基于风廓线雷达的晴空对流层动力湍流特征研究

风廓线雷达作为一种新型遥感设备，其回波信号包含丰富的湍流信息。提出了一种利用风廓线雷达回波信号反演动力湍流的方法，分析了对流层速度结构常数Cv^2的变化特征，并根据近地面速度湍流模型研究了对流层湍流速度脉动的特性。结果表明：1）动力湍流强度随高度增加逐渐减弱，夜间减弱速度大于白天，且在边界层顶处Cv^2具有较明显的日变化特征；2）Cv^2与速度起伏方差σ^2的对数值具有较好的线性关系，线性拟合度达0．896；3）对流层湍流的速度脉动较弱，σ^2量级在10^-3～10^-2m^2·s^-2之间。

基于湍流动力学模型的油水分离装置

目前,各变电站采用在变压器底部建筑蓄油池的方式处理变压器废油,废油混入雨水后形成油水混合物,不仅浪费能源、外泄造成污染,而且还会造成安全隐患。为了解决上述问题,基于新型旋流微泡浮选原理以及湍流动力学,设计一套回流式含油废水高效处理装置,在所设计浮选柱旋流器内将油水混合液体进行分离,由于油、水两相间存在密度差,在混合体系中会发生水中油滴、气泡升浮以及油中水滴沉降的现象,油滴在浮选柱气浮段发生重力场中的聚结行为,聚结形成大的油滴更有利于后续分离。油水分离后将过滤液体回流至池中,通过多次循环高效分离,实现变压器油的提取分离收集和积水清洁化。同时从理论、Fluent软件仿真、自动化和结构优化等方面对该设备进行了研究,通过试验加以验证并且得出了一系列最优控制参数,在最优参数下油水分离效率可达90%。

船舶动力机械螺旋桨在不同湍流的动力性能仿真

不同动力机械螺旋桨在湍流环境下进行动力性能仿真过程中,存在量化误差较大的问题,为此提出船舶动力机械螺旋桨在不同湍流的动力性能仿真。分别设计螺旋桨动力性能仿真平台硬件结构和软件系统,实现螺旋桨动力性能仿真平台构建;基于仿真平台对船舶动力机械螺旋桨湍流流体动力学进行分析,通过平台大数据技术,实现船舶动力机械螺旋桨在不同湍流的动力性能仿真分析。试验数据表明,本文系统仿真效果与常规仿真方法相比,量化准确率提升10.25%,适合不同环境下的船舶螺旋桨动力性能分析。

利用同步偏振辐射统计测量磁化强度

星际磁场在天体物理中具有重要作用,但测量其强度是极其困难的。本文基于同步偏振辐射理论开发了测量磁化强度的新技术,建立了同步偏振辐射强度的标准差和平均值的比值与阿尔文马赫数的幂律关系。此外,该技术也应用于Planck观测数据,实现了磁化强度的测量。

精馏塔板上气液相界面积的测量与预测

利用现代的电子光学测试仪器和计算机图像处理技术较准确地测量了精馏塔板上鼓泡液体中气泡的粒径分布和相界面积 .同时 ,还从理论上分析了湍流液体中气泡变形与破碎的机理 ,提出了预测气液相界面积的多相湍流动力学模型 .模拟计算结果与实验测量数据的比较证明 ,此模型有较高的准确性 ,而且形式简单 。

大型建筑暖通空调气体中污染物监测方法研究

大型建筑中暖通空调使用时间长,对细菌净化程度会降低,影响人体健康。为此,提出大型建筑暖通空调气体中污染物监测方法。分析暖通空调气体湍流动力,利用组分传输模型获得气体流域内混合分组情况,结合傅里叶和能量守恒定律构建导热微分方程,计算建筑物内污染源、送风及起始气体分布、建筑内壁面源的数值;当激光光束穿透暖通空调气体内污染物微粒时,部分入射激光被污染气体吸收,提取吸收光强二次谐波信号即可实现污染物浓度监测。结果证明采用所提方法可有效实现空调气体中污染物。

Simulation and analysis of airflow stability during fire in mine belt roadway

According to fluid dynamics analysis during the fire, the criteria k-ε two-equation model for solving three-dimensional turbulence was determined, the pollutants generated in the fire disaster were set by adopting Mixture multiphase flow, and the SIMPLE algorithm was used for solving on the basis of comprehensive consideration on the heat radia- tion and components transmission during fire. By simulating the airflow flowing state inside the tunnel during fire disaster of downward ventilation, drift ventilation, and ascensional ventilation, respectively, with regard to the actual situation of No.l, No.3, and No.5 belt roadway in Kongzhuang Coal Mine, the velocity vector distributions of pollutants under different inlet air volumes were obtained, and the damage degree and influential factors of disaster were also clear, which is helpful to control and avoid disaster during belt roadway fire.

