基本型脉管制冷机的全三维数值模拟计算

建立了基本型脉管制冷机的三维物理和数学模型,在可压缩流动程序的基础上,开发了基本型脉管制冷机的三维非稳态可压缩交变流动与传热耦合计算的数值模拟计算程序。考察了截面平均参数在一个周期内随时间的变化情况,详细分析了脉管内的流场和温度场以及其他各主要参数的变化,对脉管制冷机的工作过程和制冷机理有了进一步的了解和认识,为脉管制冷机的结构改进和实用化奠定了一定的基础。     

一种隐式预处理方法及其在定常和非定常流动数值模拟中的应用

将Choi-Merkle矩阵预处理方法与LU-SGS隐式方法、双时间法以及多重网格方法结合,发展适用于绕飞行器定常和非定常粘性流动的高效隐式预处理计算方法和程序.介绍一种针对定常和非定常流动的LU-SGS隐式预处理方法的统一表述方法.在不改变流动解的前提下,对Navier-Stokes方程的伪时间导数项实施Choi-Merkle矩阵预处理,从而改善可压缩控制方程在低速情况下的系统刚性,使基于LU-SGS时间推进格式的数值模拟方法同时适用于从极低马赫数到可压缩范围内的数值模拟.对Jameson中心格式的人工粘性进行相应的修改,以提高低速流动的计算精度.翼型、机翼以及翼身组合体绕流的数值模拟研究表明,隐式预处理方法获得了很高的计算效率,可使马赫数0.1左右的低速流动计算时间减少50%以上;通过对现有可压缩计算程序进行小量改动,便可使其均匀覆盖整个低速流动范围,提高CFD程序在飞行器绕流数值模拟中的实用性.     

声波衰减的数值模拟

为了采用计算流体力学方法对热声制冷机进行数值模拟,以突破热声热机现有计算方法的限制,基于压力修正算法的基本思想开发了用于模拟非稳态小马赫数可压缩流动的数值程序,并将其应用于声波衰减的数值模拟.对一维及二维声波衰减过程的模拟显示,数值计算的结果与声学理论的预测符合良好,说明了方法的正确性.     

以压力为主变量求解喷管内的气体流动

一、引言 以压力为主变量求解气体流动问题的计算方法,早在七十年代,Hirt就证明是一种可有效地用于全马赫数的流动问题。但是由于一些技术上的困难,以压力为主变量的方法主要限于求解不可压的低速流动问题。本文将作者原有的非正交坐标下的,以压力为主变量求解不可压缩流动问题的计算方法和程序进行了改进。通过在动量方程中采用混合张量的形式而提高了计算的精度和稳定性,并通过在压力修正方程中隐式地引入密度的影响而将计算方法推广到用于求解可压缩流动问题。采用这种方法对两种喷管内的流动进行了计算,并将计算结果与实验结果进行了比较,结果是令人满意的。     

数值分析带二次流跨音速尾喷管流场

本文用有限元法数值分析带二次流可调收—扩喷管跨音速流动,紊流粘性采用ｋ—ε双方程模型来描述,并利用加权余量法中的Ｇａｌｅｒｋｉｎ法建立有限元方程,求解可压缩粘性流体流动Ｎ－Ｓ方程,喷管壁面采用壁面函数。通过四种不同喷管、不同工况下尾喷管内部流场计算,并用实验数据进行对比表明：计算结果合理,程序可靠,可利用有限元法对喷管超音速流动进行数值研究。     

离心式压缩机叶轮内部流场的数值计算

本文利用κ-ε湍流模型方法和叶轮进出口测试结果计算离心叶轮内部流动。计算采用了SIMPLEC方法,对压力修正方法进行了适当改进。为适应可压缩流动计算的需要,利用局部摩擦损失建立了压力与密度的联系。文中给出了两个叶轮的计算结果。     

可压缩流动离散涡方法

推导了可压缩流动旋涡动力学基本方程,并分析了其基本性质。如同不可压流动,在可压缩流动中旋涡同样具有场与物质两重特征。得出了可压缩流中的旋涡诱导速度公式,对Ｂｉｏｔ－Ｓａｖａｒｔ方程进行了可压缩修正。基于Ｌａｇｒａｎｇｉａｎ框架下的粒子方法,求解可压缩流中的胀量项,从而用离散涡模型求解了非定常、不稳定、可压缩流场。数值实验验证了提议的计算方法有效性。并分析了可压缩流动中旋涡运动的特征,与不可压流动的差别。     

一种求解可压缩Navier-Stokes方程的隐式迭代时间推进方法

针对有壁面边界的可压缩流动问题,提出与基于非等距网格的高精度紧致型差分格式相结合的简化隐式迭代时间推进法,建立求解可压缩Navier-Stokes方程的直接数值模拟方法,提高了计算效率.应用该方法,直接数值模拟两种有壁面边界的二维可压缩流动问题,即可压缩平板边界层流动和可压缩槽道流动.     

