前向多翼叶轮流动分析及出口滑移的计算

本文分析了离心风机前向多翼叶轮内的流动特性,计算了跨叶片面内的理想流场和湍流边界层.用三次样条平滑和旋转坐标变换方法解决了用流线曲率法数值解大曲率流场时的收敛问题;用考虑旋转和曲率对流动结构影响的Richardson数修正理想流场.提出了一种予测叶片边界层分离及流动滑移的方法.     

气固两相流离心风机叶片载荷特性的研究

本文利用气－固两相流单相耦合和简化的双相耦合模型,计算了离心风机四种典型荷规律叶片的磨损与积尘特性,考察了叶片的加载规律与其磨损部位,磨损量和积尘趋势的关系以及固粒在叶片上的碰撞角,碰撞速度的分布规律,为设计高效含尘风机提出了新的建议。经过固相对风机特性影响的实验研究。证了用于予测风机磨损特性的“单相耦合”模型的可行性。     

固粒直径对含尘风机磨损恶化规律的影响

本文对含尘离心风机内粒子的直径与叶轮磨损的关系进行了计算与分析，用Ｌａｇｒａｎｇｅ法计算了固粒在叶轮中的运动轨迹和不同粒径时叶片的磨损状况。发现小粒径粒子对叶片磨损较均匀，而大粒径粒子使叶片磨损恶化；存在一个临界粒径Ｄ＿ｃｒ，当粒径ｄ＿ｐ＜Ｄ＿ｃｒ时，随着粒径的增长，粒子对叶片磨损急剧恶化，而ｄ＿ｐ＞Ｄ＿ｃｒ时，叶片磨损随粒径增长的变化趋于平缓；固相浓度对叶轮磨损的影响也与粒子直径有关。     

离心泵叶片边界层分离对水动力特性的影响

给出了离心泵叶片近壁表面流体粘性流动的分析方法,通过对叶片压力面边界层参数的计算和边界层分离的判断,确定分离型和流线型叶片型线,又通过对测试泵的性能对比试验,验证了叶片型线对水动力特性的影响,明确了这种影响主要体现在离心泵的水力效率、动力性能方面,并指出叶片形状的变化是导致其表面流体边界层分离点位置移动的主要原因,它决定了边界层是否分离,而过大的分离将使测试泵的性能下降,振动剧烈、噪声增大,并强调应重视边界层分析在叶片水力设计中的作用,同时给出了叶片型线水力设计的评价依据。所得结论对低比转速离心泵水动力特性的改善有参考价值。     

水泵叶片表面三维边界层计算

本文用有限差分法计算混流式可逆水力机械水泵工况叶片表面的三维边界层。水泵叶轮中主流区的三维势流由直接边界元法计算。对于叶片面附近的粘性流动。用三维半正交坐标系中的边界层方程表示。为了提高计算精度采用贴体坐标技术生成边界层区域的计算网格。并利用Cebeci等变换函数及Keller差分格式离散方程。用分块解法求解。计算叶轮叶片表面的压力分布与相应试验结果进行了对比。     

柱形罐爆炸碎片抛射的Monte-Carlo分析

在动力学分析的基础上,将二维体系内的碎片轨迹方程扩展到三维体系内,将风这一影响因素考 虑在内。以墨西哥事故中水平圆柱储罐发生沸腾液体扩展为蒸气云爆炸(BLEVE)为例,利用Monte-Carlo法 模拟出碎片的轨迹曲线,计算得到有风和无风情况下碎片抛射距离的概率分布,得到一般情况下风对碎片危 害的影响较小。计算了无风情况下碎片碰撞目标容器的概率,得到碰撞概率随罐间距的增大而呈现严格的指 数衰减趋势,通过此关系式可以计算出符合安全要求的罐间距。研究结果对于提高储罐的安全性、缓解和控 制碎片产生的风险具有一定的指导意义。     

风机叶片包容性分析

应用有限元方法对丢失的失效风机叶片撞击机匣的非线性瞬态响应进行了数值计算研究,模拟了叶片的包容过程,分析了包容过程中叶片、机匣的变形与能量变化。结果表明:有限元方法能较好的模拟风机叶片丢失后撞击机匣的过程,该型风机机匣对叶片具有包容性。研究结果对于进行风机叶片包容性设计具有重要参考价值。     

高速碰撞数值计算中的SPH自适应粒子分布法

针对传统光滑粒子法在计算高速碰撞问题时会出现近邻粒子逸出核函数影响域而产生数值破坏这一缺陷,提出了一种根据粒子间距变化自动添加、合并粒子的SPH自适应粒子分布算法。采用该方法对Taylor碰撞和超高速碰撞问题进行了数值模拟,结果表明,该方法可以有效地消除计算中出现的数值破坏,提高计算精度。     

