离心叶轮外侧间隙内的流动计算

应用低Re数κ-ε模型，计算了离心叶轮外侧间隙内具有径向向内流动、间隙比G=0．005和0．0113时紊流流动的问题。计算结果显示，间隙内流动主要是径向流动。静止盘边界层内是径向向内流动，旋转盘边界层内是径向向外流动，不存在核心区。     

轴对称弯道内粘性不可压缩流动的研究

提出了一种用边界层理论对轴对称弯曲流道内部流动进行分析的方法,即主流区用流线曲率法计算,边界层利用Partanker-Spolding方法,并采用了k-ε,紊流模式。在边界层方程组及k-ε方程中均考虑了轴对称情形下曲率的影响,并在紊流模式中考虑了曲壁对紊流结构的影响。此外还以“分离点的奇异性”预测了边界层的分离,给出了轴对称曲壁发生分离时型参数的大小。经实验与计算比较,结果令人满意。     

一种低流阻表面的流动与传热特性

采用数值模拟方法对流体在有圆孔表面的流动及传热特性进行研究。研究中分别对四种不同的工况进行数值模拟。数值模拟结果所得换热面努塞尔数Nu与采用迪图斯—波尔特(Dittus-Boelter)公式计算所得Nu数进行比较,计算误差均小于5%。研究结果表明,在四种工况下,圆孔表面由于圆孔的存在改变其表面附近流动边界层的流动结构,使得边界层内垂直于壁面的法向速度梯度变小,进而使得边界层厚度增加,且由于圆孔表面下方流体可吸收部分来自边界层以外的动量传递,降低壁面附近的湍流扰动,从而减少损耗,达到明显的减阻效果。计算结果显示:四种工况下圆孔表面的存在使得流动均有不同程度的减阻效果,四种工况中减阻效果最大可达14%;但是随着流动减阻效果的改善,圆孔表面的换热性能均有所降低。     

定常固液两相流动边界层的数学模型

利用两相流动理论和边界层理论，分析了固液两相流动中的受力情况，以及边界层中的流动特征，对二维粘性定常不可压流体边界层中的层流运动进行了讨论，推导出了边界层的数学模型，为进一步全面研究固液两相流动流场奠定了基础。     

锚链提升器水平液压管内气泡流型及其对边界层速度梯度影响分析

为有效提取气泡对管路边界层的扰动参数,达到提前预测和判断空气对液压管路污染的目的,基于管路流动边界层理论和气液两相流动理论,通过Fluent仿真平台建立气液管路模型,计算得到气泡流型及其对边界层速度梯度的影响规律。通过实验验证了仿真模型中气泡流型变化的一致性,并提出了一种液压系统空气污染诊断的新方法。计算结果表明,该方法能通过提取边界层微观变化规律来监测液压系统宏观空气污染故障;但是,当气泡直径小于0.01 mm时,则面临监测不到边界层速度梯度变化的情况。     

基于轴流泵间隙流动的新水力设计方法

轴流泵叶轮轮毂与轮缘处间隙流动及边界层对轴流泵性能的影响很大,应用Numeca及Flu-ent等软件对轴流泵叶轮轮缘间隙中的流动进行数值模拟,根据流动模拟结果对叶轮叶片型线及轮毂、轮缘处的叶型设计进行修正,使其速度-压力分布比较理想,并提出了基于间隙流动的轴流泵水力设计方法,这种新的水力设计方法有利于改进轮缘和轮毂处边界层以及轮缘间隙中的流动,达到提高轴流泵效率的目的。     

