线性变壁厚药型罩形成射流的数值模拟

采用有限元程序对顶部薄、底部厚的变壁厚药型罩爆破形成聚能射流的过程进行二维仿真模拟。以罩壁的变化率为特征,讨论了线性变化率为0.78%-7.83%的8种药型罩爆破形成射流的形态和射流形态参数的变化,并与等壁厚药型罩爆破形成的射流进行了对比。结果表明,罩壁的变化率对射流的形状、长度和断裂时间均有较明显的影响;对于本文所采用的装药结构而言,变化率在2%左右的线性变壁厚药型罩爆破效果最佳,并优于同等装药条件下线性等壁厚药型罩的爆破效果。     

线性变壁厚药型罩形成射流的数值模拟

采用有限元程序对顶部薄、底部厚的变壁厚药型罩爆破形成聚能射流的过程进行二维仿真模拟。以罩壁的变化率为特征,讨论了线性变化率为0.78%-7.83%的8种药型罩爆破形成射流的形态和射流形态参数的变化,并与等壁厚药型罩爆破形成的射流进行了对比。结果表明,罩壁的变化率对射流的形状、长度和断裂时间均有较明显的影响;对于本文所采用的装药结构而言,变化率在2%左右的线性变壁厚药型罩爆破效果最佳,并优于同等装药条件下线性等壁厚药型罩的爆破效果。     

An empirical model for predicting air infiltration into refrigerated stores through doors

An empirical model based on Tamm's equation was developed to predict the rate of air infiltration through doors into refrigerated buildings. The model sums the contributions of air-tightness, air infiltration due to door openings and the additional air exchange caused by forklift traffic through the doors. The model was validated against measured air infiltration rates through rapid-roll and sliding doors into 7 commercial coldstores with sizes ranging from 740 to 12,000 m³ operating at temperatures ranging from 3.3 to –21.8 °C.     

Rapid decompression of pressurized aircraft fuselages

A methodology for determining compartment pressures at any point during a rapid decompression of a pressurized aircraft fuselage is presented. The approach takes into consideration the mass and mass moment of inertia of panels and doors through which pressurized air must pass. Failure to consider vent panel mass is shown to severely underestimate the pressure differential across partitions separating compartments during a rapid-decompression event.     

尺度效应对水下合成射流推力特性影响研究

该文通过数值方法研究了尺度效应对水环境下合成射流推力及推进效率的影响,不同尺度下激励器的网格采用等比例缩放的方式得到,数值计算在fluent进行,且数值计算方法通过实验数据进行了验证。数值计算结果发现,当激励器尺度为0.1 mm时,推力曲线与速度曲线非常接近,此时平均推力及推进效率均较小。随着尺度增加,当激励器尺度大于1 mm时,推力曲线不对称度增加,且推力曲线的上升区间所占周期增加而下降区间所占周期减小,此时平均推力及推进效率都有明显提高。建立了合成射流的推力模型,该模型将合成射流推力分解为三部分：质量效应、加速效应及外部流场的压强效应。给出了不同尺度下的涡量图、速度分布图,通过对其分析可知,尺度较小时粘性作用较强,此时,内部流体的加速效应及外流场压强效应均很小,导致推进效率较低。随着尺度增加,粘性作用减弱,推进效率开始增加,当尺度增加到粘性可以忽略时,推进效率不再随尺度增加。     

Monte Carlo code for microdosimetry of inhaled alpha emitters

A Monte Carlo code has been developed to calculate the local energy deposited by alpha emitters deposited on the inner surface in the lung airway. Developed to deal further with airway bifurcations, this code has been as a first step validated in a cylindrical airway configuration by comparison with well-established analytical codes in the case of contamination of bronchiolar airways with actinides. The code has then been applied to the study of uniform and non-uniform contamination of cylindrical bronchial airways by radon progeny in indoor and mine exposure conditions. In addition to the microdosimetric spectra, the average microdosimetric parameters (zp, n, z) have been evaluated. The work currently in progress consists in adapting this developed Monte Carlo code to the configuration of an airway bifurcation with realistic particles deposition.     

Study of the dispersion of natural gas issuing from compressor stations through silencers with upper cover

The aim of the present study is the simulation of the dispersion of natural gas issuing from the silencer of compressor stations during vent operations. The objective is to analyze the dispersion of the gas emitted under different conditions of mass flow rate at the exit and ambient cross-flow velocity. We have considered a silencer with an upper cover to protect it from the rain and the fall of objects. The influence of the upper cover of the silencer on the dispersion of natural gas has also been studied, and non-dimensional approaches of the model have been proposed to simplify the problem. Seven different cases have been solved, using two models: a 3D model based on the commercial code FLUENT, and a simplified quasi-one-dimensional model. The results obtained in both cases have been compared, and the range of validity of the one-dimensional model in non-dimensional form has been discussed.     