激波诱导含灰气体边界层中的粒子分布

本文研究当激波沿着一个固体表面等速地穿越含灰气体运动时所诱导的层流边界层特性。考虑了作用在气体边界层中球形粒子的 Saffman 升力,建议了一种计算近壁区中弥散相密度剖面的方法,并给出了数值计算结果。本文结果表明:在激波后方存在着一个弯曲的薄层区域,其中的粒子密度可以比其波前原始值增加许多倍。这种粒子聚集效应对于工业中粉尘爆炸等实际问题具有重要意义。     

串列叶片式前向离心风机气动与噪声特性的优化研究

对采用串列叶片的某前向离心风机内部三维非定常流动进行了数值计算,重点研究了串列叶片不同叶片相对长度和不同叶片相对周向位置两个参数对风机气动性能及气动噪声的影响.通过响应面方法对数值结果进行二次回归拟合,得到两个参数与风机效率和A声级间的函数关系,并进行了优化分析.数值结果表明:两个参数对串列叶片式前向离心风机效率和A声级均有较大影响,合理的串列叶片设计能够在保持气动性能基本不变的情况下降低风机的气动噪声.将可靠的CFD数值技术与响应面方法结合起来用于指导离心风机的改进及试验设计是可行的,本文的研究结果可为串列式离心风机在节能与降噪的总体设计方面提供参考.     

Investigation of a Gas Flow with Solid Particles in a Supersonic Nozzle

A two-phase flow with high Reynolds numbers in the subsonic, transonic, and supersonic parts of the nozzle is considered within the framework of the Prandtl model, i.e., the flow is divided into an inviscid core and a thin boundary layer. Mutual influence of the gas and solid particles is taken into account. The Euler equations are solved for the gas in the flow core, and the boundary-layer equations are used in the near-wall region. The particle motion in the inviscid region is described by the Lagrangian approach, and trajectories and temperatures of particle packets are tracked. The behavior of particles in the boundary layer is described by the Euler equations for volume-averaged parameters of particles. The computed particle-velocity distributions are compared with experiments in a plane nozzle. It is noted that particles inserted in the subsonic part of the nozzle are focused at the nozzle centerline, which leads to substantial flow deceleration in the supersonic part of the nozzle. The effect of various boundary conditions for the flow of particles in the inviscid region is considered. For an axisymmetric nozzle, the influence of the contour of the subsonic part of the nozzle, the loading ratio, and the particle diameter on the particle-flow parameters in the inviscid region and in the boundary layer is studied. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 6, pp. 65–77, November–December, 2005.     

Numerical study of elbow erosion due to sand particles under annular flow considering liquid entrainment

Sand particle erosion is always a challenge in natural gas production. In particular, the erosion in gas–liquid–solid annular flow is more complicated. In this study, a three-phase flow numerical model that couples the volume of fluid multiphase flow model and the discrete phase model was developed for prediction of erosion in annular flow. The ability of the numerical model to simulate the gas–liquid annular flow is validated through comparison with the experimental data. On the basis of the above numerical model, the phase distribution in the pipe was analyzed. The liquid entrainment behavior was reasonably simulated through the numerical model, which guaranteed the accuracy of predicting the particle erosion. Additionally, four erosion prediction models were used for the erosion calculation, among them, the Zhang et al. erosion model predicted the realistic results. Through the analysis of the particle trajectory and the particle impact behavior on the elbow, the cushion effect of the liquid film on the particles and the erosion morphology generation at the elbow were revealed.     

采用不同黏性处理方法的宽无叶扩压器不稳定流动研究

径向无叶扩压器的全局稳定性可能受到核心主流失稳,出口回流与壁面边界层分离等因素影响,对于宽无叶扩压器,无黏核心主流与壁面边界层流动对不稳定扰动诱发的作用机理是当前研究的重点.本文首先通过数值计算获得了大宽度比孤立无叶扩压器平均流动,然后基于小扰动理论和周向均质假设,分别对欧拉方程与 Navier-Stokes 方程进行线性化,建立了基于无黏核心流动的稳定性分析方法,以及基于涡黏性与分子黏性的混合稳定性分析方法;通过与实验结果的对比,验证了混合稳定性分析方法预测所得流动失稳频率和全局直接模态的准确性;最后基于伴随方法获得了特征值的结构敏感性,揭示了不同黏性处理条件下宽无叶扩压器内全局不失稳扰动的源发区域.在只考虑核心主流的无黏条件下,宽无叶扩压器内流动不稳定扰动来源于流场中部,为二维的离心失稳;在同时考虑核心主流与边界层的作用时,宽无叶扩压器不稳定扰动不仅来源于扩压器流场中部的核心主流,壁面回流对于不稳定扰动的产生了重要影响.      

Gas and particle motion in jets in fluidized beds

Entrainment of solid particles by gas jets discharged downwards through slotted nozzles into bubble-free beds of fluidized particles is considered. The gas flow in the jet is calculated for irrotational flow, using a correlation established previously for slot opening as a function of operating variables. The momentum boundary layer thickness and shear stress at the horizontal interface between jet and particles are then calculated by integral boundary layer analysis. The calculated shear stress distributions are consistent with measurements of the momentum of bed particles caused to saltate by the jet, and explain the dependence of particle movement on the various operating variables. The results provide a direct confirmation of a hypothesis due to Owen on the mechanism of saltation.     

