带沟槽涡轮叶片颗粒沉积特性和气膜冷却性能研究

为探究带沟槽叶片的颗粒沉积特性以及气膜冷却性能,以某型高压涡轮含有尾缘劈缝结构的涡轮叶片为原型,针对实际工况建立沉积模型,采用数值模拟方法研究了0<M≤2不同吹风比下沟槽结构对叶片表面颗粒沉积特性和叶片表面气膜冷却性能的影响规律。结果表明：沟槽结构提高了总碰撞效率,降低了总沉积效率,颗粒易沉积于气膜孔下游以外区域以及端壁两侧,沟槽导致压力面中后部颗粒沉积的区域增大;随着吹风比的增加,沟槽内部捕获效率提高,整体颗粒捕获效率降低,沟槽内部的气膜冷却性能不断下降,但沟槽下游部分区域的气膜冷却性能优于原始结构;沟槽的存在使下游附近沿展向的气膜覆盖区域变大,冷却性能提升,沿孔流向的展向平均气膜冷却效率最高可提升18%。     

仿螺旋肋片内冷通道流动与传热数值分析

利用数值分析方法研究了新型仿螺旋肋片内冷通道的传热与流动特性。采用横截面积为矩形、上下表面带有间断性倾斜矩形肋片叉排且对置的仿螺旋肋片内部冷却通道。分析了在通道宽高比AR=2.9、肋化比Ff/F=2.545、肋高与通道当量直径比e/Dh=0.336、肋间距与肋高比p/e=0.6、肋片与轴面的夹角β=15°及R e在1×104~2×105时的非旋转情况下,R e、肋片与主流方向夹角α等参数对内冷通道强化传热与流动阻力特性的影响。计算结果表明,该仿螺旋矩形肋片作为旋流形成装置起到了迫使流体旋转运动、提高流速和减小层流底层厚度的作用,通道内流体流动达到了预期的螺旋流动效果,通道平均换热系数得到了明显的提高,但同时流动阻力也显著增加。     

楔形仿螺旋肋片内冷通道的流动与换热

利用有限体积法对三维不可压缩的N-S方程进行离散,对上下表面带有错排间断性楔形肋片且对置的仿螺旋内冷通道进行了数值模拟。网格划分采用非结构化混合网格,湍流模型为kε-两方程模型,在近壁面处采用标准壁面函数法进行处理,速度和压力的耦合采用S IM PLE算法。计算获得了楔形仿螺旋肋片内冷通道在楔形肋片与主流方向夹角分别为0°、15°、30°时的三维流场分布。结果表明楔形仿螺旋肋片内冷通道的流场结构比较复杂,通道内流体流动达到了预期的仿螺旋流动效果。通道的平均努谢尔数随楔形肋片与主流夹角的增大而呈增大趋势,通道换热强度得到了明显的提高,但同时流动阻力也显著增加。     

带肋壁与气膜孔内流通道中肋高度对流量系数的影响

在根据相似理论放大的模型上,测量了同时带肋壁与气膜孔内流通道中沿主流流向分布的各气膜孔的流量系数Cd。实验在内流通道进口雷诺数Re为20000～80000,通道总出流比SR为0 30～0 60,肋截面高宽比h/e为1 0和2 0以及肋角为60°的范围内进行,重点分析了肋高度对Cd的影响规律,并且进行了相应的数值模拟研究。结果显示:在低进口雷诺数Re(20000)和低通道总出流比SR(0 3),沿内流通道布置的各出流孔Cd通道前半部是上升的,在第五对孔时达到最大值,然后又沿通道而下降;在相同流动状况下,随肋高度的增大,肋所诱导的二次流强度增大,对带60°肋的通道而言,气膜孔流量系数降低。     

矩形肋片导流角度对内冷通道流动与换热特性的影响

利用数值模拟方法分析了矩形仿螺旋肋片内冷通道中肋片导流角度对内冷通道三维流场特性、换热特性以及流动阻力特性的影响。数值计算结果表明,肋片导流角度对内冷通道的流动与换热特性具有较大的影响。流场中冷却介质螺旋流动的强度随着肋片导流角增大而增强,肋片导流角度越大则内冷通道的换热强度越强,同时通道中流动阻力也明显增大。从内冷通道的综合换热效果来看,当肋片导流角度为7。时,矩形仿螺旋肋片内冷通道的综合换热效果最好。     

