Surface temperature reduction by using dimples/protrusions in a realistic turbine blade trailing edge

Abstract

In this article, numerical simulations have been conducted on the heat transfer effect of dimple/protrusion layouts of a pin-finned wedge duct. Conjugate heat transfer calculations are further performed to investigate the cooling effect of modified schemes with dimples and protrusions added. Comparisons are carried out with a turbine second stage guide vane employed as the prototype. The dimple/protrusion-pin fin arrangement is set as the optimum one obtained above, and dimple depth/protrusion height varies from 0.2 to 0.3 times the structure diameter. It is found that the side-by-side arrangement and protrusion structure is more beneficial for the wedge duct endwall heat transfer. Comparison with the prototype blade shows that the addition of both dimples and protrusions are helpful in enhancing the trailing edge cooling effect. The cooling effect is increased with an increase in dimple depth/protrusion height. The results also show that the modified blade with protrusions attached at 0.3 height saves 0.48?g/s cooling mass flow and reaches the most positive performance with a 17?K, 14?K average temperature reduction, 0.022, 0.018 cooling effect increasing for pressure, suction side, respectively.     

Heat transfer in high‐aspect‐ratio rectangular passage with skewed ribs

The heat transfer characteristics and flow behavior in a rectangular passage with two opposite 45° skewed ribs for turbine rotor blade have been investigated for Reynolds numbers from 7800 to 19,000. In this blade, the spanwise coolant passage at the trailing edge region whose thickness is very thin is chosen, so the channel aspect ratio (=width/height of channel) is extremely high, 4.76. Therefore the heat transfer experiment in the high‐aspect‐ratio cooling channel was performed using thermochromic liquid crystal and thermocouples. Furthermore, the calculation of flow and heat transfer was carried out using CFD analysis code to understand the heat transfer experimental results. The enhanced heat transfer coefficients on the smooth side wall at the rib's leading end were the same level as those on the rib‐roughened walls. © 2002 Scripta Technica, Heat Trans Asian Res, 31(2): 89–104, 2002; DOI 10.1002/htj.10018     

水介质中尾部锯齿结构叶片数值计算

为了验证将空气动力学中翼型部件采用的锯齿形尾部结构引入到水力机械翼型部件中的可行性,建立了NACA0012型对称型叶片的几何模型,并在此基础上建立了尾部带锯齿的NACA0012型叶片修改模型,利用数值计算方法计算了在入流速度10 m/s下带锯齿与不带锯齿的NACA0012型叶片在0°及10°攻角下的流场数据及压力脉动数据。计算结果表明,锯齿形边缘结构在攻角为10°时能有效减小叶片尾部、背水面的脱流及尾迹中的漩涡和流场中的水力振动,锯齿结构改善叶片水力性能效果显著;而攻角为0°时流场中水力振动轻微增加。由此说明,锯齿结构可起到改善水介质中翼型部件水力特性的作用。     

基于流热耦合的燃气轮机透平叶顶冷却设计

燃气轮机透平叶顶区域存在复杂的流动和换热问题,承受很高的热负荷。为了降低透平动叶叶顶温度,在透平叶顶现有结构的基础上提出气膜冷却和气膜+内冷通道冷却两种叶顶冷却方案,并通过流热耦合计算分析冷却升级前后叶顶区域的换热和流动特性。研究发现：叶顶气膜冷却方案可有效降低叶顶温度,特别是叶顶前缘至中弦区域;而气膜＋内冷通道冷却方案基于外部气膜冷却,结合内部冷却通道设计,可进一步降低叶顶尾缘的温度;与原型叶片相比,气膜+内部冷气通道的复合冷却设计可以使叶顶尾缘最高温度降低24 K。     

具有新型双层壁结构的透平叶片流热耦合研究

多通道壁面射流冷却结构是一种新型的燃气透平动叶内部冷却结构,具有消耗冷气少、压力损失小等优点。本文构建了简化的壁面射流冷却叶片与GE-E3冷却结构叶片模型,采用流热耦合方法对比研究了其流动与换热特性。结果表明,壁面射流冷却通道内的狭小空间抑制了横流的产生,冷气在冷却通道中形成了流向涡;前缘冷气流道中的大量冷气流经吸力侧冷却区,并从出口压力更小、面积更大的尾缘排出,使得前缘气膜孔出流的冷气流量和动量较小,冷气在叶片外表面的气膜覆盖特性更好;离心力的影响导致前缘冷气流道中叶根处的压力较低,叶根附近的气膜孔出现燃气主流入侵现象。相比于GE-E3叶片,壁面射流冷却叶片的前缘温度和温度梯度都较小,因此多通道壁面射流冷却在前缘具有更优异的冷却特性。     

Conjugate heat transfer investigation on the cooling performance of air cooled turbine blade with thermal barrier coating

A hot wind tunnel of annular cascade test rig is established for measuring temperature distribution on a real gas turbine blade surface with infrared camera. Besides, conjugate heat transfer numerical simulation is performed to obtain cooling efficiency distribution on both blade substrate surface and coating surface for comparison. The effect of thermal barrier coating on the overall cooling performance for blades is compared under varied mass flow rate of coolant, and spatial difference is also discussed. Results indicate that the cooling efficiency in the leading edge and trailing edge areas of the blade is the lowest. The cooling performance is not only influenced by the internal cooling structures layout inside the blade but also by the flow condition of the mainstream in the external cascade path. Thermal barrier effects of the coating vary at different regions of the blade surface, where higher internal cooling performance exists, more effective the thermal barrier will be, which means the thermal protection effect of coatings is remarkable in these regions. At the designed mass flow ratio condition, the cooling efficiency on the pressure side varies by 0.13 for the coating surface and substrate surface, while this value is 0.09 on the suction side.     

