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Search Results: 1 - 10 of 1830 matches for " Computational Aeroacoustics "
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Numerical Modelling of Aerodynamic Noise in Compressible Flows  [PDF]
S?awomir Dykas, Sebastian Rulik, W?odzimierz Wroblewski
Open Journal of Fluid Dynamics (OJFD) , 2012, DOI: 10.4236/ojfd.2012.23007
Abstract: The solution of the AeroAcoustics (CAA) problems by means of the Direct Numerical Simulation (DNS) or even the Large Eddy Simulation (LES) for a large computational domain is very time consuming and cannot be applied widely for engineering applications. In this paper the in-house CFD and CAA codes are presented. The in-house CFD code is based on the LES approach whereas the CAA code is an acoustic postprocessor solving the non-linearized Euler equations for fluctuating (acoustic) variables. These codes are used to solve the aerodynamically generated sound field by a flow over a rectangular cavity with inlet Mach number 0.53.
Optimized difference schemes for multidimensional hyperbolic partial differential equations
Adrian Sescu,Abdollah A. Afjeh,Ray Hixon
Electronic Journal of Differential Equations , 2009,
Abstract: In numerical solutions to hyperbolic partial differential equations in multidimensions, in addition to dispersion and dissipation errors, there is a grid-related error (referred to as isotropy error or numerical anisotropy) that affects the directional dependence of the wave propagation. Difference schemes are mostly analyzed and optimized in one dimension, wherein the anisotropy correction may not be effective enough. In this work, optimized multidimensional difference schemes with arbitrary order of accuracy are designed to have improved isotropy compared to conventional schemes. The derivation is performed based on Taylor series expansion and Fourier analysis. The schemes are restricted to equally-spaced Cartesian grids, so the generalized curvilinear transformation method and Cartesian grid methods are good candidates.
NUMERICAL SIMULATION OF FLOW-INDUCED OSCILLATION AND SOUND GENERATION IN A CAVITY
空腔流激振荡发声的数值模拟研究

Li Xiaodong,Liu Jingdong,Gao Junhui,
李晓东
,刘靖东,高军辉

力学学报 , 2006,
Abstract: 通过求解二维非定常雷诺平均Navier—Stokes方程,对亚音速情况下长宽比为L/D=2的空腔流动进行了计算气动声学数值模拟研究.湍流模型选取标准κ-ε模型,空间离散采用频散相关保持格式,时间积分采用低耗散低频散龙格库塔法,进出口远场边界采用以摄动解为基础的无反射边界条件,计算结果首先与Krishnamurty实验观测的密度场纹影图进行了对比,不论是在腔内流场分布还是腔外辐射指向性上,都与实验结果符合较好;然后与Rossiter公式进行了频率对比,其结果不但较为准确地捕捉到了振荡低阶模态的频率,而且也捕捉到了振荡高阶模态的频率特性,在此基础上研究了边界层厚度对振荡性质的影响,研究表明边界层厚度对振荡幅值影响较大,而且使振荡频率发生小幅偏移,最后探讨了振荡的发声机理,分析了振荡发声及声反馈的过程,发现了空腔前缘的二次发声现象。
计算气动声学中的伽辽金玻尔兹曼方法研究
Study on the Galerkin Boltzmann Method for Computational Aeroacoustics

