Investigation of the flow in the impeller side clearances of a centrifugal pump with volute casing

The paper is concerned with the fluid flow in the impeller side clearances of a centrifugal pump with volute cas-ing.The flow conditions in these small axial gaps are of significant importance for a number of effects such as disk friction,leakage losses or hydraulic axial thrust to name but a few.In the investigated single stage pump,the flow pattern in the volute turns out to be asymmetric even at design flow rate.To gain a detailed insight into the flow structure,numerical simulations of the complete pump including the impeller side clearances are accom-plished.Additionally,the hydraulic head and the radial pressure distributions in the impeller side clearances are measured and compared with the numerical results.Two configurations of the impeller,either with or without balancing holes,are examined.Moreover,three different operating points,i.e.:design point,part load or overload conditions are considered.In addition,analytical calculations are accomplished to determine the pressure distri-butions in the impeller side clearances.If accurate boundary conditions are available,the 1D flow models used in this paper can provide reasonable results for the radial static pressure distribution in the impeller side clearances.Furthermore,a counter rotating wake region develops in the rear impeller side clearances in absence of balancing holes which severely affects the inflow and outflow conditions of the cavity in circumferential direction.     

D6114ZQ柴油机活塞三维有限元分析及其结构改进

通过对Ｄ６１１４ＺＱ柴油机活塞在最高爆发压力和最大侧压力作用下的三维有限元分析,获得了其温度场和应力分布情况等,根据分析结果,对活塞工作的疲劳安全系数进行了计算。计算结果表明：侧压力的作用及销座下部与裙部侧壁间过渡处的应力集中是影响活塞裙部裂纹产生的主要原因,据此,提出了相应的结构改进措施。     

Study on Shock Wave and Turbulent Boundary Layer Interactions in a Square Duct at Mach 2 and 4

In this paper, the outline of the Mach 4 supersonic wind tunnel for the investigation of the supersonic internal flows in ducts was firstly described. Secondly, the location, structure and characteristics of the Mach 2 and Mach 4 pseudo-shock waves in a square duct were investigated by color schlieren photographs and duct wall pressure fluctuation measurements. Finally, the wall shear stress distributions on the side, top and bottom walls of the square duct with the Mach 4 pseudo-shock wave were investigated qualitatively by the shear stress-sensitive liquid crystal visualization method. The side wall boundary layer separation region under the first shock is narrow near the top wall, while the side wall boundary layer separation region under the first shock is very wide near the bottom wall.     

Stress evolution and coal seam deformation through the mining of a remote upper protective layer

Protective layer mining is considered to be an effective method to resolve the outburst risk of coal seams, but limited theoretical and experimental results exist for remote upper protective layer mining. To study the effect of the remote upper protective layer mining, a case study of the Renlou Coal Mine is selected. The stress evolution in the protected layer is analyzed using Flac^3D and is verified by the measurement of coal seam deformation and investigation of the unloading boundary. The results indicate that remote upper protective layer mining induces an unloading of stress within the protected layer, while a stress concentration occurs outside of the unloading area. The coal seam deformation is consistent with the stress evolution, for which the maximum compressional and expansional deformation are 0.5‰ and 7.19‰, respectively. The gas pressure decreases significantly as a consequence of these applications, following which the gas pressures within the theoretical unloading boundary are 0.30 MPa and 0.35 MPa along-strike and along the tendency of the protected layer, respectively.     

SDCAD4.0在水工隧洞衬砌内力与配筋计算中的应用

为克服传统结构力学在水工隧洞结构计算中的不足,采用边值法计算方法,引进专用水工隧洞结构计算软件SDCAD4.0,对输水隧洞在3种工况、不同荷载组合下进行内力及配筋计算,并与理正岩土程序6.5的计算结果相比较。结果表明,输水隧洞衬砌结构在外水压力的作用下,3种工况弯矩最大值均位于边墙与底板的交接处,底板的跨中弯矩也偏大;3种工况下隧洞在边墙和底板交接处出现较大的拉应力和压应力,抗剪力也很难满足要求;2种不同软件计算所得内力结果接近,但理正岩土程序6.5选筋结果偏大,选筋较为保守,SDCAD4.0软件在选筋上较为经济合理。     

Implementation of boundary conditions in pressure-based finite volume methods on unstructured grids

In this study, the implementation of boundary conditions for the Navier–Stokes and the energy equations, including the pressure and pressure correction equations, are presented in the context of finite volume formulation on cell-centered, colocated unstructured grids. The implementation of boundary conditions is formulated in terms of the contribution of boundary face of a cell to the coefficients of the discretized equation for either Dirichlet- or Neumann-type boundary conditions. Open boundaries through which the flow is not fully developed are also considered. In this case, a data reconstruction method is proposed for finding the boundary values of the variables at the correction stage. The validity of implementations is checked by comparing the results with some well-known benchmark problems.     