并联矩形突扩微通道气液两相流动特性研究

微尺度下的相变强化传热是微电子领域散热的研究热点,而微通道内气液两相流流型和压降分析是微流动系统设计和控制的基础。本文针对并联矩形突扩微通道,通过流型可视化、理论分析及实验研究的方式,对微通道内两相流动特性进行了分析研究。通过可视化实验,在并联矩形突扩微通道内观察到了4种典型流动,分别为泡状流、塞状流、弹状流和环状流。当Qg=110 m L/min、Ql=20 m L/min时,两相流动流型达到最大程度的射流状态,出现充分流体射流情况。通过建立压降预测模型,结合实验结果分析了压降模型的适用性和精度,结果表明:含有突扩结构的并联矩形微通道在质量流速为367～691 kg/(m2·s)范围内的压降预测模型的平均预测误差为18. 56%,优于经典文献中的预测精度,且随着整体压降的增大,预测精度增大。     

External failure pressure of a frangible laminated composite canister cover

The static failure strength of a frangible laminated composite canister cover subjected to uniform external pressure is studied via both theoretical and experimental approaches. The frangible canister cover, which is fabricated with four plate-like laminated composite parts, which is designed in such a way that it will fail in a predetermined pattern when subjected to an impulsive internal pressure and its external failure pressure is much higher than its internal failure pressure. The stress distribution in the canister cover is determined using the finite element method and the failure of the cover identified on the basis of an appropriate failure criterion. A number of laminated composite canister covers were fabricated and subjected to static external pressure testing. The failure modes of the frangible covers are studied and the experimental results are used to verify the theoretical predictions. Close agreements between the experimental and theoretical results have been observed. The present study shows that the design of frangible covers with external failure pressure much higher than the internal failure pressure can be achieved.     

CFD simulation of estimating critical shear stress for cleaning flat soiled surface

Turbulent water jet impingement on surfaces has several applications in cleaning processes and heat transfer equipment. This work aims to find the effect of variation in inlet jet Reynolds number on variation wall shear stress and pressure on surfaces encountered in equipment used in food processing industries, particularly in the dishwasher domain. Computational fluid dynamics simulation of turbulent water jet for Re >6000 is performed in ANSYS Fluent. Simulations are run using the volume of fluid Eulerian multi-phase model with the standard k-ε turbulence modeling. Discretisation is carried out by the implicit unsteady solver scheme, and the SIMPLE algorithm is chosen to solve the set of equations. Shear stress at Re = 6300 is validated with experimental results. There is drastic variation in the static pressure and wall shear stress with Reynolds number. Critical jet exit velocity required for effective cleaning of flat plaste is found to be 3 m/s.     

Research on Torque Calculation Method of Permanent-Magnet Spherical Motor Based on the Finite-Element Method

In this paper, the finite-element method (FEM) is used to calculate the spinning torque of the permanent-magnet (PM) spherical motor. Three-dimensional (3-D) FE model of the PM spherical motor is established. Spinning torque distribution on the spherical surface and its variation curve on the equator are obtained respectively. In order to avoid the complicated torque calculation process under 3-D magnetic field and thus reduce the computational burden, the torque calculation method based on the 2-D conversion model is proposed. This method equivalently simplifies the magnetic field of the spherical PMs and the shape of cylindrical stator windings to be simulation parameters of the 2-D conversion model. With these parameters, 2-D conversion model of the PM spherical motor is established. Spinning torque variation curves obtained by the 3-D model and the 2-D conversion model respectively are compared and the results agree extremely well. By comparing the maximum static torque (MST) obtained under different configuration parameters of the PM spherical motor, it is found that the errors are within the allowable range. Therefore, the reliability of the proposed torque calculation method in the paper is verified. Finally, based on the 2-D conversion model, variation curves of the MST with the length of the air gap, the ampere turns, the length of stator windings and the outer radius of stator windings are obtained, and they are validated by those based on the 3-D model. These results can provide the basis for the optimization of the PM spherical motor.      

Influence of water pressure and apex angle on prediction of particle size for atomization of copper powder

Water atomization can be used to produce wide range of particle size, shape and particle size distribution of metal powder efficiently by varying operating variables which include design parameters, process parameters and thermophysical properties of metal and water. Liquid copper was water atomized in a laboratory fabricated atomizer. Few experiments were conducted to produce copper powder by varying water jet pressure. In the present work, mathematical model was formulated to propose a relationship between particle size of copper powder and operating variables. Proposed mathematical model is developed to predict particle size affected by different parameters and validated with experimental results. 3-D surface response was analyzed by varying water pressure and apex angle.     

