二维气固两相混合层中固粒对流场影响的研究

采用双向耦合模型对含有固粒的二维气固两相混合层流场进行了研究。流场采用拟谱方法直接数值模拟,固粒采用颗粒-轨道模型,在考虑流场对固粒作用的同时,考虑固粒对流场的反作用。结果发现固粒的浓度和Stokes数对流场影响明显。固粒的作用使涡量扩散加快,并阻碍流场的变化,减弱了流场中拟序结构的强度,缩短涡的生存期;固粒在流场中的分布规律与单相耦合所得结果相似。     

含悬浮固粒射流界面稳定性研究

利用气固两相耦合模型,理论推导出含悬浮固粒射流的稳定性方程,通过数值计算得到了两相射流稳定性特征曲线、固气扰动速度比值幅值曲线及固气相位差曲线,进而得到了关于固粒对流场中扰动增长和传播的影响及失稳过程中固粒扰动特性的结论。这些结论对于两相射流发展的认识和工程实际中实施对两相射流场的人工控制有重要意义。     

高浓度悬浮固粒对射流界面的粘性稳定性影响

该文首次利用双流体模型和扰动速度势理论,推得含高浓度悬浮固粒的射流界面粘性稳定性方程和对应的固气扰动速度比值方程．通过数值计算,得到了不同雷诺数及固粒属性的射流界面粘性稳定性曲线和对应的固气扰动速度比值曲线．在分析和比较所得的粘性稳定性曲线的基础上,得到了流场雷诺数及固粒特性对射流界面粘性稳定性影响的结论．同时,通过分析所得的固气扰动速度比值曲线,得到了流场雷诺数及固粒等效斯托克斯数对固粒跟随气流的扰动 性能的影响的结论．这些结论是首次在计入气流的粘性的条件下得到的,不同于文献［８］和文献［１０］相关的囿于无粘情形的研究,对于两相射流发展的认识和工程实际中实施对两相射流场的人工控制有重要意义．     

含高浓度悬浮固粒运动射流稳定性研究

首先用连续介质耦合模型推导出含高浓度悬浮固粒运动射流的空间稳定性方程,然后借助渐进分析法和欧拉守恒差分格式,用有限差分数值解法得到不同流向位置、流场雷诺数、固粒属性和喷射装置运动速度时流场的稳定性特征曲线,说明喷射装置的反向运动使不稳定扰动频率范围扩大,正向运动则相反。固粒抑制流场的不稳定性,随着固粒等效斯托克斯数的减小,这种效应增强。这些结论,对于两相运动射流发展的认识有重要意义。     

二维流面上的流动问题的速度图方法

对于一些特殊的流动,尤其是平面上的位势流动,速度图方法有其显著的优点．对于理想流体来说,流面总是存在的,在流面上,流动的速度向量总是在其切空间里．通过引入流函数和势函数,采用张量分析作为工具,给出了二维曲流面上位势流动的速度图方法,得到了流函数满足的速度图方程,为一些特殊的流动问题提供了一类分析方法．并且,对于得到的二维速度图方程,得到了相应的特征方程和特征根,从而可以对方程的类型进行分类．最后,给出了一些特殊流动的实例．     

粉末注射成形填充过程的数值模拟

本文将粉末注射成形喂料在薄壁模腔中的流动视为二维流动，以流变学的基本方程为基础，建立了从动量方程、连续方程和热传递方程得到的描述PIM喂料充模二维流动的数学模型。在无滑移边界的条件下，推导了喂料熔体流导率的计算公式和压力场的控制方程，得到的压力场控制方程是一非线性椭圆偏微分方程．从而可用Galerkin方法进行数值求解，使模型的数值求解成为可能，为进一步对粉末注射成形进行计算机模拟和数值分析奠定了数学基础。     

海水入侵数值模拟的特征块中心差分法

本文研究二维海水入侵数值模拟的有限差分法．对关于压力的流动方程本文采用块中心差分法,对关于含盐浓度方程的对流扩散方程采用基于完全二次矩形插值的特征差分法,运用先验估计的理论和技巧得到了最佳阶L~2误差估计的结果．     

增强可压缩混合层混合的一种方法

通过数值模拟的方法,研究在二维可压缩混合层的低速入口部分强迫流向流速振荡,以探讨是否有可能提高可压缩混合层的混合.对来流Mach数M=0.6的二维可压缩混合层进行系统的计算,结果证实了这种方法确实可以提高混合的效率.     

