Investigation of Non-Axisymmetric Endwall Contouring in a Compressor Cascade

The current paper presents experimental and computational results to assess the effectiveness of non-axisymmetric endwall contouring in a compressor linear cascade. The endwaU was designed by an endwall design optimi- zation platform at 0° incidence （design condition）. The optimization method is based on a genetic algorithm. The design objective was to minimize the total pressure losses. The experiments were carried out in a compressor cascade at a low-speed test facility with a Mach number of 0.15. Four nominal inlet flow angles were chosen to test the performance of non-axisymmetric Contoured Endwall （CEW）. A five-hole pressure probe with a head diameter of 2 mm was used to traverse the downstream flow fields of the flat-endwall （FEW） and CEW cascades. Both the measured and predicted results indicated that the implementation of CEW results in smaller comer stall, and reduction of total pressure losses. The CEW gets 15.6% total pressure loss coefficient reduction at design condition, and 22.6% at off-design condition （＋7° incidence）. And the mechanism of the improvement of CEW based on both measured and calculated results is that the adverse pressure gradient （APG） has been reduced through the groove configuration near the leading edge （LE） of the suction surface （SS）.

Optimum Profiles of Endwall Contouring for Enhanced Net Heat Flux Reduction and Aerodynamic Performance

Successfully utilized non-axisymmetric endwalls to enhance turbine efficiencies(aerodynamic and turbine inlet temperatures)by controlling the characteristics of the secondary flow in a blade passage.This is accomplished by steady-state numerical hydrodynamics and deep knowledge of the field of flow.Because of the interaction between mainstream and purge flow contributing supplementary losses in the stage,non-axisymmetric endwalls are highly susceptible to the inception of purge flow exit compared to the flat and any advantage rapidly vanishes.The conclusions reveal that the supreme endwall pattern could yield a lowering of the gross pressure loss at the design stage and is related to the size of the top-loss location being productively lowered.This has led to diminished global thermal exchange lowered in the passage of the vane alone.The reverse flow adjacent to the suction side corner of the endwall is migrated farther from the vane surface,as the deviated pressure spread on the endwall accelerates the flow and progresses the reverse flow core still downstream.The depleted association between the tornado-like vortex and the corner vortex adjacent to the suction side corner of the endwall is the dominant mechanism of control in the contoured end wall.In this publication,we show that the non-axisymmetric endwall contouring by selective numerical shape change method at most prominent locations is advantageous in lowering the thermal load in turbines to augment the net heat flux reduction as well as the aerodynamic performance using multi-objective optimization.

Optimal Design of Non-axisymmetric Endwall with Variable-fidelity CFD Model

Non-axisymmetric endwall is numerically investigated to suppress the secondary endwall flow in a HP turbine suction surface.The endwall contour is represented by a non-uniform rational B-spline surface.Two solution spaces are designed by the rule of hypercube sampling through variation of nodal radial extension.Final most effective endwall contour is obtained through screening all available samples with surrogate-based model.Results show that non axisymmetric endwall reduces the turbulence kinetic energy of the passage vortex by 5.5%and the total pressure loss 1.6%.Local heat transfer coefficient is lowered on the afore passage endwall surface with a certain increment on the aft passage endwall.Overall averaged heat transfer coefficient is reduced.

Influence of Endwall Contouring on the Secondary Flow in Turbine Nozzle Guide Vane

Numerical simulations are carried out to investigate the effect of the endwall contouring on the secondary flow in turbine nozzle guide vane.The three contoured cascades with the same contouring profile and the different positions where the contoured profile locates at are researched.The results show that the contouring configuration can reduce the aerodynamic losses of the cascade.The flat side takes advantage of a stronger decrease of the losses,compared to the contoured side.The contouring configuration can also inhibit the secondary flow.The contoured cascade in which the contouring profile starts upstream of the airfoil,ends at the middle of the airfoil has the best effect of improving secondary flow.

Effect of Incoming Vortex on Secondary Flows in Turbine Cascades with Planar and Non-Axisymmetric Endwall

