共查询到17条相似文献,搜索用时 93 毫秒
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用颗粒运动的拉氏分析和PDF方法,改进了颗粒相的二阶矩模型。由拉氏两相运动的随机微分方程出发,采用随机过程分析和信号分析法得到湍流两相流动的PDF输运方程,双流体模型方程和两相脉动速度相关的基本模式的封闭式,和用其它方法导出的方程与封闭式的结果一致,对封闭式作了重要的改进,在分析颗粒轨道上的流体湍流作用时间时,全面地引入拉氏分析的轨道穿越效应、惯性效应、连续效应和湍流的各向异性。 相似文献
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旋流泵无叶腔内盐析颗粒湍流脉动特性研究 总被引:4,自引:0,他引:4
盐析晶体颗粒脉动特性是研究湍流输运状态下盐析过程的重要问题之一.为探索泵内盐析晶体颗粒湍流脉动规律及其对液相流场的影响,采用相位多普勒粒子速度场仪对旋流式输送泵无叶腔内的盐析湍流流场进行了测量,通过对改变泵运行工况、运行介质温度后颗粒脉动速度分布情况的分析,初步掌握了无叶腔中盐析晶体颗粒的湍流脉动特性;同时,讨论了晶体颗粒存在对液相湍流结构的影响。实验结果表明,随着流量的增加,颗粒的周向、径向及轴向脉动速度相应提高;盐析颗粒脉动速度值随温度发生变化,较高温度时速度脉动也较大;在一定条件下,盐析晶体颗粒表现出抑制湍流的行为。 相似文献
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本文采用直接数值模拟方法,对惯性颗粒所见均匀各向同性湍流中具有平均标量梯度的被动标量场统计特性进行了研究。模拟结果表明:与颗粒所见流体速度的自相关特性不同,颗粒所见标量的自相关特性随颗粒惯性的增加而单调减少;颗粒所见标量脉动能随颗粒惯性的增加先减少再增大,在St≈1.0的临界颗粒附近达到最小值,而颗粒所见标量耗散率随颗粒惯性的变化行为与颗粒所见标量脉动能的变化行为相反;数值模拟的结果进一步揭示,在St≈1.0时颗粒所见流体标量脉动能和耗散率的极值是因为St≈1.0的临界颗粒聚集于低涡量、高应变区域和标量场在高应变区域形成强耗散的片状结构所致。 相似文献
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The influence of time-averaging on bias is investigated in the finite-volume/particle hybrid algorithm for the joint PDF equation for statistically-stationary turbulent reactive flows. It is found that the time-averaging of the mean fluctuating velocity (TAu) leads to the same variances of the fluctuating velocity before and after the velocity correction, whereas without TAu the estimates are different, and an additional numerical dissipation rate is introduced for the turbulent kinetic energy (TKE). When 100 particles per cell are used without TAu, a large bias error is found to be involved in the unconditional statistics of the statistically-stationary solutions of two tested turbulent flames, the Cabra H2/N2 lifted flame and the Sandia piloted flame E. The use of TAu reduces this bias dramatically for the same number of particles per cell. The conditional statistics in these flames, however, are hardly affected by TAu. To a large extent, the effect of the bias error on the unconditional statistics is similar to the effect of increasing the model constant C ω 1 in the stochastic turbulence frequency model. 相似文献
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研究两相流中固粒对流体湍动特性影响的新方法 总被引:1,自引:0,他引:1
本文提出了计算两相流中固粒对流体湍动特性影响的一种新方法,得到不同情况下固粒对流体端动特性的影响。将该方法用于槽流湍流场的求解,说明该方法是可行的。 相似文献
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用视密度加权平均二阶矩模型模拟旋流两相流动 总被引:1,自引:0,他引:1
本文用视密度加权平均代替时平均,建立了视密度加权平均的统一二阶矩两相湍流模型方程组(MUSM),其中用体积分数代替了数密度,用颗粒驰豫时间作为封闭两相脉动速度关联方程耗散项的时间尺度,并引入了颗粒视在的气体速度脉动的输运方程。用MUSM模型模拟了旋流数为0.47的气粒两相流动。并和实验结果及时间平均的USM模型的模拟结果进行了对照,两种模型均能较好地预报的两相的轴向和切向速度,轴向和切向脉动速度。此外,MUSM模型可以减少所用方程数,节省计算量。因此视密度加权平均的统一二阶矩两相湍流模型是一种对时间平均的统一二阶矩模型的改进,今后可以进一步扩大应用。 相似文献
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钝体后湍流预混燃烧的PDF模拟 总被引:3,自引:0,他引:3
本文采用PDF方法对矩形燃烧室内钝体后的湍流预混火焰进行了数值模拟。脉动速度-频率-标量联合的PDF输运方程用Monte Carlo方法求解,质量、动量和能量的平均值由基于无结构网格的有限体积法求解,压力通过状态方程获得。PDF方程中所需的平均密度、平均速度和压力由有限体积法提供,并将用Monte Carlo方法求出的雷诺应力、化学反应源项和比热比传递给有限体积法。本文对丙烷和空气燃烧的不同简化化学反应机理进行了研究,并与实验结果进行比较,获得满意的结果。 相似文献
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LIU Nansheng LU Xiyun & ZHUANG Lixian Department of Mechanics Mechanical Engineering University of Science Technology of China Hefei China 《中国科学G辑(英文版)》2005,48(2)
Turbulent flow in an axially rotating pipe, involving complicated physical mecha- nism of turbulence, is a typical problem for the study of rotating turbulent flow. The pipe rotation induces two effects on the flow. One is the stabilizing effect due to the centrifu- gal and Coriolis forces, which accounts for the relaminarization of the turbulence[1—3] and the reduction of the friction coefficient at the pipe wall. The behavior is also related to the wall streaks inclining to the azimuthal di… 相似文献
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Chunkan Yu Paola Breda Michael Pfitzner Ulrich Maas 《Proceedings of the Combustion Institute》2021,38(2):2645-2653
For general reacting flows the numerical simulation faces two main challenges. One is the high dimensionality and stiffness of the governing conservation equations due to detailed chemistry, which can be solved by using simplified chemical kinetics. The other one is the difficulty of modeling the coupling of turbulence with thermo-chemical source term. The probability density function (PDF) method allows to calculate turbulent reacting flows by solving the thermal-chemical source term in closed form. Usually, the PDF method for turbulent processes such as mixing processes and the reduction method for chemical kinetics are developed separately. However, coupling of both processes plays an important role for the numerical accuracy. To investigate the importance of coupling between turbulence and simplified chemistry, two different coupling strategies for mixing and reduced chemistry are discussed and tested for the well-known Sandia Flames E and F, in which there is a strong interaction between turbulence and chemical kinetics. The EMST mixing model is chosen for turbulent mixing, while the Reaction-Diffusion Manifolds (REDIMs) is used as simplified chemistry. However, the proposed strategies are also valid for other mixing models and manifold based simplified chemistry. 相似文献