滑移线法求解挡土墙主动土压力

滑移线法常用来求解挡土墙极限土压力,但至今仍有一些问题尚未得到解决。基于极限平衡理论,视墙后填土为服从Mohr-Coulomb屈服准则的理想弹塑性材料,并且假定它是各向同性的、均匀的以及不可压缩(膨胀)的理想连续介质,计算模型中考虑各种影响因素,提出弹性覆盖层替代传统的张拉裂缝,引进一个新概念“应力奇点”及其应力边界条件,建立静定可解的极限平衡问题数学模型而没有考虑土的应力-应变关系,采用滑移线法求解墙后塑性区的滑移线应力场,进而求解挡土墙主动土压力和滑裂面土反力,并且通过无量纲分析首次提出几何力学相似原理。研究结果表明,主动土压力的滑移线解一般总是大于或等于库仑解,朗肯解或满足非奇异条件的经典库仑解与滑移线解一致,Hencky第一定理和第二定理不具有普遍适用性。     

Thermal Buckling Analysis of a Mindlin Rectangular FGM Microplate Based on the Strain Gradient Theory

This article is aimed at developing a nonclassical Mindlin rectangular functionally graded material (FGM) microplate based on the strain gradient theory (SGT) to study the thermal buckling behavior of microplates with different boundary conditions. This theory comprises material length scale parameters to interpret size effects. The developed model encompasses classical and modified couple stress Mindlin microplate models, if all the material length scale parameters or two of them are taken to be zero, respectively. The Mindlin rectangular FGM microplate is considered to be made of a mixture of metal and ceramic of which the volume fraction is described through a power low function. According to Hamilton's principle and the generalized differential quadrature (GDQ) method, the stability equations and associated boundary conditions are obtained and discretized, respectively. Current formulations provide a possibility to have all types of boundary conditions which herein, FGM microplates with three commonly used boundary conditions are considered. Three different types of thermal loads including uniform, linear and nonlinear temperature rises along the thickness of FGM microplates are considered. The dimensionless critical buckling temperature difference (DCBTD) predicted by SGT is compared with that of modified couple stress theory (CST) and classical theory (CT) which it is found that CST and CT underestimate the DCBTD. Also, effects of the boundary conditions, length scale parameter and material gradient index of FGM microplates on the DCBTD are judiciously investigated.     

Self-similar condensing flows in porous media

Similarity solutions are obtained for the propagation of a condensation wave into an initially dry porous matrix which receives an inflow of saturated vapor due to a step increase in temperature and pressure at the boundary. The generalized Darcy (low Reynolds number) formulation of two-phase flow leads to hyperbolic/parabolic equations in which capillarity and heat conduction are suppressed in order to emphasize the shock-like behavior. Application of the x/√t similarity transformation gives ordinary differential equations which are solved by shooting methods, using jump-balance (Rankine-Hugoniot) conditions to preserve discontinuities in saturation (quality), pressure gradient and sometimes temperature. The distribution of condensate (saturation) is wave-shaped, with a forward-facing shock on the leading side. For a small temperature difference, there is little condensate and it is nearly immobile; the saturation shock lies close to the boundary, and the outer region is described by a reduced system of equations. With increasing temperature difference, the shock moves forward into the flow and gains in strength until the medium is liquid-full behind the shock. Beyond this, the shock splits into a pair of back-to-back shocks separated by a subcooled liquid slug. The considered prototypic problem is representative of a broad class of two-phase flows which occur in energy-related and geologic applications.     

GREEN'S FUNCTIONS OF POINT HEAT SOURCE IN VARIOUS THERMOELASTIC BOUNDARY VALUE PROBLEMS

With an emphasis on derivation, this paper reviews Green's functions for a point heat source in various thermoelastic boundary value problems for an infinite plane with an inhomogeneity. The inhomogeneity boundary conditions considered are external force, displacement, and mixed boundaries. The derivation is accomplished with three kinds of function for mapping, temperature, and stress. Stress functions for different boundary value problems are presented, and stress distributions along the inhomogeneity boundary are plotted in figures.     