基于预处理HLLEW格式的全速域数值算法

基于HLLEW(Harten-Lax-Van Leer-Einfeldt-Wada)格式引入预处理技术发展适合求解全速域流场的三维Navier-Stokes求解器.引入低速预处理技术,重新构造HLLEW格式的耗散项,给出预处理后的HLLEW格式,并根据预处理后的雅克比矩阵构造相应的隐式时间推进方程.利用预处理方法求解NACA 4412低速不可压流动与RAE 2822跨声速可压缩流动,并与实验结果及原有方法的计算结果对比.结果表明:预处理HLLEW格式不仅提高低速不可压缩流动的计算效率和精度,也保持了对可压缩流动的处理能力,是一种适用于全速域流场数值模拟的有效方法.     

基于高精度WENO格式的平面叶栅内流大涡模拟

基于5阶WENO格式结合AUSM+-up通量分裂方法编制密度基有限差分数值计算程序,并对NACA 65平面叶栅在不可压和亚音速工况下的流动进行三维大涡模拟研究,计算所得翼型表面时均压力系数分布与文献中实验结果符合较好,使数值算法和计算程序的可用性得到验证。大涡模拟获得了叶栅流道内瞬态流场的细节特征,体现了高分辨率格式捕捉精细流动结构的能力。本文工作为针对叶轮机械复杂可压缩内流问题进行更深入的高精度LES研究奠定了基础。     

Theoretical and Experimental Investigations of the Flow Field for Asymmetric Dual-Flow Interrupter Nozzles

Experimental investigations have indicated that electrode vapor can have a significant negative effect in thermal interruption speed for the gas-blast circuit breakers. This electrode vapor contamination can be minimized by the use of asymmetric dual-flow nozzle configuration. A computer program was developed to design the nozzle and electrode geometries of the asymmetric dual-flow interrupter and to calculate both the subsonic and supersonic cold flow fields. The Variational Principle of the finite element method, together with a Newton-Raphson iterative scheme, was used to solve the continuity equation for compressible flow. The supersonic flow field in the conical nozzle was calculated by the one-dimensional flow relationship. Two asymmetric dual-flow nozzle models were constructed to investigate the effects of orifice opening and nozzle divergent angle. The cold flow experiments were conducted in the Rensselaer Polytechnic Institute (RPI) Transonic and Supersonic Wind Tunnel Laboratory. Various upstream-to-downstream nozzle pressure ratios were used to obtain the subsonic and supersonic experimental flow-field data. The experimental flow measurements were correlated with the calculated values to validate the computer program.     

小孔流速实验中的排水时间和流量系数的研究

本文以水作为理想流体,考虑到水头损失和孔口缩流效应,对小孔流速实验涉及的容器排水问题进行了系统的理论和实验研究.从理论上推导得出了圆柱形容器排水时间的解析解,分析了排水时间和自由液面速度、流量系数之间的规律,提出了排水时间的等效性.实验上,加工了底部开有不同小孔的大型圆柱形容器,测量了容器排水时间随液面高度的变化关系,借助实验结果计算了流量系数值,验证了容器排水时间的等效性关系,实验结果与理论计算符合较好.     

高压联合进汽阀门三维粘性流场数值分析

本文采用多分区 ＳＩＭＰＬＥＣ算法对 ６００ ＭＷ汽轮机高压联合进汽阀门内部复杂流动进行了三维粘性数值分析。流场计算结果表明总压损失主要集中在调节阀喉口附近。调节阀阀碟前后的两股高速气流在阀碟的正上方位置相碰引起较大的掺混损失;气流经过调节阀喉口后,附面层急剧增厚,形成一层较厚的沿管壁的低总压区。计算得到的流场特性为即将开展的阀门结构优化设计提供了重要依据。     

Gas flow characteristics of argon inductively coupled plasma and advections of plasma species under incompressible and compressible flows

In this work, incompressible and compressible flows of background gas are characterized in argon inductively coupled plasma by using a fluid model, and the respective influence of the two flows on the plasma properties is specified. In the incompressible flow, only the velocity variable is calculated, while in the compressible flow, both the velocity and density variables are calculated. The compressible flow is more realistic; nevertheless, a comparison of the two types of flow is convenient for people to investigate the respective role of velocity and density variables. The peripheral symmetric profile of metastable density near the chamber sidewall is broken in the incompressible flow. At the compressible flow, the electron density increases and the electron temperature decreases. Meanwhile, the metastable density peak shifts to the dielectric window from the discharge center, besides for the peripheral density profile distortion, similar to the incompressible flow.The velocity profile at incompressible flow is not altered when changing the inlet velocity, whereas clear peak shift of velocity profile from the inlet to the outlet at compressible flow is observed as increasing the gas flow rate. The shift of velocity peak is more obvious at low pressures for it is easy to compress the rarefied gas. The velocity profile variations at compressible flow show people the concrete residing processes of background molecule and plasma species in the chamber at different flow rates. Of more significance is it implied that in the usual linear method that people use to calculate the residence time, one important parameter in the gas flow dynamics, needs to be rectified. The spatial profile of pressure simulated exhibits obvious spatial gradient. This is helpful for experimentalists to understand their gas pressure measurements that are always taken at the chamber outlet. At the end, the work specification and limitations are listed.     