某制冷机房氨气泄漏时气流组织优化分析

本文针对氨制冷压缩机低压吸气管道破裂后氨制冷剂泄漏的场景,采用计算流体力学(CFD)的方法对不同气流组织下事故通风过程进行了数值模拟,对比了不同气流组织下的事故通风有效性.计算结果表明:侧墙排风口上沿距顶在0～0.2 m范围内对污染物排除几乎没有影响.在氨制冷机房两端有门,中部有上、下两排窗的情况下,对于通风120 s...     

A New Frangible Composite Canister Cover with the Function of Specified Direction Separation

A lightweight and auto-separated canister cover is required for quick launching in some specific missile launchers. In this paper, a new frangible composite canister cover with the function of specified direction separation is proposed and studied via both experimental and numerical approaches. The frangible canister cover with local non-split weak zone structure, which is manufactured by traditional hand lay-up process with vacuum assisted resin infusion (VARI) method, is designed to fail and separate in a predetermined and specified direction in comparison with the cover with full split weak zone structure. This design is innovative and also necessary for reduction of potential risk to peripheral equipment around the missile launcher. The failure pressure of the cover is determined on the basis of the failure criteria used in finite element (FE) model. In experimental pressurized testing, a number of frangible canister covers subjected to pressure loadings in six cases are studied. Close agreements between the experimental and numerical results have been examined. The frangible canister covers with local non-split weak zone structure which have been studied can be separated and fly out to the specified direction.     

Modeling the characteristic types and heat release of stretched premixed impinging flames

 A numerical code has been developed for the simulation of the impingement of a turbulent jet on a plane surface. The performance of three turbulence models is assessed under isothermal conditions. Predictions are compared with experimental data from the literature. Based on the results an appropriate turbulence model is selected to model a premixed jet flame impinging on a solid surface. Mass transfer and combustion are modeled with a two-equation model simulating volumetric and kinetically controlled chemical reaction rates. Modeling of heat transfer accounts for convection and radiation effects. Results show that under high pressure environment turbulent premixed flames are of wrinkled-thickened type near the outlet of the nozzle (free jet region) and of wrinkled reaction sheets in the area near the surface (impingement region and radial wall jet). The results establish that appropriate choice of turbulence and combustion models can lead to accurate prediction of the flow characteristics.     

Jet sharpening by turbulent mixing

Jets or localized strong currents in planetary atmospheres, as well as in the Earth's oceans, are often associated with sharp potential-vorticity gradients owing to the inherent balance exhibited by these flows. Here, we explore and quantify jet sharpening in a simple idealized single-layer quasi-geostrophic model on a mid-latitude β-plane. The advantages of this idealization are that just two parameters control the flow development (the Rossby deformation length and the amplitude of the initial random flow perturbation), and that numerical experiments can comprehensively and accurately cover the parameter space. These experiments, carried out at unprecedented numerical resolution, reveal how an initially broad jet is sharpened, and the role played by coherent vortices in the vicinity of jets.     

基于CFD/CSD耦合的颤振与动载荷分析方法

采用CFD/CSD耦合方法,建立了气动弹性仿真系统。基于系统辨识的方法,使用Volterra级数建立了降阶模型(ROM),实现了颤振边界的快速求解,分别使用CFD/CSD全耦合方法与ROM完成了AGARD 445.6标模的颤振分析,计算结果与实验相符较好。使用ROM完成了带边条平直翼的颤振分析。使用CFD/CSD耦合方法计算了此机翼在飞行动压下的气弹响应,结果表明即使在颤振边界内,仍然有可能出现极限环振荡（LCO）。对此,分析了其气弹响应中的动载情况。结果表明基于CFD/CSD耦合的方法可以真实地仿真气弹响应过程,准确地分析气弹响应中的动态载荷情况     

A toroidal approximation of capillary forces in polydisperse granular assemblies

In this paper we propose a numerical procedure for the prediction of capillary forces in polydisperse granular assemblies at a degree of moisture content that corresponds to the so-called pendular regime. The capillary force model is adopted within the Laplace–Young framework with a toroidal approximation of the liquid bridge geometry. Governing equations are first derived in a form that highlights the role of intrinsic parameters such as inter-particle separation distance, ratio of particle radii and liquid volume. A proper scaling of these equations is adopted so that the solution applies to any particle pair configuration. Numerical integration algorithms are provided in a way that facilitates implementations in macroscopic procedures for computer simulations. A qualitative evaluation is undertaken to highlight model predictions of the effects on capillary force of various intrinsic parameters that characterise the particle pair and liquid bridge. The model is validated against the experimental results provided by Willet et al. (Langmuir 16:9396–9405, 2000) for a wide range of liquid volumes and particle-pair polydispersity.