服役工况下汽轮机平衡盘区域强度及间隙变化

以某超超临界机组的高压模块的平衡盘作为研究对象,利用ABAQUS软件建立高压模块的轴对称模型,并根据电厂实际运行工况的蒸汽温度压力数据计算加载边界条件,分析了实际启动和满负荷运行工况下高压平衡盘及前后密封区域的温度、应力和位移的变化及密封处径向间隙变化规律。研究表明:运行过程中服役工况下温度和应力产生了波动,在启动阶段最为剧烈,稳态运行时波动幅度较小;启动阶段径向间隙会明显减小。     

EFFECT OF VARIOUS DRIVING FORCES ON HEAT AND MASS TRANSFER IN ARC WELDING

Abstract

In this study the heat transfer and fluid flow of the molten pool in stationary gas tungsten arc welding using argon shielding gas were investigated. Transporting phenomena from the welding arc to the base material surface, such as current density, heat flux, arc pressure, and shear stress acting on the weld pool surface, were taken from the simulation results of the corresponding welding arc. Various driving forces for the weld pool convection were considered: self-induced electromagnetic, surface tension, buoyancy, and impinging plasma arc forces. Furthermore, the effect of surface depression due to the arc pressure acting on the molten pool surface was considered. Because the fusion boundary has a curved and unknown shape during welding, a boundary-fitted coordinate system was adopted to precisely describe the boundary for the momentum equation. The numerical model was applied to AISI304 stainless steel and compared with the experimental results.     

Influences of geometry and flow pattern on hydrogen separation in a Pd-based membrane tube

The abatement of concentration polarization in a membrane tube is of the utmost importance for improving the efficiency of hydrogen separation. In order to enhance the performance of hydrogen separation, the characteristics of hydrogen permeation in a Pd-based membrane system under various operating conditions and geometric designs are studied numerically. The effects of Reynolds numbers, shell size, baffle, and pressure difference on hydrogen mass transfer across the membrane are evaluated. The predictions suggest that a larger shell deteriorates concentration polarization, stemming from a larger H₂ concentration boundary layer. Baffles equipped in the shell are conducive to disturbing H₂ concentration boundary layer and reducing concentration polarization at the retentate side, thereby intensifying H₂ permeation. The more the number of baffles, the less the increment of improvement in H₂ permeation is. The installation of one baffle is recommended for enhancing H₂ separation and it is especially obvious under the environments of high pressure difference. Within the investigated ranges of Reynolds number at the permeate side and the retentate side, the feasible operating conditions are suggested in this study.     

Free-stream turbulence effects on the boundary layer of a high-lift low-pressure-turbine blade

The suction side boundary layer evolution of a high-lift low-pressure turbine cascade has been experimentally investigated at low and high free-stream turbulence intensity conditions.Measurements have been carried out in order to analyze the boundary layer transition and separation processes at a low Reynolds number,under both steady and unsteady inflows.Static pressure distributions along the blade surfaces as well as total pressure distributions in a downstream tangential plane have been measured to evaluate the overall aerodynamic efficiency of the blade for the different conditions.Particle Image Velocimetry has been adopted to analyze the time-mean and time-varying velocity fields.The flow field has been surveyed in two orthogonal planes (a blade-to-blade plane and a wall-parallel one).These measurements allow the identification of the Kelvin-Helmholtz large scale coherent structures shed as a consequence of the boundary layer laminar separation under steady inflow,as well as the investigation of the three-dimensional effects induced by the intermittent passage of low and high speed streaks.A close inspection of the time-mean velocity profiles as well as of the boundary layer integral parameters helps to characterize the suction side boundary layer state,thus justifying the influence of free-stream turbulence intensity on the blade aerodynamic losses measured under steady and unsteady inflows.     

