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1.
The assumption of homogeneous isotropic turbulence when modeling drop breakage in industrially relevant geometries is questionable. We describe the development of an anisotropic breakage model, where the anisotropy is introduced via the inclusion of a perturbed turbulence spectrum. The selection of the perturbed spectrum is itself motivated by our previous large-eddy simulations of high-pressure homogenizers. The model redistributes energy from small to large scales, and assumes that the anisotropic part of the Reynolds stresses is confined to the energy-containing range. The second-order structure function arising from the perturbed spectrum is used in the standard framework of Coulaloglou and Tavlarides to calculate breakage frequency. While the base model exhibits non-monotonic behavior (by predicting a maximum value for a certain drop size), the effect of anisotropy is shown to increase breakage frequency in length scales larger than this peak, thereby reducing non-monotonicity. This effect is more pronounced for small turbulence Reynolds numbers.  相似文献   
2.
Large eddy simulations based on the CFD software OpenFOAM have been used to study the effect of Reynolds number and turbulence intensity on the flow and mixing characteristics of an argon thermal plasma jet.Detailed analysis was carried out with respect to four aspects:the average flow field,the instantaneous flow field,turbulence statistical characteristics and the self-similarity.It was shown that for the argon thermal plasma jet with low Reynolds number,increasing the turbulence intensity will increase the turbulent transport mechanism in the mixing layer rather than in the jet axis,leading to the faster development of turbulence.The effect of the turbulent transport mechanism increases with increasing Reynolds number.However,the characteristics of flow and mixing are not affected by turbulence intensity for high Reynolds number situations.It was also found that the mean axial velocity and mean temperature in the axis of the turbulent thermal plasma jet satisfy the self-similarity aspects downstream.In addition,decay constant K is 1.25,which is much smaller than that(5.7-6.1)of the turbulent cold gas jet and has nothing to do with the Reynolds number or turbulence intensity in the jet inlet.  相似文献   
3.
为了研究基于光子灯笼的模式分集接收系统在星地链路中对大气湍流的补偿作用。采用平行光管模拟星地下行链路的平行光,使用30cm口径的接收望远镜进行了演示验证实验。实验结果表明,采用光子灯笼的接收系统的基模比单模光纤的接收功率大4dB左右,而光子灯笼的3个模式总接收功率比单模光纤的接收功率大5dB左右。采用光子灯笼接收之后,中断概率下降39%以上。  相似文献   
4.
为了研究分形网格湍流中小尺度结构的运动规律,在具有高分辨率的空间网格中,开展分形流场时间演化的直接数值模拟,并通过模拟具有相同阻塞率的规则流场进行对比研究. 通过给流场中注入合适的能量扰动,促使2类流场从层流初始状态向湍流状态过渡. 数值模拟结果表明,与规则流场相比,分形流场受到初始条件影响的持续时间更久,同时在时间演化的初期,分形流场产生的动能更小,但分形流场在衰减期的大尺度运动起到强化湍流的作用,导致其产生的动能更大、湍流强度更高,有利于实现对流场的被动控制. 分形流场和规则流场均在截断波数 $ kM \approx 20 $时满足能量与耗散水平相等,但有别于能量级串过程中能量传输与耗散的平衡. 当流场达到统计均匀后,规则流场衰减符合Saffman湍流特征的规律.  相似文献   
5.
由于解析法在研究相干光通信的相位补偿等问题中存在困难,采用多层相位屏分步传输的数值仿真方法研究大气湍流对星地相干光通信下行传输的影响。首先建立了卫星地面之间的大气湍流中激光传输的仿真模型,可以实现不同天顶角和不同湍流条件下的光传输仿真计算。然后用其进行地球同步轨道(GEO)卫星下行光通信的数值仿真分析,并通过与理论值的对比来检验算法的可靠性。最后结合二进制相移键控(binary phase shift keying, BPSK)相干激光通信系统的误码率(bit error rate, BER)模型,计算分析了下行激光通信信号的衰落系数和BER。  相似文献   
6.
