旋转固体发动机燃烧室-喷管两相流数值仿真

针对旋转引起的固体发动机内弹道性能和热防护性能变化影响发动机推力性能,从旋转对发动机内部燃气流动影响出发,用Reynolds时均N-S方程、Reynolds应力方程湍流模型(RSM)和颗粒随机轨道模型,在FLUENT软件上对不同旋转转速的固体发动机燃烧室-喷管内气-固两相流动进行了一体化数值仿真,比较了有无旋转两种状态下的流场结构,研究了转速对流场结构和发动机热结构的影响,并进一步研究了发动机的工作特性.仿真结果表明,发动机旋转使燃烧室内部流场结构发生显著变化,流场结构呈组合涡形式,粒子严重偏离发动机对称轴,导致燃烧室压强升高,推进剂燃速增大,发动机工作时间变短,热防护环境恶化,工作性能降低.这些变化随转速的增加呈现加剧趋势.研究结果为发动机设计提供了一定的技术支持.     

旋转发动机燃烧室头部气-固两相流场结构分析

在固体火箭发动机性能的研究中,采用N-S方程、Reynolds湍流模型和颗粒随机轨道模型建立了旋转固体火箭发动机头部区域气-固两相流数学模型,针对安全性,使用FLUENT软件对不同转速发动机头部区域流场进行了数值仿真,分析和比较了有无旋转两种状态下燃烧室头部区域流场结构,研究了转速对燃烧室头部流场结构及热环境的影响.结果表明:发动机的旋转使燃烧室内部流动与传热发生显著变化,导致燃烧室头部压强升高,热防护环境恶化,而且,变化随着转速的增加而迅速加剧,影响发动机内弹道性能和头部热防护性能,为发动机设计提供安全保障的依据.     

锤击实验台冲击盘三维流场数值仿真

在锤击实验台控制优化的设计中,引信的性能直接影响到弹丸发射的精确性,通过测试引信性能的锤击实验台高速旋转受到空气阻力的作用,对冲击盘有重要影响,从理论上分析锤击实验台冲击盘的外流场非常重要。通过数值仿真,可以大大缩短冲击盘的改进设计周期,减少研制经费。建立了实验台冲击盘的三维计算模型,采用Navier-Stokes理论、以AN-SYS/FLOTRAN流场计算软件为平台对实验台冲击盘进行了三维流场数值仿真。得到了冲击盘外流场的速度及压力的分布图并对其进行了分析,仿真结果为实验台冲击盘的优化设计和三维旋转物体的流场模拟提供了理论参考。     

双层桨搅拌浸出槽固液两相流场的数值仿真

在石煤提钒搅拌浸出槽的研究中,针对双层桨搅拌浸出槽固液悬浮特性以及混合浸出效果进行了研究.由于实验成本大、操作困难,提出了数值仿真的方法.运用计算流体力学(CFD)软件FLUENT对石煤提钒搅拌浸出槽进行流场仿真,用GAMBIT建立流场实体模型,采用k-ε湍流模型以及多重参考系法(MRF)处理搅拌桨区.探讨了双层桨同向旋转和双层桨异向旋转两种情况下的搅拌效果,结果表明在相同的情况下,双层桨异向旋转时湍动能分布更为合理,并且能够缓解底部沉积,搅拌混合效果更好.仿真结果对于研究搅拌反应容器内部流场规律,进而对搅拌反应容器的结构优化和浸出率的提高具有一定参考价值.     

双侧切向进气固冲发动机二次燃烧仿真

研究发动机性能优化问题,燃烧是关键技术.为提高同冲发动机二次燃烧效率,提出了一种新型切向进气方式,采用Realizablek-ε湍流模型及单步涡团耗散燃烧模型,对双侧切向进气式固冲发动机补燃室内三维反应流场进行了数值仿真,研究了切向进气对同冲发动机二次燃烧的影响.当空气射流以切向进入补燃室时,气流产生旋转,燃料与空气的...     

