Effect of winglet geometry arrangement and incidence on tip clearance control in a compressor cascade

An experimental study is conducted to investigate the influences of blade tip winglet on the flow field of a compressor cascade. The tests are performed in a low speed linear cascade with stationary endwall, with three blade tip configurations, including the baseline tip, the suction-side winglet tip and the pressure-side winglet tip. The flowfield downstream of the cascade is measured using five-hole probe, from which the three-dimensional velocity field, vorticity field and pressure field are obtained. Static pressure measurements are made on the endwall above the blade row using pressure taps embedded in the plywood endwall. All measurements are made at both design and off-design conditions for tip clearance level of about 2 percent of the blade chord. The results revealed the incidence variation significantly affects the secondary flow and the associated loss field downstream of the cascade, where the tip leakage vortex and passage vortex exist as the major contributors on the field. The winglet geometry arrangements can change the trajectory of the tip leakage vortex. The suction-side winglet tip blade provides a lower overall total pressure loss coefficient when compared to the baseline tip blade and pressure-side winglet tip blade at all incidence angles.     

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…     

中等折转角涡轮直叶栅端壁流场结构和涡系效应的分析

应用商用软件Fine/Turbo对一中等折转角涡轮直叶栅的流场进行了数值模拟,清晰地捕捉到了叶栅端壁处叶片前缘的马蹄涡及其吸、压力面分支,对马蹄涡的吸、压力面分支的相互作用过程和通道涡的发生发展过程给出了较为清晰的描述,获得了较为详细的叶栅端壁处二次流流动结构。通过对叶栅流道中各个近似垂直于流动方向的截面上的总压分布图的分析,揭示了在上述各个截面上端壁区域流动损失产生的机理。     

冲角和孔排间距对端壁气膜冷却效率的影响

燃气轮机在变工况运转时透平叶栅和级的特性对燃机总体性能影响极大,而叶栅端壁气膜冷却效率是关键因素。为了提高端壁气膜冷却效率,通过优化气膜孔间距排列的方法,在叶栅端壁20%、50%、90%轴向弦长处和距前缘-10%轴向弦长端壁处布置单排带复合角度的圆柱形气膜冷却孔,运用CFD(计算流体动力学)方法对冲角(10°、0°、-10°)在不同吹风比(1、1.5、2)条件下端壁气膜冷却效率进行对比分析。结果表明:采用气膜孔非等距排列方式能有效缓解因横向压力梯度变化引起的马蹄涡在压力侧的阻隔作用,压力侧冷却效率较高;高吹风比的冷却射流会出现抛射冷却,能有效抑制冷却射流脱离壁面,壁面平均冷却效率提高;主流正冲角有利于提高端壁吸力侧气膜冷却效率,压力侧变化不大。     

非设计工况下涡轮叶栅前缘壁角的作用

透平叶栅端区二次流具有复杂的涡系结构。Langston实验描述了两支马蹄涡和通道涡的演变和发展过程。基于Langston叶型构造出有效的前缘壁角,建立涡轮叶栅带有前缘壁角的端壁流动计算模型,分析前缘壁角对端壁流动与传热特性的影响,并评估其在非设计条件下的适应性。结果表明:在一定的非设计工况范围内,前缘壁角削弱了前缘马蹄涡和通道涡的强度,降低了流道内部的气动损失,增加了近端壁的流动损失。有效的前缘壁角使前缘附近端壁换热水平减弱,流道端壁换热整体减弱,端壁高换热区沿流向下移,尾缘附近换热有所增加。在一定的非设计工况范围内,前缘壁角都是有效的。     

Influence of flow injection angle on a leading-edge horseshoe vortex

Junction flows that develop at the base of protruding obstructions occur in many applications. An unsteady horseshoe vortex is formed as a component of these junction flows, which increases the local heat transfer on the associated endwall. Augmenting this junction flow can be achieved through the injection of fluid upstream of the obstruction. This experimental study evaluated the effects of injection angle for a two-dimensional slot placed upstream of a vane leading-edge with four injection angles of 90°, 65°, 45°, and 30°. Results showed that high momentum injection increased the endwall heat transfer at each slot angle while low momentum injection resulted in a relatively lower augmentation of endwall heat transfer. A leading-edge vortex turning into the endwall was formed at the junction in the stagnation plane for high momentum injection at 90° and 65° while a leading-edge vortex turning away from the wall was formed for 45° and 30° injection. For low momentum injection, a vortex turning into the endwall was formed at all injection angles.     