二维超音速混合层增强混合的研究

数值模拟了二维超音速混合层在入口处引入T-S波和在低速部分加入沿流向的振荡这两种不同的激励方式后流动的演化.结果表明，对于对流Mach数小于１的超音速混合层，两种方法均可增强混合，而加入振荡比引入T-S波更为有效.对加入振荡方式，还系统计算分析了各种参数对混合的影响.     

两相流中柱状固粒对流体湍动特性影响的研究

对含柱状固粒的两相流场,建立了包含柱状固粒对流场影响的流体脉动速度方程,在求解脉动速度方程的基础上,经平均得到流体的湍流强度和雷诺应力.将该方法用于槽流湍流场的求解,并与单相流实验结果进行了比较.计算中变化柱状固粒的参数,给出了固粒的体积分数、长径比、松驰时间对流场湍动特性的影响,说明粒子对流场的湍动特性起着抑制作用,其抑制的程度与粒子的体积分数、长径比成正比,与粒子的松弛时间成反比.     

Surface wave propagation in a liquid-saturated porous solid layer lying over a heterogeneous elastic solid half-space

Dispersion equation is derived for the propagation of Rayleigh type surface waves in a liquid saturated porous solid layer lying over an inhomogeneous elastic solid half-space. Effect of heterogeneity on the phase velocity is studied by taking different numerical values of heterogeneity factor for particular models. Dispersion curves have been drawn showing the effect of heterogeneity on the phase velocity.     

柱状固粒两相边界层流场稳定性研究

从运动方程和本构方程出发,推导得到了含柱状粒子两相流场的修正Orr-Sommerfeld方程,然后在边界层流场中,采用数值计算方法,得到了含柱状粒子流场的稳定性中性曲线,给出了流场失稳的临界雷诺数.结果表明在所述情况下,柱状粒子对流场起着抑制失稳的作用,而且抑制的程度随着柱状粒子体积分数和长径比的增加而提高.     

Rayleigh type wave dispersion in an incompressible functionally graded orthotropic half-space loaded by a thin fluid-saturated aeolotropic porous layer

This paper is concerned with the Rayleigh wave dispersion in an incompressible functionally graded orthotropic half-space loaded by a thin fluid-saturated aeolotropic porous layer under initial stress. Both the layer and half-space have subjected to the incompressible in nature. The particle motion of the Rayleigh type wave is elliptically polarized in the plane, which described by the normal to the surface and the focal point along with wave generation. The dispersion of waves refers typically to frequency dispersion, which means different wavelengths travel at a different velocity of phase. To deal with the analytical solution of displacement components of Rayleigh type waves in a layer over a half-space, we have taken the assistance of different methods like exponential, characteristic polynomial and undetermined coefficients. The dispersion relation has been derived based upon suitable boundary conditions. The finite difference scheme has been introduced to calculate the phase velocity and group velocity of the Rayleigh type waves. We also have derived the stability condition of the finite difference scheme (FDS) for the phase and group velocities. If a wave equation has to travel in the time domain, it is necessary to achieve both accuracy and stability requirements. In such cases, FDS is preferred because of its power, accuracy, reliability, rapidity, and flexibility. The effect of various parameters involved in the model like non-homogeneity, porosity, and internal pre-stress on the propagation of Rayleigh type waves have been studied in detail. Graphical representations for the effects of various parameters on the dispersion equation have been represented. Numerical results demonstrated the accuracy and versatility of the group and phase velocity depending on the stability ratio of the FDS.     

Propagation of Rayleigh waves in generalized magneto-thermoelastic orthotropic material under initial stress and gravity field

In this paper the influence of the gravity field, relaxation times and initial stress on propagation of Rayleigh waves in an orthotropic magneto-thermoelastic solid medium has been investigated. The solution of the more general equations are obtained for thermoelastic coupling by Helmoltz’s theorem. The frequency equation which determines Rayleigh wave velocity have been obtained. Many special cases are investigated from the present problem. Numerical results analyzing the frequency equation are obtained and presented graphically. Relevant results of previous investigations are deduced as special cases from these results. The results indicate that the effect of initial stress, magnetic field and gravity field are very pronounced.     