Non-Axisymmetric Endwall Profiling(NAEP) is commonly utilized in turbines to eliminate secondary flows.Nevertheless,most of the NAEP methods consider a single-blade row environment without incorporating the effect of the stage environment.This paper aims to investigate the influence mechanism of the incoming vortex on the endwall secondary flow structures of NAEP in a highly loaded turbine cascade.To model the incoming vortex in a stage environment,this study considers a half-delta wing as the vortex generator at the upstream of the turbine cascade.The NAEP is then carried out for a highly loaded turbine cascade with an in-house numerical optimization design platform subject to no incoming vortex.Numerical simulation is also carried out under the influence of the incoming vortex for the turbine cascades with both planar and non-axisymmetric endwall.This paper furthers investigated the pitchwise effect of the incoming vortex on the near endwall secondary flow.The results indicate that the NAEP effectively improves the endwall secondary flow of the turbine cascade,where the total pressure loss coefficient and the secondary kinetic energy(SKE) are reduced by 7.3%,and 45.7%,respectively.It is further seen that with the incoming vortex,the NAEP achieves a considerable control effect on the endwall secondary flow of the turbine cascade.With incoming vortex,the NAEP can still achieve considerable control effect on the endwall secondary flow of the turbine cascade;the averaged reductions of loss coefficient and SKE are 7.8% and 14.2%,respectively.Under some pitchwise locations,incoming vortex can suppress the convection of cross-passage flow toward the suction corner greatly and reduce the loss coefficient of the baseline cascade.The incoming vortex at 4/7 pitch impinged right at the blade leading edge,leading to the generation of low-momentum fluid,which increased the size and the strength of the horseshoe vortex.Under all the pitchwise locations,NAEP can suppress the secondary vortices,e.g.,the passage vortex and the counter vortex,considerably.

Optimization of endwall contouring in axial compressor S-shaped ducts

This paper presents a numerical investigation of the potential aerodynamic benefits of using endwall contouring in a fairly aggressive duct with six struts based on the platform for endwall design optimization.The platform is constructed by integrating adaptive genetic algorithm（AGA）, design of experiments（DOE）, response surface methodology（RSM） based on the artificial neural network（ANN）, and a 3D Navier–Stokes solver.The visual analysis method based on DOE is used to define the design space and analyze the impact of the design parameters on the target function（response）.Optimization of the axisymmetric and the non-axisymmetric endwall contouring in an S-shaped duct is performed and evaluated to minimize the total pressure loss.The optimal ducts are found to reduce the hub corner separation and suppress the migration of the low momentum fluid.The non-axisymmetric endwall contouring is shown to remove the separation completely and reduce the net duct loss by 32.7%.

Numerical Investigation and Non-Axisymmetric Endwall Profiling of a Turbine Stage

This paper presents an optimization of a high pressure turbine by constructing non-axisymmetric endwalls to the stator row and the rotor hub.The optimization was quantified by using optimization algorithms based on the multi-objective function.The objective was to increase total-to-total efficiency with the constraint on the mass flow rate equal to the design point value.In order to ensure that global optimum could be achieved,the function of parameters was first approximated through the artificial neural network,and then optimum was achieved by implementing the genetic algorithm.It was adopted through the design and optimization environment of FineTM/Design3 D.Three individual treatments of the endwalls were presented.Firstly,the hub and the shroud of the stator were optimized together.Secondly,the hub of the rotor was optimized.Thirdly,the rotor hub was optimized in the presence of the optimized stator.The result of the investigation showed that the optimized shape of the endwalls can significantly help to increase the efficiency up to 0.18%with the help of a reduction of the transverse pressure gradient.The coefficient of secondary kinetic energy,entropy coefficient,spanwise mass averaged entropy were reduced.In order to investigate the periodic effects,the design of the optimized turbine under steady simulations was confirmed through unsteady simulations.The last part of the investigation made sure that the performance improvement remained consistent over the full operating line at off-design conditions by the implementation of non-axisymmetric endwalls.

Static pressure redistribution mechanism of non-axisymmetric endwall based on radial equilibrium

Non-axisymmetric endwall contouring has been proved to be an effective flow control technique in turbomachinery.Several different flow control mechanisms and qualitative design strategies have been proposed.The endwall contouring mechanism based on the flow governing equations is significant for exploring the quantitative design strategies of the nonaxisymmetric endwall contouring.In this paper,the static pressure redistribution mechanism of endwall contouring was explained based on the radial equilibrium equation.A quantified expression of the static pressure redistribution mechanism was proposed.Compressor cascades were simulated using an experimentally validated numerical method to validate the static pressure redistribution mechanism.A geometric parameter named meridional curvature(Cme)is defined to quantify the concave and convex features of the endwall.Results indicate that the contoured endwall changes the streamline curvature,inducing a centrifugal acceleration.Consequently,the radial pressure gradient is reformed to maintain the radial equilibrium.The convex endwall represented by positive Cme increases the radial pressure gradient,decreasing the endwall static pressure,while the concave endwall represented by negative Cme increases the endwall static pressure.The Cme helps to establish the quantified relation between the change in the endwall radial pressure gradient and the endwall geometry.Besides,there is a great correlation between the distributions of the Cme and the change in the endwall static pressure.It can be concluded that the parameter Cme can be considered as a significant parameter to parameterize the endwall surface and to explore the quantitative design strategies of the nonaxisymmetric endwall contouring.