邵卫东,李军
- , 2016, DOI: 10.7652/xjtuxb201603021
Abstract: 为获得气动声学的高精度和低耗散特性的数值方法,发展了伽辽金玻尔兹曼方法和相应的无反射边界条件。首先,引入新粒子分布函数到格子玻尔兹曼BGK方程中并重构欧拉方程;然后,在空间上采用高精度的交点间断伽辽金有限元方法,在时间上采用显式五级四阶龙格库塔离散方法对解耦得到的对流步方程进行离散求解;最后,通过数值通量构造速度边界、声学硬壁面边界和无反射边界条件。采用包含声反射和多普勒效应的数值算例进行验证,可得模拟值与解析解吻合一致,从而证明了伽辽金玻尔兹曼方法和无反射边界条件用于气动声学计算的有效性和准确性。
To get high??accuracy and low dissipative numerical method in aeroacoustics, Galerkin Boltzmann method and corresponding nonreflecting boundary condition (NRBC) were developed. A modified particle distribution function was introduced to lattice Boltzmann BGK equation in order to reconstruct the Euler equation. After decoupling the collision step from the streaming step, we implemented the high??accuracy nodal discontinuous Galerkin spatial discretization and fourth??order, five??stage Runge??Kutta time marching scheme to solve the resulting advection equation. Velocity boundary condition, acoustically hard wall boundary condition and NRBC were constructed through numerical flux. A benchmark problem including acoustic reflection and Doppler effects was used to test the functionality and accuracy of this method and NRBC. Computational results are in good agreement with the analytical solution, implying that it is a promising method for computational aeroacoustics
Simultaneous measurements of aeroacoustic sounds and wall vibration for exploring the contribution of tooth vibration in the production of sibilant sounds/s/  [PDF]
Masanori Nakamura, Kazunori Nozaki, Haruka Takimoto, Kazuya Nagamune, Motoharu Fujigaki, Shigeo Wada
Journal of Biomedical Science and Engineering (JBiSE) , 2011, DOI: 10.4236/jbise.2011.42011
Abstract: In order to understand the contribution of teeth vibration to the production of sibilant/s/, the pre-sent study was designed to develop a method of simultaneously measuring aeroacoustic sounds and the vibration of an obstacle. To measure the vibration without disturbing flow, the Michelson interferometer was employed. The flow channel, which had an obstacle wall inside of it, was fabricated such that it morphologically mimicked the simplified geometry of the oral cavity. Given airflows at a flow rate of 7.5 × 10–4 m3/s from the inlet, aeroacoustic sounds were generated. A spectrum analy-sis of the data demonstrated two prominent peaks in the sound at 1,300 and 3,500 Hz and one peak in the wall vibration at 3,500 Hz. The correlation in peak frequencies between the sound and wall vibration suggests that the sound at 3,500 Hz was induced by the wall vibration. In fact, the sound amplitude at 3,500 Hz decreased when the obstacle wall was thickened, which increased its rigidity (p < 0.05, t-test). The experimental results demonstrate that the developed techniques are capable of measuring aeroacoustic sound and obstacle wall vibration simultaneously, and suggest the potential to pave the way for detailed analysis of the production of sibilant sounds /s/.
A Numerical Approach to Possible Identification of the Noisiest Zones of a Wall Surface with a Flow Interaction  [PDF]
Tenon Charly Kone, Yann Marchesse, Raymond Panneton
Open Journal of Fluid Dynamics (OJFD) , 2017, DOI: 10.4236/ojfd.2017.74036
Abstract:
This paper examines the use of proper orthogonal decomposition (POD) and singular value decomposition (SVD) to identify zones on the surface of the source that contribute the most to the sound power the source radiates. First, computational fluid dynamics (CFD) is used to obtain the pressure field at the surface of the blade in a subsonic regime. Then the fluctuation of this pressure field is used as the input for the loading noise in the Ffowcs Williams and Hawkings (FW&H) acoustic analogy. The FW&H analogy is used to calculate the sound power that is radiated by the blade. Secondly, the most important acoustic modes of POD and SVD are used to reconstruct the radiated sound power. The results obtained through POD and SVD are similar to the acoustic power directly obtained with the FW&H analogy. It was observed that the importance of the modes to the radiated sound power is not necessarily in ascending order (for the studied case, the seventh mode was the main contributor). Finally, maps of the most contributing POD and SVD modes have been produced. These maps show the zones on the surface of the blade, where the dipolar aeroacoustic sources contribute the most to the radiated sound power. These identifications are expected to be used as a guide to design and shape the blade surface in order to reduce its radiated noise.
高频不稳定燃烧的声学数值仿真
Acoustic numerical simulation of high frequency combustion instability

