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1.
预测直升机旋翼气动噪声的新方法   总被引:4,自引:0,他引:4  
本文详细介绍了Kirchhoff方法,并且针对具体计算模型作了相应修改,在求解直升 机旋翼流场的基础上,预测了旅翼在悬停状态下的高速冲击运场噪声,计算结果与理论分析 一致,体现出旋翼CFD与Kirchhoff方法相结合的良好应用前景。  相似文献
2.
In this paper, the dual-reciprocity boundary-element method is used to model acoustic radiation in a subsonic non-uniform-flow field. The boundary-integral formulation is based on a direct boundary-integral equation developed very recently by the authors for acoustic radiation in a subsonic uniform flow. All the terms due to the non-uniform-flow effect are taken to the right-hand side and treated as source terms. The source terms result in a domain integral in the standard boundary-integral formulation. The dual-reciprocity method is then used to transform the resulting domain integral into boundary integrals. Numerical tests show reasonably good agreement with an analytical soution for a pulsating sphere submerged in a potential-flow field.  相似文献
3.
剪切层形态对开式空腔气动噪声的抑制   总被引:2,自引:0,他引:2  
如何抑制开式空腔内的气动噪声是航空研究领域的一个研究热点。采用非线性扰动方程和基于雷诺平均NS方程的湍流人工重构方法对空腔标模进行数值模拟,通过与风洞试验数据的对比,验证了该计算方法的可靠性。基于此,在空腔前缘上方采用不同几何形状的栅板措施,以此来改变空腔前缘的剪切层形态,对比分析其对空腔湍动能、速度型、声源、声压级分布及压力脉动频谱特性的影响,分析可得:仅改变剪切层的方向和强度并不能降低空腔中的声源强度,还需通过改变剪切层的稳定性来影响空腔中声源的分布及强弱,这样才能有效降低流激振荡效果。研究结果表明:采用被动控制措施改变剪切层形态能有效抑制空腔中的气动噪声,其具备一定的工程应用价值。  相似文献
4.
High-speed cinematography of gas-metal atomization   总被引:1,自引:0,他引:1  
A high-speed cinematographic footage of a 304L stainless steel gas atomization, recorded at the National Institute of Standard and Technology (NIST), was analyzed using a discrete Fourier transform (DFT) algorithm. The analysis showed the gas atomization process possesses two prominent frequency ranges of melt oscillation (pulsation). A low-frequency oscillation in the melt flow occurring between 5.41 and 123 Hz, with a dominant frequency at 9.93 Hz, was seen in the recirculation zone adjacent to the melt orifice. A high-frequency melt oscillation range was observed above 123 Hz, and was more prominent one melt-tip-diameter downstream in the melt atomization image than upstream near the melt tip. This high-frequency range may reflect the melt atomization frequency used to produce finely atomized powder. This range also included a prominent high frequency at 1273 Hz, which dominated in the image further away downstream from the melt tip. This discrete high-frequency oscillation is most probably caused by the aeroacoustic “screech” phenomenon, intrasound (<20 kHz), a result of the atomizing gas jets undergoing flow resonance. It is hypothesized that this discrete intrinsic aeroacoustic tone may enhance melt breakup in the atomization process with evidence of this fact in the melt images.  相似文献
5.
气动声学Lighthill方程的Kirchhoff积分解分析   总被引:1,自引:0,他引:1  
Lighthill的声类比(acoustic analogy)是目前气动声定量预测中应用最为广泛的一种方法.使用非齐次波动方程的Kirchhoff积分公式对Ligthhill方程进行求解.Kirchhoff公式中的延迟时间表示不同位置点声源对场点声压叠加时的相位作用,推导时强调延迟时间函数的导数运算.基于Kirchhoff积分公式对于有物体存在于流场中的情况,详细推导了Curle解,并对Curle公式中的各声源项进行了分析.文章有助于气动声学初学者正确地认识声类比理论,加深对Curle公式的理解.  相似文献
6.
不同雷诺数下圆柱绕流气动噪声数值模拟   总被引:1,自引:0,他引:1  
龙双丽  聂宏  许鑫 《声学技术》2011,30(2):111-116
基于大涡模拟和声类比相结合的混合方法对不同雷诺数下二维圆柱绕流的远场气动噪声进行预测。预测值与试验数据吻合良好。根据预测结果分析圆柱绕流气动噪声的声场特性,研究流场振荡规律对远场噪声的影响和圆柱绕流气动噪声的辐射特性,并寻找降低圆柱绕流气动噪声的途径。结果表明:随着雷诺数的增加,远场各测量点的总声压级增大;声场的最大声压级与流场的振荡规律相关;圆柱绕流气动噪声的辐射指向性与偶极子声源的辐射指向性最相似;减小雷诺数或者圆柱表面涡脱落引起的非定常脉动力能够降低圆柱绕流气动噪声。  相似文献
7.
This paper is a review of the present state of understanding of aerodynamically generated noise. Based on an invited lecture given at the Sixth Canadian Congress of Applied Mechanics, Vancouver, May–June 1977, and at the Indian Academy of Science, Bangalore, July 1977  相似文献
8.
分析了掠形叶片轴流叶轮的降噪机理。依据气-固相互作用的声辐射机制,推导了叶片第k叶元体环形运动的声辐射理论,建立了掠形叶片轴流叶轮旋转频率噪声数学模型,并通过实验验证了理论的正确性。  相似文献
9.
Shape optimization is applied to time-dependent trailing-edge flow in order to minimize aerodynamic noise. Optimization is performed using the surrogate management framework (SMF), a non-gradient based pattern search method chosen for its efficiency and rigorous convergence properties. Using SMF, design space exploration is performed not with the expensive actual function but with an inexpensive surrogate function. The use of a polling step in the SMF guarantees that the algorithm generates a convergent subsequence of mesh points in the parameter space. Each term of this subsequence is a weak local minimizer of the cost function on the mesh in a sense to be made precise later. We will discuss necessary optimality conditions for the design problem that are satisfied by the limit of this subsequence. Results are presented for an unsteady laminar flow past an acoustically compact airfoil. Constraints on lift and drag are handled within SMF by applying the filter pattern search method of Audet and Dennis, within which a penalty function is used to form and optimize a surrogate function. Optimal shapes that minimize noise have been identified for the trailing-edge problem in constrained and unconstrained cases. Results show a significant reduction (as much as 80%) in acoustic power with reasonable computational cost using several shape parameters. Physical mechanisms for noise reduction are discussed.  相似文献
10.
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