二硝基甲苯加氢反应器气液两相的数值模拟

对二硝基甲苯加氢反应采用的六叶轮自吸式反应器进行改进,并对改进前后反应器的气液分散性能进行实验及计算流体力学(CFD)模拟研究;采用模拟软件ANSYS fluent对自吸式反应器分别在600 rpm、800 rpm、1000 rpm条件下进行数值模拟;获得了反应器内气液混合过程的流场、局部气含率和整体气含率。结果表明:反应器的局部气含率分布较均匀;近壁处设置挡板可以有效改善气液两相的分散性能;改进后的反应器使二硝基甲苯加氢反应的速度加快了近10%。     

气相剪切旋转填料床流场特性的数值模拟

气相剪切旋转填料床是化工领域中一类新型高效的传质过程强化设备,适用于受气相阻力控制的吸收、精馏等过程。本文以计算流体力学方法(CFD)对该设备内气相流场进行了模拟研究,分析了气量为140 m~3/h、转速为1200 rpm时床内气相压力、速度和湍动能的分布情况,计算使用RSM湍流模型和SIMPLEC算法,填料部分用Porous Media模型。结果表明,GPS-RPB内压降主要来自旋转填料区;流场以旋流为主,切向速度远大于径向速度,沿径向的变化规律与实验值基本一致;扰流翅片可明显增强气相湍流,湍动能高于分层式填料旋转床。     

水平轴洋流涡轮的水动力特性研究

关于发电涡轮在各种洋流速度和不同的桨距角度下所产生的拉力和功率。同时对旋转流场的流场机理进行了研究。使用根据三维粘性结构网格和非定常雷诺平均Navier-Stokes方程的CFD程序,在多重网格方法针对800毫米直径的洋流发电涡轮进行数值仿真,并与其实验模型在水洞和实验水槽中的实验结果加以比较,通过比较,数值仿真和实验结果比较吻合,同时数值仿真很好地反映了水洞和水槽实验的水动力特性,证明了开发的CFD计算方法同传统方法相比,能够完全满足后续洋流涡轮水动力设计上的要求,可为设计提供参考。     

数值模拟喷嘴对多级多尺度液柱塔内部流场的影响

为了探索不同喷嘴对液柱塔的影响,本文希望以新型的多级多尺度液柱塔为研究对象,利用流体力学软件CFD模拟压力旋转和扇形雾化喷嘴,找出它们影响塔内流场分布的规律.以雷诺时均的奈维-斯托克斯方程(N-S)为基础,采用Lagrange离散相模型,预测喷嘴对气体流场分布的影响.数值模拟与实验结果表明,在压力旋转和扇形喷嘴组合使用条件下,浆液喷淋对烟气具有明显的整合作用,防止气体撞击,避免了雾沫夹带现象.模拟液气比与实验值的误差为4.6%,证明模拟液柱塔的模型比较实用.由于在模拟过程中忽略了内部构件对气液运动轨迹的影响,所以模拟结果存在一定的局限性.尽管模拟结果与实验数据有一定差距,但二者显示了相同的现象.尤其是通过颗粒轨迹的模拟研究之后,可以清楚地看出单级喷嘴存在的缺陷,为液柱塔喷嘴选择提供了重要的参考依据.     

Helmholtz共振腔气动噪声数值仿真

为探究出一套完整、准确的气动噪声仿真方法,用FLUENT和Actran仿真Helmholtz共振腔旁接管道系统模型.针对流场仿真,采用六面体网格建模,分析选择合适的网格密度,明确网格及边界条件的影响,以获得准确的声源信息;运用Lighthill声类比方法对声场进行仿真,采用数值计算、传声损失仿真和气动噪声仿真计算等3种方法提取管道内部场点声压级频谱曲线,分析曲线峰值频率特征,包括共振频率分析和声模态分析等.采用CFD软件与声学仿真软件相结合的方法,可以有效进行流场和声场的仿真.     

Modeling, analysis and design of centrifugal force driven transient filling flow into rectangular microchannel

Recently, centrifugal pumping has been discovered to be an excellent alternative method for controlling the fluid flow inside microchannels. In this paper, we have developed the physical modeling and carried out the analysis for the centrifugal force driven transient filling flow into a rectangular microchannel. Two types of analytic solutions for the transient flow were obtained: (1) a pseudo-static approximate solution, and (2) an exact solution. Analytic solutions include expressions for flow front advancement, detailed velocity profile and pressure distribution. The obtained analytical results show that the filling flow driven by centrifugal force is affected by three dimensionless parameters which combine fluid properties, rectangular channel geometry and processing condition of rotational speed. Effects of inertia, viscous and centrifugal forces were also discussed based on the parametric study. Furthermore, we have also successfully provided a simple and convenient analytical design tool for such rectangular microchannels, demonstrating two design application examples.     

