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1.
姜楠 《力学与实践》1999,21(3):67-68
用热膜测速仪测量水槽中平板湍流边界展,用条件采样方法中的mu-level法和VITA法检测壁湍流相干结构的猝发过程,认识壁湍流相干结构猝发过程中的速度信号变化特征.  相似文献   

2.
用自相关法确定VITA法的门限K   总被引:1,自引:1,他引:0  
姜楠  王振东  舒玮 《实验力学》2000,15(1):30-35
研究了用VITA条件采样方法壁湍猝发的门限值与壁湍流猝发平均周期之间的关系,根据用壁湍流流向脉动速度自相关函数检测得到的壁湍流猝发平均周期,确定壁,湍猝发VITA条件采样的门限值K。  相似文献   

3.
固壁温度对壁湍流相干结构的影响   总被引:2,自引:0,他引:2  
石建军  舒玮 《力学学报》1997,29(1):17-23
用半导体元件对平板进行加热,用VITA法和mu-level法两种条件采样技术研究了固壁温度对湍流相干结构的影响,改进了Tiederman等人提出的“归组”方法,并且用“归组”的VI-TA法和mu-level法研究了固壁加热对湍流猝发平均周期的影响.实验结果表明,固壁加热使得湍流脉动速度均方根值变大,条件采样检测到的事件数量增多,但猝发周期维持不变  相似文献   

4.
姜楠 《力学与实践》1999,21(3):67-68,70
用热膜测速仪测量水槽中平板湍流边界层,用条件采样方法中的mu-level法和VITA法检测壁湍流相干结构的猝发过程,认识壁湍流相干结构猝发过程中的速度信号变化特征。  相似文献   

5.
姜楠  王立坤 《实验力学》1999,14(2):165-169
研究了用条件采样方法检测壁湍流相干结构的门限值与壁湍流相干结构平均粹发周期检测结果之间的关系,根据用壁湍流流向脉动速度自相关函数检测壁湍流相干结构平均猝发周期的方法,提出了用自相关法确定壁湍流相干结构条件采样的门限值,从而检测壁湍流相干结构的方法  相似文献   

6.
壁面加热湍流相干结构的实验研究   总被引:1,自引:1,他引:0  
姜楠  王玉春  刘欣 《实验力学》2001,16(2):127-134
用热线风速仪测量了风洞中壁面加热平板湍流边界层不同法向位置的流向脉动速度,用条件采样方法中的m-u-level法和VITA法研究了壁面加热对壁湍流相干结构猝发条件平均波形的影响,发现壁面另热能够提高猝发强度,缩短喷射时间,使一次猝发中出现多次喷射事件的现象明显增多,增强猝发的间歇性。  相似文献   

7.
刘薇  赵瑞杰  姜楠 《实验力学》2008,23(1):17-26
用IFA300恒温热线风速仪和×形二分量热线探针,以采样间隔小于最小湍流时间尺度的分辨率,精细测量了风洞中平板湍流边界层不同法向位置的瞬时流向、展向速度分量的时间序列信号.用子波分析辨识壁湍流相干结构猝发事件的能量最大准则,确定壁湍流相干结构猝发事件的时间尺度;用条件相位平均技术提取了相干结构猝发过程中流向、展向脉动速度分量条件相位平均波形,用互相关方法研究了相干结构猝发过程中流向、展向脉动速度分量条件相位平均波形的相位差关系及其对雷诺应力的影响,发现在缓冲层和对数律区,展向脉动速度与流向脉动速度的条件相位平均波形具有不同的相位;当两者相位基本一致时,雷诺应力达到正的最大值,此时湍流相干结构的产生非常活跃;当两者相位差分别集中在90°和270°附近时,雷诺应力的幅值减小并接近于零,此时湍流相干结构的产生和猝发都得到了抑制.  相似文献   

8.
用VITA法检测壁湍流喷射事件的归组问题   总被引:1,自引:0,他引:1  
姜楠  安海玲 《实验力学》1999,14(4):509-514
用子波分析和能量最大准则解决了VITA法检测壁湍流猝发中的喷射事件的归组问题  相似文献   

9.
夏振炎  姜楠  王振东  舒玮 《力学学报》2006,38(6):741-748
采用热线风速仪测量受吹吸扰动的壁湍流边界层的流向速度,用傅里叶变换和子波变换研究 吹吸扰动对壁湍流能谱的影响,结果显示施加的低频扰动使边界层内层大尺度结构的能量减 少,小尺度结构的能量有所增强,远离壁面时扰动强度逐步衰减直到在外层中消失;通过VITA 法和子波变换法检测猝发事件,表明该扰动降低了猝发强度,使猝发周期延长,条件平均速 度波形的幅值降低、持续时间变短,说明扰动明显抑制了相干结构的猝发过程. 利用子波变 换可以实现湍谱分析,能有效检测猝发中的湍流结构,是一种客观的分析工具.  相似文献   

