进口导叶/叶轮/扩压器非定常相干的数值研究

在非零进口导叶预旋角度下,采用非定常的方法对进口导叶/叶轮/扩压器三部件之间非定常相干进行了数值模拟,研究了进口导叶/叶轮/扩压器三部件之间动静相干的机理。结果表明,叶轮由于受进口导叶尾流和扩压器势反冲效应的双重非定常影响,叶轮受非定常影响最小的区域出现在叶片50%弧长附近,最大的非定常影响出现在叶轮和扩压器之间的动静交界面上。当离心压缩机前带有进口导叶预旋时,扩压器受前面两部件的同时影响,扩压器叶片上的非定常变化沿流向比较均匀。     

船舶艉流场受预旋定子影响试验研究

为探究船舶艉流场流动机理以及节能附体节能机理,本文以某散货船缩比模型为研究对象,在哈尔滨工程大学船模拖曳水池大型利用粒子图像测速系统开展艉流场测量试验。首先对有/无前置预旋定子的艉部伴流场分别进行了三向伴流测量试验,展现出前置预旋定子周围的流动结构,对比有/无前置预旋定子的艉流场轴向速度分布、周向速度分布、旋涡分布并提取不同半径处的轴向速度,阐述了前置预旋定子对艉流场的影响及其节能机理。研究表明:预旋定子能够在桨前产生与桨旋向方向相反的预旋流,定子中下方叶片对流场分布的影响较大,造成附近速度峰值角度偏移、峰值增加,桨盘面流体的进流速度增加,从而改善伴流条件,提升推进性能。     

离心泵叶轮回转S1流面流函数方程的理论研究

根据离心泵叶轮Ｓ１流面的流体运动方程,推导了间接边界元法所需的流函数方程,它适用地不可压理想流体的绝对流动能旋或无旋流动,利用分离变量法从中分离出特解和通解,特解主要受流体的预旋、叶轮理论流量、叶轮旋转,流面形状和厚度的影响,通解主要受叶片形状的影响。     

前导预旋装置调节离心泵的工况

离心泵采用前置导叶进行预旋调节是一种新型的调节节能方式.它扩大了离心泵的高效工作范围,本文通过试验数据及计算分析表明,用前导预旋调节来代替节流调节将大大节约能源.前导调节尤其适合工况中需要泵的流量有较大的变化而扬程改变不大的情形.     

具有前置诱导轮的低比转速复合叶轮的数值模拟

选用Navier-Stokes方程和Spalart-Allmaras湍流模型分析诱导轮对复合叶轮内部流动的影响,采用Numeca软件对具有前置诱导轮及无诱导轮两种工况下的低比转速复合叶轮进行了数值模拟研究。对比分析结果表明:与无诱导轮的叶轮相比,前置诱导轮复合叶轮叶片进口前端和叶片流道间回流区域减小,叶片进口处压力增加,叶轮内部液体流动更加均匀并提高了叶轮的抗汽蚀性能,有效改善了叶轮的水力性能。     

旋喷泵叶轮及内部流场的数值研究

对由矩形流道叶轮、复合式叶轮与大包角后弯叶轮组成的旋喷泵进行全流道数值模拟。研究发现,矩形流道叶轮的压力、速度分布都较均匀,泵的扬程、效率均能达到要求;后两种形式的叶轮的压力梯度分布不均匀,出口处压力分布不理想,速度分布也不均匀。速度分布的不均匀反映出内部流动的不平稳,有回流和大旋涡产生,效率很低。因此,旋喷泵的叶轮选择矩形流道的叶轮较好。     

不同起始直径分流叶片的离心泵内部流场数值分析

为研究不同起始直径分流叶片离心泵内部非定常流动特性,利用计算流体力学软件,针对3种不同起始直径分流叶片的低比转速离心泵,进行了三维非定常数值计算。对比分析了3种起始直径分流叶片离心泵内部流体速度和压力分布。计算结果表明:叶轮Ⅰ的内部流动情况最为理想,分流叶片的起始直径在一定的程度上会影响叶轮内部的流动情况,合理的起始直径能够减小回流漩涡区域,从而提高其过载能力;由于动静干涉作用,在蜗壳壁面产生了较大的压力波动,3个叶轮的波动各不相同,在叶轮Ⅱ中波动较另外2个叶轮更为明显。     

失水事故初期核主泵气液两相流动特性

为研究失水事故下核主泵内气液两相流动情况,本文依据核主泵性能参数、几何结构建立核主泵三维造型,通过使用商业模拟软件ANSYS CFX仿真边界条件、布置密集监测点,从外特性、含气率分布、压力和径向力变化四个方面分析计算结果。分析发现:事故发生后核主泵的效率和轴扭矩总体上单调减小,扬程变化较为复杂,流道内气相聚集与含气率波动规律主要受气体物理特性、流动不稳定性和叶片动静干涉等影响。导叶内压力波动程度与距离动静叶片交界面位置有关,比叶轮内波动更为剧烈。叶轮所受径向力大小总体上不断下降,在叶轮转动一周过程中径向力存在数个极大值,随着事故持续,叶轮转动一圈过程中的数个极大值趋于相等。     