微圆孔非线性声阻抗及声整流现象的实验研究

在高声强下测量了微圆孔处声激发射流的速度和微圆孔的非线性声阻抗。随声压级的增加声激发射流的速度增大,实验中射流速度在 ０－１９ｍ／ｓ范围内变化,这表明出现一种强烈声整流现象;与此同时微圆孔声阻明显增大,而声抗减小,声抗最小值约是其线性值的０．７倍。此外实验结果还验证了一种微园孔声学非线性效应离散涡模型的合理性。     

气泡雾化喷嘴喷雾平均直径在下游流场中的分布

文利用激光衍射粒度仪对气泡雾化喷嘴下游流场进行了实验研究,主要分析了雾化颗粒直径随径向和轴向距离变化的趋势．由于喷嘴出口处气液两相流型和颗粒自身重量的影响,液雾颗粒沿径向呈现非轴对称分布;而液雾颗粒直径随着轴向距离的增加呈现先减小、后增大的趋势,颗粒直径的减小是大量气泡爆炸的结果,而后的增加则是由于颗粒之间的相互粘结造成的。     

离心压气机级三元粘性计算

使用叶片排间隙混合平面概念，完成离心压气机级多叶片排三元N-S方程计算。每个动静叶片排内的流动被认为是定常的且由相对独立的程序段进行运算。这样的串行程序很容易被改造为在并行系统上运行的SPMD并行程序。     

Investigation of piezoelectrically generated synthetic jet flow

The purpose of this paper is to investigate the compressible turbulent synthetic jet flow characteristics of a dual diaphragm piezoelectric actuator. Experimentally, a flow visualization system was established to obtain the particle streak images scattered from 10-μm red fluorescent spheres for observing the synthetic jet flowfield produced by a dual diaphragm piezo actuator. The centerline velocity of the synthetic jet was also measured by using a hot-wire anemometry system. In the analysis, the computational approach adopted the transient three-dimensional conservation equations of mass and momentum with the moving boundary specified to represent the piezo diaphragm motion. The standard k-∈ two-equation turbulent model was employed for turbulence closure. For the actuator operating at the frequency of 648 Hz, the particle streakline images in the cross-sectional plane visualized a turbulent jet flow pattern in the far-field area. The hot-wire anemometry data indicated that the measured centerline velocity of synthetic jets reached 3.8 m/s at y/d= 50. The predictions were compared with the visualized particle streak images and centerline velocity of the synthetic jet in order to validate the computer code. The numerical simulation revealed the time-periodic formation and advection of discrete vortex pairs. Caused by the outward movement of the piezo diaphragms, air near the orifice was entrained into the actuator cavity when the vortex pairs were sufficiently distant from the orifice.     

A pressure-based algorithm for multi-phase flow at all speeds

A new finite volume-based numerical algorithm for predicting incompressible and compressible multi-phase flow phenomena is presented. The technique is equally applicable in the subsonic, transonic, and supersonic regimes. The method is formulated on a non-orthogonal coordinate system in collocated primitive variables. Pressure is selected as a dependent variable in preference to density because changes in pressure are significant at all speeds as opposed to variations in density, which become very small at low Mach numbers. The pressure equation is derived from overall mass conservation. The performance of the new method is assessed by solving the following two-dimensional two-phase flow problems: (i) incompressible turbulent bubbly flow in a pipe, (ii) incompressible turbulent air–particle flow in a pipe, (iii) compressible dilute gas–solid flow over a flat plate, and (iv) compressible dusty flow in a converging diverging nozzle. Predictions are shown to be in excellent agreement with published numerical and/or experimental data.     

高速离心压气机叶轮性能预测及流场分析

用时间推进法数值求解相对圆柱坐标系下的雷诺平均N-S方程,模拟高速离心叶轮内部的三维粘性流场.计算是在设计转速9个不同的流动工况下进行的.与实验结果比较了三个不同流量下的轮缘周向平均静压,对典型通道位置截面的子午速度分布与实验进行了定量比较,最后得到了转子在设计转速下的压比和等熵效率曲线.研究结果表明,本文发展的数值方法可较好的预测离心压气机叶轮的性能曲线.