垂直轴5叶片阻力型风力机的动态特性

采用CFD对风轮直径为4 m的垂直轴5叶片阻力型风力机的瞬态流场进行数值模拟. 通过对不同入口风速和风力机转速条件下风力机流场和力矩系数随时间的变化情况的计算模拟,分析了垂直轴5叶片阻力型风力机的动态特性. 结果表明,流场和力矩系数的变化具有周期性,随转速增加,力矩系数的均值和周期均减小,振荡幅度增大;随风速增加,力矩系数均值和振荡幅度均大幅上涨. 力矩系数呈调制波形式,风速对曲线形态有较大影响. 随风速增大,风力机的最佳转速和风能利用率逐渐增加. 当入口风速从7.5 m/s增加到9 m/s时,风力机的最佳转速和风力机的风能利用率最大值分别从13 r/min和23.2%增加到19 r/min和25.8%.     

搅拌槽内黏性流体流动的DPIV测量与CFD模拟

搅拌槽是化学工业及其相关工业广泛应用的设备之一,由于其内部流动的复杂性,搅拌混合操作目前尚未形成完善的理论体系．对搅拌槽的设计和放大,主要是依赖半经验的方法,对其内部流场有必要进行更深入的研究．目前对不同黏性流体的流动测量及计算流体力学模拟工作见诸报道较少,而     

Effect of impeller design and power consumption on crystal size distribution

Crystallization processes in a 500 mL stirred tank crystallizer with computational fluid dynamics (CFD) and population balances toward estimating how crystal size distributions (CSDs) are influenced by flow inhomogeneities was explored. The flow pattern and CSD are presented here though extensive phase Doppler particle analyzer measurements and CFD predictions for three different impeller designs (disc turbine, pitched blade turbine, and Propeller) and each rotated at three different speeds (2.5, 5, and10 r/s). As crystallization processes in practice could involve break‐up and aggregation of crystals, some selected break‐up and aggregation kernels are incorporated. Extensive comparison of simulations with experimental data showed consistent trends in the proper quantitative range. An attempt has also been made to develop scaling laws: (a) mean particle size with average power consumption per unit mass and (b) particle‐size distribution with the turbulent energy dissipation distribution. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3596–3613, 2014     

搅拌槽内近桨区流动场的数值研究

利用滑移网格方法，采用三种不同密度的网格，计算了六直叶涡轮搅拌桨的三维流动场。利用数值方法得到了桨叶附近流动场中产生的尾涡，并将不同密度网格下的数值模拟结果与实验数据进行了比较。计算结果表明，在高密度的网格下可以清楚地观察到桨叶附近所产生的尾涡，其大小与实验结果一致，但尾涡衰减较快：叶端的径向与切向速度分布与实验值吻合较好，加密网格对最大径向及切向速度的预测精度有明显提高；即使采用很高的网格密度，对湍流动能的预测仍然偏低。     

CFD simulation of stirred tanks: Comparison of turbulence models. Part I: Radial flow impellers

A critical review of the published literature regarding the computational fluid dynamics (CFD) modelling of single‐phase turbulent flow in stirred tank reactors is presented. In this part of review, CFD simulations of radial flow impellers (mainly disc turbine (DT)) in a fully baffled vessel operating in a turbulent regime have been presented. Simulated results obtained with different impeller modelling approaches (impeller boundary condition, multiple reference frame, computational snap shot and the sliding mesh approaches) and different turbulence models (standard k ? ε model, RNG k ? ε model, the Reynolds stress model (RSM) and large eddy simulation) have been compared with the in‐house laser Doppler anemometry (LDA) experimental data. In addition, recently proposed modifications to the standard k ? ε models were also evaluated. The model predictions (of all the mean velocities, turbulent kinetic energy and its dissipation rate) have been compared with the experimental measurements at various locations in the tank. A discussion is presented to highlight strengths and weaknesses of currently used CFD models. A preliminary analysis of sensitivity of modelling assumptions in the k ? ε models and RSM has been carried out using LES database. The quantitative comparison of exact and modelled turbulence production, transport and dissipation terms has highlighted the reasons behind the partial success of various modifications of standard k ? ε model as well as RSM. The volume integral of predicted energy dissipation rate is compared with the energy input rate. Based on these results, suggestions have been made for the future work in this area.     