A 3-dimensional Eulerian–Eulerian CFD simulation of a hydrocyclone

Hydrocyclones are used in mineral industries for classification and separation of solid particles of different sizes and densities suspended in water medium. In the present study an Eulerian–Eulerian CFD simulation of a solid–liquid hydrocyclone has been carried out taking into account two solid phases and one liquid phase. The average size of the larger particle was 0.6117 and that of the smaller particle was 0.09875 mm. Three separate momentum balance equations for the three phases have been considered unlike that in the mixture model where a single momentum equation is solved for the three phases. Two turbulent models i.e. the Reynolds stress model (RSM) and the standard k–ε model were studied. Comparison of the two turbulence models showed slight variation in prediction of the velocity profile and the separation efficiency. The maximum deviation between the two models was observed near the wall where the stress was maximum for larger size particles.     

Influence of radiation on MHD free convection from a vertical flat plate embedded in porous media with thermophoretic deposition of particles

Magneto-hydrodynamics and thermal radiation effects on heat and mass transfer in steady laminar boundary layer flow of a Newtonian, viscous fluid over a vertical flat plate embedded in a fluid saturated porous media in the presence of the thermophoresis particle deposition effect is studied in this paper. The governing equations are transformed by special transformations. Brownian motion of particles and thermophoretic transport are considered in the flow equations. The magnetic field is considered to be applied. Rosseland approximation is used to describe the radiative heat flux in the energy equation. The resulting similarity equations are solved numerically by the fourth-order Runge–Kutta method with shooting technique. Many results are obtained and representative set is displayed graphically to illustrate the influence of the various parameters on the wall thermophoretic deposition velocity, concentration, temperature and velocity profiles.     

Stagnation point flow of dusty Casson fluid with thermal radiation and buoyancy effects

The aim of the study is to examine the stagnation point flow of a dusty Casson fluid over a stretching sheet with thermal radiation and buoyancy effects. The governing boundary layer equations are represented by a system of partial differential equation. After applying suitable similarity transformations, the resulting boundary layer equations are solved numerically using the Runge Kutta Fehlberg fourth-fifth order method (RKF-45 method). The behaviors of velocity, temperature and concentration profiles of fluid and dusty particles with respect to change in fluid particle interaction parameter, Casson paramter, Grashof number, radiation parameter, Prandtl number, number density, thermal equilibrium time, relaxation time, specific heat of fluid and dusty particles, ratio of diffusion coefficients, Schmidt number and Eckert number are analysed graphically and discussed. Our computed results interpret that velocity distribution decays for higher estimation of Casson parameter while temperature distribution shows increasing behavior for larger radiation parameter.     

Steady state numerical simulation of the particle collection efficiency of a new urban sustainable gravity settler using design of experiments by FVM

The aim of this work is to analyze the efficiency of a new sustainable urban gravity settler to avoid the solid particle transport, to improve the water waste quality and to prevent pollution problems due to rain water harvesting in areas with no drainage pavement. In order to get this objective, it is necessary to solve particle transport equations along with the turbulent fluid flow equations since there are two phases: solid phase (sand particles) and fluid phase (water). In the first place, the turbulent flow is modelled by solving the Reynolds-averaged Navier-Stokes (RANS) equations for incompressible viscous flows through the finite volume method (FVM) and then, once the flow velocity field has been determined, representative particles are tracked using the Lagrangian approach. Within the particle transport models, a particle transport model termed as Lagrangian particle tracking model is used, where particulates are tracked through the flow in a Lagrangian way. The full particulate phase is modelled by just a sample of about 2,000 individual particles. The tracking is carried out by forming a set of ordinary differential equations in time for each particle, consisting of equations for position and velocity. These equations are then integrated using a simple integration method to calculate the behaviour of the particles as they traverse the flow domain. The entire FVM model is built and the design of experiments (DOE) method was used to limit the number of simulations required, saving on the computational time significantly needed to arrive at the optimum configuration of the settler. Finally, conclusions of this work are exposed.