旋转喷射泵叶轮内部流动的研究

作者介绍了通过计算出叶轮的理论扬程 ,采用软件GAMBIT里建立的旋喷泵叶轮流道模型 ,对其应用流场分析软件FLUENT ,基于N S方程 ,利用Standard湍流模型以及SIMPLEC算法 ,对旋喷泵叶轮内部流动进行了一些研究。并分析了叶轮内部流道的流动规律     

动盘带预旋喷嘴的旋转盘腔内流场的相似分析与数值模拟

采用 K -ε湍流模型对带有预旋的新型旋转盘腔内的流动进行相似分析和数值计算。分析了预旋系数βr 对某一复杂旋转盘腔流场的影响 ,在旋转盘的计算中提出了一种新的网格剖分方法 ,计算的旋转雷诺数达到 2 .2× 1 0 7。定义了一个新的压力系数 Cp ,给出了扭矩系数和压力系数随旋转雷诺数变化的关系式 ,发现它们与没有预旋时是完全不同的     

基于大涡模拟的导叶式混流泵叶轮内压力脉动特性分析

为研究导叶式混流泵叶轮内部非定常压力脉动特性,在其叶轮进口截面及出口截面附近分别设置8个压力脉动监测点,采用大涡模拟方法(LES)对导叶式混流泵内全三维流道(进水管、叶轮、导叶及出水管)进行模拟,并对8个监测点进行压力脉动时域图和频域图的分析。结果表明:由于旋转叶轮旋转失速、脱流效应及静止导叶的干涉作用,叶轮出口处压力脉动系数幅值均大于进口处脉动系数幅值,且其最大压力脉动发生在叶轮出口处,脉动波衰减较慢;叶轮进、出口截面上监测点的压力脉动频率以叶轮叶频为主频次,且压力脉动主要频率为叶频的倍数。     

核电站重要厂用水泵叶片磨损对其性能的影响

为研究叶片磨损对重要厂用水泵水力性能、内流特性等的影响,应用CFD 软件基于标准k?ε 湍流模型,通过数值计算方法对重要厂用水泵进行定常与非定常计算,分析叶片不同程度磨损下蜗壳流道内水力性能、内流特性、压力脉动的情况。结果表明:叶片磨损会使叶轮流道内湍动能增加,局部产生低压区;随着磨损程度的增加,低压区逐渐向叶轮流道内扩散并最终至全部流道,使重要厂用水泵流场运行不稳定,扬程、效率降低,磨损5/20 时扬程和效率与未磨损时相比均降低1.2%;随着磨损程度的增加,压力脉动的波形变得紊乱,轴频幅值仅次于主频,且越来越高,开始占据主导地位;频域图中,峰值随着磨损程度的增加逐渐上升,说明叶片磨损使泵内流动变得不稳定,波动加剧。     

叶片圆形切割对离心泵流动诱导噪声的影响

为研究叶片出口圆形切割对离心泵压力脉动及内场噪声的影响,通过固定圆形弦长以变换弦高的方法设计6种叶片切割方案,采用RNG k-ε湍流模型对各方案外特性和压力脉动进行流场数值计算,并基于Lighthill声类比理论和边界元法(BEM)对内声场进行数值计算,对原始模型额定工况的外特性和内声场也进行了试验验证。结果表明：叶轮叶片切割后的设计方案与原始方案相比,在轴频、叶频及倍叶频处压力脉动得到了明显地改善;当弦高与叶片出口宽度的比值为0.333时,设计工况的压力脉动幅值达到最低;当弦高与叶片出口宽度的比值为0.167时,进口声压级降低了3.5 dB,出口声压级降低了3.4 dB;随着圆形切割面积的不断增大,在设计工况各方案声压级呈现出先减小后增大再减小的规律;随着叶片出口圆形切割面积的增大,在0.6 Q_v～1.4 Q_v工况范围内扬程下降与其呈正相关特性,但对离心泵效率的影响较小。     

Simulation of volute tongue of small-size centrifugal compressor

A high speed and small mass-flow-rate centrifugal compressor with original and modified volute tongue shape was simulated by 3D viscous Navier-Stokes equations.A sharp and a round tongue of volute were...     

Experimental investigation of transient characteristics of mild surge and diffuser rotating stall in a centrifugal compressor with vaned diffuser