Effect of blade pitch on the structure of the trailing vortex around rushton turbine impellers

Effect of blade number on the structure of the trailing vortex around the Rushton turbine impeller is examined by analyzing the data of mean velocities, deformation rates, turbulent kinetic energy and energy dissipation rates for 2-, 4-, 6- and 8-straight blades disk turbine impellers in a baffled standard geometry stirred tank. The data of Sauter mean bubble diameter near the blade tip are combined with the turbulent characteristics around the vortex to discuss how the blade number and the strength of the vortex affect the performance of the gas dispersion around the Rushton turbines under a low gassing rate. The results of this analysis show that if power input per each blade is the same, the impeller having four blades not only has the strongest average mean deformation rates and the largest turbulent kinetic energy, but also disperses the smallest average bubbles under the same gassing rate.     

Numerical optimization for blades of Intermig impeller in solid–liquid stirred tank

The multiphase flow in the solid-liquid tank stirred with a new structure of Intermig impeller was analyzed by computational fluid dynamics(CFD).The Eulerian multiphase model and standard k-ε turbulence model were adopted to simulate the fluid flow,turbulent kinetic energy distribution,mixing performance and power consumption in a stirred tank.The simulation results were also verified by the water model experiments,and good agreement was achieved.The solid-liquid mixing performances of Intermig impeller with different blade structures were compared in detail.The results show that the improved Intermig impeller not only enhances the solid mixing and suspension,but also saves more than 20% power compared with the standard one.The inner blades have relatively little influence on power and the best angle of inner blades is 45°,while the outer blades affect greatly the power consumption and the optimized value is 45°.     

CFD predictions of flow near impeller blades in baffled stirred vessels: Assessment of computational snapshot approach

The present article summarizes simulations of turbulent flow generated by a Rushton turbine (six blades with disc) and a downflow pitched blade turbine (four blades, 45° inclined) using a computational snapshot approach. The computational snapshot approach proposed by Ranade and Dommeti was extended and generalized to suit impellers of any shape. The approach was implemented using a commercial CFD code, FLUENT (Fluent Inc., USA). Mean flow and turbulence characteristics were computed by solving the Reynolds averaged Navier-Stokes equations combined with the standard k - l turbulence model. The QUICK discretization scheme (with SUPERBEE limiter function) was used to discretize all the governing equations. Preliminary numerical experiments were carried out to identify adequate grid resolution. The predicted results were compared with the comprehensive data set available in the literature. Simulated results show a pair of trailing vortex behind the blades of a turbine. The results were also compared quantitatively in the near-impeller region with the published experimental data and published simulated results using other approaches. The simulations have captured most of the key features of near-impeller flows with sufficient accuracy. The results and conclusions drawn from this study will have important implications for extending the applicability of CFD models to simulate complex stirred reactors.     

Enhancing particle erosion resistance of glass‐reinforced polymeric composites using carbon nanofiber‐based nanopaper coatings

Sand erosion may cause severe damage of blades in wind turbine and helicopter blades as well as many surface components of airplanes. In this study, thin nanopapers made of carbon nanofibers (CNFs) are used to enhance the resistance of solid particle erosion of glass fiber (GF)/wind epoxy composites. Finite element computer simulations are used to elucidate the underlying mechanisms. The much higher particle erosion resistance of nanopapers compared to GF‐reinforced epoxy composites is attributed to the high strength of CNFs and their nanoscale structure. The excellent performance in particle erosion resistance makes the CNF‐based nanopaper a prospective protective coating material for the turbine blades in the wind energy industry. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Process Design Aspects of Jet Mixers

In the present work, mixing time measurements have been made with jet mixers over a wide range of jet velocities, liquid levels and tank sizes. The nozzle was kept along the axis of the vessel and the nozzle clearance was varied over a wide range. It was observed that the mixing time decreases with an increase in the jet path length (nozzle clearance) for a given tank size and given amount of liquid. The reasons for this behaviour are explained with the help of CFD modelling. The effect of tank diameter has been studied independent of the jet path length. A correlation has been developed for process design. Jet mixers have been compared with impeller‐stirred tanks in terms of their energy efficiency. Reasons for the observed behaviour have been provided.     

