汽轮机动叶顶部间隙泄漏流动特性的数值模拟

以一个小展弦比轴流透平级为研究对象,采用数值方法对不同动叶顶部间隙情况下的间隙泄漏流动进行了分析,研究了间隙流和间隙涡的形成、发展及其对透平级性能的影响.以三维流线和极限流线为手段,分析了6种间隙尺寸下动叶顶部的泄漏流和泄漏涡造成的损失及其与主流掺混的过程.结果表明:动叶顶部间隙两侧压力面和吸力面之间的压力差使汽流从压力面被吸入间隙,跨过叶顶,进入相邻叶栅通道的吸力面,导致泄漏流动;与无间隙的情况相比,叶顶间隙的存在使上端壁处的流场发生明显变化,引起损失迅速增长;随着间隙的增大,泄漏涡的产生位置提前,强度增大,从而导致更大的流动损失.     

间隙变化对轴流压气机转子近失速工况叶顶流场的影响研究

为研究间隙变化对轴流压气机转子近失速工况下叶顶流场结构的影响,以轴流压气机转子Rotor37为研究对象,对其叶顶流场进行定常和非定常的数值模拟。计算结果表明：随着叶顶间隙的减小,压气机的总压比和等熵效率均有所提高,稳定运行范围扩大;2倍设计间隙下,叶尖泄漏涡经激波作用后发生膨胀破碎,堵塞来流通道,诱发压气机堵塞失速;0.5倍设计间隙下,吸力面流动分离加剧,发生回流,部分回流与来流在压力面前缘上游发生干涉,进口堵塞加剧,致使部分来流从前缘溢出,导致压气机叶尖失速;不同间隙下压气机失速过程的主导因素不同,大间隙下失速由叶尖泄漏涡破碎的非定常波动引起,小间隙下失速主要由流动分离引发的周期性前缘溢流所主导。     

汽轮机叶片正弯对叶顶间隙泄漏流动影响的数值模拟

以某汽轮机高压级动叶为研究对象,采用κ-ε湍流模型,应用SIMPLEC算法对在相同叶顶间隙高度下的常规扭叶片和正弯扭叶片的叶顶间隙流动进行了数值模拟。研究结果表明:与常规扭叶片相比,叶片正弯提高了汽流在叶顶区的最低压力值,减小了叶顶压力边与吸力边的横向压力梯度;汽流在正弯扭叶片吸力面附近形成的泄漏涡的影响范围和对通道主流的扰动弱于在常规扭叶片内形成的影响;正弯扭叶片使汽流在吸力面和压力面上形成了叶顶部正径向压力梯度、叶根部负径向压力梯度的"C"型压力分布,同时降低了叶片上端部附近的总压损失。叶片正弯既降低了叶顶泄漏损失,又降低了叶栅通道内的掺混损失。     

叶尖自发射流条件下涡轮非定常流动的数值模拟

为分析自发射流条件下非定常尾迹对叶顶间隙流动、S1流面和S2流面上流场参数、叶尖泄漏比和动叶载荷变化的影响,采用数值模拟方法,以Durham叶栅为原型,将动、静叶栅流场通过滑移网格技术耦合,开展非定常计算。结果表明:在静叶非定常尾迹的影响下,转子区域流场内的流动、叶尖间隙泄漏比及叶片周向载荷均呈现出周期性变化的特征;考虑非定常效应和端壁相对运动效应,相较于无叶尖射流,单孔叶尖自发射流可使泄漏比降低4.57%,比定常计算预测的泄漏比低3.43%,表明要想准确获得叶尖射流条件下的叶栅流动特性和叶尖泄漏抑制效果,其间的非定常效应不可忽略。     

扭叶片正弯对叶栅通道内二次流动影响的数值分析

以某汽轮机高压级动叶为研究对象,采用κ-ωSST模型、SIMPLEC算法数值模拟了正弯扭叶片叶顶间隙泄漏涡的形成和发展过程及其对叶栅通道二次流的影响。结果表明:相对于常规扭叶片,汽流在正弯扭叶片吸力面附近形成的泄漏涡的影响范围和对通道主流的扰动变小,且叶顶间隙的增加削弱了正弯扭叶片吸力面的"C"型压力梯度,使得叶片两端部附面层厚度增加,造成了叶片端部损失的增大。     

叶顶开槽——小翼结构对提升轴流风机性能影响的数值研究

为了有效抑制叶顶泄漏流的发展,降低叶顶泄漏损失,针对两级动叶可调轴流风机提出在吸力面构造叶顶小翼并开设斜槽的新型叶顶改型方案。采用Fluent数值模拟了5种叶顶改型方案对风机性能和流场特征的影响,分析了不同方案下流场、叶顶静压、叶顶泄漏量和动叶区做功能力的变化。结果表明：吸力面小翼可有效降低叶顶损失,小翼上开设顺流向斜槽可进一步提高风机性能,逆流向斜槽会使性能略有降低;顺流向单斜槽为最佳改型方案,在设计流量下全压和效率分别提升166 Pa和0.942%;叶顶间隙处产生额外的涡流,叶顶泄漏流得到抑制,动叶区做功能力得以提升。     

