Design of optimal contours of supersonic parts of solid-propellant motor nozzles with use of direct variational methods

We present the results of designing the contours of supersonic parts of the solid-propellant rocket motor (solid motor) nozzles with high expansion ratios with the aid of direct variational methods. A continual model is used for the motion of a two-phase polydispersed continuum with regard for processes of interaction both between the carrying gas and the particles suspended in it and between the particles of various fractions. The method of local variations is employed as a numerical method of searching for the extremum of a multivariate function. The computational results evidence a fair efficiency of the proposed approach for the optimization of such nozzles.     

复合管道内液-固两相流浆体水击压强计算

对于单一管道的单相液体水击现象计算已经比较成熟,但是很少有对于复合管道的液固两相流系统的浆体水击 计算方面的报道。根据实际工程设计需要,提出了具有复合管道的液-固两相流浆体水击压强的计算方法。同时对某电厂 液一固两相流输灰系统浆体水击压强进行了计算与分析,提出了防止浆体水击的措施。     

撞击流中颗粒碰撞传热理论模型研究

建立了考虑颗粒接触面导热的颗粒碰撞传热模型,相应完善了气固两相撞击流理论模型,并对不同条件的撞击流干燥过程进行了模拟。计算结果与实验结果非常吻合,从而验证了所建模型的正确性。本文还分析了颗粒碰撞传热、加料方式以及喷嘴间距对撞击流干燥性能的影响规律。结果表明:在本文所涉及的撞击流干燥过程中,颗粒碰撞传热对干燥性能的影响并不明显;单边加料时颗粒物料的降水幅度及撞击流装置的干燥强度都明显大于双边加料的工况;喷嘴间距较大时,物料的降水幅度及装置的干燥强度均较大。     

基于小关联时间两相湍流色噪声的近似模型及数值模拟

从一般高斯型色噪声模型出发,通过泛函导数,应用小关联时间,近似计算多维色噪声,得到有效Fokker-Planck方程.将其应用到两相湍流中得到颗粒相的概率密度函数输运方程,从而得到颗粒相的二阶矩模型.将颗粒应力方程简化成代数方程,建立代数应力模型.将对流扩散方程的有限分析法运用到求解两相流模型中,对壁面两相射流进行数值模拟,并将求解结果与实验结果进行对比分析.     

Effect of particles on the flow structure and dispersion of solid impurities in a two-phase axisymmetric jet

The Euler approach is used for studying the structure of a flow and the propagation of a disperse impurity in a submerged two-phase jet for small values of the mass concentration of particles (M _L1 = 0 to 0.5) upon a variation of the size and material of particles in a wide range. The effect of particles on the propagation of a two-phase jet, gas turbulence, and solid phase dispersion is analyzed. The addition of particles decreases the jet opening angle, increases the jet range, suppresses turbulence, and deteriorates turbulent mixing with the surrounding submerged space. It is shown that at the first stage, particle accumulation effects (pinching) in the axial region of the jet appear upon an increase in the particle size and the density of the particle material. Then, upon an increase in the inertia of particles, pinching changes to intense scattering of the disperse phase in the initial cross sections of the jet. The results are compared with the results of measurements for mono- and polydisperse two-phase jet flows.     

A lattice Boltzmann method for a two-phase flow containing solid bodies with viscoelastic membranes

A lattice Boltzmann method (LBM) for two-phase flows containing solid bodies with viscoelastic membranes is proposed. The method is based on the two-phase LBM, in which one phase is regarded as the solid phase. In the present model, the membrane is assumed to be composed of identical particles that are connected to their neighboring particles by elastic springs to take account of stretching and compression effects. The method is applied to two representative problems, namely the behavior of a viscoelastic body under shear flow and the motion of a viscoelastic body in a Poiseuille flow. Tank-tread motion and axial migration, which are both characteristic of the motion of viscoelastic bodies, are simulated by using the method. These results indicate that the method is capable of simulating the complex behavior of viscoelastic bodies in capillaries, such as the motion of red blood cells in blood flows.     

Transport of solid particles in microfluidic channels

Transport of particles is commonly encountered in microfluidic channels that deal with solid-liquid two-phase flows in conjunction with particles and cells to focus, separate, sort, extract, and filter them. In particular, there is a resemblance between microscale flows and macroscale flows in the sense that the inertial migration of particles cannot be neglected. Thus, the objective of the present article is to review how studies on the transport of solid particles have evolved from classical fluid dynamics to up-to-date microfluidics in view of measurement techniques, flow characteristics, and applications.     