10.
姜楠  舒玮 《实验力学》1997,12(3):342-346
本文用子波变换检测了刻画壁湍流脉动信号自相似性的局部标度指数,研究了不同尺度的湍流结构的自相似性,发现在湍流边界层猝发过程中,喷射和扫掠发生时刻小尺度脉动速度信号的局部标度指数为负值,说明在大尺度猝发事件发生的时刻小尺度结构具有奇异的自相似性,在猝发过程中其作用不仅仅是对湍能的耗散.  相似文献   

11.
A Conditional Source-term Estimation (CSE) model is used to close the mean reaction rates for a turbulent premixed flame. A product-based reaction progress variable is introduced as the conditioning variable for the CSE method. Different presumed probability density function (PDF) models are studied and a modified version of a laminar flame-based PDF model is proposed. Improved predictions of the variable distribution are obtained. The conditional means of reactive scalars are evaluated with CSE and compared to the direct numerical simulation (DNS). The mean reaction rates in a turbulent premixed flame are evaluated with the CSE model and the presumed PDFs. Comparison of the CSE closure method to DNS shows promising results. This paper was presented at the 2nd ECCOMAS Thematic Conference on Computational Combustion.  相似文献   

12.
13.
Criteria are established for higher order ordinary differential equations to be compatible with lower order ordinary differential equations. Necessary and sufficient compatibility conditions are derived which can be used to construct exact solutions of higher order ordinary differential equations subject to lower order equations. We provide the connection to generalized groups through conditional symmetries. Using this approach of compatibility and generalized groups, new exact solutions of non-linear flow problems arising in the study of Newtonian and non-Newtonian fluids are derived. The ansatz approach for obtaining exact solutions for non-linear flow models of Newtonian and non-Newtonian fluids is unified with the application of the compatibility and generalized group criteria.  相似文献   

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16.
A procedure for studying the first-passage failure of strongly non-linear oscillators with time-delayed feedback control under combined harmonic and wide-band noise excitations is proposed. First, the time-delayed feedback control forces are expressed approximately in terms of the system state variables without time delay. Then, the averaged Itô stochastic differential equations for the system are derived by using the stochastic averaging method. A backward Kolmogorov equation governing the conditional reliability function and a set of generalized Pontryagin equations governing the conditional moments of first-passage time are established. Finally, the conditional reliability function, the conditional probability density and moments of first-passage time are obtained by solving the backward Kolmogorov equation and generalized Pontryagin equations with suitable initial and boundary conditions. An example is worked out in detail to illustrate the proposed procedure. The effects of time delay in feedback control forces on the conditional reliability function, conditional probability density and moments of first-passage time are analyzed. The validity of the proposed method is confirmed by digital simulation.  相似文献   

17.
当大涡模拟用于研究化学反应流动时,传统的滤波方法会导致化学反应项不封闭. 为克服这 个困难,发展了条件滤波大涡模拟方法. 在选择适当的条件变量后,条件滤波的化学反 应项可以表达为一个封闭项. 但同时也带来了新的问题:条件滤波耗散或条件滤波扩散项的 不封闭. 为解决这一问题,采用了直接数值模拟方法研究了它们在大小尺度上的统计特 性. 研究结果表明:条件滤波耗散和扩散对于大尺度的依赖主要体现在大尺度标量场中扩散 层结构的影响,同时小尺度脉动的变化几乎与条件滤波扩散无关,而它对条件滤波耗散却显 现出明显的作用. 在构造条件滤波耗散的亚格子模型时,小尺度脉动的作用不容忽视.  相似文献   

18.
First-passage failure of strongly nonlinear oscillators under combined harmonic and real noise excitations is studied. The motion equation of the system is reduced to a set of averaged Itô stochastic differential equations by stochastic averaging in the case of resonance. Then, the backward Kolmogorov equation governing the conditional reliability function and a set of generalized Pontryagin equations governing the conditional moments of first-passage time are established. Finally, the conditional reliability function and the conditional probability density and mean first-passage time are obtained by solving the backward Kolmogorov equation and Pontryagin equation with suitable initial and boundary conditions. The procedure is applied to Duffing–van der Pol system in resonant case and the analytical results are verified by Monte Carlo simulation.  相似文献   

19.
Conditional Moment Closure for Large Eddy Simulations   总被引:1,自引:0,他引:1  
A conditional moment closure (CMC) based combustion model for large-eddy simulations (LES) of turbulent reacting flow is proposed and evaluated. Transport equations for the conditionally filtered species are derived that are consistent with the LES formulation and closures are suggested for the modelling of the conditional velocity, conditional scalar dissipation and the fluctuations around the conditional mean. A conventional β-probability density distribution of the scalar is used together with dynamic modelling for the sub-grid fluxes. The model is validated by comparison of simulations with measurements of a piloted, turbulent methane-air jet diffusion flame.  相似文献   

20.
研究了OSTR试验数据的统计处理方法。给出了推断感度分布参数的两种方法 :条件推断与非条件推断方法。通过研究与模拟 ,得出条件推断方法适用于推断机械撞击作用火工品的一些R响应点的结论。  相似文献   

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