蒸汽喷射制冷系统中喷射器内特殊流动现象的研究

本文通过求解二维N-S方程来模拟蒸汽喷射器内复杂的流动混合过程,模拟时使用了蒸汽的真实物性公式。与理想气体假设不同,真实物性的带入,真实地反映了蒸汽经缩放喷嘴时,温度递减,喷嘴出口后温度场波动变化的特征．模拟时,通过对节点焓值的计算,得出了喷射器内发生相变的蒸汽的百分含量,实现了相变现象的定量分析。在激波捕捉方面,验证了喷射器内喷嘴出口后,膨胀波(压缩波)经混合层反复折射、转化、衰减的过程,以及在扩压室入口会产生斜激波的理论预测。     

Laminar incompressible viscous flow past a cylinder performing rotary oscillations

The numerical simulation of the laminar viscous flow past a cylinder performing rotary oscillations around its axis is carried out. The Navier–Stokes equations are solved by finite volume method using the program package OpenFOAM. The values of the amplitude and frequency of forced oscillations are found, at which the maximum reduction of the drag coefficient of the cylinder is achieved.     

平面叶栅中的湿蒸汽两相结流动数值模拟

对存在自发凝结的湿蒸汽两相流动建立了完全欧拉坐标系下的数值模型.考虑水蒸汽与理想气体的偏差,引入维里型状态方程对模型作了进一步完善.对平面叶栅中的两相凝结流动进行了数值模拟,计算结果与实验值比较表明本文计算模型正确,可以扩展到三维复杂两相凝结流场的计算.     

Experimental Research on Wet Steam Flow With Shock Wave

The article presents research on a wet steam transonic flow in a Laval half-nozzle with a shock wave. The motivation for this research was to investigate the shock wave/liquid phase interaction in the transonic wet steam flow. This phenomenon is responsible for the lack of good correspondence between experimental data and computational fluid dynamics results. For the tests, the geometry of the half-arc nozzle was used. The shock wave formation at the divergent section of the nozzle is caused by too high back-pressure. The observed instabilities in the flow are mainly initiated by the shock wave/liquid film (boundary layer) interaction. The numerical calculations were compared with experimental results with respect to the static pressure distribution along the nozzle.     

Formation of a vortex lattice in a rotating BCS Fermi gas

We investigate theoretically the formation of a vortex lattice in a superfluid two-spin component Fermi gas in a rotating harmonic trap, in a BCS-type regime of condensed non-bosonic pairs. Our analytical solution of the superfluid hydrodynamic equations, both for the 2D BCS equation of state and for the 3D unitary quantum gas, predicts that the vortex free gas is subject to a dynamic instability for fast enough rotation. With a numerical solution of the full time dependent BCS equations in a 2D model, we confirm the existence of this dynamic instability and we show that it leads to the formation of a regular pattern of quantum vortices in the gas.     

一维喷管中存在自发凝结的跨音速湿蒸汽两相流动数值模拟

本文结合液滴成核、生长理论及Ｅｕｌｅｒ方程组,在无滑移假设下,导出了描述存在自发凝结的湿蒸汽两相流动控制方程组。对汽液两相流动控制方程组采用ＴＶＤ格式离散、时间推进法求解。对准一维喷管中的湿蒸汽两相流动进行了数值模拟,得到了满意的计算结果。     

Investigation of oscillations of a soliton of a bose condensate of atoms in a trap in the limit of small oscillations of its walls

The motion of the center of a soliton in a trap with oscillating walls is studied analytically and numerically for the case in which the intrinsic frequency of small soliton oscillations in the equilibrium state considerably exceeds the frequency of wall oscillations. this problem can be solved either by applying the gross–pitaevskii equation, which most exactly describes the behavior of the soliton in the trap, or by using the approximate, “mechanical,” equation of motion of the newtonian type for the center of the soliton. an approximate analytical solution of the mechanical equation is obtained and is compared with the numerical solution of the newton equation, while the latter solution is compared with the numerical solution of the gross–pitaevskii equation. good agreement between the first two solutions is revealed. it is also shown that there is a range of parameters in which the numerical solutions of the newton and gross–pitaevskii equations are closest to each other. the frequency-sweeping effect of soliton center oscillations is revealed. an approximate analytical formula for the limiting frequency of these oscillations is obtained and the numerical analysis of this phenomenon is performed.     

Explicit solution of the Kepler equation

An explicit solution of the Kepler equation is expressed in terms of the Lambert hyperfunction. Calculation of this function, for example, by making use of the Maple software package, enables one to efficiently obtain the numerical solution of the Kepler equation.     

