Cellular automation model for analyzing capacity of branch road section

In order to reduce the traffic pressure of urban arterial road with the rational utilization of the branch road, the vehicle meeting behavior on the branch road without divided lane was described, and the cellular automation (CA) model was put forward by introducing meeting behavior to reflect the relation between safe meeting speed and road width. The numerical simulation results depict several relation curves between road section capacity, speed and road width under different directional distributions of traffic flow, as well as the curves between the major and minor direction saturation flow, speed and road width. These relation characteristics indicate that except the one-way road section capacity and speed remaining unchanged, other road section capacities and speeds under different directional distributions increase with the increase of road width. On narrow road, the two-way traffic capacity and speed are less than those of one-way traffic; on wide road, the two-way traffic capacity doubles that of one-way traffic, but their speeds are almost the same. As the directional distribution moves to an even distribution of 50/50, the major direction saturation flows and speeds as well as the minor direction speeds tend to decease, while the minor direction saturation flow tends to increase.     

梯状尖部间隙机匣处理对轴流压气机性能影响的实验研究

设计了3组共7种叶尖梯状间隙的机匣处理结构，并在某亚音速单级轴流压气机孤立转子上进行了实验研究，比较分析了不同机匣结构对其性能和稳定性的影响。结果 表明：(1)通过对3种径向间隙(0．517％h、0．655％h和0．741％h)的实验结果对比，发现随着径向间隙增加压气机性能和稳定性均下降；(2)在小间隙(0．517％h)水平下，叶尖梯状间隙机匣处理不但可以改善压气机的稳态性能和工作稳定性，还可以改善压气机的失速性能，而且梯状间隙的轴向尺寸对改善压气机性能和稳定性有较大影响；(3)改变梯状间隙的径向深度对压气机性能和稳定性的影响相对较小。     

航行体云状空泡稳定性通气控制

为研究水下航行体云状空泡稳定性,通过水洞实验对水下航行体模型云状空泡进行了实验研究,对比分析了不同空化数对水下航行体通气空泡稳定性的影响,分别分析了不同空化数下通气空泡发展、断裂和脱落等准周期性波动特性以及脱落速度和空泡发展对表面压力的影响,得到了通气对流动控制效果和局部不稳定性机理.结果表明:在通气作用下空泡内的透明部分逐渐增大,在逆压梯度的作用下,回射流形成并向航行体前部运动,空泡前部由透明逐渐变为浑浊,当回射流到达空泡前段,空泡表面出现波动,在回射流的作用下空泡以涡团形式发生脱落,航行体模型肩部通气空泡的发展和脱落随着空化数的控制而呈现明显的不同;当空化数较大时,空泡发生断裂、脱落两个过程;当通气量增大空化数减小后,空泡呈现断裂、融合、脱落3个过程,此时空泡呈现稳定发展的特性;空泡平均脱落速度随着空化数的减小而减小;实验结果也表明了不同时刻航行体表面压力脉动情况,空泡闭合位置存在压力峰值,航行体表面压力随着空泡的脱落出现波动.     

Flow computations of multi-stages by URANS and flux balanced mixing models

The quasi-steady methods based on mixing models have been widely applied to flow computations of turbomachinery multistages in aerospace engineering. Meanwhile, the unsteady numerical simulation has also been used due to its ability in obtaining time-dependent flow solutions. In the paper, two different mixing treatments and the corresponding flux balanced ones are presented to exchange the flow solutions on the interfaces between adjacent blade rows. The four mixing treatments are then used for flow computations of a subsonic 1.5-stage axial turbine and a quasi-1.5-stage transonic compressor rotor. The results are compared with those by unsteady numerical method, which is implemented by using the sliding mesh technique. The effects of the quasi-steady and unsteady computation methods on the conservation of flow solutions across the interfaces are presented and addressed. Furthermore, the influence of mixing treatments on shock wave and flow separation of the transonic compressor rotor is presented in detail. All the results demonstrate that the flux balanced mixing treatments can be used for multi-stage flow computations with improved performance on interface conservation, even in the complex flows.     