基于二次流控制的叶栅前缘端壁造型

基于Langston叶型的数值模拟结果,分析了叶栅前缘端区的流动特征,建立并优化了一种新型端壁造型。对比评估了新模型与原始模型的流动现象并对两者的流动机理进行分析。结果表明:新型端壁造型能够疏导前缘位置的低能流体并消除鞍点与分离线的产生;新型端壁造型能够减小马蹄涡及下游的通道涡强度,并使得叶栅出口总压损失系数下降6.831%。     

进口气流冲角对环形叶栅端壁气膜冷却效率的影响

进口气流冲角变化会改变端壁横向压力梯度致使端壁气膜冷却气体覆盖发生变化。本文在环形叶栅端壁30％、60％、90％轴向弦长处和距前缘-10％轴向弦长端壁处布置单排圆柱形气膜冷却孔,运用CFD方法在吹风比为1．0条件下对来流冲角为10°、0°和-15°时端壁气膜冷却效率进行对比分析。结果显示冲角由正值到负值,压力面和吸力面一侧两支马蹄涡夹裹冷却气膜主体向压力面偏移,致使吸力面一侧端壁未冷却区域扩大,压力面一侧端壁未冷却区域缩小。吸力面一侧端壁气膜冷却效率沿流向逐渐提升,并在流道中、下游完全冷却覆盖端壁,而压力面一侧端壁一直未能获得冷却气膜覆盖。     

环形扩压叶栅弯叶片对流场性能的影响

对比研究了直叶片叶栅与弯叶片叶栅吸力面角区和下端壁流场显示的不同表现,发现弯叶片对角区分离流结构影响较大,它对减小端区马蹄涡尺度和减弱横向二次流作用明显。将不同叶栅中三维流向涡（通道涡和集中脱落涡）沿流向截面内的位置与强度作为研究对象,细致地分析了在采用弯叶片前后涡位置和强度的变化,分析表明两种涡的位置受弯叶片影响较大;通道涡沿流向的强度变化受弯叶片影响较为明显,而集中脱落涡强度受弯叶片影响却很小。来流马赫数、叶型折转角和稠度在一定范围内对弯叶片作用有规律性影响：当马赫数为0．7时,最佳弯角弯叶片降低损失7％．而马赫数为0．2时,最佳弯角弯叶片降低损失仅4％。     

Research on the Influence of Guide Blade Trailing Edge Structure on Turbine Performance

The complex structure at trailing edge reduces the manufacturing precision, which results in an error in the size of the trailing edge structure. In this study, the performance of a stage high-pressure turbine(HP turbine) is calculated out in three dimensions. In the HP turbine guide vane, the trailing edge cutback configuration is adopted. Through three-dimensional simulation, the complex flow around the trailing edge with cutback cooling configuration is presented in this study, and the manufacturing precision reduction due to the complex structure at trailing edge is considered. Furthermore, the effect of trailing edge lip thickness and deflection of the stator on the turbine performance is discussed. Overall, as the press-side lip thickness increasing, the turbine efficiency and turbine inlet flow are reduced. However, the changes in the turbine work output are relatively complex. On the other hand, as the spacing between suction-side lip and press-side lip increases, turbine performance becomes worse. Both of the turbine efficiency and the turbine work output become smaller, while the turbine inlet flow becomes bigger. The effect of the spacing between suction-side lip and press-side lip is obviously greater than that of the press-side lip thickness. The change of the press-side lip thickness has little effect on the relation between the turbine performance and the spacing between suction-side lip and press-side lip. However, when the spacing between suction-side lip and press-side lip deviates from the baseline value, the effect law of the press-side lip thickness on the turbine performance will be affected. As the press-side lip thickness increases, it leads to an increase in the low-velocity zone at both of the pressure-side and suction-side trailing edge. And more main stream is affected or mixed into the wake flow. When the spacing between suction-side lip and press-side lip becomes smaller, the low-velocity zone at the trailing edge is smaller, and the change of vortex with the press-side lip thickness is affected. With a bigger spacing between suction-side lip and press-side lip, the variation is contrary.     