Modeling, analysis and design of centrifugal force-driven transient filling flow into a circular microchannel

Recently, centrifugal pumping has been regarded as an excellent alternative control method for fluid flow inside microchannels. In this paper, we have first developed the physical modeling and carried out the analysis for the centrifugal force-driven transient filling flow into a circular microchannel. Two types of analytic solutions for the transient flow were obtained: (1) pseudostatic approximate solution and (2) exact solution. Analytic solutions include expressions for flow front advancement, detailed velocity profile and pressure distribution. The obtained analytic results show that the filling flow driven by centrifugal force is affected by two dimensionless parameters which combine fluid properties, channel geometry and processing condition of rotational speed. Effects of inertia, viscous and centrifugal forces were also discussed based on the parametric study. Furthermore, we have also successfully provided a simple and convenient analytic design tool for such microchannels, demonstrating two design application examples.     

A numerical study of the Coriolis effect in centrifugal microfluidics with different channel arrangements

The Coriolis force has been of great interest to control the transversal flow that is critical for mixing or switching fluids in centrifugal microfluidics. Therefore, the variation in the Coriolis effect has been extensively investigated by varying the rotational speeds and the cross-sectional geometry of microchannels. However, the subject of such investigations has been limited to radially positioned microchannels even though channels can lie everywhere on the rotating platform with different arrangements. In this study, we use numerical methods to investigate the Coriolis effect resulting from the angular alignment (AA) and radial displacement (RD) of rotating microchannels. Our analysis focuses on determining the contribution that different channel arrangements have in the deviation of parabolic velocity profiles, which is generally produced by the effective Coriolis force. We found that the flow can deviate even at a low rotational speed, where the Coriolis force is negligible, with an AA of up to 33 % which is a sufficient amount for flow switching. Once the rotational speed reaches to the critical RPM, the flow deviates by an effective Coriolis force, but the deviation systematically varies with AA or RD. As the Coriolis force becomes more dominant with a high rotational speed, the deviation reaches a saturation point, while flow rate is regulated by AA or RD, enabling the flow rate to remain low even at very high RPM, without reducing the deviation. The variation in the Coriolis effect due to the different channel arrangements investigated in this study is believed to provide an essential basis to design and develop centrifugal microfluidic systems.     

多功能转速测量仪的研制

针对目前在转速测量的过程中,存在着一定的误差,结合转速测量仪的测量方法进行改进,介绍了多功能转速测量仪的研制过程.它与原有的转速测量仪相比,在不降低技术指标的前提下增加了瞬态转速测量、低转速测量、计数、计时、线速度测量、双通道测量等功能.项目成果在今后的转速检测中将显现出良好的社会效益,并为计量行政管理部门提供有力的技术保障.     

小转动惯量永磁同步电机电流环内模控制

永磁同步电机调速系统由于电流动态过程中反电势的影响,特别是小转动惯量电机,电流动态响应明显恶化.为了减小电机动态过程中反电势对电流环的影响和改进电流动态响应性能,以考虑旋转反电势永磁同步电机电流二阶系统为对象,依据内模控制原理设计出小转动惯量永磁同步电机电流内模控制器,该方法参数单一,电流动静态性能好,鲁棒性强,工程上...     

Heat transfer in cylindrical shrouded cavities

The flow field, temperature field and the heat transfer rates in cylindrical shrouded cavities with rotation, recirculation and coolant through-flow have been analyzed numerically. Two cavity configurations are considered. In the first configuration, a heated cylindrical shroud is enclosed by a stationary insulated stator disc and a rotating insulated rotor disc. The coolant air enters the cavity by a central opening in the rotor and exits through an annular gap at the rim of the rotor. The second configuration studies the heat transfer from an air cooled gas turbine disc using the model of a plane disc rotating close to an insulated shrouded stator. The coolant enters centrally through the stator disc and exits radially through a gap between the shroud and the rotor. The flow field and heat transfer rates are computed for several values of coolant flow rate, the rotor swirl speed, the cavity aspect ratio and the exit gap width in the two cavity configurations. The swirl of the rotor changes immensely the flow pattern, recirculating zones and isotherms inside such cavities. In general, increasing coolant flow rate, decreasing swirl and decreasing aspect ratio enhances the heat transfer from the shroud in the first cavity configuration. For the second cavity configuration, the heat transfer rates increase with increasing coolant flow rate, increasing swirl of the rotor, increasing size of the cavity and decreasing exit gap width between the stator and the rotor.     