转速对离心泵反转用作透平空化特性的影响

透平运行中产生的空化会影响其能量的转化,因此,使用离心泵反转用作透平,利用数值模拟 的方法,对透平分别在 5 种不同转速下的、不同空化余量的内部流动规律进行了数值模拟,得出了不同转速 下透平空化的特性曲线和内部流场特性。通过分析不同转速下的空化规律,得到了透平能量转化的最佳性能 临界点,并且建立了转速与透平产生空化的临界空化余量关系。研究结果表明,转速与透平临界空化余量呈 正相关;透平工作在临界空化余量之上,透平严重空化时,空泡聚集在尾水管处,不利于流体的流出,减小 了能量的转化。     

水洞中突出矩形腔的流激驻波振荡研究

在水洞中进行了变深度的、不带导流板的突出矩形腔在流激励下的振荡实验.对腔口附近壁面上几个典型点及腔底处测得的均方压力进行了谱分析,得到了许多有意义的结果.对驻波振荡,考虑到腔底的弹性边界作用,文中给出了推算水中腔底面反射系数的方法,得到了腔的驻波振荡频率修正公式.从修正公式得到的结果与其它腔深度的实验值比较,符合尚好.     

数值仿真注塑充模过程

使用CFD软件Polyflow,数值研究了注塑机注射充模过程中模具型腔内聚丙烯熔体的二维非等温流场,分析了不同时刻模具型腔内熔体的速度、压力、温度和剪切速率分布。研究结果表明,在充模过程中流场的各个物理量变化比较均匀,在流动前沿温度较高、压力最小。在充填过程的不同时刻,随着时间的增加,熔体的平均压力不断升高、平均温度不断降低。不同熔体的注射温度影响模具型腔内熔体的流场。较高的注射温度升高熔体平均温度,减低模腔熔体的平均压力,使熔体的粘度降低,改善熔体的流动性。研究结果对注塑机模具的设计和注射充模工艺参数的选择有一定的理论指导意义。     

Numerical investigation of radial inflow in the impeller rear cavity with and without baffle

In typical small engines, the cooling air for high pressure turbine(HPT) in a gas turbine engine is commonly bled off from the main flow at the tip of the centrifugal impeller. The pressurized air flow is drawn radially inwards through the impeller rear cavity. The centripetal air flow creates a strong vortex because of high inlet tangential velocity, which results in significant pressure losses. This not only restricts the mass flow rate, but also reduces the cooling air pressure for down-stream hot components. The present study is devoted to the numerical modeling of flow in an impeller rear cavity. The simulations are carried out with axisymmetric and 3-D sector models for various inlet swirl ratio β_0(0–0.6), turbulent flow parameter lT(0.028–0.280) with and without baffle. The baffle is a thin plate attached to the stationary wall of the cavity, and is proved to be useful in reducing the pressure loss of centripetal flow in the impeller rear cavity in the current paper. Further flow details in impeller rear cavity with and without baffle are displayed using CFD techniques. The CFD results show that for any specified geometry, the outlet pressure coefficient of impeller rear cavity with or without baffle depends only on the inlet swirl ratio and turbulent flow parameter. Meanwhile, the outlet pressure coefficient of the cavity with baffle is indeed smaller than that of cavity without baffle, especially for the cases with high inlet swirl ratio. The suppression of the effect of centrifugal pumping and the mixing beween the main air which is downstream of the baffle and the recirculating flow of the vortex in the stationary cavity, which are caused by the use of baffle, are the underlying reasons that lead to the reduction of outlet pressure loss.     

变马赫数下压力面小翼对扩压叶栅气动特性的影响

为探究变来流马赫数下压力面叶尖小翼对扩压叶栅气动特性的影响,对Ma=0.5、Ma=0.6和Ma=0.7来流马赫数下的原型叶栅和加装不同宽度的压力面叶尖小翼的扩压叶栅流场特性进行了实验研究. 结果表明:在高亚声速的来流条件下,压力面叶尖小翼可以有效减小叶顶两侧压力梯度,阻碍流体流入叶顶间隙,控制叶顶泄漏流动,减小流场损失,改善流场流动状况. 随着小翼宽度的增加,改善程度增大,同时马赫数的变化与控制效果成正比. 当Ma=0.7时,与原型叶栅相比,PW2.0方案的流场改善程度最大,总压损失系数降低了6.53%.     