Three-Dimensional Modeling of Thermohydrodynamic Lubrication in Slider Bearings Using Streamline Upwind Petrov-Galerkin Method

A three-dimensional thermohydrodynamic lubrication model which couples the Reynolds and energy equations is developed in the finite-element program Sepran. The model uses the streamline upwind Petrov-Galerkin method. Model results indicate the peak temperature is not on the mid-plane surface. This position shifts toward the mid-plane as the width-to-length ratio is reduced from 10 to 1 as well as when pressure boundary conditions are altered in such a way that the inlet/outlet pressure is higher than the side pressure. The adiabatic temperature profiles of an infinite slider and a square slider are compared. The wider slider shows a higher peak temperature. The side flow plays a major role in determining the value and position of the peak temperature. Model results also indicate peak side flow at a width-to-length ratio of 2.     

Bimaterial problems with an interfacial cavity for some boundary conditions subjected to uniform heat flux normal to the interface

Abstract

Stress analysis is carried out for a bimaterial infinite plane with an interfacial cavity. Uniform heat flux applies to the normal to the interface. Four combinations of boundary conditions are considered, that is, isothermal and adiabatic boundary conditions for heat flux analysis, and external force and displacement boundary conditions for stress analyses. The infinite plane consists of two bonded dissimilar materials of a half plane with a single notch. To achieve analytical solutions, a rational mapping function and a complex variable method are used. By changing the mapping function, other geometries for the notch can be analyzed. Complex stress functions for isothermal and external boundary conditions can be only achieved for stress calculation. The stress intensities of debonding are investigated for various debonding lengths for some elliptical holes, and for the debonding extensions. Complex stress functions for isothermal and displacement boundary conditions can be expressed by an infinite series and stress components et al. cannot be calculated. However, a solution of interfacial rigid inclusion can be solved. Complex stress functions for the adiabatic boundary are achieved by the integral forms for external force and displacement boundary conditions, and the integral cannot be carried out, and therefore, stress components cannot be achieved.     

Conjugate film condensation and natural convection along the interface between a porous and an open space

This paper reports a theoretical investigation focusing on the interaction between film condensation and natural convection along a vertical wall separating a fluid reservoir from a fluid-saturated porous reservoir. The two reservoirs are maintained at different temperatures. The study consists of two parts: in the first part the condensation phenomenon takes place in the fluid reservoir and the natural convection phenomenon in the porous layer. In the second part, the opposite situation is considered. The main heat transfer and flow characteristics in the two counterflowing layers, namely, the condensation film and the natural convection boundary layer are documented for a wide range of the problem parameters. These parameters appear after boundary layer scaling of the governing equations. Important engineering results regarding the overall heat flux from the condensation side to the natural convection side are summarized in the course of the study. Finally, the effect of the thermal resistance of the wall constituting the interface separating the two reservoirs, on the overall heat flux from the condensation side to the natural convection side is determined.     

Design of pressure vessels using shape optimization: An integrated approach

Previous papers related to the optimization of pressure vessels have considered the optimization of the nozzle independently from the dished end. This approach generates problems such as thickness variation from nozzle to dished end (coupling cylindrical region) and, as a consequence, it reduces the optimality of the final result which may also be influenced by the boundary conditions. Thus, this work discusses shape optimization of axisymmetric pressure vessels considering an integrated approach in which the entire pressure vessel model is used in conjunction with a multi-objective function that aims to minimize the von-Mises mechanical stress from nozzle to head. Representative examples are examined and solutions obtained for the entire vessel considering temperature and pressure loading. It is noteworthy that different shapes from the usual ones are obtained. Even though such different shapes may not be profitable considering present manufacturing processes, they may be competitive for future manufacturing technologies, and contribute to a better understanding of the actual influence of shape in the behavior of pressure vessels.     

Three-dimensional thermo-elastic analysis of a functionally graded cylindrical shell with piezoelectric layers by differential quadrature method

Three-dimensional thermo-elastic analysis of a functionally graded cylindrical shell with piezoelectric layers under the effect of asymmetric thermo-electro-mechanical loads is carried out. Numerical results of displacement, stress and thermal fields are obtained using two versions of the differential quadrature methods, namely polynomial and Fourier quadrature methods. Material properties of the shell are assumed to be graded in the radial direction according to a power law but the Poisson’s ratio is assumed to be constant. Shells are considered to be under the effect of the pressure loading in the form of cosine and ring pressure loads, electric potentials and temperature fields. Numerical results for various boundary conditions are obtained and the effects of the thickness of piezoelectric layers, grading index of material properties and the ratio of the thickness to the radius of the shell on these results is presented.