The centrifugal compressor is widely used for gas compression in various industrial fields such as aero-engine, gas turbine and turbocharger. However, the stable operating range is usually restricted by the occurrence of flow instability such as stall and surge. The paper experimentally examines the developing process of surge and stall occurring in a centrifugal compressor to advance the understanding on flow mechanism of flow instability. It is found that three types of pressure fluctuation can be observed at low flowrate region. At the critical point, the local stall firstly occurs in some specific diffuser passages and the enlarged local diffuser stall eventually induces the mild surge of compression system indicated by the sinusoidal pressure fluctuation. At lower mass flow rate, the diffuser stall cell begins to circumferentially propagate along the impeller rotating direction at 11% of rotor speed with the existence of mild surge. In comparative analysis of IGV pre-swirl angle on the occurrence of mild surge, the mild surge still occurs at the operating condition when the slope of the characteristic map of test stage is still obviously negative, in which the compression system is supposed to be stable in previous study. And a new suggested criterion for the prediction of mild surge is demonstrated that the occurrence of mild surge depends on the destabilization effect of downstream components about diffuser and volute. Combined with the experimental data, the streamwise distribution characteristic of diffuser stall can be used to develop the simplified model of lumped parameters for the analysis on the generation mechanism of the diffuser rotating stall. The quantitative investigation on the relation between the pressure-rise characteristic of subcomponents and the occurrence of mild surge and diffuser rotating stall not only advances the prediction of stability limit but also lays the theoretic foundation for controlling these unsteady behaviors to improve the operating range.     

通气孔对动叶冷却结构流动和换热特性的影响

为深入研究某型燃气轮高温旋转动叶片内部先进的复合冷却结构,采用三维气热耦合数值计算方法,模拟该叶片外部高温流场、内部前后冷却腔内蛇形折流通道复合冷却结构的流动性能与换热特性,研究前腔蛇形折流冷却通道在采用局部通气孔改进设计的条件下对整个旋转叶片外表面冷却效果与内部冷却通道流阻系数的改善程度。计算结果表明:在给定的冷气流量条件下,无通气孔设计时,叶片内部蛇形折流通道采用的气膜/冲击/扰流复合冷却结构能够对叶片整体带来较好的换热效果,并且叶片内、外表面温度分布都处于合理范围,但由于整个内部折流冷却通道流动阻力较高,导致对冷却气源供应压力要求过大,且前后冷却腔室进口设计压力差别较大;在内冷前腔局部位置设计冷气通孔结构,可有效降低前腔折流通道的流动阻力,在保证叶片换热效果没有受到明显影响的前提下,实现了所需冷气供应压力和冷气量同时显著下降,多腔冷却气体用量得到更好匹配。该改型设计提高了原型叶片的工程应用价值。     

气固搅拌流化床内的压力脉动特性

为考察搅拌桨的转动作用对流化特性的影响，研究了不同转速和气速下搅拌流化床的压力脉动行为.采用188 mm的内径和400 mm的静床高，以Geldart B类和D类颗粒为实验物料，进行了压力脉动信号的统计分析和功率谱分析.实验结果表明，搅拌桨的转动对最小流化速度没有影响，但使B类和D类颗粒呈现了A类颗粒特有的散式流态化现象.随搅拌转速的增大，压力脉动的标准偏差减小，最小鼓泡速度增加. 最小鼓泡速度与最小流化速度之比与搅拌转速成正比.当搅拌转速增加到一定程度后，压力脉动的功率谱主频等于搅拌桨转动频率，流化床从鼓泡流态化状态转化为散式流态化状态.     

One-dimensional/three-dimensional analysis of transient cavitating flow in a venturi tube with special emphasis on cavitation excited pressure fluctuation prediction

The large eddy simulation (LES) method is used to simulate cavitating flow in a venturi tube. The simulated results agree fairly well with the experimental data. To quantitatively describe the relationship between cavitation evolution and excited pressure fluctuation in the venturi tube, a modified prediction model is proposed and its accuracy is verified by the LES results. Based on the original one-dimensional model for the external cavitating flow around a hydrofoil, this model is corrected according to the internal cavitating flow characteristics in the venturi tube. The results show that the original one-dimensional model ignores the choking effect of cavitating flow, which is obvious in a venturi tube with a narrow flow channel, thus leading to an inaccurate prediction of pressure fluctuation in the venturi tube. The modified model can significantly overcome its deficiencies and improve the accuracy of the pressure fluctuation prediction, providing a theoretical basis and guidance for engineering application to controlling the pressure fluctuation in a venturi tube or for other internal flows.     

Large eddy simulation of unsteady transitional flow on the low-pressure turbine blade

The aim of this paper is to predict the phenomenon of laminar separation,transition and reattachment in a low-pressure turbine(LPT).Self-developed large eddy simulation program of compressible N-S equations was used to describe the flow structures of T106A LPT blade profile at Reynolds number of 1.1X105 based on the exit isentropic velocity and chord length.The computational results show the distributions of time-averaged wall-static pressure coefficient and mean skin-friction coefficient on the blade surface.The locations of laminar separation and reattachment points occur around 87%and 98%axial chord,which agree well with experiment data.The two-dimensional shear layer is gradually unstable along the downstream half of the suction side as a result of the spanwise fluctuation and the roll up of shear layer via Kelvin-Helmholtz(KH)instability.Three-dimensional motions appear near 84%axial chord which later triggers spanwise vortexes and streamwise vortexes,leading to transition to turbulence in the separation bubble.Through introducing the concept of dissipation function,the high loss mainly comes from the places where strong shear layer and intense fluctuation exist.Furthermore,the separation region is only an accumulation center of the low-energy fluid rather than an area of loss source.