全球风电复合材料发展概况

概述了全球风电市场的发展形势，简介了复合材料风轮叶片的规格、产量和市场价值，着重介绍了叶片各部分的制造工艺实例和制造叶片用的各种材料的研发情况。     

Simulation of Barium Sulfate Precipitation using CFD and FM‐PDF Modeling in a Continuous Stirred Tank

A mixing‐precipitation model combining computational fluid dynamics (CFD), finite‐mode PDF (probability density function) model, population balance and kinetic modeling has been proposed to simulate the barium sulfate precipitation process in a continuous stirred tank agitated by a Rushton turbine. The effect of various operating conditions such as impeller speed, feed concentration, feed position and mean residence time on the barium sulfate precipitation process is clearly demonstrated. It is shown that the mean crystal size increases by increasing the impeller speed and mean residence time. However, when the feed concentration is increased, the mean crystal size decreases. The predictions are in reasonable agreement with the experimental data in the literature.     

CFD simulation of flow and mixing characteristics in a stirred tank agitated by improved disc turbines

To reduce the power consumption and improve the mixing performance in stirred tanks, two improved disc turbines namely swept-back parabolic disc turbine (SPDT) and staggered fan-shaped parabolic disc turbine (SFPDT) are developed. After validation of computational fluid dynamics (CFD) model with experimental results, CFD simulations are carried out to study the flow pattern, mean velocity, power consumption, pumping capacity and mixing efficiency of the improved and traditional impellers in a dished-bottom tank under turbulent flow conditions. The results indicate that compared with the commonly used parabolic disc turbine (PDT), the power number of proposed SPDT and SFPDT impellers is reduced by 43% and 12%, and the pumping efficiency is increased by 68% and 13%, respectively. Furthermore, under the same power consumption (0-700 W·m^-3), the mixing performance of both SPDT and SFPDT is also superior to that of Rushton turbine and PDT.     

半椭圆管盘式涡轮桨搅拌槽内湍流结构的时间解析PIV研究(英文)

The turbulence structure in the stirred tank with a deep hollow blade (semi-ellispe) disc turbine (HEDT) was investigated by using time-resolved particle image velocimetry (TRPIV) and traditional PIV. In the stirred tank, the turbulence generated by blade passage includes the periodic components and the random turbulent ones. Traditional PIV with angle-resolved measurement and TRPIV with wavelet analysis were both used to obtain the random turbulent kinetic energy as a comparison. The wavelet analysis method was successfully used in this work to separate the random turbulent kinetic energy. The distributions of the periodic kinetic energy and the random turbulent kinetic energy were obtained. In the impeller region, the averaged random turbulent kinetic energy was about 2.6 times of the averaged periodic one. The kinetic energies at different wavelet scales from a6 to d1 were also calculated and compared. TRPIV was used to record the sequence of instantaneous velocity in the impeller stream. The evolution of the impeller stream was observed clearly and the sequence of the vorticity field was also obtained for the identification of vortices. The slope of the energy spectrum was approximately &;#61485;5/3 in high frequency representing the existence of inertial subrange and some isotropic properties in stirred tank. From the power spectral density (PSD), one peak existed evidently, which was located at f0 (blade passage frequency) generated by the blade passage.     

Numerical Simulation of Flow and Particle Collision in a Rotating‐Drum Bioreactor

Fluid flow and particle collision intensity in a rotating‐drum bioreactor are investigated by numerical simulation and a conventional stirred‐tank bioreactor is selected for comparison. Fluid flow is simulated by the computational fluid dynamics (CFD) software package FLUENT® whereas particle collision intensity is approached numerically through a hard‐sphere model. The dissipation rate of turbulent kinetic energy and the maximum particle collision intensity in the rotating‐drum bioreactor are about one order of magnitude smaller than those in the stirred‐tank bioreactor. The rotating‐drum bioreactor is likely to have a less severe impact on bioleaching microorganisms, and thus is expected to have great potential in the field of bioleaching processes.     

