The non‐reflective interface: an innovative forcing technique for computational acoustic hybrid methods

The present article concerns a commonly used methodology for the numerical simulation of acoustic emission and propagation phenomena. We consider the so‐called multi‐stage hybrid acoustic approach, in which a given noise problem is simulated via a sequence of weakly coupled computations of noise generation and acoustic propagation stages, wherein the simulation of the propagation stage is based on advanced Computational AeroAcoustics (CAA) techniques. The paper introduces an original forcing technique, namely, the Non‐Reflective Interface (NRI), to enable the transfer of an acoustic signal from an a priori noise generation stage into a CAA‐based acoustic propagation phase. Unlike most existing forcing techniques, the NRI is non‐reflective (or anechoic) in nature and, therefore, can properly handle the backscattering effects arising during the noise propagation stage. This attribute makes the NRI‐based weak‐coupling procedure and the associated CAA‐based hybrid approach compatible with a larger variety of realistic noise problems (such as those involving installed configurations in wind tunnel experiments, for instance). The NRI technique is first validated via several test cases of increasing complexity and is then applied to two aerodynamic noise problems. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.     

Computational Aeroacoustics: An Overview of Computational Challenges and Applications

The objective of this paper is to present an overview of recent advances in computational aeroacoustics (CAA). During the last decade, CAA has developed quite independent of computational fluid dynamics (CFD). There are computational issues that are unique to CAA and are, generally, not considered in CFD. In this paper, these issues are discussed and explained. In CAA, there is a great need to resolve high-frequency short waves with the minimum number of mesh points per wavelength. There is also a special need to minimize numerical dispersion and dissipation associated with wave propagation computation. All these have led to the development of large-stencil high-resolution schemes for CAA. A careful examination of dispersion and dissipation errors due to spatial and temporal discretization is provided. These errors are quantified and analyzed in wave number space through the use of Fourier-Laplace transforms. At this time, some of the original computational challenges to CAA have been resolved satisfactorily. A discussion of how some of these computational issues are resolved is presented. Several important CAA applications with interesting or unusual computational innovations are highlighted. Finally, a few of the most pressing outstanding computational challenges to CAA are elaborated.     

吸气式高超声速飞行器动力学建模研究进展

高超声速飞行以及飞行器机身/超燃冲压发动机一体化设计的典型特点导致吸气式高超声速飞行器具有不同于常规飞行器的飞行动力学特性,而飞行器总体设计和控制系统设计都必须考虑这些新动力学特性的影响,因此为吸气式高超声速飞行器建立能够包含这些新特性的飞行动力学模型非常重要.本文对吸气式高超声速飞行器动力学建模的相关研究进行了总结: 首先,简略地回顾了从超燃冲压发动机研究到飞行器系统研究发展历程; 其次,详细阐述了宽飞行包线、高超声速效应、超燃冲压发动机约束、气动/推进耦合和气动弹性效应等吸气式高超声速飞行器的新动力学特性;然后,讨论了在选择坐标系、抽象飞行器外形、建立弹性机身模型、建立空气动力模型、建立超燃冲压发动机系统模型以及推导运动方程等每个具体步骤中需要考虑的问题和可用的方法;最后,评述了现有吸气式高超声速飞行器动力学模型,并指明了未来发展方向.      

Contributions of Computational Aeroacoustics to Jet Noise Research and Prediction

A brief review of recent progress in the field of computational aeroacoustics (CAA) is proposed. This paper is complementary to the previous reviews of Tam [(1995a) “Computational aeroacoustics: issues and methods”, AIAA J. 33(10), 1788–1796], Lele [(1997) “Computational Aeroacoustics: a review”, AIAA Paper 97–0018, 35th Aerospace Sciences Meeting and Exhibit, Reno, Nevada] and Glegg [(1999) “Recent advances aeroacoustics: the influence of computational fluid dynamics”, 6th International Congress on Sound and Vibration, Copenhagen, Danemark, 5–8 July, 43–58] on advances in CAA. After a short introduction concerning the current motivations of jet noise studies, connections between computational fluid dynamics (CFD) and CAA using hybrid approaches are discussed in the first part. The most spectacular advances are probably provided by the direct computation of jet noise, and some recent results are shown in the second part.     

