湍流边界层激励下加筋平板振声响应特性研究

船舶、汽车和飞机等高速运动时,其外壳受湍流边界层壁面脉动压力激励而产生的内场声辐射成为该类交通工具自噪声的重要成分。基于模态叠加法计算结构振动响应。采用湍流壁面脉动压力功率谱Corcos模型,计算了外侧气流或水流湍流边界层激励下简支平板振动及内场辐射声,计算值与解析解和试验值吻合良好,验证了算法的有效性。采用湍流壁面脉动压力功率谱改进型Corcos模型,研究了外侧水流湍流边界层激励下平板及板格的振声响应特性,结果表明:水流马赫数低,壁面脉动压力迁移波数大于平板结构弯曲波数,壁面脉动压力波数-频率谱的迁移脊对平板的激励作用可以忽略;横向或纵向加筋对板格振动速度自功率谱级基本无影响;减小板格宽度与长度之比,适当增大板格流向长度可使平板振动辐射声功率在2 000 Hz以上明显降低。     

随机激励下结构振动声辐射的灵敏度分析和优化设计

基于有限元法、边界元法和虚拟激励法,对随机激励下结构振动声辐射灵敏度分析及优化设计问题进行研究.有限元法用于计算结构谐振响应,边界元法用于计算结构振动声辐射,虚拟激励法结合有限元和边界元计算随机激励下结构振动声辐射问题.提出随机激励下结构振动声辐射问题的优化模型及求解算法流程,重点推导了其灵敏度分析公式.数值算例验证了灵敏度分析的准确性及优化求解算法的有效性.     

矩形高层建筑横风向风振动力反应分析计算

从湍流理论的基本方程出发,根据Taylor关于湍流的"冻结"假定,导出了湍流脉动风压谱密度函数的解析计算公式。在分析过程中考虑了压力控制方程源项中全部"紊动-剪切"项的影响。若取用合适的湍流积分尺度,则由此公式得出的横风向脉动风压谱密度函数值与足尺观测数据相吻合。在接近建筑物第一阶自振频率附近谱值函数高于由风洞实验得出的结果。因此根据湍流脉动风压谱密度函数计算得出的结构横风向风振动力反应位移值与加速度值均高于由日本规范公式等计算得出的值。     

离心泵流动诱发振动特性数值计算分析

建立了一种适用于离心泵等叶轮机械流动诱发振动工程计算的数值模型和方法流程。基于URANS方程求解泵内流场,在流场非定常计算过程中输出叶轮所受时域脉动压力,将脉动压力通过FFT转换到频谱并以之作为泵组结构的振动激励源,采用隐式有限元方法进行泵组结构振动响应的计算。计算方法通过测试得到验证,可以用于离心泵流动诱发振动特性的计算评估和低噪声设计。完成了原型和改进型船用海水泵在设计工况下流动诱发振动响应的计算,分析了两型泵流场、振动激励源和振动响应等特性。计算表明,泵的改型设计显著减小泵内压力脉动以及振动激励源,改型泵振动小于原泵。     

立式水泵泵体辐射噪声计算研究

针对水泵的空间噪声,在结构有限元分析的基础上,提出了一种计算水泵在流体脉动压力下辐射声场的方法.考虑流体诱导产生的脉动压力,通过有限元分析计算出泵体表面的振动速度分布,采用直接边界元的方法,计算空间的辐射噪声.这种计算方法可以用来预估水泵的空间辐射噪声声场,具有一定的工程意义.     

水下开口腔体流激振动实验与仿真研究

采用实验与数值计算相结合的方法,研究流体流经开口腔时在开口处的压力脉动规律,以及开口腔在压力脉动作用下的振动特性。研究的内容主要有:通过实验和有限元/边界元方法获得开口腔模型在空气中和水中的模态振型以及频率;在开口腔的孔口后缘10毫米处布置一个压力传感器来测量流速对涡脱落频率的影响,通过开闭孔口的方式确认涡脱落的频率分量;使用大涡模拟计算得到不同流速条件下压力传感器对应位置的压力脉动规律,并与实验结果进行比较验证;在开口腔体侧面布置一个加速度传感器来测量不同流速条件下腔体结构振动情况;以CFD计算得到的压力脉动为输入,使用有限元/边界元方法计算得到加速度传感器对应位置处的加速度值,并与实验结果进行对比分析。     