带肋矩形直通道内的冷却空气换热特性研究

采用ANSYS CFX商用软件对带肋矩形直通道内的冷却空气换热特性进行了数值计算,并与文献[4]的实验数据进行了对比,分析了雷诺数Re和肋片角度对努塞尔特数Nu的影响。结果表明:Nu数计算平均值与实验值的变化趋势一致,但计算结果大于实验值;由于肋片的扰流作用,在两个肋片之间的壁面区域产生了两个旋涡,强化了冷却空气与固体壁面的换热;随着Re数的增大,Nu数增大,平均摩擦阻力系数也增大;当肋片角度在45°～60°之间时,冷却通道的强化对流换热效果最好。     

高温涡轮交叉肋冷却通道的流动换热特性研究

本文在给定通道大小的条件下,研究了不同肋倾角、肋宽/子通道宽和不同子通道数7种方案在雷诺数10000～ 50000范围内的流动和换热情况.研究结果表明,交叉肋对子通道的流动影响十分显著,会产生二次流和纵向涡,能够大幅度地增强冷却通道的换热能力,但同时也会使阻力损失急剧上升.当肋倾角减小或者肋宽/子通道宽增大时,通道的换...     

内冷通道特性对外表面气膜冷却换热影响研究

采用混合网格和realizable к-ε紊流模型,求解三维N-S方程,对气膜孔入口无横流、仅有横流和横流通道中有扰流肋的情况下,外表面气膜冷却换热特性进行了数值研究.具体分析了横流及肋的存在对气膜冷却外表面换热系数的影响.结果表明,横流及肋的存在使通道流场变得非常复杂,横流提高了外表面的换热系数,且使流动及换热呈现不对称特性分布;而扰流肋的存在减弱了横流对外表面的影响,换热系数相对于仅有横流时降低,且使外表面流动及换热的对称性有所改善.     

带交错叉排肋的矩形通道流场和壁面换热特性的数值模拟

为了获得高的换热系数和流动损失小的涡轮叶片内冷通道,提出了在上下壁面交错叉排布置肋的通道结构,利用数值计算的方法研究了通道各个壁面的换热特性、流动特性和流体的温度分布规律。入口雷诺数变化范围为30000~120000。采用结构化网格进行网格划分,利用realizablek-ε湍流模型和增强壁面函数封闭方程。计算结果表明,所提出的通道结构不仅在带肋的上下壁面具有较高的换热系数,大约为2.2~2.4,光滑的左右壁面的换热也增强了1.4~1.6倍,通道内的温度分布呈现出同心圆的分布,在靠近壁面的位置,二次流动较强。     

带45°肋矩形通道冷却性能及熵产特性实验研究

以带45°肋矩形通道为研究对象,实验测量了通道进、出口温度和压力以及壁面温度,分析了雷诺数(Re=10000～60000)和宽高比(W/H=0.25～4)对通道内冷气流动和传热性能及其引起的不可逆熵产的影响规律,对比了蒸汽冷却和空气冷却的不同.研究表明:不同雷诺数时,蒸汽冷却的传热性能较空气冷却提高了25％～33％;蒸...     

冷却通道参数对发汗冷却性能影响的数值研究

为了解决传统多孔材料孔隙结构不可控的问题,制备具有可控微冷通道的冷却结构对提高涡轮叶片冷却效率有着重要意义。为了研究不同冷却通道参数对叶片发汗冷却效率的影响,通过数值模拟方法研究了不同注入比下,仿生树形通道和传统直孔通道发汗冷却多孔板的换热特性及流动机理。同时,研究了6种不同模型参数多孔板在不同注入比下的冷却性能及流场的变化情况。研究结果表明：在内表面比和冷却剂出口面积基本一致的条件下,仿生树形多孔板具有更高的冷却效率;当注入比为2%时,仿生树形多孔板的平均冷却效率提高了5%,且存在一个最佳的注入比使得整体的冷却效率最高;冷却剂的出口面积是影响发汗冷却效率的关键性独立参数,与冷却剂的注入比大小有关;孔隙率对整体的冷却效率影响较小,内表面积比越大,发汗冷却的整体冷却效率越高。     

