbacks of current methods, such as the Doppler singularity when using supersonically rotating grids. The paper then recalls formulas for calculations in the aircraft reference frame, and the computational efficiency of the proposed integration method is demonstrated by its application to the prediction of helicopter rotor noise directivity contours.     

Numerical analysis on noise of rotor with unconventional blade tips based on CFD/Kirchhoff method

A solver is developed aiming at efficiently predicting rotor noise in hover and forward flight. In this solver, the nonlinear near-field solutions are calculated by a hybrid approach which includes the Navier-Stokes and Euler equations based on a moving-embedded grid system and adaptive grid methodology. A combination of the third-order upwind scheme and flux-difference splitting scheme, instead of the second-order center-difference scheme which may cause larger wake dissipation, has been employed in the present computational fluid dynamics (CFD) method. The sound pressure data in the near field can be calculated directly by solving the Navier-Stokes equations, and the sound propagation can be predicted by the Kirchhoff method. A harmonic expansion approach is presented for rotor far-field noise prediction, which gives an analytical expression for the integral function in the Kirchhoff formula. As a result, the interpolation process is simplified and the efficiency and accuracy of the interpolation are improved. Then, the high-speed impulsive (HIS) noise of a helicopter rotor at different tip Mach numbers and on different observers is calculated and analyzed in hover and forward flight, which shows a highly directional characteristic of the rotor HIS noise with a maximum value in the rotor plane, and the HSI noise weakens rapidly with the increasing of the directivity angle. In order to investigate the effects of the rotor blade-tip shape on its aeroacoustic characteristics, four kinds of blade tips are designed and their noise characteristics have been simulated. At last, a new unconventional CLOR-II blade tip has been designed, and the noise characteristics of the presented CLOR-II model rotor have been simulated and measured compared to the reference rotors with a rectangular or swept-back platform blade tip. The results demonstrate that the unconventional CLOR-II blade tip can significantly reduce the HSI noise of a rotor.     

An adaptive integration surface for predicting transonic rotor noise in hovering and forward flights

In this paper, a new permeable adaptive integration surface is developed in order to evaluate transonic rotor noise in accordance with FW-H_pds equations(Ffowcs Williams-Hawkings equations with penetrable data surface). Firstly, a nonlinear near-field solution is computed on the basis of Navier-Stokes equations, which is developed on moving-embedded grid methodology.The solution calculated through the present CFD method is used as the input for acoustic calculations by FW-H_pds equations. Then, two criteria for constructing integration surfaces are established based on the analysis of the quadrupole source strength and the nonlinear characteristic.A new surface is determined adaptively by the pressure gradient or density in a given flowfield,eschewing the uncertainties associated with determining cylinder-shaped integration surfaces. For varying hover cases, transonic noises are simulated with new integration surfaces for a UH-1 model rotor. Furthermore, numerical results of the new integration surface derived from the density perturbation value conform better to experimental data than results derived from the pressure gradient.Finally, the integration surface given by jrqj being 0.1, which is an applicable criterion obtained from hover cases, is used to predict transonic rotor noise in forward flight. The computational accuracy of the new integration surface method has been validated in predicting transonic rotor noise of an AH-1 model rotor at different advance ratios.     

消失球方法及其对旋翼厚度噪声的分析研究

对旋翼厚度噪声及其数值模拟方法进行了讨论,着重解决了以下两个问题：（1）通过理论和数值分析,讨论了使用消失球公式计算旋翼旋转噪声时计算结果的有效性;（2）通过计算机模拟,深入分析了旋翼厚度噪声的特征。     

Numerical study of the rotor thickness noise reduction based on the concept of sound field cancellation

Numerical studies were performed to investigate the mechanism and potential of several active rotors for reducing low-frequency in-plane thickness noise generated by rotating blades. A numerical method coupling the blade element theory, prescribed wake model and Fowcs Williams-Hawkings(FW-H) equation was established for rotor noise prediction. It is indicated that the excitation force on the blade tip can generate anti-noise that to partly cancel the in-plane thickness noise with an appropriate ...