初敏,徐旭
- , 2015, DOI: 10.13700/j.bh.1001-5965.2014.0527
Abstract: 摘要 高频不稳定燃烧一直是液体火箭发动机研制过程中所要面临的重大难题之一.采用具有低色散低耗散特点的计算气动声学方法,对自燃推进剂变轨发动机(OME)的高频不稳定燃烧进行时域下的数值仿真.由Crocco的压力时滞模型对燃烧热释放和声波之间的耦合进行模拟,并对不同的时滞模型参数对稳定性结果的影响进行了分析,给出发动机的稳定性极限图,确定一阶切向及一阶径向振型为主的不稳定振型,与地面试车实验捕捉到的不稳定振型相一致.结果表明:采用计算气动声学方法对带有Crocco压力时滞模型的声波扰动方程进行时域下的数值求解,可以对发动机的高频不稳定燃烧进行成功地预测.
Abstract:High frequency combustion instability is one of the major issues existed in design process of liquid rocket engine. A time domain numerical simulation was used to predict high frequency combustion instability of hypergolic propellant orbit maneuvering engine (OME) by computational aeroacoustics, which was less dispersive and dissipative. The coupling between unsteady heat release and acoustics was realized by Crocco's pressure time lag model. The effects of different parameters of pressure time lag model on stability were analyzed, and the stability map was obtained. The first order transverse mode and the first order radial mode were recognized as the most dominant instable modes, which were consisted with the instable modes recognized from experimental results of ground test. The results show that high frequency combustion instability can be successfully predicted, when acoustic perturbation equations with Crocco's pressure time lag model are solved in the time domain by computational aeroacoustics.
基于SNGR方法的二维增升装置噪声数值模拟
Numerical Simulation of on Two-Dimensional High Lift Device Noise by SNGR Method

周旺仪,白俊强,余培汛,韩啸
- , 2017,
Abstract: 在大型客机起飞着陆阶段,增升装置噪声成为主要的机体噪声。由于增升装置特殊的气动外形及其与空气相互作用所形成的复杂流场结构,致使其噪声难以预测。除了试验和理论计算方法,数值模拟方法成为研究气动噪声的重要手段。依据随机噪声生成与传播(SNGR)方法的思路,先求解RANS方程得到时均流场解;然后运用随机模型构造声源项;最后采用高精度、低色散的时空格式离散求解非定常声扰动方程。基于SNGR方法建立的声场预测程序对二维增升装置30P30N的声场传播过程进行了模拟,分析了监测点的声压级频谱特性,实现了对声场的快速预测,为二维増升装置的气动、噪声一体化设计奠定了基础。
Noise of high lift device accounts for much in the airframe noise at approach period of airliners. What makes the noise of high lift device hard to predict is the complex geometrical conffiguration and the intricate flow structure. Apart from the means of experimental and theoretical methods, numerical simulation is also a important process to study aero-acoustics. On the basis of the Stochastic Noise Generation and Radiation(SNGR), obtain the time-averaged flow field first, then construct the acoustic source term by stochastic model, and finally solve the acoustic perturbation equation using high-accuracy and low-dispersion time and spatial schemes. A whole noise prediction system based on SNGR method is built, adopting two-dimension high lift device model 30P30N to simulate the acoustic propagation process, and analyzing the Sound Pressure Level frequency spectrum of monitor, thus realizing the fast noise prediction of 2D high lift device and laying foundation for the aerodynamic and acoustic integral design of 2D high lift device
Bluff body flow-induced noise control with sliding plasma actuators
Igor Vinogradov,Xun Huang
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-011-4687-5
Abstract: Sliding plasma actuators were used to control the flow-induced broadband noise radiating from a bluff body. The structure consisted of a cylinder and a torque link that was installed on the lee side of the cylinder. The objective was to reduce the noise generated during the cylinder wake impinging on the torque link. By manipulating cylinder wake with the externally-imposed body force generated by the plasma actuators, the flow-structure interaction was reduced, leading to an attenuation of the broadband noise up to 3 dB in overall sound pressure level at a free stream speed of 30 m/s.
Numerical solution to nonlinear Tricomi equation using WENO schemes
Adrian Sescu,Abdollah A. Afjeh,Carmen Sescu
Electronic Journal of Differential Equations , 2010,
Abstract: Nonlinear Tricomi equation is a hybrid (hyperbolic-elliptic) second order partial differential equation, modelling the sonic boom focusing. In this paper, the Tricomi equation is transformed into a hyperbolic system of first order equations, in conservation law form. On the upper boundary, a new mixed boundary condition for the acoustic pressure is used to avoid the inclusion of the Dirac function in the numerical solution. Weighted Essentially Non-Oscillatory (WENO) schemes are used for the spatial discretization, and the time marching is carried out using the second order accurate Runge-Kutta total-variation diminishing (TVD) scheme.
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