关于气动声学数值计算的方法与进展

气动声学数值计算是近年才出现的研究领域。本文介绍了气动声学数值计算的方法和有关的问题、边界条件的处理以及计算非线性声波的数值方法和进展。讨论了计算气动声学(CAA)的特性及其与计算流体力学(CFD)的差异，指出气动声学数值方法的关键是建立能保持色散关系的差分方程和正确处理无反射边界条件。对于非线性声波传播的问题，为了得到正确的解，应注意提高差分格式对短波的分辨能力，同时发展能抑制“伪”振荡(短波)而对长波基本不起作用的数值方法。     

Research status and trend of wind turbine aerodynamic noise

The main components of the wind turbine aerodynamic noise are introduced. A detailed review is given on the theoretical prediction, experimental measurement, and numerical simulation methods of wind turbine noise, with specific attention to applications. Furthermore, suppression techniques of wind turbine aerodynamic noise are discussed. The perspective of future research on the wind turbine aerodynamic noise is presented.     

CFD contributions to high-speed shock-related problems

Computational Fluid Dynamics (CFD) has contributed extensively to high speed shock-wave research. With study examples by the author’s group in the past, effectiveness of CFD both for design of transportation vehicles and for understanding of fluid physics is discussed. Trends of CFD for further use are then discussed based on recent applications and three key features: computer progress, spectral-like high-resolution schemes and LES and LES/RANS hybrid methods are focused. Recent CFD research reveals that high-speed flows, even the ones considered to be steady state have inherently unsteady nature that requires LES-like computations for successful simulations. Such simulations require remarkably higher grid resolution, but emerging numerical techniques having spectral-like high resolution would help reducing the number of grid points required for such simulations and make them feasible. The paper is summarized by addressing issues of future CFD.     

SWT-120风洞稳定段的性能测量

在普通超音速风洞中,由于受到噪声干扰,很难进行有效的边界层转捩特性试验研究,针对超声速流动特点发展较低噪声风洞十分必要,而稳定段设计的好坏直接影响到下游试验段噪声水平。本文介绍一座低噪声风洞稳定段的结构和性能测量结果。先对稳定段的结构设计做了简单介绍,然后对实验结果进行分析,实验结果表明在大角度扩散段内装置孔锥,稳定段安装消音夹层和阻尼网组等部件后,气流的速度脉动和压力脉动明显降低,其中压力脉动降低一个量级,速度脉动为1%。进一步优化设计和改进工艺,速度脉动还可进一步降低。测量结果表明SWT-120稳定段的设计是成功的,对我们以后发展更高性能的静风洞有借鉴和参考价值。     

Toward accurate hybrid prediction techniques for cavity flow noise applications

A large variety of hybrid computational aeroacoustics (CAA) approaches exist differing from each other in the way the source region is modeled, in the way the equations are used to compute the propagation of acoustic waves in a non-quiescent medium, and in the way the coupling between source and acoustic propagation regions is made. This paper makes a comparison between some commonly used numerical methods for aeroacoustic applications. The aerodynamically generated tonal noise by a flow over a 2D rectangular cavity is investigated. Two different cavities are studied. In the first cavity (L/D=4, M=0.5), the sound field is dominated by the cavity wake mode and its higher harmonics, originating from a periodical vortex shedding at the cavity leading edge. In the second cavity (L/D=2, M=0.6), shear-layer modes, due to flow-acoustic interaction phenomena, generate the major components in the noise spectrum. Source domain modeling is carried out using a second-order finite-volume large eddy simulation. Propagation equations, taking into account convection and refraction effects, are solved using high-order finite-difference schemes for the linearized Euler equations and the acoustic perturbation equations. Both schemes are compared with each other for various coupling methods between source region and acoustic region. Conventional acoustic analogies and Kirchhoff methods are rewritten for the various propagation equations and used to obtain near-field acoustic results. The accuracy of the various coupling methods in identifying the noise-generating mechanisms is evaluated. In this way, this paper provides more insight into the practical use of various hybrid CAA techniques to predict the aerodynamically generated sound field by a flow over rectangular cavities. Copyright © 2009 John Wiley & Sons, Ltd.     