Numerical simulation and PIV measurement of the flow-field in optical disc drives

A system of numerical flow simulation with an automated mesh generator and parallelized solver was developed and applied to the flow-field inside an optical disc drive. In this simulation system, a uniformly spaced Cartesian grid is used to reduce time and automatically generate a mesh from CAD data for complicated geometries, such as optical disc drives. The simulation results of optical disc drives are validated by particle image velocimetry (PIV) and pressure-distribution measurements. The measured velocity distributions above a rotating disc and around a pick-up unit show quantitative agreement with the simulated distributions. For the pressure distributions on a top case of an optical disc drive, although there is an error of 10% between simulated and measured results, the position of the peaks and distribution of pressure show good agreement. Comparing both sets of measurements, the simulation results in a Cartesian grid system are sufficiently accurate to enable the flow-field to be quantitatively assessed. This numerical flow simulation is applied to investigate the detailed flow-field in a commercial optical disc drive.     

一种无刷直流电动机快速制动准确定位控制方案的设计

介绍了一种新的无刷直流电动机快速制动准确定位的控制方案。该方案在电动机刹车制动时使电动机电源端短接,利用制动单元使电动机惯性所产生的电流在电动机内产生一个与惯性旋转方向相反的旋转磁场,从而在电动机内部产生较大的阻尼磁场,使电动机快速制动;当电动机断电制动时,由3个角位移传感器检测出电动机转速,根据转速的高低计算并确定电动机的启控位置,并传输到PLC,由PLC控制电动机在设计的位置完全停止,从而实现准确定位。实验测试结果表明,该方案准确、可靠。     

Critical rotational speed,critical velocity of fluid flow and free vibration analysis of a spinning SWCNT conveying viscous fluid

In this article, the influences of rotational speed and velocity of viscous fluid flow on free vibration behavior of spinning single-walled carbon nanotubes (SWCNTs) are investigated using the modified couple stress theory (MCST). Taking attention to the first-order shear deformation theory, the modeled rotating SWCNT and its equations of motion are derived using Hamilton’s principle. The formulations include Coriolis, centrifugal and initial hoop tension effects due to rotation of the SWCNT. This system is conveying viscous fluid, and the related force is calculated by modified Navier–Stokes relation considering slip boundary condition and Knudsen number. The accuracy of the presented model is validated with some cases in the literatures. Novelty of this study is considering the effects of spinning, conveying viscous flow and MCST in addition to considering the various boundary conditions of the SWCNT. Generalized differential quadrature method is used to approximately discretize the model and to approximate the equations of motion. Then, influence of material length scale parameter, velocity of viscous fluid flow, angular velocity, length, length-to-radius ratio, radius-to-thickness ratio and boundary conditions on critical speed, critical velocity and natural frequency of the rotating SWCNT conveying viscous fluid flow are investigated.     

An experimental study on the flow behavior near the read-and-write arm in a hard disk drive model with a shroud opening

Complex flow inside a hard disk drive (HDD) was investigated using a simplified 3.5″ model for clarifying the mechanism causing flow-induced vibration. In contrast to the authors’ related study in the past, our model had a non-axisymmetric geometry equipped with a shroud opening and a read/write arm (RWA). The model is designed to serve as a benchmark to study HDD flows both in experiments and in numerical simulations. The complex flow behavior in the disk-to-disk space was investigated with the RWA inserted into the inter-disk space. Flow measurements were carried out with a test rig which consisted of transparent disks, RWA and covers. The measurements were performed at the disk Reynolds number Re _d  = 1.2 × 10⁵ which corresponds to the rotation speed of 7,700 rpm of a real 3.5″ HDD. Two sets of the flow measurements were performed—the first Reynolds stress components measured along four different lines with the RWA inserted at a shallow angle (experiment I), and the other mean and rms velocity statistics along several selected lines with two different RWA insertion angles (experiment II). The mean velocity and velocity variance were obtained at a spatial resolution of 30 μm along eight different lines perpendicular to the disk surfaces. The high spatial resolution of the results was achieved using a laser Doppler velocity profile sensor with a physical resolution in micrometers and a velocity uncertainty of 0.2 %. In the experiment I, the mean velocity and velocity variance statistics were mostly consistent with the common findings in other studies using axisymmetric models except for the flow behavior in the radial direction at the shroud opening. The secondary flow behavior was likely caused by the shroud opening which was not included in most of the models in the past. In experiment II, the mean velocity and velocity variance were successfully measured through examination of the flow above and below the RWA in the space between the rotating disks. The resulting velocity statistics exhibit turbulent Couette-like flow in the narrow 1 mm space between the disks and the RWA.