叶轮机械数值计算与设计方法进展及其在汽轮机中的应用──第二部分:汽轮机通流部分若干关键技术开发及工业应用

本文介绍了后加载叶型、子午收缩静叶栅、弯扭静叶栅与全三维流型设计等当代汽轮机通流部分关键新技术的技术开发，以及这些技术在200MW汽轮机改造中的应用情况．由于采用了以数值计算为主、辅以必要的实验验证的原则，与传统开发方式相比，节省了大量时间与经费．现场实测结果表明，高、中压缸效率分别达到84．09％和90．40％，比改造前分别提高4．58％和1．12％，不仅国内领先，也优于不少进口大机组．     

氦原子基态能量的Roothaan-Hartree-Fock计算

采用包含两个斯莱特基的"双ζ"函数说明了利用自洽场法求解基态氦原子Roothaan-Hartree-Fock方程的数值过程,计算得基态能量为-2.862 568 Hartree.利用基态的对称性,提出了通过求解泊松方程来计算库仑算符的方法,给出了交叠矩阵和单电子算符的矩阵元,并对自洽的标准作了讨论.     

加力室隔热屏流场计算

加力室隔热屏流场计算赵坚行，刘全忠（南京航空航天大学动力工程系南京２１００１６）关键词隔热屏，改值计算，紊流反应流１引言本文采用数值计算的方法模拟带有隔热屏、外冷却气流、尾喷口的加力室热态流场。计算中采用修正卜。紊流模型来预估粘性系数。燃烧模型采用卜...     

A review of time-domain impedance modelling and applications

Time-domain impedance boundary conditions are reviewed and similarities between the models are shown. The extended Helmholtz resonator model is used with a time-domain impedance boundary condition for impedance eduction and simulation of the noise radiation from a lined aeroengine nozzle. Model parameters obtained by impedance eduction from flow duct measurements and then used to predict the noise radiation for realistic aeroengine nozzle flow and geometry. The prediction of sound radiation from a coaxial jet nozzle at approach conditions with the educed model parameters is performed in 2D and 3D. Various features of the numerical method that enable it to be used for realistic applications are presented. This includes the suppression of flow instabilities in the linear inviscid solution and analysis of the solution to prove the global conservation of acoustic energy in each individual result. It is found that the current approach is too time consuming for optimisation, even for a 2D simulation using parallel processing. Thus, finally the potential of porting a CAA method to the graphics processing unit (GPU) is shown in one example. The GPU based computation is about 100 times faster. The results are encouraging, even though the GPU variant needs further validation.     

Influence of the opening angle of a conical supersonic nozzle on the structure of initial interval of non-isobaric jet

The ideal gas exhaustion from an infinite volume into a gas at rest through a supersonic conical Laval nozzle is considered. The problem was solved numerically by steadying in time in a unified formulation for the regions inside the nozzle and in the ambient environment. In such a statement, the nozzle outlet section is no internal boundary of the region under consideration, and there is no need of specifying the boundary conditions here. Local subsonic zones arising in the flow lie inside the region under consideration, which eliminates the possibility of using a marching technique along one of the coordinates. The numerical solution is constructed by a unified algorithm for the entire flow region, which gives a possibility of obtaining a higher accuracy. The computations are carried out in the jet initial interval, where, according to monograph [1], the wave phenomena predominate over the viscous effects. The exhaustion process is described by the system of gas dynamics equations. Their solution is constructed with the aid of a finite difference Harten’s TVD (Total Variation Diminishing) scheme [2], which has the second approximation order in space. The second approximation order in time is achieved with the aid of a five-stage Runge-Kutta method. The solution algorithm has been parallelized in space and implemented on the multi-processor computer systems of the ITAM SB RAS and the MVS-128 of the Siberian Supercomputer Center of SB RAS. The influence of the semi-apex angle of the nozzle supersonic part and the pressure jump between the nozzle outlet section and the ambient environment on the flow in the initial interval of a non-isobaric jet is investigated in the work. A comparison with experimental data is presented. The computations are carried out for the semi-apex angles of the nozzle supersonic part from 0 (parallel flow) to 20 degrees. For all considered nozzles, the Mach number in the nozzle outlet section, which was computed from the one-dimensional theory, equaled three. Computations showed that in the case of flow acceleration in a conical supersonic nozzle, its geometry is one of the main factors determining the formation of the jet initial interval in ambient environment.     