Navier-Stokes方程预处理方法及其对翼型绕流数值模拟的应用

在与定常方程相容的情况下,通过对N av ier-Stokes方程的时间导数项实施Cho i及Turkel矩阵预处理,发展了适用于低、亚、跨声速粘性流动的有效的预处理方法。对预处理后的控制方程采用了Jam eson格式进行有限体积空间离散和Runge-K utta显示时间推进求解,以及采用了FA S多重网格方法加速收敛。对RAE 2822、GAW-1等不同类型翼型进行了低速和跨声速流动的数值模拟。算例表明:Cho i预处理方法和Turkel预处理方法均有效改善了时间推进方法对低马赫数流动计算的收敛性,而且提高了计算精度;预处理方法同样适用于跨声速非线性流动的计算,且表现出了一定的加速收敛效果。     

不同头型运动体高速入水空泡数值模拟

运动体头型对其入水流场的流动分布、流体动力及入水弹道均有较大的影响。针对此问题基于有限体积法离散、求解雷诺平均的Navier?Stokes方程,考虑空化效应,并引入动网格技术,对带有不同角度锥头圆柱体的高速入水问题开展数值模拟研究,得到不同头型条件下高速入水运动参数及空泡形态发展规律、流场的压力分布及速度分布规律,分析了头型对入水空泡流场的影响。研究结果表明,空泡半径的扩张规律受头型及其阻力系数的影响,半径大小与阻力系数近似满足一定的关系式;入水初期,运动体头部受到极强的冲击载荷,锥角越大,压力峰值也越高;锥体表面压力系数与锥角大小直接相关,锥角较大时压力系数也较大。同时,锥角大小对运动体肩部排开水的速度也有较大影响,运动体在相同速度下,锥角较大时,肩部排开水的速度也较大。     

方腔涡流运动对压力脉动噪声影响的数值分析

为了研究水下方腔内的湍流流动情况,采用k-ε模型和大涡模拟(LES)方法分析了腔内流场的涡旋分布及其发展规律、关键位置的压力脉动特征,运用MATLAB平台对时域下的压力脉动信息进行快速傅里叶变换,得到频域脉动压力级结果,进而讨论了腔内关键压力点的脉动特征.结果表明:压力脉动的峰、谷特征与涡流运动状态具有良好的对应性;方腔不同位置点的压力脉动频率和压力级特征不同,与相应的涡流运动状态密切相关;通过与相同方腔模型脉动声压实验数据的对比表明,在40 Hz以上频率,方腔涡流压力脉动级与实验具有很好的符合度,验证了数值模拟和傅里叶分析方法的可行性和准确性.     

水翼非定常空化流场的数值模拟

采用修正的RNGk-ε湍流模型对8°攻角NACA0015水翼的非定常二维空化流场进行数值模拟,分析当空化数分别为1和1.5,对应雷诺数为3×105时绕翼型的非定常流动,得到不同空化数下的非定常空化流场结构及其演化过程的流动特性.计算结果表明,回射流在空泡的形成和发展过程中起着重要的作用.空泡首先出现于水翼的前缘,在其产生的位置形成一个顺时针的漩涡,漩涡沿水翼上表面向下游移动.空泡逐渐长大并脱落,在不同空化数下,空泡脱落的位置不同.空泡形成和发展过程中均伴有压力的波动,大空化数流场的压力波动幅度和频率都明显高于小空化数流场.     

运动参数对回转体倾斜入水流场特性影响

为分析回转体低速倾斜入水过程中入水空泡形态及流体动力特性演化规律,基于Fluent流体计算平台,并利用动网格技术,针对小型回转体以不同入水速度和入水角度的倾斜入水过程开展数值仿真研究.数值仿真结果与试验结果良好一致性,证明了文中数值仿真方法的正确性与有效性.基于该数值仿真方法,针对不同入水速度和不同入水角度回转体低速倾斜入水过程流场特性进行分析.数值计算结果表明:在距离自由液面相同位置处,回转体倾斜入水产生所产生的入水空泡,其直径随着入水速度的增加而小幅增大,随着入水角度的增加而减小;入水速度对流场中压力分布规律有较大影响,在同一入水深度处不同入水速度回转体入水过程中流场的最大压力随着入水速度的增加而增大;入水角度对回转体附近流域的最大压力影响较小,但最小压力随着回转体入水角度的增加而增大;不同入水角度回转体,母线压力峰值位置随着入水角度的增加而逐渐向母线右端点偏移,但其值差别较小;不同入水速度回转体其阻力系数峰值差别不大,不同入水角度阻力系数峰值随着入水角度的增加而增大,但稳定后的阻力系数值随着入水速度的增加而减小.     