电厂球磨机筒体辐射声场的计算

本文将噪声预测理论应用到球磨机的降噪工程上,针对球磨机建立了结构和激励简化模型,采用半解析的组合梁函数法求解出振动响应后,结合边界元方法计算了辐射声场分布。计算结果正确预测出近场中低频段的指向性特点和远场声压级水平,与实测谱值有较好的一致性。     

平稳随机振动响应的实数域虚拟激励法

针对时不变平稳系统,建议了计算线性随机振动响应功率谱密度的一种实数域虚拟激励算法。基本原理是根据哈特莱变换与傅里叶变换变换关系构造系统的实数型虚拟激励和实数型系统函数,计算结构的实数型虚拟振动响应,由实数型虚拟激励和虚拟响应计算结果确定系统随机振动响应的功率谱密度。研究结果表明,建议的方法可以方便地处理随机激励间的相关性和相干性,与传统的复数型虚拟激励法相比较,只需确定实数型虚拟激励和在频域计算实数型虚拟响应,就能精确算出结构随机振动响应的功率谱密度,计算形式比较简单和可行。     

西堠门大桥涡激振动特征分析

准确描述涡激振动的风场特征和动力响应特征是实现桥梁振动控制的前提,基于大跨度悬索桥结构健康监测系统获取的风场和振动加速度数据,对比分析了环境振动和涡激振动的风速、风向、湍流强度、阵风系数、脉动风功率谱密度、振动加速度及其功率谱密度的参数特征。结果表明：加劲梁典型的第6阶竖弯涡激振动中的风速可达7.24 m/s～12.24 m/s,风向基本垂直于桥轴向;三向湍流强度、阵风系数和脉动风功率谱在涡激振动中无明显不同于环境振动的特征。不同于多模态耦合的环境振动,涡激振动呈现单模态振动特征;通过功率谱峰值差异率量化该特征可区分环境振动和涡激振动。     

电子球磨机筒体辐射声场的计算

本文将噪声预测理论应用到球磨机的降噪工程上，针对球磨机建立了结构和激励简化模型，采用半解析的组合梁函数法求解出振动响应后，结合边界元方法计算了辐射声场分布，计算结果正确预测出近场中低频段的指向性特点和远场声压级水平，与实测谱值有较好的一致性。     

多风扇主动控制风洞类平板断面抖振力识别研究

针对目前一般的大气边界层物理风洞采用被动格栅产生的紊流脉动风场功率谱密度能量分布难以调整以及积分尺度过小的问题,借助于主动控制方法善于改变来流功率谱及积分尺度的特点,利用日本宫崎大学多风扇主动控制风洞调试出多种宽带紊流风场和谐波脉动风场,采用脉动风速和气动力同步采集监控装置,使用测量稳定性好、精度较高的节段模型高频天平测力方法识别类平板模型的抖振力,对影响模型抖振力的主要参数(积分尺度、紊流度、攻角等)进行分析。     

Effect of the mode of flow in the initial boundary layer on the turbulence attenuation effect in a jet exposed to acoustic irradiation

Based on an analysis of experimental data on high-frequency acoustic excitation of turbulent jets, we investigate the effect of the mode of flow in the boundary layer of the outlet section of the nozzle on realization of the turbulence attenuation effect. It is claimed that high-frequency acoustic excitation of jets leads to a decrease in turbulent fluctuations on the axis of the initial stretch of the jet and to reduction of noise in both initially laminar and initially turbulent boundary layers at the nozzle outlet. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 1, pp. 81–85, January–February, 1998.     