不同参数端壁翼刀控制二次流机理的实验研究

不同周向和轴向位置的压气机叶栅上安装1／2轴向弦长翼刀的叶栅出口流场测量结果表明,两种方案的叶栅总损失随翼刀周向位置变化的总体趋势是翼刀靠近压力面时叶栅总损失降低。翼刀安装在流道前半部的最佳周向位置是距离吸力面60％相对节距处;安装在流道后半部的翼刀最佳周向位置是距离吸力面80％相对节距处。通过对比初步探讨了翼刀减小二次流损失的机理：一方面通过降低流道内端壁附面层内横向压力梯度,减弱低能流体向吸力面／壁角区的堆积;另一方面是通过产生的反向翼刀涡限制马蹄涡的压力面分支发展,从而减小通道涡的尺寸和强度。     

Turbine endwall film cooling with combustor-turbine interface gap leakage flow: Effect of incidence angle

This paper is focused on the film cooling performance of combustor-turbine leakage flow at off-design condition. The influence of incidence angle on film cooling effectiveness on first-stage vane endwall with combustor-turbine interface slot is studied. A baseline slot configuration is tested in a low speed four-blade cascade comprising a large-scale model of the GE-E³Nozzle Guide Vane (NGV). The slot has a forward expansion angle of 30 deg. to the endwall surface. The Reynolds number based on the axial chord and inlet velocity of the free-stream flow is 3.5 × 10⁵ and the testing is done in a four-blade cascade with low Mach number condition (0.1 at the inlet). The blowing ratio of the coolant through the interface gap varies from M = 0.1 to M = 0.3, while the blowing ratio varies from M = 0.7 to M = 1.3 for the endwall film cooling holes. The film-cooling effectiveness distributions are obtained using the pressure sensitive paint (PSP) technique. The results show that with an increasing blowing ratio the film-cooling effectiveness increases on the endwall. As the incidence angle varies from i = +10 deg. to i = ?10 deg., at low blowing ratio, the averaged film-cooling effectiveness changes slightly near the leading edge suction side area. The case of i = +10 deg. has better film-cooling performance at the downstream part of this region where the axial chord is between 0.15 and 0.25. However, the disadvantage of positive incidence appears when the blowing ratio increases, especially at the upstream part of near suction side region where the axial chord is between 0 and 0.15. On the main passage endwall surface, as the incidence angle changes from i = +10 deg. to i = ?10 deg., the averaged film-cooling effectiveness changes slightly and the negative incidence appears to be more effective for the downstream part film cooling of the endwall surface where the axial chord is between 0.6 and 0.8.     

Analysis of wind flow around a parabolic collector (1) fluid flow

Applications of parabolic collectors for solar heating and solar thermal power plant increased in the recent years. Most of the solar power plants installed with parabolic collectors are on flat terrain and they may be subjected to some environmental problems. One of problems for large parabolic collector is their stability to track the sun with respect to time very accurately. Any small off tracking as well as the collector structure stability will be affected by strong wind blowing for the regions where the wind velocity is high.In the present study, a two-dimensional numerical simulation of turbulent flow around a parabolic trough collector of the 250 kW solar power plants in Shiraz, Iran is performed taking into account the effects of variation of collector angle of attack, wind velocity and its distribution with respect to height from the ground.Computation is carried for wind velocity of 2.5, 5, 10, and 15 m/s and collector angles of 90°, 60°, 30°, 0°, −30°, −60°, and −90° with respect to wind directions. Various recirculation regions on the leeward and forward sides of the collector are observed, and both pressure field around the collector and total force on the collector are determined for each condition. The effect of absorber tube on the flow field was found negligible, while the effect of the gap between the two sections of parabola at midsection and the gap between the collector and ground were found considerable on both flow field and pressure distribution around the collector.     

高压涡轮动叶前缘新型几何特征对流场结构影响研究

本文提出一种前缘前伸内凹且根部叶片略厚的新型动叶片设计方法,旨在通过这种新型叶片控制前缘马蹄涡的生成和发展,通过根部叶片较厚到中间区域叶片厚度略低的三维设计和积叠方法,实现动叶片的弯叶片效果。论文以某高压涡轮叶片为研究对象,从能量损失系数、型面压力分布、旋涡沿流向变化对比分析了新型叶片与原型叶片对流场结构的影响。研究表明叶型前缘新的几何特征使马蹄涡得到控制,流场内流动得到改善。     