Influence mechanism of dynamic and static liquid bridge forces on particle deposition behaviors in solar photovoltaic mirrors

Solar energy is one of the most promising forms of renewable energy for solving the energy crisis and environmental problems. Dust deposition on photovoltaic mirrors has a serious negative impact on the photoelectric conversion efficiency of solar power stations. In this paper, the influence mechanism of the dynamic and static liquid bridge forces on particle deposition behaviors on solar photovoltaic mirrors is investigated. In addition, the expression and physical meaning of the particle critical separation velocity are proposed. The research results show that the static liquid bridge force can be the primary deposition force causing dust particles to adhere to photovoltaic mirrors. However, the dynamic liquid bridge force can act as a resistance force for the particle motion process and even make dust particles roll along and finally stay on the mirror. The contact force is the primary separation force that causes dust particles to flow away from the mirror. Whether dust particles adhere to the mirror depends on the relative size of the deposition and separating forces. The particle critical separation velocity describes the relative size of the collision-rebound effect and mirror adhesion effect and is expressed in Eq. (16). These research findings can provide theoretical guidance for mirror cleaning methods in the operation process of photovoltaic mirrors.     

An experimental investigation of heat transfer characteristics for steam cooling in a rectangular channel with parallel ribs

An experimental study of heat transfer characteristics in superheated steam cooled rectangular channels with parallel ribs was conducted.The distribution of the heat transfer coefficient on the rib-roughed channel was measured by IR camera.The blockage ratio(e/Dh) of the tested channel is 0.078 and the aspect ratio(W/H) is fixed at3.0.Influences of the rib pitch-to-height ratio(P/e) and the rib angle on heat transfer for steam cooling were investigated.In this paper,the Reynolds number(Re) for steam ranges from 3070 to 14800,the rib pitch-to-height ratios were 8,10 and 12,and rib angles were 90°,75°,60°,and 45°.Based on results above,we have concluded that:In case of channels with 90° tranverse ribs,for larger rib pitch models(the rib pitch-to-height ratio=10 and12),areas with low heat transfer coefficient in front of rib is larger and its minimum is lower,while the position of the region with high heat transfer coefficient nearly remains the same,but its maximun of heat transfer coefficient becomes higher.In case of channels with inclined ribs,heat transfer coefficients on the surface decrease along the direction of each rib and show an apparent nonuniformity,consequently the regions with low Nusselt number values closely following each rib expand along the aforementioned direction and that of relative high Nusselt number values vary inversely.For a square channel with 90° ribs at Re= 14800,wider spacing rib configurations(the rib pitch-to-height ratio=10 and 12) give an area-averaged heat transfer on the rib-roughened surface about8.4%and 11.4%more than P/e=8 model,respectively;for inclined parallel ribs with different rib angles at Re=14800,the area-averaged heat transfer coefficients of 75°,60° and 45° ribbed surfaces increase by 20.1%,42.0%and 44.4%in comparison with 90° rib angle model.45° angle rib-roughened channel leads to a maximal augmentation of the area-averaged heat transfer coefficient in all research objects in this paper.     

Flow structure and heat exchange analysis in internal cooling channel of gas turbine blade

This paper presents the study of the flow structure and heat transfer, and also their correlations on the four walls of a radial cooling passage model of a gas turbine blade. The investigations focus on heat transfer and aerodynamic measurements in the channel, which is an accurate representation of the configuration used in aeroengines. Correlations for the heat transfer coefficient and the pressure drop used in the design of radial cooling passages are often developed from simplified models. It is important to note that real engine passages do not have perfect rectangular cross sections, but include corner fillet, ribs with fillet radii and special orientation. Therefore, this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which possesses very realistic features.     

