含油污水处理用旋流气浮一体化设备的CFD数值模拟

借助商业计算流体动力学(CFD)软件Fluent,对国内自主研发的含油污水处理用BIPTCFU-1型旋流气浮一体化设备进行内部流场的数值模拟研究,讨论了射流器挡板和缓流板等主要结构参数对设备分离性能的影响,并对污水处理量和回流比等运行参数对设备除油率的影响进行了评估。为下一步通过CFD数值模拟手段进行优化设计,进而成功研发含油污水旋流气浮一体化处理设备奠定了较为坚实的基础。     

臭氧接触池与清水池合建的三维数值模拟

利用计算流体力学软件Fluent,结合标准κ-ε模型和组分输运模型,建立了臭氧接触池和清水池的三维紊流模型;通过计算流体的停留时间分布曲线(RTD),对臭氧接触池的水力效率进行了模拟研究。在此基础上,提出了在清水池前段第一廊道设置臭氧接触池的合建方案。结果表明:单一的臭氧接触池水力效率较低,T10/HRT值仅为0.42;而臭氧接触池与清水池经过合建后,T10/HRT值达到0.65,其臭氧消毒水力效率提高了55%。     

天然气净化厂管道泄漏H2S毒害后果影响因素数值分析

为定量评估高含硫天然气开敞空间泄漏过程中风速、风向、泄漏速度、泄漏方向对毒害后果的影响,以天然气净化厂管道泄漏为例,采用正交实验设计方法设计实验场景,基于CFD进行泄漏扩散仿真实验,以吸入剂量、毒害面积、最大毒害面积到达时间、毒害体积、最大毒害体积到达时间作为毒害效应指标,分析不同因素对毒害后果的影响,并提出后果控制建议。研究结果表明:采用CFD方法进行泄漏扩散仿真能够还原泄漏扩散过程;利用正交实验进行影响因素分析可以节省实验资源、获取准确结果;风向和风速对各后果指标均比较敏感,在天然气净化厂建设过程中应着重考虑风的影响。仿真与正交实验结合的方法能够有效评估毒害后果影响因素的敏感性,可为毒害气体泄漏风险防控提供指导。     

井喷失控点火时间与方位探讨

利用计算流体力学方法(CFD)对井喷失控后天然气扩散过程进行研究,在有限元基础上建立模型,采用κ-ε紊流模型求解得出井喷失控后可燃性蒸气云随时间、风速变化的影响情况,求出稳态以后易爆区域的蒸气云形状。取5.0%和15%作为甲烷的爆炸上、下限,在不同区域进行点火求解爆燃结果,通过比较给出推荐的点火时间和点火方位。该研究成果可对井喷失控蒸气云爆燃危害性进行预测,有助于指导井喷失控进行点火放喷工作,避免爆燃事故的发生。     

基于FLUENT和ADAMS 的环境实验室压力平衡窗联合仿真分析

目的提出针对环境实验室发动机地面开车试验压力平衡系统的压力平衡窗设计方案,研究压力平衡窗对于室内压力的作用情况,并验证优化设计方案。方法基于FLUENT及ADAMS技术,通过动力学及流体力学联合仿真分析得到不同结构作用下的流场变化情况。结果压力平衡窗窗体结构形式决定其动力学特性,压力平衡窗的动力学特性与其受力耦合作用影响环境实验室压力。结论联合仿真模拟结果可以清晰地描述流场变化情况,合理设计压力平衡窗可以有效地保证实验室内压力在规定范围内,所设计的压力平衡窗能够满足设计要求。     