不同供气总压下高压圆盘气体轴承边界层对流换热系数的研究

传统的气体轴承供气压力小,气流速度低,气流温度变化小,气膜内的流场可看成恒温流动。而高压圆盘气体轴承中的气流速度可达超音速,气膜内边界层的温度梯度大,因此,需对气膜内的边界层对流换热问题进行研究。对轴承气膜内的流场进行数值模拟,结果表明:边界层厚度沿轴承半径方向增加,边界层在气膜内完全发展,主流区消失;边界层的作用致使气流速度下降;对速度边界层的特征进行分析,预测了气膜内边界层的转捩位置。计算了不同供气总压下的对流换热系数,并与Bartz公式的计算结果进行对比分析,验证了所采用的计算方法的可靠性和计算结果的准确性。     

平行圆板径向湍流不可压缩边界层的近似解

为研究两平行圆板间不可压缩径向扩散流动的规律,从动量积分方程出发,推导出在采用双对称收缩段供气的圆盘止推气体轴承中,描述平行间隙内湍流不可压缩无因次边界层厚度与无因次半径比之间变化规律的新公式;采用湍流边界层中的幂次速度型假设,分析得到两平行圆板间径向流动的速度分布的近似解。利用数值模拟的方式,计算得到圆盘气体轴承平行间隙内部的速度分布,并与近似解进行比较。结果表明,新公式能够比较准地反映边界层厚度的发展过程,从而能迅速得到平行间隙内部的速度分布特点。     

基于控制速度分布的离心鼓风机三维叶片优化设计方法研究

本文对离心鼓风机三维叶片优化设计进行了研究,采用控制叶轮流道内的相对速度分布的三维叶片优化设计方法,通过控制流道内沿流线方向的相对速度分布,控制叶轮流道内的边界层增长与分离、二次流、分层效应等流动效应。在优化判据方面采用考虑旋转和曲率效应的边界层计算方法,根据不同的相对速度分布计算边界层发展状况作为优化判据。基于MATLAB编写了优化设计程序设计出一种离心鼓风机的三维优化叶片,通过CFD数值模拟分析和对比证明该优化方法实现了优化设计的目的。     

轴流通风机端壁边界层的计算

给出了一个端壁边界层的求解计算方法，并将端壁边界层的计算结果与无粘主流进行迭代，最终计算得到的转子叶片出口轴向速度与试验结果相吻合的结论。     

Dynamic analysis of free-surface thin film flows driven by gravity over undulated substrate

This paper studies thin film flows with free surfaces driven by gravity through two types of undulated planes: periodically sinusoidal plane and triangle. The substrate plane is fixed and inclined to a certain angle and the flow with a free surface. Through finite element method (FEM), commenced from Navier-Stokes equations and continuity equation, the exact numerical results of free-surface film flows are obtained through discretization solution to finite equations in flowing areas. Based on the numerical calculations, the streamlines and wall shearing stress during the flowing process are visualized via post-proceeding, and the streamlines separation, the onset and evolution of vortex near the substrate boundary during the flow are also analyzed. The influences from the waviness of the substrate planes profile, height of the triangle plane, and change of the film height on film flow dynamics properties are shown.     

Dynamic analysis of free-surface thin film flows driven by gravity over undulated substrate

This paper studies thin film flows with free surfaces driven by gravity through two types of undulated planes: periodically sinusoidal plane and triangle. The substrate plane is fixed and inclined to a certain angle and the flow with a free surface. Through finite element method (FEM), commenced from Navier-Stokes equations and continuity equation, the exact numerical results of free-surface film flows are obtained through discretization solution to finite equations in flowing areas. Based on the numerical calculations, the streamlines and wall shearing stress during the flowing process are visualized via post-proceeding, and the streamlines separation, the onset and evolution of vortex near the substrate boundary during the flow are also analyzed. The influences from the waviness of the substrate planes profile, height of the triangle plane, and change of the film height on film flow dynamics properties are shown.     