具有温度场的冷却叶片振动特性计算方法研究

根据稳态热传导的相关理论,建立了透平冷却叶片温度场和热应力场的四面体三维有限元分析模型和方法,并在此基础上建立了透平冷却叶片振动特性三维有限元分析方法,开发了相关计算软件。对某航空发动机透平高压第1级冷却叶片在不同工作条件下的振动特性进行了计算分析,同时研究了热应力、温度场、转速等对叶片振动特性的影响,表明本文中所建立模型和方法是科学、合理和精确的,为开展透平冷却叶片的设计和振动安全性评价奠定了基础。     

矩形冷却通道内超临界RP-3航空煤油对流传热数值研究

对超临界压力下RP-3航空煤油在内截面宽为4mm、高为4mm、固体壁面厚为1mm、加热段长度为500mm的水平矩形冷却通道内的对流传热特性进行了数值模拟研究。分析了通道内速度场的分布规律,讨论了热流密度、压力、进口温度对传热的影响。计算结果表明:当主流温度处于拟临界温度附近时,流体物性参数变化剧烈,导致传热系数降低,传热出现恶化。在超临界压力下,较低的热流密度、增大压力、降低进口流体温度或提高质量流速均有利于改善冷却通道内的传热性能。     

Effect of embedding a porous medium on the deposition rate in a vertical rotating MOCVD reactor based on CFD modeling

This paper investigates numerically the effect of embedding a porous medium on the deposition rate in a two-dimensional (2-D) axi-symmetric vertical rotating metalorganic chemical vapor deposition (MOCVD) reactor. The 2-D Navier–Stokes, thermal-energy, and mass transfer equations as well as the wall surface reaction for growth rate in this model are solved by using commercial computational fluid dynamics (CFD) package, FLUENT (version 6.2), with a segregated method. As shown in the results, the recirculation cell caused by a buoyancy effect above the susceptor may be eliminated due to a large pressure drop during CVD process. Under a condition of the appropriate porosity and the appropriate distance between a porous medium and the susceptor, the film uniformity may be increased about 53.3% owing to a thin boundary layer near the susceptor. In addition, the case of a porous medium embedded in a modified MOCVD reactor is considered in this study to increase the film uniformity further. The numerical results show that the uniformity of the film may be enhanced about 77.9%.     

Evaluation and analysis of evaporation cooling on thermodynamic and pressure characteristics of intake air in a precooled turbine engine

The precooled turbine engine is applied to overcome the limitation of Mach number due to high temperature inlet air. This paper aims to investigate the effect of water injection cooling on the high-temperature intake air. Then, the theory evaluation and Eulerian-Lagrangian multiphase flow method are conducted to explore the thermodynamic process and resistance characteristics of the pre-cooling section built-in even spray apparatus with a drag reduction. Results show that larger amount of the injection flow rate at higher Mach number will deteriorate total pressure loss and flow field uniformity. Evaporation cooling can decrease flow loss by 9.4%–60.7%. Within 27 ms, total-temperature drop is in 14–144 K range with a low total-pressure drop coefficient of 0.56%–1.29%. Especially, mass flow will increase by 1.15%–18.50%. Thus, water injection cooling is conducive to a higher acceleration, as well as for improving the thermodynamics characteristics of inlet air for a turbine engine at a high Mach number.     

流化床内不同密度颗粒流动特性的数值模拟

将计算流体力学和离散单元法相结合,在自行开发程序上对流化床内随机生成的密度服从正态分布的颗粒的流动特性进行数值模拟,得到了不同床层表观气速下床内颗粒的流化过程图、气相速度场以及不同密度颗粒的速度场、体积分数沿床高的分布和分离率.结果表明:在较小床层表观气速下,床内不同密度的颗粒会出现分离现象,并且颗粒的密度差越大,颗粒分离越明显,当增大床层表观气速后,颗粒间的分离程度减弱;小密度颗粒的速度大于大密度颗粒,颗粒间的密度差越大,颗粒间的速度差也越大.