针对轴流压气机的非轴对称端壁造型优化设计

针对某轴流压气机构建了一种新的非轴对称端壁造型,该造型可通过抑制角区分离来达到减小通道内二次流损失的目的。首先,在设计工况下,针对基准叶栅建立非轴对称端壁的自动优化设计方法。然后,在设计和非设计工况下,用NUMECA/Fine turbo模块分别对基准叶栅和优化叶栅进行定常流场计算。结果表明,两种工况下,优化叶栅有效抑制了角区分离,原因为非轴对称端壁造型改变了通道内的涡系结构;优化叶栅出口截面总压损失系数显著降低,叶栅出口气流角更加均匀和平衡。

非轴对称端壁造型技术在透平中的应用和发展

非轴对称端壁的设计和应用可以有效地减少透平叶栅中的二次流损失,提高透平机械通流部分的气动性能。对非轴对称端壁造型技术的应用背景、端壁造型方法及其在透平机械中的研究现状进行了综述,详细介绍了非轴对称端壁对叶栅和透平级气动性能的影响,阐述了气动性能得以提高的机理,结合实验结果介绍了非轴对称端壁对叶栅和透平级变工况特性的影响。在透平叶栅非轴对称端壁成型研究进展的基础上,对非轴对称端壁造型技术在高负荷透平叶片研发和叶片三维造型中的应用前景进行了展望。

端壁收缩对环形叶栅气动性能影响的数值研究

采用数值计算软件Numeca模拟了汽轮机低展弦比端壁收缩喷嘴中气动性能和二次流涡系的发展,并与相同边界条件下的平直端壁喷嘴比较,得到了端壁收缩对流场性能的影响。结果表明:在端壁收缩喷嘴中,较大的进口面积使得马蹄涡发展较弱,顶部区域显著的后加载特性更进一步抑制了顶部通道涡的发展,因此通道涡尤其是上通道涡的尺度和损失均较小。同时,顶部收缩导致了顶部气流出气角增大和根部出气角减小,虽然变化幅度不大,但是气流角沿叶高的分布更加均匀,对下排叶栅内的流动更加有利。另外还计算了不同高度收缩比喷嘴流动,给出了高度收缩比对叶栅流动的影响。

弧形端壁造型对不带冠涡轮气动性能的影响

采用商用计算流体力学软件CFX,湍流模型采用标准k-w两方程湍流模型,叶型为单涡轮动叶叶片,应用数值模拟方法研究了弧形端壁造型对动叶泄漏流动及涡轮气动性能的影响。数值研究结果表明:适当优化的弧形端壁造型可以改善泄漏涡和通道涡作用状况、提高出口总压和改善气流角分布、降低叶顶间隙泄漏和提高效率。最优端壁造型可以减少间隙泄漏0.27%,提高效率0.77%。在变攻角下,最优端壁造型效率最高点出现在设计攻角下,但攻角变化越大,间隙泄漏流动越少。

外端壁收缩与单向倾斜组合涡轮导叶的三维气动力研究

低展弦比涡轮导叶的外端壁收缩与单向正倾斜组合设计是既可减小两端二次流损失又可以满足冲击冷却叶片叶身需平直要求的技术措施。本文简要阐述了组合设计可减小二次流损失的力学机制、流场特征及三维流场设计分析的评价准则。通过三维流场计算 ,详细分析了诸如单向倾斜角度、子午面外端壁轮廓收缩起点、内外曲率半径等主要特征参数对流场品质的影响。给出了组合设计的方法与步骤及评价流场的定性准则。该组合设计方法对低展弦比高温涡轮导向叶片的成功设计具有指导意义。

透平端壁冷却及泛冷却最优的端壁造型设计研究

结合克里金代理模型、NSGA-II算法和数值评估方法构建了涡轮叶栅非轴对称端壁造型优化设计系统,以端壁冷却和叶片泛冷却效率最优为设计目标,开展了考虑上游槽缝射流的非轴对称端壁造型多目标优化研究。对比分析了预旋射流下,优化设计的非轴对称端壁和参考设计端壁的冷却性能。结果表明:相比于参考设计,端壁冷却效率最优的优化设计1和综合端壁冷却与叶片泛冷却效率性能的优化设计2的端壁平均冷却效率分别提高了3.52%和2.18%;压力侧端壁冷却覆盖面积在非轴对称造型后显著增大;非轴对称端壁造型设计通过抑制二次涡而降低了叶片的泛冷却效率;非轴对称端壁造型设计改变了通道涡引起的高换热区位置。槽缝冷气量为1%时,2种优化设计在槽缝冷气射流预旋比0.6下均提高了压力侧端壁的冷却效率;槽缝冷气量为1.5%时,2种优化设计均扩大了压力侧端壁冷气覆盖面积,但是在槽缝冷却射流预旋作用下降低了叶栅端壁前部区域的冷却效率。