圆盘涡轮式桨叶对搅拌槽混合特性影响的CFD研究

利用CFD 技术对圆盘涡轮式搅拌槽内的浓度场进行数值模拟研究,主要考察了常见的平直桨叶（90°）、斜桨叶（60°和45°）的安装位置对混合时间θm、单位体积混合能Wr和浓度标准差σ的影响。在标准安装高度的平直桨叶下,对槽内速度进行分析,得到的数据与实验值非常吻合。研究表明：圆盘涡轮式桨叶由标准安装高度降低时,搅拌槽内的流型由径向流转变为轴向流,并且90°、60°和45°的转变为轴向流的相对安装高度（C/H）分别为0.20、0.233和0.267;混合时间是由槽内顶部和底部检测位置决定的;桨叶的标准相对安装高度（C/H=1/3）并不是混合性能最优的位置,针对90°、60°和 45°三种倾角的桨叶,在相对安装高度分别为0.213、0.267和0.320时的搅拌混合性能最佳;综合考虑省时、节能和混合均匀性的因素,倾角为45°的桨叶最佳,60°的桨叶次之。     

Experimental determination and numerical simulation of mixing time in a gas-liquid stirred tank

In this work, mixing experiments and numerical simulations of flow and macro-mixing were carried out in a 0.24 m i.d. gas-liquid stirred tank agitated by a Rushton turbine. The conductivity technique was used to measure the mixing time. A two-phase CFD (computational fluid dynamics) model was developed to calculate the flow field, k and ε distributions and holdup. Comparison between the predictions and the reported experimental data [Lu, W.M., Ju, S.J., 1987. Local gas holdup, mean liquid velocity and turbulence in an aerated stirred tank using hot-film anemometry. Chemical Engineering Journal 35 (1), 9-17] of flow field and holdup at same conditions were investigated and good agreements have been got. As the complexity of gas-liquid systems, there was still no report on the prediction of mixing time through CFD models in a gas-liquid stirred tank. In this paper, the two-phase CFD model was extended for the prediction of the mixing time in the gas-liquid stirred tank for the first time. The effects of operating parameters such as impeller speed, gas flow rate and feed position on the mixing time were compared. Good agreements between the simulations and experimental values of the mixing time have also been achieved.     

Effects of geometrical and physical factors on light particles dispersion by agitation characteristic curve

In this study, the effects of geometrical and physical factors on light particles dispersion in stirred tank were investigated by agitation characteristic curve. The experiments and CFD simulations with discrete phase model (DPM) and volume of fluid model (VOF) were conducted in this paper. Five factors, which include four geometrical factors (submergence, impeller-to-tank ratio, number of impeller blades and baffling mode) and a physical factor (liquid viscosity) were considered. For each factor, the power consumption curve and agitation characteristic curve were drawn to compare the power consumption and mixing results in the stirred tank. Characteristics of the agitation characteristic curves were compared with the previous published literatures and theories. It is found that the agitation characteristic curves reflect the tendency of power consumption and particles distribution well in stirred tank. The good agreement indicates the applicability of the agitation characteristic curves for the study of light particles distribution in stirred tank.     

风电叶片用聚氨酯模内胶衣的工艺适用性研究

模内涂装是提高风电叶片涂装效率的一种有效方式。相比模外涂层体系,风电叶片用模内涂层体系在工艺性能方面有一些特殊性要求。研究了三种聚氨酯模内胶衣在风电叶片中的工艺适用性,通过可操作性、占模时间、与玻璃钢之间的附着力、在实际叶片模具上的脱模性能以及脱模后对其覆盖的玻璃钢中灌注缺陷的可观察性等性能研究发现,其中两种聚氨酯模内胶衣适用于风电叶片的生产工艺过程。     

Numerical simulation of fluid dynamics in the stirred tank by the SSG Reynolds Stress Model

The Speziale, Sarkar and Gatski Reynolds Stress Model (SSG RSM) is utilized to simulate the fluid dynamics in a full baffled stirred tank with a Rushton turbine impeller. Four levels of grid resolutions are chosen to determine an optimised number of grids for further simulations. CFD model data in terms of the flow field, trailing vortex, and the power number are compared with published experimental results. The comparison shows that the global fluid dynamics throughout the stirred tank and the local characteristics of trailing vortices near the blade tips can be captured by the SSG RSM. The predicted mean velocity components in axial, radial and tangential direction are also in good agreement with experiment data. The power number predicted is quite close to the designed value, which demonstrates that this model can accurately calculate the power number in the stirred tank. Therefore, the simulation by using a combination of SSG RSM and MRF impeller rotational model can accurately model turbulent fluid flow in the stirred tank, and it offers an alternative method for design and optimisation of stirred tanks.