改进粒子水平集法及其应用

针对传统粒子水平集方法的缺陷提出一种虚拟粒子对距离函数的修正方法.改进算法针对虚拟粒子与待修正网格点的各种相对位置进行误差修正,可以避免虚拟粒子在非界面法线方向移动而产生的误差.数值求解涡旋流场问题显示:改进算法的界面捕捉性能得到显著提高.在此基础上,结合投影法求解Navier-Stokes方程组,数值模拟存在高密度比(10³量级)及粘性比(10²量级)的不可压缩两相流问题(气泡上升及自由面不稳定性问题).计算结果与已有结果吻合良好,详细分析主要控制参数对瑞利-泰勒不稳定性现象的影响.     

Modeling two-phase flows in channels and nozzles

The gas dynamics of the flow of a two-phase mixture, consisting of a gaseous phase and polydisperse liquid particles of oxides suspended in it, plays a major role in determining the thrust parameters of rocket engines and the power characteristics of MHD stations based on metallized fuels. A number of monographs and reviews have now been published that reflect the current state in this branch of continuum mechanics. Here we give the results of a numerical investigation of certain features of two-phase streams in combustion chambers, Laval nozzles, and MHD generators.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 71–81, August, 1992.     

稠密气固流动二阶矩摩擦应力模型和模拟

基于统一二阶矩两相湍流应力模型和稠密颗粒动力学理论,建立了欧拉-欧拉双流体二阶矩颗粒摩擦应力模型。模型充分反映各向异性的气固两相相间雷诺应力相互作用,并引入有效颗粒弹性恢复系数,考虑了因颗粒表面不光滑产生的摩擦力对湍流流动结构和颗粒弥散特性的影响,对于下降管的计算结果与实验吻合较好。因颗粒摩擦产生能量耗散降低了颗粒温度和导致颗粒雷诺应力再分布。在入口和出口区域因颗粒碰撞频率较高而产生的能量耗散对流动结构影响明显。     

Numerical simulations of gas-liquid two-phase flows in a micro porous structure

The lattice Boltzmann method for two-phase fluid flows is applied to the simulations of gas-liquid two-phase flows in a micro porous structure for various capillary numbers at low Reynolds numbers. The behaviors of the gas-liquid interface and the velocities of the two-phase fluid in the structure are simulated, and the permeability of gas and liquid through the structure are estimated from the calculated results. By changing the void fraction, the contact angle of the interface on walls, and the surface tension, the effect of these properties on the behaviors and the permeability of the two-phase flows in the micro porous structure is investigated. It is found that the permeability of liquid flows depends on the contact angle and it increases for hydrophobic walls. It is also seen that liquid flows are choked in pores for large void fractions and low capillary numbers.     

燃尽风率对新型W火焰锅炉主燃区气固流动特性的影响

针对采用偏心旋流二次风燃烧技术的300 MWe旋流燃烧器W火焰炉,借助1/10冷模试验台,通过三维激光颗粒动态分析仪测量研究了不同燃尽风率下其主燃区内气固流动特性。随着燃尽风率减小,拱下回流区内回流速度不断增加,且回流区尺寸不断增大。随着燃尽风率由25%减小到10%,在分级分区域,颗粒的最大竖直速度由2 m/s增大到4 m/s.燃尽风率由20.3%减小到10%,拱下回流区内气固两相竖直脉动速度明显增大,气固两相湍流强度将不断增大.在乏气和分级风区域,燃尽风率15%下最大颗粒体积流率是燃尽风率20.3%的2至2.7倍,拱上气流下冲深度明显增加.随着燃尽风率减小,下冲颗粒开始折转向上的位置被推迟,下炉膛空间利用率将不断增加.     

Numerical simulation of instantaneous flow structure of swirling and non-swirling coaxial-jet particle-laden turbulence flows

A subgrid scale two-phase second-order-moment (SGS-SOM) model based on the two-fluid continuum approach is presented for the analysis of the instantaneous flow structures of swirling and non-swirling coaxial-jet particle-laden turbulence flows. Since the interaction between the two-phase subgrid scale stresses and the anisotropy of two-phase subgrid scale stresses is fully considered, it is superior to the conventional subgrid scale model on the basis of single gas phase or together with their similar forms for the particle phase for not taken these characters thoroughly into account. The swirling numbers s=0.47 and s=0 of coaxial-jet particle-laden turbulence flows (measured by M. Sommerfeld, H.H. Qiu, Detailed measurements in a swirling particulate two-phase flow by a phase Doppler anemometer, Int. J. Heat Fluid Flow 12 (1991) 20-28) are numerically simulated by large eddy simulation using this model, together with a Reynolds-averaged Navier-Stokes model using the unified second-order-moment two-phase turbulence model (RANS-USM). The instantaneous results show that the multiple recirculating gas flow structure is similar to that of single-phase swirling flows; but the particle flow structure contains less vortices. Both SGS-SOM and RANS-USM predicted that the two-phase time-averaged velocities and the root-mean-square fluctuation velocities are validated and are in good agreement with the experimental results. It is seen that for the two-phase time-averaged velocities both the models give almost the same results, hence the RANS-USM modeling is validated by large eddy simulation. For the two-phase root-mean-square fluctuation velocities the SGS-SOM results are obviously better than the RANS-USM results.     