直升机旋翼/机体动稳定性研究进展

首先对直升机旋翼/机体动不稳定性问题的种类进行了简要概述,包括旋翼挥舞/变距、变距/摆振、挥舞/摆振和挥舞/摆振/变距耦合等孤立旋翼动不稳定性问题,以及直升机地面共振和空中共振等旋翼/机体耦合动不稳定性问题,然后分别从气动力与结构的高精度数值模型、动稳定性的计算分析方法和实验模型测试3 个方面详细介绍了直升机旋翼/机体动不稳定性问题的研究现状,并着重讨论了直升机旋翼/机体动稳定性分析技术最近的主要研究方向:耦合CFD(computational fluid dynamics)/CSD(computational structuraldynamics) 的直升机旋翼气弹动稳定性分析、复合材料旋翼动稳定性分析及其材料不确定性影响、带减摆器的旋翼/机体动稳定性分析和先进直升机构型的旋翼/机体动稳定性分析,最后对直升机旋翼/机体动稳定性研究的发展趋势进行了展望.     

Hybrid methods for airframe noise numerical prediction

This paper describes some significant steps made towards the numerical simulation of the noise radiated by the high-lift devices of a plane. Since the full numerical simulation of such configuration is still out of reach for present supercomputers, some hybrid strategies have been developed to reduce the overall cost of such simulations. The proposed strategy relies on the coupling of an unsteady nearfield CFD with an acoustic propagation solver based on the resolution of the Euler equations for midfield propagation in an inhomogeneous field, and the use of an integral solver for farfield acoustic predictions.In the first part of this paper, this CFD/CAA coupling strategy is presented. In particular, the numerical method used in the propagation solver is detailed, and two applications of this coupling method to the numerical prediction of the aerodynamic noise of an airfoil are presented.Then, a hybrid RANS/LES method is proposed in order to perform some unsteady simulations of complex noise sources. This method allows for significant reduction of the cost of such a simulation by considerably reducing the extent of the LES zone. This method is described and some results of the numerical simulation of the three-dimensional unsteady flow in the slat cove of a high-lift profile are presented. While these results remain very difficult to validate with experiments on similar configurations, they represent up to now the first 3D computations of this kind of flow.     

A Zonal RANS/LES Approach for Noise Sources Prediction

Hybrid CFD/CAA methods have generally to be used for the numerical simulation of trailing-edge noise (see [9, 20] for instance). This study focuses on the first step of such hybrid methods, which is to predict the unsteady aerodynamic sources by the mean of a 3D unsteady simulation of the flow. Such a simulation is however generally still away from the numerical capabilities of ‘usual’ supercomputers. This paper investigates the use of a zonal LES method (based on the NLDE – Non-Linear Disturbance Equations – technique) for the numerical prediction of the aerodynamic noise sources. This method makes it possible to perform only zonal LES close to the main elements responsible of sound generation, while the overall configuration is only treated by a RANS approach. Attention will be paid to the specific boundary treatment at the interface between the RANS and LES regions. More precisely, the problem of the generation of turbulent inflow conditions for the LES region will be carefully addressed. The method is first assessed in the simulation of a flat plate ended by a blunted trailing-edge, and then applied to the simulation of the flow over a NACA0012 airfoil with blunted trailing-edge.     

NO_x生成湍流反应率数值模拟的进展

利用计算机数值模拟来优选燃烧器或炉内降低氮氧化物的各种措施,如空气分级,燃料分级（再燃烧）,烟气再循环,煤和生物质混烧等,预测其效果,受到国际上越来越大的重视．如何建立合理而经济的数学模型,是其中的关键问题之一．根据近年来国际上发表的不同研究者的研究结果,对湍流燃烧氮氧化物生成湍流反应率数值模拟的研究现状进行了评述,并且讨论了有待解决的问题和今后的发展方向．     