离心叶轮正冲角流场计算的边界层方法

本文使用stanitz快速分析法计算主流,用积分法计算带旋转和曲率的二维不可压湍流边界层.通过流量方程将两者紧密联系起来、同时求解,能够连续计算至分离区.可方便快速地用于估算离心叶轮在正冲角工况下的流场.     

Modeling of Ice Accretion on the Airfoil Surface in an Air Flow Containing Ice Particles

The process of airfoil icing caused by incidence of ice crystals is considered. A physicomathematical model of motion of spheroidal crystals in the gas flow and their interaction with the body is formulated. The model takes into account the non-spherical particle orientation with respect to the velocity vector of the gas flow. It is assumed that the particle impact onto the body surface leads to partial destruction of the particle under the action of normal and tangential stresses, and some part of the particle mass remains in the vicinity of the impact point. An inviscid flow around the airfoil with a time-dependent shape is calculated by the method of approximate conformal mapping.     

Two-phase couette flow

A study is made of plane laminar Couette flow, in which foreign particles are injected through the upper boundary. The effect of the particles on friction and heat transfer is analyzed on the basis of the equations of two-fluid theory. A two-phase boundary layer on a plate has been considered in [1, 2] with the effect of the particles on the gas flow field neglected. A solution has been obtained in [3] for a laminar boundary layer on a plate with allowance for the dynamic and thermal effects of the particles on the gas parameters. There are also solutions for the case of the impulsive motion of a plate in a two-phase medium [4–6], and local rotation of the particles is taken into account in [5, 6]. The simplest model accounting for the effect of the particles on friction and heat transfer for the general case, when the particles are not in equilibrium with the gas at the outer edge of the boundary layer, is Couette flow. This type of flow with particle injection and a fixed surface has been considered in [7] under the assumptions of constant gas viscosity and the simplest drag and heat-transfer law. A solution for an accelerated Couette flow without particle injection and with a wall has been obtained in [6]. In the present paper fairly general assumptions are used to obtain a numerical solution of the problem of two-phase Couette flow with particle injection, and simple formulas useful for estimating the effect of the particles on friction and heat transfer are also obtained.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 42–46, May–June, 1976.     

Three-dimensional gas flow in a rotating cylinder with a retarding cover

The study of rotating flows is of interest due to both the development of the centrifugal method of separation of gas and isotope mixtures and the possibility of astrophysical applications. An analytical nonlinear model for calculating the hydrodynamic characteristics of the viscous incompressible fluid flow in a rotating cylinder in the presence of a retarding cover is presented. The cases of stationary and rotating covers are considered. The analysis is performed on the basis of the system of hydrodynamic Navier-Stokes equations. The flow domain is divided up into the main flow and end boundary layers at the cylinder bottom and at the rotating cover. In its turn, the main flow is divided up into an inviscid quasi-rigid core and a lateral layer within which almost the entire upward circulatory flow is concentrated. The equations of the boundary layers at the end surfaces are analyzed by the approximate Slezkin-Targ method. The solutions in the boundary and lateral layers are “stitched” together with the velocity distribution in the main flow core. The unknown angular velocity ω ₁ and radial boundary R ₁ of the core are determined from the balance of the moments of the friction forces acting on the main rotating flow and the continuity condition for the circulatory flow. The experimental and calculated data are compared.     

Numerische Berechnung des Partikeltransportes zu einer laminar angeströmten Kreisscheibe

Increasingly process steps become important, in which particles as product particles or contaminants are deposited on substrates out of the gas phase. In this paper the particles transport processes are investigated close to the surface of a circular plate surrounded by a laminar flow. The analogy between the governing equations of momentum, energy and mass is applied to the extended diffusion equation. In the nondimensional form the results of the numerical calculations give informations about velocity, temperature and particle concentration boundary layer thickness as well as their distributions. Especially the impact of external forces on particle concentration boundary layer thickness and profile is discussed. The transport of submicron particles to the surface due to convection, diffusion, gravity and thermophoretic forces acting independently is investigated. In the used normalized form the different forces are acting as one resulting force independently of their origin. Their resulting effect in comparison to the effect due to convective diffusive transport is important for particle deposition.     

The erosion of dust by a shock wave in air: initial stages with laminar flow

The erosion of dust by a shock wave in air and by the subsequent air flow was investigated theoretically and experimentally. The paths of single particles were calculated for the initial state of erosion when the flow in the shock tube boundary layer was still laminar. High-speed cinematographic experiments performed with a shock tube yielded mapping of the development of the dust cloud. From the agreement between the measured height of the cloud and the calculated height of flight of the particles one can conclude that the assumed model for the motion of the particles adequately describes the removal of particles from the wall.