Numerical simulation of powder transport behavior in laser cladding with coaxial powder feeding

Laser cladding with coaxial powder feeding is one of the new processes applied to produce well bonding coating on the component to improve performance of its surface. In the process, the clad material is transported by the carrying gas through the coaxial nozzle, generating gas-powder flow. The powder feeding process in the coaxial laser cladding has important influence on the clad qualities. A 3D numerical model was developed to study the powder stream structure of a coaxial feeding nozzle. The predicted powder stream structure was well agreed with the experimental one. The validated model was used to explore the collision behavior of particles in the coaxial nozzle, as well as powder concentration distribution. It was found that the particle diameter and restitution coefficient greatly affect the velocity vector at outlet of nozzle due to the collisions, as well as the powder stream convergence characteristics below the nozzle. The results indicated a practical approach to optimize the powder stream for the coaxial laser cladding.     

液氢贮箱零蒸发数值模拟与分析

采用CFD技术,对处于微重力下的零蒸发(ZBO)液氢贮箱内采用喷嘴棒强迫混合的流场进行稳态数值模拟,建立了二维轴对称模型,预测了在不同几何参数下贮箱内温度场及速度场分布情况。研究表明,喷嘴棒伸入贮箱长度、入口直径等因素均会对系统内温度场产生影响。贮箱内平均温度和最大温度随喷嘴棒长度和入口直径的增大而减小,而喷口直径对贮箱内温度场影响不明显。由上述可以看出,通过增大入口直径、选择合适的喷嘴棒伸入长度,可以改善系统性能。     

汽轮机调节级静叶片排内流动分析

本文以数值手段研究了汽轮机调节级静叶栅内粘性流动。数值方法采用三维可压缩粘性流动压力校正算法求解Favre平均的N－S方程及湍流动能k方程和湍流动能耗散率。方程。传统汽轮机调节级静叶栅由于展弦比很小，通道二次流强烈，损失较大。本文分析了采用子午流道收缩及叶片弯曲对降低二次流损失的作用。数值计算的结果同实验结果吻合较好。     

蒸汽浸没射流凝结引起的冲击特性研究

本文在广泛的蒸汽压力和过冷水温度范围内,针对饱和蒸汽通过不同出口直径的喷嘴在过冷水中浸没射流凝结引起的压力冲击特性进行了实验研究,测量得到了不同轴向位置和径向位置的冲击压力,并分析了入口蒸汽压力,过冷水温度和喷嘴出口直径对冲击压力的影响规律。结果表明冲击压力主要受入口蒸汽压力和过冷水温度的影响;同时,当汽水参数以及无量纲轴向和径向距离相同时,不同出口直径的喷嘴对应的冲击压力变化很小,从而表明喷嘴出口直径对压力冲击影响很小。     

镉镍蓄电池及其在大功率脉冲恒流源中的应用

 介绍了碱性镉镍蓄电池用作脉冲大电流恒流源的可行性，叙述了该类电池放电电流的规律和消除记忆效应的办法，并列出了用镉镍蓄电池组装有关恒流源样机的测试数据和实际考验结果。实验证明：在脉冲式大电流场合下，使用蓄电池作能源，可以消除常用的高功率脉冲源对市电电网的冲击，节省大量设备投资，获得具有高稳定度性能的恒流源。     

基于OpenFOAM的投影法磁流体求解器开发与验证

在开源计算流体力学C++工具包OpenFOAM环境下开发了低磁雷诺数条件下的磁流体求解器,并进行了验证。采用投影算法求解动量方程和压力泊松方程;采用非结构网格同位相容守恒算法求解电势泊松方程、感应电流和洛伦兹力;采用边界耦合方法求解流固耦合电势场。通过对均匀磁场下导电方管和导电圆管内的完全发展磁流体层流的数值模拟和解析解的对比,对求解器进行了验证。进一步对非均匀强磁场作用下导电方管和导电圆管内完全发展磁流体层流进行了数值模拟,并与ALEX实验结果进行了比较。数值解和实验结果吻合良好。所开发的求解器可用于复杂结构强磁场作用下磁流体的数值模拟研究。     

Differential model for 2D turbulence

We present a phenomenological model for 2D turbulence in which the energy spectrum obeys a nonlinear fourth-order differential equation. This equation respects the scaling properties of the original Navier-Stokes equations, and it has both the −5/3 inverse-cascade and the −3 direct-cascade spectra. In addition, our model has Raleigh-Jeans thermodynamic distributions as exact steady state solutions. We use the model to derive a relation between the direct-cascade and the inverse-cascade Kolmogorov constants, which is in good qualitative agreement with the laboratory and numerical experiments. We discuss a steady state solution where both the enstrophy and the energy cascades are present simultaneously, and we discuss it in the context of the Nastrom-Gage spectrum observed in atmospheric turbulence. We also consider the effect of the bottom friction on the cascade solutions and show that it leads to an additional decrease and finite-wavenumber cutoffs of the respective cascade spectra, which agrees with the existing experimental and numerical results. The text was submitted by the authors in English.