Turbulent boundary layers and hydrodynamic flow analysis of nanofluids over a plate

A numerical analysis of the log-law behavior for the turbulent boundary layer of a wall-bounded flow is performed over a flat plate immersed in three nanofluids(Zn O-water,SiO_(2)-water,TiO_(2)-water).Numerical simulations using CFD code are employed to investigate the boundary layer and the hydrodynamic flow.To validate the current numerical model,measurement points from published works were used,and the compared results were in good compliance.Simulations were carried out for the velocity series of 0.04,0.4 and 4 m/s and nanoparticle concentrations0.1% and 5%.The influence of nanoparticles’ concentration on velocity,temperature profiles,wall shear stress,and turbulent intensity was investigated.The obtained results showed that the viscous sub-layer,the buffer layer,and the loglaw layer along the potential-flow layer could be analyzed based on their curving quality in the regions which have just a single wall distance.It was seen that the viscous sub-layer is the biggest area in comparison with other areas.Alternatively,the section where the temperature changes considerably correspond to the thermal boundary layer’s thickness goes a downward trend when the velocity decreases.The thermal boundary layer gets deep away from the leading edge.However,a rise in the volume fraction of nanoparticles indicated a minor impact on the shear stress developed in the wall.In all cases,the thickness of the boundary layer undergoes a downward trend as the velocity increases,whereas increasing the nanoparticle concentrations would enhance the thickness.More precisely,the log layer is closed with log law,and it is minimal between Y^(+)=50 and Y^(+)=95.The temperature for nanoparticle concentration φ=5%is higher than that for φ=0.1%,in boundary layers,for all studied nanofluids.However,it is established that the behavior is inverted from the value of Y^(+)=1 and the temperature for φ =0.1% is more important than the case of φ =5%.For turbulence intensity peak,this peak exists at Y^(+)=100 for v=4 m/s,Y^(+)=10 for v=0.4 m/s and Y^(+)=8 for v=0.04 m/s.

Numerical Simulation on Ship Bubbly Wake

Based on a volume of fluid two-phase model imbedded in the general computational fluid dynamics code FLUENT6.3.26, the viscous flow with free surface around a model-scaled KRISO container ship （KCS） was first numerically simulated. Then with a rigid-lid-free-surface method, the underwater flow field was computed based on the mixture muitiphase model to simulate the bubbly wake around the KCS hull. The realizable k-e two-equation turbulence model and Reynolds stress model were used to analyze the effects of turbulence model on the ship bubbly wake. The air entrainment model, which is relative to the normal velocity gradient of the free surface, and the solving method were verified by the qualitatively reasonable computed results.

CFD Simulation of Orifice Flow in Orifice-type Liquid Distributor

In this study,a suitable CFD(computational fluid dynamics)model has been developed to investigate the influence of liquid height on the discharge coefficient of the orifice-type liquid distributors.The orifice flow in different diameters and liquid heights has been realized using the shear stress transport(SST)turbulence model and the Gamma Theta transition(GTT)model.In the ANSYS CFX software,two models are used in conjunction with an automatic wall treatment which allows for a smooth shift from a wall function(WF)to a low turbulent-Re near wall formulation(LTRW).The results of the models coupled with LTRW are closer to the experimental results compared with the models with WF,indicating that LTRW is more appropriate for the prediction of boundary layer characteristics of orifice flow.Simulation results show that the flow conditions of orifices change with the variation of liquid height.With respect to the turbulence in orifice,the SST model coupled with LTRW is recommended.However,with respect to the transition to turbulence in orifice with an increase in liquid height,the predictions of GTT model coupled with LTRW are superior to those obtained using other models.

Kinematic Characteristics and Thermophoretic Deposition of Inhalable Particles in Turbulent Duct Flow

The kinematical characteristics and thermophoretic deposition of inhalable particles with the diameters of 0-2.5μm （hereafter referred to as PM2.5） suspended in turbulent air flow in a rectangular duct with temperature distribution were experimentally studied. Particle dynamics analyzer （PDA） was used for the on-line measurement of particle motion and particle concentration distribution in the cross-sections of the duct. The influences of the parameters such as the ratio of the bulk air temperature to the cold wall temperature and the air flow rate in the duct on the kinematical characteristics and the deposition efficiencies of PM2.5 were investigated. The experimental re- sults show that the deposition efficiencies of PM2.5 mainly depend on the temperature difference between the air and the cold wail, wffile the air flow rate and the particlecon^centration almost affect hardly tile clep0si-tion-effi ciency. The radial force thermophoresis to push PM2.5 to the cold wail is found the key factor for PM2.5 deposition.Based on the experimental results, an empirical modified Romay correlation for the calculation of thermophoretic deposition efficiency of PM2.5 is presenlext. The empirical correlation agrees reasonably well with the experimental data.