端壁运动对自发射流抑制叶尖泄漏影响的数值研究

通过数值手段分析了端壁运动对带有叶尖自发射流的叶栅流场特性、叶顶间隙泄漏流量特性及叶片周向载荷分布特性的影响。结果表明:端壁运动的反向刮削作用会显著影响间隙附近流场,随着端壁运动速度增大,泄漏涡和上通道涡会逐渐向叶片吸力面靠近,同时,泄漏涡强度逐渐削弱,而上通道涡强度逐渐增强,平均总压损失增大;端壁运动对叶尖自发射流抑制泄漏流的效果有放大作用;端壁运动会显著改变叶尖吸力面附近静压系数的分布,使其具有后加载的特性。     

轴向间距对两级轴流风机失速先兆的影响机制

基于节流阀函数以及SSTk-ω湍流模型,对某电站两级动叶可调式轴流风机的非定常失稳过程进行数值模拟,分析了3种轴向间距对风机失速先兆起始位置、表现形式以及失速三维非定常演化过程的影响机制.结果表明:风机稳定运行范围随着轴向间距的缩短得到拓宽;不同轴向间距下,第二级动叶内首先出现失速先兆,且失速先兆表现形式相同,均为突尖型;轴向间距增大时,失速先兆从第二级动叶传播至第一级动叶所用时间增加;轴向间距对叶顶间隙分离涡的产生具有重要影响,轴向间距较小时,分离涡主要由相邻流道的泄漏流绕过尾缘附近反向流入流道并与主流相互作用形成,轴向间距较大时分离涡的形成主要与叶顶间隙的泄漏流有关.     

汽轮机末级旋转不稳定性研究

基于汽轮机低压末级流动的非稳态数值计算结果,研究了低质量流量下低压末级流道发生的旋转不稳定现象。为了更好地了解在低流量下汽轮机运行的旋转不稳定性,采用低压末级整圈动静叶流道耦合排汽缸进行非稳态数值计算。发现末级动叶已经处于压气机状态并且流动的周向均匀性被破坏,以及在叶顶间隙泄漏流与主流的挤压下形成的泄漏涡撞击到毗邻叶片吸力面并发生溢出、形成二次泄漏流等情况。泄漏涡进一步影响叶片间叶顶前缘的压差分布,以长波的性质形成旋转不稳定。频谱分析捕捉到了旋转不稳定在绝对与相对坐标系下的旋转频率以及周向扰动个数。     

微型燃气轮机向心透平内部流动分析

对某2.6kW微型燃气轮机向心透平叶轮进行了全三维粘性数值模拟.分析了设计工况下通道中的二次流动现象、各个涡系的发展以及不同叶尖间隙对流动的影响.结果表明:通道内吸力面侧二次流动明显,由于通道涡、泄漏涡的共同作用,叶轮的损失主要集中于吸力面侧靠近叶顶区域;叶轮顶部间隙增加,透平叶轮通流能力下降较慢,而效率降低较快.由于刮削流的影响,使得径向间隙变化对透平效率和质量流量的影响要比轴向间隙更明显.     

Numerical investigation of the unsteady tip leakage flow and rotating stall inception in a transonic compressor

<正>It is well known that tip leakage flow has a strong effect on the compressor performance and stability. This paper reports on a numerical investigation of detailed flow structures in an isolated transonic compressor rotor-NASA Rotor 37 at near stall and stalled conditions aimed at improving understanding of changes in 3D tip leakage flow structures with rotating stall inception.Steady and unsteady 3D Navier-Stokes analyses were conducted to investigate flow structures in the same rotor.For steady analysis,the predicted results agree well with the experimental data for the estimation of compressor rotor global performance.For unsteady flow analysis, the unsteady flow nature caused by the breakdown of the tip leakage vortex in blade tip region in the transonic compressor rotor at near stall condition has been captured with a single blade passage.On the other hand, the time-accurate unsteady computations of multi-blade passage at near stall condition indicate that the unsteady breakdown of the tip leakage vortex triggered the short length-scale-spike type rotating stall inception at blade tip region.It was the forward spillage of the tip leakage flow at blade leading edge resulting in the spike stall inception. As the mass flow ratio is decreased,the rotating stall cell was further developed in the blade passage.     