Performance analysis of non-isothermal solar reactors for methanol decomposition

A procedure for analyzing the performance of non-isothermal solar reactors for methanol decomposition was developed, based on a model of thermal loss from direct steam generation collector and a comprehensive kinetic model of methanol decomposition employing BASF K3-110 catalyst. It was found that catalytic bed temperature tends towards a certain value, which depends on the chemical reaction type, radiation intensity and collector structure mainly. For a beam incidence angle of 0°, system efficiency increases from 56% at a radiation intensity of 400 W m⁻² to almost 58% at a radiation intensity of 1000 W m⁻². For a radiation intensity of 400 W m⁻², beam incidence angle of 20°, absorber length of 10 m, feed temperature of 373 K and ratio of reaction section of 0.9, the mole flow rate of feed in the range of 0.21–0.23 mol s⁻¹ results in a maximum quantity of reacted methanol of 0.146 mol s⁻¹, while a mole flow rate of feed of 0.15 mol s⁻¹ leads to a maximum system efficiency of 54.2%. The research indicates that the pre-heating section should be as short as possible for effective use of solar energy.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Influences of Incidence Angle on 2D-Flow and Secondary Flow Structure in Ultra-Highly Loaded Turbine Cascade简

An increase of turbine blade loading can reduce the numbers of blade and stage of gas turbines. However, an in- crease of blade loading makes the secondary flow much stronger because of the steep pitch-wise pressure gradient in the cascade passage, and consequently deteriorates the turbine efficiency. In this study, the computations were performed for the flow in an ultra-highly loaded turbine cascade with high turning angle in order to clarify the ef- fects of the incidence angle on the two dimensional flow and the secondary flow in the cascade passage, which cause the profile loss and the secondary loss, respectively. The computed results showed good agreement with the experimental surface oil flow visualizations and the blade surface static pressure at mid-span of the blade. The profile loss was strongly increased by the increase of incidence angle especially in the positive range. Moreover, the positive incidences not only strengthened the horseshoe vortex and the passage vortex but also induced a new vortex on the end-wall. Moreover, the newly formed vortex influenced the formation of the pressure side leg of horseshoe vortex.     

CVT-growth of AgGaSe2 single crystals: Electrical and photoluminescence properties

Single crystals of AgGaSe₂ were grown by the Chemical Vapor Transport (CVT) -method using iodine as transport agent. Growth temperatures of 770°C and concentrations of the transport agent of 1.6–1.7 mg I₂/cm³ yielded compact single crystals with a size of up to 8 X 5 X 5 mm³ and a habitus dominated by the {112}-faces. The as-grown crystals were highly insulating (σ < 10⁻⁸(Ω cm)⁻¹). Annealing of the crystals in vacuum at 700°C resulted in n-type conductivity of 2 · 10⁻¹ (Ω cm)⁻¹ with a dominant peak in the photoluminescence spectra at 4 K associated with a donor level of 164 meV. Annealing in Se-atmosphere at 600°C lead to p-type conductivity of 6 · 10⁻⁶ (Ωcm)⁻¹ within a surface layer of the AgGaSe₂ single crystals. The corresponding photoluminescence spectra and the activation energy of the electrical conductivity (between 100 K and 300 K) suggest the presence of an acceptor (V_cation) with an activation energy of 60 meV and a donor (V_Se) with an activation energy of 100 meV.     

基于LES的压气机叶栅通道非定常流动结构研究

为了进一步理解压气机叶栅通道内的非定常流动结构,采用大涡模拟(LES)方法研究了来流附面层厚度和稠度变化对叶栅通道内涡系结构及总压损失系数的影响。研究表明：来流附面层增厚将导致端壁处流体的轴向动能降低,使得马蹄涡压力面分支更早地流向相邻叶片吸力面;来流附面层越厚,通道涡在叶栅尾缘沿展向抬升的高度越高,角区分离的范围也越大;叶栅的总压损失随附面层增厚而增加,附面层损失增加显著,二次流损失有所增大;稠度较低时叶栅吸力面表面存在分离,会对通道涡及角区分离产生影响;稠度增大,横向压力梯度减小,叶栅流道的速度分布更均匀,通道涡的强度和尺度减小,角区分离的范围减小;稠度增大使叶表不再分离时,总压损失显著降低,但稠度继续增大会使气流与叶片表面的摩擦损失增加。     

Electrical parameters for clay samples in the frequency and temperature dependence (first results)

In this work some results are given referring to laboratory experiments carried out on clay samples in the ranges 1 · 10⁻² − 5 · 10³ Hz and 20° − 100°C. The diagrams of conductivity, permittivity and loss-tangent have been obtained, and certain anomalies can be recognized in them.