流路矩阵在铸造工艺CAD中的应用

浇注系统计算机辅助设计是实现铸造工艺CAD系统的重要部分。本研究在分析与总结水平分型、垂直分型等各类浇注系统的基础上,提出利用流路矩阵法解决设计软件的通用性问题。浇注系统流路矩阵可以直观地描述液态金属在各种复杂浇注系统中的流动路线,各组元中流速、流量关系。它为解决铸造工艺设计软件的通用性,提供了一种非常有效的计算方法。这种方法较图论法具有方法简单、通用性强、程序短、计算速度快、占用内存少等优点。     

Control of boundary layer flow transition via distributed

A reduced-order linear feedback controller, which is used to control the linear disturbance in two-dimensional plane Poiseuille flow, is applied to a boundary layer flow for stability control. Using model reduction and linear-quadratic-Gaussian/loop-transfer-recovery control synthesis, a distributed controller is designed from the linearized two-dimensional Navier-Stokes equations. This reduced-order controller, requiring only the wall-shear information, is shown to effectively suppress the linear disturbance in boundary layer flow under the uncertainty of Reynolds number. The controller also suppresses the nonlinear disturbance in the boundary layer flow, which would lead to unstable flow regime without control. The flow is relaminarized in the long run. Other effects of the controller on the flow are also discussed.     

三维斜流线性完全耦合层吸收边界条件

采用傅里叶与拉普拉斯变换方法分析了三维斜流背景下声波、涡波与熵波的色散关系;根据各物理波的色散轨迹特征,结合频率变化的时空坐标变换方法,给出了一组时间与空间坐标变换关系式,并将三维斜流线性欧拉方程变换至新坐标系;采用复数变换方法,引入阻尼,分别构建了x层、y层、z层及角层的完全耦合层（PML）吸收边界条件,给出了吸收项的施加原则;最后通过三维脉冲声波、对称涡环与周期性点声源在斜时均流中的传播问题验证了该吸收边界条件的正确性。研究结果表明：所提出的坐标变换关系能够有效解决各物理波相位速度与群速度不一致的问题;在斜背景流下,该PML吸收边界条件能较好地吸收物理波,有效抑制边界反射,可用于气动声学计算。     

Ideal profile of a die for the crimping of thick-walled tubes

A model of a stationary plastic flow process during the crimping of a thick-walled tube with a specified internal profile under the Mises yield criterion is given which takes into account the material strengthening during cold deformation and the absence of friction at the boundary of the contact with the die. An ideal plastic flow process is considered when the directions of the principal stresses in the meridional plane coincide with the flow lines and normals to the flow lines. An inverse method of solving is applied: the free boundary of the plastic range is specified, from which the flow lines, the fields of the stresses and strain rates, and the curvilinear profile of the die are calculated.     

Study on the compressible viscous flows through a straight pipe

When sonic nozzles of significantly smaller diameter are used as standard flow meters, the critical backpressure ratio is affected by the boundary layer at the nozzle throat. It is known that, as the flow pathway is complicated in actual valves, the critical pressure ratio differs from the ideal value. However, the effect of the boundary layer thickness on choking criteria is still controversial. Choking phenomenon in a sonic nozzle fitted with a straight circular pipe of variable length is investigated numerically and the results are compared with experimental and theoretical ones. The results show that the actual critical pressure ratio is less than the ideal value and it decreases with increase in pipe length. The effect of boundary layer thickness on main flow Mach number is also made clear in this work. In addition, sonic conductance and pressure loss in actual viscous flows computed are compared with the ISO 6358 standard.     

Modeling of Coriolis mass flow meter of a general plane-shape pipe

The vibration of a general plane tube with a flowing fluid, which is the measuring element in a Coriolis mass flow meter (CMF), is studied. The dynamic stiffness matrix method is used to model such a tube. The tube is divided into straight and circular elements. The elements dynamic stiffness matrices are derived from the equations of motion. By assembling the elements matrices into a global matrix the natural frequencies are obtained. The mode shapes are obtained by applying the boundary conditions at the supports and the compatibility conditions at the nodes. The effects of the flow velocity on the natural frequency and the relative phase difference are modeled. The method is applied to different tube shapes. The results are compared to the published data which reveals good agreement.