The non-linear evolution of modulated waves in a boundary layer

The series of experiments by Schubauer and Skramstad (1948) provided the first experimental evidence of the role that the instability of Tollmien-Schlichting waves played in the transition of a zero pressure-gradient flat plate boundary layer. The initial experiments studied the oscillations in the boundary layer excited by the freestream fluctuations. This was only possible after the background disturbances in the wind tunnel had been reduced to a very low level. The background wind tunnel environment excited a broad band of amplitude modulated disturbance waves that grew as they propagated downstream, eventually leading to the formation of turbulent spots. Further experiments used artificial two-dimensional harmonic excitation to produce regular wavetrains that could be directly compared with linear theory. Unfortunately, two-dimensional harmonic excitation of this type has also been used in many of the subsequent nonlinear transition investigations; the modulation of the disturbance waves, essential in nonlinear studies, has been largely ignored. Gaster and Grant (1975) used a short duration acoustic pulse to excite the boundary layer and found that the modulated wavepacket that was created admitted bursts of high frequency oscillations. These occurred at amplitudes that were insufficient to generate non-linear behaviour in purely periodic wavetrains. Gaster (1980) suggested that the modulation of the wavepacket played an important role in the non-linear region of transition. This investigation used computer generated deterministic white noise to excite the boundary layer on a flat plate through a single buried loudspeaker. This type of excitation produced amplitude modulated T-S waves at some point downstream from the source. By repeatedly exciting the boundary layer with the same white noise sequence it was possible to map the entire flow-field with a single hot-wire probe and so study the evolution of the modulated wavetrains and the eventual development of turbulent spots. The modulated wavetrains were found to grow initially according to linear theory. But downstream, departures from the linear pattern were observed at isolated time instants. The amplitude of the irregular portions of the signal increased rapidly with downstream distance until bursts of oscillations of frequencies five or six times the basic T-S frequency were observed. These regions developed even higher frequency bursts until a turbulent spot could be considered to have formed. Excitation signals of various amplitudes with different phase relations between the spectral components were used in these experiments. It was found that the phases between the Fourier components played an important role in the highly non-linear behaviour that is the precursor to a turbulent spot. Novel signal processing techniques, such as the wavelet transform and Singular Value Decomposition were used to investigate the fine structure and the propagation characteristics of the high frequency disturbances.     

Turbulence in a Roughness Layer

Consideration is given to a model of turbulent flow in a roughness layer; the model is formed by the equations for turbulent momentum and turbulence-energy density and by free boundary conditions at self-establishing boundaries of the turbulent zone in the entire layer and in roughness cells. The model describes the interactions of the flow with the elements of roughness and the processes in the cells of different scales. Certain calculated characteristics of turbulence in vegetation are given. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 4, pp. 143–151, July–August, 2005.     

The Use of a Honeycomb Surface for Controlling the Boundary Layer

The results are given of an experimental investigation of the boundary layer forming on the wall of a diffusor channel made of a honeycomb structure. The distribution of the averaged velocity and turbulent pulsations and the integral characteristics of the boundary layer are described.     

Boundary layer on a permeable wall with suction of gas

The differential model of turbulence, supplemented with transport equation for turbulent heat flux, is used to perform a numerical investigation of the boundary layer on a permeable wall with suction of gas. It is demonstrated that the protraction of transition from laminar to turbulent mode of flow and the laminarization of the initial turbulent boundary layer occur under conditions of suction of gas. This is evidenced both by the behavior of integral and local characteristics of flow and heat transfer and by the degeneracy of turbulence when the suction of laminar turbulent layer becomes asymptotic. The critical values of the suction parameter are determined.     

Velocity profiles and pressure fluctuations in the boundary layer on the roof of a railway coach

A rake of Pitot tubes was used to measure velocity profiles in the tubulent boundary layer on the roof of an Intercity passenger coach travelling at speeds between 120 and 250 km/h. Results show that the relationship between boundary layer thickness and displacement thickness is similar to that found in the turbulent boundary layer on a flat plate. Problems associated with making measurements of fluctuating pressures within the boundary layer are dicussed, and measurements made by Betzhold and Gahlau within the boundary layer on the roof of an Intercity coach are analyzed. It is found that fluctuating pressures within the fully turbulent region of the boundary layer are identical to those that would be obtained on the surface of a flat plate under the same conditions.     

Influence of an external heat liberation source on separation of the turbulent boundary layer before a flat step

This Letter is devoted to numerical investigation of the effect of the electric discharge on the separation of a turbulent boundary layer before a flat step. Electric discharge is simulated by a heat liberation source of the specified intensity and configuration. It is shown that separation is possible at a sufficiently large discharge power and nonzero bias voltage across the wall.     

颗粒状粗糙元对可蚀性地表的保护作用

应用粗糙壁面附近湍流边界层的阻力分解规律,研究了可蚀性地表上散布的颗粒状粗糙元的防风蚀效应。认为按一定密度散布在地表的颗粒状粗糙元(例如粗沙和砾石等),对抑制风蚀起到了两个关键作用:其一,增大地表盖度以减少暴露面积;其二,削弱了暴露面积上的风阻力。基于这一认识,应用量纲分析原理,建立了地表风蚀率与边界层外风速、粗糙元分布密度之间关系的理论公式,并依据有关实验数据分析了公式的可靠性。