Monitoring of multiphase flows for superconducting accelerators and others applications

This paper is a review on implementation of measuring systems for two-phase helium, hydrogen, liquefied natural gas (LNG), and oil-formation/salty water flows. Two types of such systems are presented. The first type is based on two-phase flow-meters combining void fraction radio-frequency (RF) sensors and narrowing devices. They can be applied for superconducting accelerators cooled with two-phase helium, refueling hydrogen system for space ships and some applications in oil production industry. The second one is based on combination of a gamma-densitometer and a narrowing device. These systems can be used to monitor large two-phase LNG and oil-formation water flows. An electronics system based on a modular industrial computer is described as well. The metrological characteristics for different flow-meters are presented and the obtained results are discussed. It is also shown that the experience gained allows separationless flow-meter for three-phase oil-gas-formation water flows to be produced.     

喷嘴雾化特性实验研究

液体雾化是当前两相流研究中非常重要的课题,在农业、能源以及环境工程中具有广泛的应用价值,进行深入系统的研究具有重要意义。本文以空气、水为工质,使用马尔文粒度仪对单相和两相雾化器喷嘴的雾化特性进行了比较实验研究。测量了不同压力配比条件下液体雾化粒子的粒径分布,详细讨论了压力对于喷嘴雾化效果的影响。同时得出了两相流量与压力之间的变化规律。     

两相湍流色噪声扩维法PDF模型及数值模拟

由颗粒运动的朗之万方程出发,对流体脉动速度采用扩维方法,得到两个不同层次的PDF输运方程.通过对颗粒运动方程求解和高斯分布假设,解决PDF方程的封闭问题,获得颗粒二阶矩模型,然后将颗粒应力方程简化成代数方程,建立代数应力模型.将对流扩散方程的有限分析法运用到求解两相流模型中,对壁面两相射流进行数值模拟,对比分析数值结果与实验结果.     

Interspecies stress in momentum equations for dense binary particulate systems

For two-species particulate systems, ensemble averaged continuity and momentum equations for each species are derived based on the Liouville equation of the system. The ensemble average used is species specific. It is found that the interaction between species results in not only the interspecies force but also a stress in the momentum equations. In the limit that particles of one of the species can be considered as a continuum, the existence of the interspecies stress enables us to reduce the derived equations to the familiar form for dispersed two-phase flows.     

Arc-Gas Flow Interactions in a Double-Nozzle Flow System

The physical phenomena in cold and arc heated double-nozzle gas flows have been investigated for SF6 by interference and shadow methods. The cold-flow phenomena are discussed as a basis for a better understanding of the arc-gas flow interactions, their interference pattern is clearly interpreted: the observed fringes, which also can be calculated theoretically, are lines of constant flow velocity. In the case of arc heated flows a sharp distinction is made for the first time between different types of arc-gas flow interactions. At low peak currents the interference pattern still shows a cold gas flow around the arc. At higher current levels a fringe system, which indicates a density reduction, expands into the volume around the nozzles; however, the flow is still directed towards the gap between the nozzles. In contrast to this case the strongest form of interaction is characterized by the appearance of arc heated gas, which flows turbulently back into the high-pressure volume. The radial temperature distribution for a special arc has been calculated theoretically and is discussed in detail.     

使用莫尔条纹法测量气流密度

把莫尔条纹应用于对称的和非对称的流场，测出了从喷嘴喷出的不完全膨胀气流的密度分布。气流的内部密度分布通过使用数字表示的转化方法转变成了莫尔条纹图像数据，这些莫尔条纹图像数据表明了同种光在穿过气流时将会发生折射。这一现象可以通过改变气体喷口的压力比来完成并观察到。实验表明：不同形状的喷嘴喷出的气流密度分布各不相同，而且复杂程度也不同，但沿着喷嘴气流轴的气流密度变化大致相似。     

Peculiarities of propagation of the dispersed phase in a gas-droplet flow downstream of a pipe sudden expansion

The results of numerical simulation of the propagation of the dispersed phase in a gas-droplet flow downstream of a pipe sudden expansion for small initial mass concentrations of particles (M _L1 = 0–0.1) are presented. Fine-dispersed droplets with the Stokes numbers Stk < 1 are entrained by a separated flow and are present in the whole cross section of the pipe. The near-wall region of the pipe is free of fine particles due to intense evaporation. Heavy particles (Stk > 1) do not get in the recirculation flow region and are present only in the mixing layer and in the flow core. It is shown that the addition of fine-dispersed droplets suppresses the energy of the gaseous phase turbulence in the separated flow. The results are compared with the experimental data for two-phase separated flows and are found to be in the conformity with these data.