Analysis of drop deformation dynamics in turbulent flow

Drop breakage and coalescence influence the particle formation in liquid-liquid dispersions. In order to reduce the influencing factors of the whole dispersion process, single drops where coalescence processes can be neglected were analyzed in this work. Drops passing the turbulent vicinity of a single stirrer blade were investi- gated by high-speed imaging. In order to gain a statistically relevant amount of drops passing the area of interest and corresponding breakage events, at least 1600 droplets were considered for each parameter set of this work. A specially developed fully automatic image analysis based on Matlab was used for the evaluation of the resulting high amount of image data. This allowed the elimination of the time-consuming manual analysis and further- more, allowed the objective evaluation of the drops＇ behavior. Different deformation parameters were consid- ered in order to describe the drop deformation dynamics properly. Regarding the ratio of both main particle axes （0axes）, which was therefore approximated through an ellipse, allowed the determination of very small de- viations from the spherical shape. The perimeter of the particle （0peri） was used for the description of highly de- formed shapes. In this work the results of a higher viscosity paraffin oil （ηd =127 mPa. s） and a low viscosity solvent （petroleum, ηd = 1.7 mPa-s） are presented with and without the addition of SDS to the continuous water phase. All results show that the experimentally determined oscillation but also deformation times underlie a wide spreading. Drop deformations significantly increased not only with increasing droplet viscosity, but also with decreasing interfacial tension. Highly deformed particles of one droplet species were more likely to break than more or less spherical particles. As droplet fragmentation results from a variety of different macro-scale de- formed particles, it is not assumed that a critical deformation value must be reached for the fragmentation pro- cess to occur. Especially for highly deformed particles thin particle filaments are assumed to induce the breakage process and, therefore, be responsible for the separation of drops.

Wind Force Coefficients for Designing Porous Canopy Roofs

Wind force coefficients for designing porous canopy roofs have been investigated based on a series of wind tunnel experiments. Gable, troughed and mono-sloped roofs were tested. The roof models were made of 0.5 mm thick perforated duralumin plates, the porosity of which was changed from 0 to about 0.4. Overall aerodynamic forces and moments acting on the roof model were measured in a turbulent boundary layer with a six-component force balance for various wind directions. The results indicate that the wind loads on canopy roofs generally decrease with an increase in porosity of the roof. Assuming that the roof is rigid and supported by the four corner columns with no walls, the axial forces induced in the columns are regarded as the most important load effect for discussing the design wind loads. Two loading patterns causing the maximum tension and compression in the columns are considered. Based on a combination of the lift and moment coefficients, the design wind force coefficients on the windward and leeward halves of the roof are presented for the two loading patterns as a function of the roof pitch and porosity. The effect of porosity is taken into account as a reduction factor of the wind loads.

Computational fluid dynamics simulation of gas-liquid two phases flow in 320 m^3 air-blowing mechanical flotation cell using different turbulence models

According to the recently developed single-trough floating machine with the world's largest volume(inflatable mechanical agitation flotation machine with volume of 320 m3) in China, the gas-fluid two-phase flow in flotation cell was simulated using computational fluid dynamics method. It is shown that hexahedral mesh scheme is more suitable for the complex structure of the flotation cell than tetrahedral mesh scheme, and a mesh quality ranging from 0.7 to 1.0 is obtained. Comparative studies of the standard k-ε, k-ω and realizable k-ε turbulence models were carried out. It is indicated that the standard k-ε turbulence model could give a result relatively close to the practice and the liquid phase flow field is well characterized. In addition, two obvious recirculation zones are formed in the mixing zones, and the pressure on the rotor and stator is well characterized. Furthermore, the simulation results using improved standard k-ε turbulence model show that surface tension coefficient of 0.072, drag model of Grace and coefficient of 4, and lift coefficient of 0.001 can be achieved. The research results suggest that gas-fluid two-phase flow in large flotation cell can be well simulated using computational fluid dynamics method.