Surface wave breaking is a challenging two-phase flow process which plays an important role in numerous physical processes. A highly-turbulent unsteady breaking surge was investigated experimentally in a large facility, and substantial aeration occurred in the roller. The application of three optical flow techniques (Lucas-Kanade, Horn-Schunck and Farnback) to the air-water region was tested. The results indicated that the Farnback technique provided most accurate results, although some misleading results could be obtained near the air-water boundaries of the roller. The bore generation by a rapid gate closure showed a highly-unsteady complicated velocity field, with substantial free-surface deformations, wave breaking and formation of large coherent structures before the surge detached from the gate. Further upstream, the surge propagated as a hydraulic jump in translation and the data showed a marked shear region with a recirculation zone above, showing air-water flow features comparable to stationary hydraulic jumps. The upper and lower bounds of air-water flow region yielded data implying an air-to-water velocity ratio about 4–5 for a Froude number Fr1 = 2.1.  相似文献   
7.
In accordance with the extended Huygens–Fresnel principle, the evolution of linear edge dislocation propagating through atmospheric turbulence is studied, and the effects of waist width and the slope of linear edge dislocation are investigated. It is shown that when linear edge dislocation beams propagate through atmospheric turbulence, if the waist width is not equal and the slope is not zero, then the linear edge dislocation vanishes and transforms into an optical vortex with a topological charge of ?1 or +1. The optical vortex and an optical vortex that is created annihilate when the transmission distance is far enough. The linear edge dislocation vanishes when the slope is zero. If the waist width is equal, then the linear edge dislocation will vanish regardless of the slope value. For linear edge dislocation beams in free space, when selecting specific parameters, linear edge dislocation always exists.  相似文献   
8.
铅铋快堆是第4代核能系统的主要堆型之一,但由于液态金属铅铋的热物性与传统工质如水、空气等有很大不同,假设流动边界层与热边界层相似的雷诺比拟原理已不再适用。本文在开源程序OpenFOAM中开发了基于k-ε-kθθ四因子模型的自定义求解器,考虑热边界层与流动边界层的差异性,对带绕丝棒束通道中液态金属铅铋的流动换热现象进行数值模拟,得到了速度、温度等重要热工水力参数的三维分布,揭示了绕丝对冷却剂流动传热过程的影响规律,并将计算结果与经典实验关联式进行对比,结果符合良好,证明了所用模型和程序的正确性。本研究可为在OpenFOAM中添加新模型、开发自定义求解器以及开展针对液态金属流动换热问题的计算流体动力学(CFD)模拟提供参考。  相似文献   
9.
Buying firms’ sales and reputation will be greatly damaged by any non-responsible behaviors on the part of suppliers, especially when those suppliers, like small and medium-sized enterprises (SMEs), have restricted resources and capabilities. To eradicate these risks, a growing number of buying firms have introduced socially responsible supplier development (SRSD). SRSD, including monitoring and evaluating suppliers, can provide them with incentives and assistance. Based on configuration theory and contingency theory, fuzzy-set qualitative comparative analysis (fsQCA) is adopted in this study to examine how SRSD practices adopted by buying firms, supply chain partnership, and market turbulence affect the corporate social responsibility (CSR) performance of their SME suppliers. We find that, as core factors, supplier monitoring, supplier assistance, and supply chain partnership can work together with peripheral conditions to achieve superior CSR performance. In addition, even at different levels of market turbulence, superior CSR performance can be realized through different causal configurations.  相似文献   
10.
This research presents an application of the sampling moiré method, a novel technique originally developed for measuring slight deformation of a static object such as a plate, to fluctuating free water surface in rough open channel flows. The method was used to capture the two-dimensional water surface deformation at a high sampling rate by dyeing the color of water white. The target flow was a very shallow subcritical flow with a depth of 1.5 times the height of the roughness. As a result, a series of instantaneous water surface profiles with non-uniform rough planes were successfully measured at a sampling rate of 100 Hz.It has become clear that the effect of dispersive gravity waves traveling on the water surface is greater than that of non-dispersive waves driven by the turbulence, and that this feature becomes more pronounced as the Froude number increases in such shallow flow conditions. Furthermore, it was experimentally and theoretically verified that the intensity of water surface fluctuation increases with the square of the Froude number. The decomposition of surface fluctuations due to gravity waves and subsurface turbulence using the wavenumber frequency spectrum revealed that the effects of subsurface turbulence are about 20%. This is much less than the contribution from gravity waves in very shallow flows as in this experiment.  相似文献   
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