Spill-over characteristics of peroxy-fuels: Two-phase CFD investigations

Two-phase CFD (Computational Fluid Dynamics) model for characterising the spill-over/dispersion of peroxy-fuels is presented. The model is independent of type and burning rate of the spilled/dispersed fuel and considers only overflow Reynolds number (Re) to characterise the spill/dispersion behaviour. Additional simulations are performed for LNG (Liquified Natural Gas) dispersion and it is found that the model can be used for different fuels within a defined range of Re. Different scenarios with Re = 100 to 3 × 10⁵ are investigated covering a wide range of mass flow rates, opening sizes and viscosities. Depending on Lower Flammability Limits (LFL) of the fuels spill/dispersion (vapour cloud) diameters (D_CFD) and heights (h_CFD) are predicted. A generalised correlation between D_CFD and Re is established to predict the dispersion occurring at varying scales. The model is validated by: (1) conducting an extensive grid independent study; (2) comparing the results with the existing analytical methods and (3) comparing against the standard field test data on LNG dispersions.     

Spatial impacts of climate factors on regional agricultural and forestry biomass resources in north-eastern province of China

The dynamics of agricultural and forestry biomass are highly sensitive to climate change, particularly in high latitude regions. Heilongjiang Province was selected as research area in North-east China. We explored the trend of regional climate warming and distribution feature of biomass resources, and then analyzed on the spatial relationship between climate factors and biomass resources. Net primary productivity (NPP) is one of the key indicators of vegetation productivity, and was simulated as base data to calculate the distribution of agricultural and forestry biomass. The results show that temperatures rose by up to 0.37°C/10a from 1961 to 2013. Spatially, the variation of agricultural biomass per unit area changed from -1.93 to 5.85 t·km^–2·a^–1 during 2000–2013. More than 85% of farmland areas showed a positive relationship between agricultural biomass and precipitation. The results suggest that precipitation exerts an overwhelming climate influence on agricultural biomass. The mean density of forestry biomass varied from 10 to 30 t·km^–2. Temperature had a significant negative effect on forestry biomass in Lesser Khingan and northern Changbai Mountain, because increased temperature leads to decreased Rubisco activity and increased respiration in these areas. Precipitation had a significant positive relationship with forestry biomass in south-western Changbai Mountain, because this area had a warmer climate and stress from insufficient precipitation may induce xylem cavitation. Understanding the effects of climate factors on regional biomass resources is of great significance in improving environmental management and promoting sustainable development of further biomass resource use.

Open image in new window

     

A methodological framework for integrating computational fluid dynamics and ecological models applied to juvenile freshwater mussel dispersal in the Upper Mississippi River

Interdisciplinary research in hydraulics and ecology for river management and restoration must integrate processes that occur over a wide range of spatial and temporal scales, which presents a challenge to ecohydraulics modelers. Computational fluid dynamics (CFD) models are being more widely used to determine flow fields for ecohydraulics applications. In the Upper Mississippi River (UMR), the mussel dynamics model was developed as a tool for management and conservation of freshwater mussels (Unionidae), which are benthic organisms, imperiled in North America, that are inextricably linked with the hydraulics of river flow. We updated the juvenile dispersal component of the mussel dynamics model by using stochastic Lagrangian particle tracking in a three dimensional flow field output from CFD models of reaches in the UMR. We developed a methodological framework to integrate hydrodynamic data with the mussel dynamics model, and we demonstrate the use of the juvenile dispersal model employed within the methodological framework in two reaches of the UMR. The method was used to test the hypothesis that impoundment affects the relationship of some hydraulic parameters with juvenile settling distribution. Simulation results were consistent with this hypothesis, and the relationships of bed shear stress and Froude number with juvenile settling were altered by impoundment most likely through effects on local hydraulics. The methodological framework is robust, integrates Eulerian and Lagrangian reference frameworks, and incorporates processes over a wide range of temporal and spatial scales, from watershed scale hydrologic processes (decades), to reach scale (km) processes that occur over hours or days, and turbulent processes on spatial scales of meter to millimeter and times scales of seconds. The methods are presently being used to assess the impacts of pre- and early post-settlement processes on mussel distributions, including the effects of bed shear stress, and the sensitivity of the location of the host fish when juveniles excyst, on juvenile settling distribution.