Numerical investigation on the thermal protection mechanism for blunt body with forward-facing cavity

Numerical experiments are carried out using the standard hypersonic ballistic-type model (HB-2) to investigate the effect of forward-facing cavity on the aerodynamic heating. A general concept is proposed which utilizes the flow disturbances generated passively in the nosed subsonic region to weaken the detached shock wave. Several aspects are mainly studied, including shock shape and standoff distance, surface heat flux and pressure, flowfield feature and cooling mechanism. The numerical results indicate that shock strength and standoff distance increase with an increase in the L/D ratio of the cavity. Interestingly, a bulge structure of the detached shock associated with a deep cavity is observed for the first time. Local surface heat flux and pressure around the concave nose are much lower respectively than those at the stagnation point of the baseline model. In addition, both surface heat and pressure reductions are proportional to the L/D ratio. A negative heating phenomenon may occur in the vicinity of a sharp lip or on the base wall of a deep cavity. If the L/D ratio exceeds 0.7, the detached shock appears as a self-sustained oscillation which can be referred to as the cooling mechanism.     

旋转填料床流体力学特性的研究

利用离心传质分离设备——旋转填料床, 对其流体力学特性进行了研究, 测定了该装置在不同转速、气流量和液流量下的干、湿床压降。通过对大量实验数据的分析表明, 旋转填料床的干、湿床压降均受气流量及转速的影响, 且受气流量影响较大, 而与液流量基本无关     

球体入水空泡动态特性

为研究球体低速入水的空泡特性以及空泡的形成对球体运动特性的影响,基于独立膨胀原理对充分发展后的空泡形态建立了理论模型,采用高速相机对不同速度的球体入水过程进行拍摄,观察球体入水从没有空泡到空泡充分发展的过程,分析了空泡的形成对球体后方射流的影响以及空泡对球体的运动特性的影响,研究了空泡的动态特性.结果表明,在球体入水没有形成空泡时,球体后方的射流以水柱的形式向上溅射;在形成稳定的空泡后,在空泡表面闭合前射流向四周溅射,空泡表面闭合后射流主要向上溅射.由于球体入水速度的变化、入水空泡的形成以及入水撞击时冲击力的影响,球体的加速度变化比较复杂,球体的阻力系数受到入水空泡的影响而明显减小.用建立的空泡形态理论模型得到了入水空泡截面积随时间的变化,并与实验结果进行了对比,对比结果显示了较好的一致性,分析表明不同深度处空泡从发展到破灭的时间大致相同,深度较小处的空泡截面积较大.     

基于欧拉方程的一种机翼气动弹性计算方法

利用一种双时间方法求解三维非定常欧拉方程，采用无限插值理论生成O－H型代数网格，考虑了机翼变形时的网格生成问题，通过与气动力方程的联立求解，在时间域内用二阶龙－库塔方法求解机翼弹性运动方程。计算结果表明，本计算方法具有较高的计算效率，所计算的颤振临界速度与风洞实验一致。     

Numerical Simulation of Twin-Screw Extrusion with Wall Slip

Wall slip boundary condition is first introduced into twin-screw extrusion with the Navier slip law. Three-dimensional isothermal flow in the twin-screw extruder is simulated by using the finite element package POLYFLOW. Profiles of velocity contours in the screw channel and shear rate distributions in the intermeshing region are presented for different slip coefficients. Curves of axial pressure difference, average shear rate and dispersive mixing index vs. the slip coefficient are plotted and discussed. Comparisons are also made between the wall slip conditions and the non-slip condition. The simulation results indicate that, as the level of wall slip decreases, the axial pressure difference rises, the shear effect is intensified and the axial mixing is also enhanced. All these flow characteristics seem to level off with the increase of the slip coefficient. However, because of the inherent limitation of the Navier slip law, use of an overestimated slip coefficient would predict an over-sticky state between the screw surface and the polymer melt.     

挤压铸造金属液流充型特性研究

研究了挤压铸造中金属液流的充型特性 ,利用高速摄影观察溶体的充填状态。结果表明 :采用不同的浇口尺寸及充型速度 ,所得到的液流充型状态和特性各不相同。层流充填时伴随的是压力流和补缩流 ,紊流充填时呈现的是喷射流和压力流 ;金属液在型腔中的流动速度是不均匀的 ,中心处流体的流动阻力最小 ,流速最大 ,受到的剪切力作用最小。