CFD Simulation of Propane Cracking Tube Using Detailed Radical Kinetic Mechanism

In the radiant section of cracking furnace,the thermal cracking process is highly coupled with turbulent flow,heat transfer and mass transfer.In this paper,a three-dimensional simulation of propane pyrolysis reactor tube is performed based on a detailed kinetic radical cracking scheme,combined with a comprehensive rigorous computational fluid dynamics(CFD)model.The eddy-dissipation-concept(EDC)model is introduced to deal with turbulence-chemistry interaction of cracking gas,especially for the multi-step radical kinetics.Considering the high aspect ratio and severe gradient phenomenon,numerical strategies such as grid resolution and refinement,stepping method and relaxation technique at different levels are employed to accelerate convergence.Large scale of radial nonuniformity in the vicinity of the tube wall is investigated.Spatial distributions of each radical reaction rate are first studied,and made it possible to identify the dominant elementary reactions.Additionally,a series of operating conditions including the feedstock feed rate,wall temperature profile and heat flux profile towards the reactor tubes are investigated.The obtained results can be used as scientific guide for further technical retrofit and operation optimization aiming at high conversion and selectivity of pyrolysis process.

Chemical Kinetics for NO Emissions in System of Methane-Air Turbulent-Jet Diffusion Flame

An explicit expression for local, instantaneous NO production rate model was proposed to simulate NO formation in turbulent methane-air combustion. The average production rates of mixture fraction and scalar dissipation were obtained from asymptotes through approximation of two single-variable probability-density function. The theory predicted significant contributions from the Zeldovich mechanism, but negligible contributions from the nitrous-oxide mechanism in the oxygenconsumption zone. The proposed model was used to simulate NO formation in the pilot methane-air jet diffusion combustion. The simulation results were compared with those obtained by the CFD software FLUENT module. Validation of predictions with the experimental data given by Sandia National Laboratory of the USA indicates that the proposed model yields better results than other models, and the deviation is under 5%. And in some complete reaction zones, the simulation results are even the same as the experimental data. Realizable κ-ε model, Reynold stress model and standard κ-ε model were also investigated to predict the turbulent combustion reaction, which shows that the simulation results of velocities, temperatures, and concentrations of combustion productions by standard κ-ε model are in accordance with the experimental data.

Numerical Investigation on Two-dimensional Boundary Layer Flow with Transition

As a basic problem in many engineering applications, transition from laminar to turbulence still remains a difficult problem in computational fluid dynamics （CFD）. A numerical study of one transitional flow in two-dimensional is conducted by Reynolds averaged numerical simulation （RANS） in this paper. Turbulence model plays a significant role in the complex flows＇ simulation, and four advanced turbulence models are evaluated. Numerical solution of frictional resistance coefficient is compared with the measured one in the transitional zone, which indicates that Wilcox （2006） k-ω model with correction is the best candidate. Comparisons of numerical and analytical solutions for dimensionless velocity show that averaged streamwise dimensionless velocity profiles correct the shape rapidly in transitional region. Furthermore, turbulence quantities such as turbulence kinetic energy, eddy viscosity, and Reynolds stress are also studied, which are helpful to learn the transition＇s behavior.

MHD from a Microscopic Concept and Onset of Turbulence in Hartmann Flow

We derive higher order magneto-hydrodynamic （MHD） equations from a microscopic picture using pro-jection and perturbation formalism. In an application to Hartmann flow we find velocity profiles flattening towards the center at the onset of turbulence in hydrodynamic limit. Comparison with the system under the effect of a uniform magnetic field yields difference in the onset of turbulence consistent with observations, showing that the presence of magnetic field inhibits onset of instability or turbulence. The laminar-turbulent transition is demonstrated in a phase transition plot of the development in time of the relative average velocities vs. Reynolds number showing a sharp increase of the relative average velocity at the transition point as determined by the critical Reynolds number.

Dynamics Behaviors and Scaling in Intermittent Turbulence of a Shell Model

In this paper, the dynamics behaviors on fo-δ parameter surface is investigated for Gledzer-Ohkitani- Yamada model We indicate the type of intermittency chaos transitions is saddle node bifurcation. We plot phase diagram on fo-δ parameter surface, which is divided into periodic, quasi-periodic, and intermittent chaos areas. By means of varying Taylor-microscale Reynolds number, we calculate the extended self-similarity of velocity structure function.

Comparison of the Reynolds-averaged Turbulence Models on Single Phase Flow Simulation in Agitated Extraction Columns

The flow field of liquid phase (water) of agitated extraction columns is simulated with the help of computational fluid dynamics (CFD). Four kinds of Reynolds-averaged turbulence models, i.e. the standard k-ε model, the RNG (renormalization group) k-s model, the realizable k-ε model and the Reynolds stress model, are compared in detail in order to judge which is the best model in terms of the accuracy, less CPU time and memory required. The performance of the realizable k-s model is obviously improved by reducing the model constant from C2 = 1.90 to C2 = 1.61. It is concluded that the improved realizable k-e model is the optimal model.