A similitude method and the corresponding blade design of a low-speed large-scale axial compressor rotor

A similitude method to model the tip clearance flow in a high-speed compressor with a low-speed model is presented in this paper. The first step of this method is the derivation of similarity criteria for tip clearance flow, on the basis of an inviscid model of tip clearance flow. The aerodynamic parameters needed for the model design are then obtained from a numerical simulation of the target high-speed compressor rotor. According to the aerodynamic and geometric parameters of the target compressor rotor, a large-scale low-speed rotor blade is designed with an inverse blade design program. In order to validate the similitude method, the features of tip clearance flow in the low-speed model compressor are compared with the ones in the high-speed compressor at both design and small flow rate points. It is found that not only the trajectory of the tip leakage vortex but also the interface between the tip leakage flow and the incoming main flow in the high-speed compressor match well with that of its low speed model. These results validate the effectiveness of the similitude method for the tip clearance flow proposed in this paper.     

Stereoscopic PIV measurements of the flow field in a turbine cascade

This paper presents experimental measurements of the flow field in a Low-speed Turbine Cascade using a stereoscopic particle-image velocimetry(SPIV). During the measurements, a pair of frame-straddling-based CCD cameras were configured at different sides of the laser light sheet, and appropriate tracing particles(DEHS) were employed. The measurements were conducted at the incidence angle of 0 degree and exit Reynolds number of 1.7 × 105 with the tip clearance 1.18% of blade chord. The tip flow features, such as the evolution and breakdown of tip leakage vortex, the horseshoe vortex, turbulence characteristics of tip leakage flow, were studied for the flow field analysis. The results showed that the tip leakage flow/vortex mainly dominate flow fields in the tip region. The tip leakage vortex performs as a concentrated vortex before its breaking down and splitting into small vortices. The highest turbulence intensity mainly occurs in the tip region along with the trajectory of tip leakage vortex, and when the vortex breaks down, the turbulence intensity reduces rapidly. Additionally, the SPIV with this configuration also shows an advantage in investigating the flow structures and mechanism inside the turbine cascade.     

Experimental Study of Endwall and Tip Clearance Flows in a Two—Dimensional Turbine Rotor Blade Cascade—Effect of Incidence Angle

IntroductionA ttirbomachinery rotor must have a slhall hilt finite clearance relative to its surrounding casing. Theflow, which leaks thlough this fililte gap, has a surprisingly large effect on the aerodynamics of the flow.The loss produced due to the tip clearance is an.unavoidable loss. The presence of tip clearance ajtersthe endwall flow siglilflcaotly. The normal secondaryflow interacts with the leakage fluid ajs it easts fromthe suction surface. The leakage fluid rolls into whatis known…     

Unsteady tip clearance flow in an isolated axial compressor rotor

Introduction Background It is well known that the rotor tip clearance flow has profound effects on the performance and stability of axial compressor (Wisler[1], Howard[2]). Numerous studies on the tip clearance flow were carried out in the past fifty years. Rain[3] proposed a model to predict the loss due to tip leakage flow assuming that the kinetic energy of the leakage flow velocity component normal to the mean chamber line would be dissipated. Lakshminarayana[4] developed a model to pre…     

Numerical investigations on the steady and unsteady leakage flow and heat transfer characteristics of rotor blade squealer tip

The steady and unsteady leakage flow and heat transfer characteristics of the rotor blade squealer tip were conducted by solving Reynolds-Averaged Navier-Stokes(RANS) equations with k-ω turbulence model.The first stage of GE-E3 engine with squealer tip in the rotor was adopted to perform this work.The tip clearance was set to be 1% of the rotor blade height and the groove depth was specified as 2% of the span.The results showed that there were two vortexes in the tip gap which determined the local heat transfer characteristics.In the steady flow field,the high heat transfer coefficient existed at several positions.In the unsteady case,the flow field in the squealer tip was mainly influenced by the upstream wake and the interaction of the blades potential fields.These unsteady effects induced the periodic variation of the leakage flow and the vortexes,which resulted in the fluctuation of the heat transfer coefficient.The largest fluctuation of the heat transfer coefficient on the surface of the groove bottom exceeded 16% of the averaged value on the surface of the squealer tip.     

Factors affecting small axial cooling fan performance

Many factors such as outer diameter,hub ratio,blade numbers,shape and stagger angle affect the performance of small cooling fans.A small cooling fan was simulated using CFD software for three blade stagger angles (30.5°,37.5°,44.5°)and obtained the internal flow field and the static characteristics.Research indicated that the stagger angle has an obvious effect on the static characteristics of a fan.For flow rates below 0.0104 m3/s,total pressure is the greatest when the stagger angle is 37.5°;flow rates higher than 0.0104 m3/s,the total pressure is greatest when the stagger angle is 44.5° For the same flow rates,the velocity at inlet of pressure surface increases with increasing stagger angle,but the change of velocity on the suction surface is very small.For one model,vortices and the speed of revolution surfaces decrease with tip clearance increasing.But for other three models,increasing the stagger angle,the vortex intensity and speed of revolution surfaces at same height tip clearance increases,simultaneously,the position of vortex offset from the top of the rotor blade to the suction surface.