高速列车头型长细比对气动噪声的影响

高速列车的头尾车外形对气动噪声具有重要的影响.工程实践中随着车速的增加,车辆头部越来越细长,日本高速磁悬浮列车实践中甚至出现了具有极端长细比的头部形状.本文以讨论头型长细比对列车气动噪声的影响规律为出发点,应用非线性声学求解器(NLAS)和FW-H声学比拟法的混合算法,在3种运行速度下对基于CRH380A高速列车头型概化的4种不同头型长细比的模型车的气动噪声进行了数值模拟.给出了不同头型长细比列车的流场特征、气动阻力和气动噪声.结果表明,列车的气动总阻力随头型长细比的增大而减小,且头型长细比对列车总气动阻力的影响随运行速度的增加而增强.而头型长细比对气动噪声的影响呈现出较为复杂的影响,并不存在单调的影响关系;综合考虑气动阻力和气动噪声,长细比最大的头型综合性能较优,但差异并不显著,因此在不考虑微气压波等因素的条件下,简单增加车头长细比并不一定能带来明显的气动噪声性能提升.     

柔性多体系统的计算策略

对柔性多体系统计算建模的研究现状和近期进展进行了总结. 重点讨论了柔性多体 动力学的以下内容: 柔性构件的建模, 约束建模, 求解技术, 控制策略, 耦合问 题, 设计和实验的研究. 对柔性多体系统建模的浮动坐标系,转动坐标系和惯性系 等3种坐标系的特点进行了对比. 指出了未来的研究方向, 包括柔性多体系统的新 的应用,如微观力学系统和超微观力学系统等; 提高这些模型的计算精度和效率的 技巧和策略; 以及可以用于改善柔性多体系统的工具. 本综述文章引用了877篇参 考文献.     

民机机身结构耐撞性研究的进展与挑战

应急着陆场景下的民机耐撞性与乘员安全直接相关,是民机安全性的重要体现,其中机身结构耐撞性是民机结构强度领域内的研究热点。机身结构耐撞性是复杂的非线性冲击动力学问题,涉及到结构的大变形、断裂失效与动态接触等。运输类飞机适航标准对机身结构耐撞性做出了明确规定,要求通过合理的设计,避免乘员承受过于严酷的冲击载荷,维持客舱内大质量体的有效约束,保持乘员的可生存空间以及维持乘员应急撤离通道的可用等,相关的设计需要通过实验方法或经验证的分析方法进行评估。本文对民机机身结构耐撞性研究中的几个关键问题,如紧固件和机械连接结构的冲击动力学行为,高效吸能元件与吸能结构设计方法,机身结构耐撞性评估的实验与数值方法等近年来的研究情况进行了分析,总结了主要研究进展,并分析了当前研究面临的主要挑战。     

叶轮机械气动噪声的研究进展

从机理研究、数值预测和控制方法3方面对叶轮机械气动噪声的研究进展和现状进行综述.主要内容包括: 离散噪声和宽频噪声的机理研究,离散噪声包括叶轮旋转的自身噪声和动静干涉噪声,宽频噪声包括进气畸变噪声、叶顶间隙流动噪声、尾迹噪声、涡脱落噪声;基于声比拟理论的方法在噪声预测方面的应用;有源控制、叶片尾迹控制、非等距叶片和多孔材料等新型噪声控制技术的综述.最后对叶轮机械气动噪声的研究现状进行了总结并对今后的研究工作进行了展望.      

State-of-the-art and prospects for orbital dynamics and control near small celestial bodies

小天体探测是未来深空探测的重点领域之一, 而小天体附近轨道动力学与控制问题是小天体探测任务迫切需要解决的关键问题. 该问题涉及形状不规则小天体附近的动力学环境建模与小天体附近轨道动力学机理. 本文从不规则形状小天体引力场的建模、小天体附近的自然轨道动力学、小天体附近的受控轨道动力学3 个方面综述了小天体附近轨道动力学与控制的研究现状与发展趋势, 并分析了小天体附近轨道动力学所面临的挑战与难题, 最后对我国未来小天体探测任务可能涉及的轨道动力学与控制问题的发展方向进行了展望.