Endwall aerodynamic losses from turbine components within gas turbine engines

A survey of research on aerodynamic loss investigations for turbine components of gas tuibine engines is presented.Experimental and numerically predicted results are presented from investigations undertaken over the past 65 plus years.Of particular interest are losses from the development of secondary flows from airfoil/endwall interactions.The most important of the airfoilAmdwall secondary flows are passage vortices,counter voitices,and corner vortices.The structure and development of these secondaiy flows are described as they affect aerodynamic perfonnance within and downstream of turbine passage flows in compressible,high speed flows with either subsonic or transonic Mach number distributions,as well as within low-speed,incompressible flows.Also discussed are methods of endwall contouring,and its consequences in regard to airfoil/endwall secondary flows.

广电工程中数字音频技术的运用

在我国现代化科学技术不断发展的背景下,广电工程发展过程当中更加注重数字音频技术的应用,这也是因为音频处理技术的不断提升,确实可以更好地保障音频文件本身的质量,同时也可以将音频文件在传输以及处理过程当中常见的问题进行解决,在一定程度上切实提高了国家广电工程的整体发展水准。本文首先针对数字音频技术的相关概念进行阐述,对其意义以及优势进行分析和研究,论述了在广电工程中实现数字音频技术的具体措施和方法,以及其在未来的具体应用方向和趋势,希望能够为相关的技术研究人员提供必要的参考和帮助。

端壁型线对转子性能影响的研究

为探究改变轴向端壁型线能否有效控制二次流现象,进而达到提高压气机性能的目的,以Rotor37为研究对象,利用造型函数对端壁型线进行了3种造型,并进行了三维数值模拟。结果显示:端壁型线对压气机流场特别是叶片尾缘处的流场有显著影响,与原型相比,Convex型端壁增大了发生附面层分离的可能,流量和效率有所下降,而Concave型端壁和S型端壁均能有效改善转子通道内的流动,使流量和效率均有一定程度的增加,且S型端壁的效果要优于Concave端壁。

非轴对称端壁造型在大径向落差长度比压气机中介机匣中的应用

为探索非轴对称端壁造型在大径向落差长度比压气机中介机匣中的应用潜力,采用数值仿真方法研究了该类中介机匣的气动特性,以及轮毂非轴对称端壁造型对中介机匣流动特性和节流特性的影响。结果表明:中介机匣内部流动损失和出口流场畸变主要源于支板角区分离,且均随流体流量的增大而变强,而支板角区分离范围的变化趋势则相反,即随流量的增大而减小。由此,提出一种基于三角函数的非轴对称端壁造型方法,通过改变支板附近轮毂型线的曲率和轴向压力梯度,有效削弱支板角区分离强度,显著改善了中介机匣大流量工作范围内(相对流量不低于0.6)出口流场的畸变强度,使中介机匣总压损失系数降低约6.4%。

进气畸变及非轴对称端壁造型对紧凑型压气机中介机匣性能的影响

为掌握畸变进气下非轴对称端壁造型对大径向落差长度比紧凑型压气机中介机匣气动特性的影响机制,采用数值模拟方法研究了畸变进气条件下中介机匣的流动特性,并进一步探索了轮毂非轴对称端壁造型对中介机匣内部流动结构和节流特性的影响。结果显示:进气畸变下中介机匣出口流场高总压损失与畸变主要来源于轮毂表面附面层分离产生的旋流和支板角区分离的共同作用。采用提出的基于三角函数的非轴对称端壁造型方法可有效消除轮毂表面的分离螺旋节点和支板角区分离,使中介机匣性能得到明显提升,总压损失系数降低约11.4%,且畸变进气下轮毂端壁造型对中介机匣节流特性的影响规律与均匀进气不同。

非轴造型对涡轮损失控制的攻角适应性研究

非轴对称端壁技术能够有效减小横向二次流带来的气动损失,提升涡轮效率。为了评估不同来流条件下非轴造型在涡轮叶栅中的作用效果,以高压涡轮的静叶叶栅上端壁为研究对象。在0°攻角条件下以涡轮的出口总压损失为优化目标进行了叶栅非轴对称端壁的造型和优化,研究得到了一种能够有效减小叶栅二次流动能和气动损失的非轴造型,并在变攻角情况下对该造型的损失控制效果进行了分析。结果表明:在所考察的攻角范围内,本研究使用的非轴对称端壁造型均能有效降低叶栅气动损失,且该造型对几个主要的二次流结构的作用效果在不同攻角下没有太大的变化;在二次流强度较弱的负攻角条件下,造型对马蹄涡结构的控制效果相比于其他攻角条件更为显著。