Conjugate heat transfer analysis of a rotor blade with coolant channels

The present study deals with the conjugate heat transfer analysis of a cooled high-pressure turbine rotor blade consisting of eight cooling channels. Computational investigations are performed in a five-bladed cascade to determine characteristics of flow and heat transfer at different values of mainstream and coolant flow rate. Surface temperature measurements using infrared thermography are performed for validating the computational fluid dynamics results. The results show nonuniform variation of surface effectiveness: (a) higher average surface temperature on the pressure side than on the suction side, (b) peak surface temperature at the pressure side trailing edge region, (c) lowest temperature at midspan region of both pressure and suction sides, (d) intermediate values of temperature on the leading edge, and (e) these temperature patterns vary with the changes in mainstream Reynolds number and coolant flow rates, signifying the importance of carrying out conjugate heat transfer analysis. This study also emphasizes the importance of considering realistic coolant channel geometry over the idealized, an illustration showed that the maximum Nusselt number may vary up to 200% due to idealization.     

燃气轮机透平叶片传热和冷却研究：内部冷却

随着燃气轮机透平进口温度的不断提高,其换热与冷却问题已然成为现代高性能燃气轮机研发中亟待解决的核心关键技术之一.透平叶片的冷却可以分为内部冷却和外部冷却,结合作者近年的研究工作,详细综述了燃气轮机透平叶片内部换热与冷却问题的研究现状与进展,着重介绍了叶片内部蛇形通道冷却、叶片内部冲击冷却和前缘的旋流冷却及尾缘柱肋冷却,指出了它们各自在相关方面需要进一步开展的工作.其中：在蛇形通道冷却方面,需要进一步研究旋转状态下蛇形通道内流动与换热特性、发展高性能的扰流装置及通道弯头结构、设计新颖高效的叶顶内部冷却结构、获得带气膜孔或冲击孔的蛇形通道内的换热与冷却特性;在叶片前缘内部冲击冷却方面,需要研究不同曲率面上的冲击冷却换热特性、旋转条件下的冲击冷却以及冲击气膜复合冷却特性;在旋流冷却方面,需要对其结构参数的影响开展进一步的广泛研究,并开展旋转状态下旋流冷却特性的研究;在尾缘柱肋冷却方面,需要进一步研究复杂流场下柱肋阵列通道中的流动换热与众敏感因子之间的关系.     

基于遗传算法的燃气轮机叶片内部柱肋蒸汽冷却通道的优化分析

针对叶片尾缘内部柱肋冷却方式进行数值仿真和优化分析。采用CFX软件进行数值仿真计算,建立圆形柱肋、水滴形柱肋和正方形柱肋3种柱肋形状下,不同柱肋间距的矩形通道模型,验证数值模型的正确性以及网格无关性。分析了顺排和叉排的排列方式下,柱肋形状和柱肋间距对下底面努塞尔数以及整个通道内压力损失的影响,最后通过MATLAB的遗传算法对仿真结果进行优化。研究表明：柱肋模型中,横向和纵向柱肋间距最小时,换热效果最佳,压力损失最大;在顺排和叉排中,正方形柱肋对通道的换热强度的提升效果最明显,圆形柱肋提升效果最小。     

Feasibility of using multiport minichannel as thermosyphon for cooling of miniaturized electronic devices

The feasibility of using multiport minichannel (MPMC) as thermosyphon for cooling miniaturized electronic products is experimentally investigated with acetone as the working fluid. A detailed analysis on thermal performance and entropy generation due to heat transfer and pressure drop with the effects of heat load (10-50 W), filling ratio (FR; 40%, 50%, and 60%), and inclination angle (45°, 60°, and 90°) has been carried out. The results showed a reduction of 22.2% and 9.31% in thermal resistance and evaporator wall temperature at optimum filling ratio (OFR) of 50%. Reduction in entropy generation due to heat transfer and pressure drop of 16.6% and 12.3%, respectively, was observed at OFR. Internal fins in MPMC increase the surface area and evaporation rate by enhancing heat transfer leading to a decrease in the rate of entropy generation. Multiport increases surface tension of condensate at right angles to the flow direction along with the effects of gravity and enhancing rate of condensation. A new correlation is developed to predict evaporator wall temperature as a function of heat load and FR. The proposed correlation agrees well with a deviation of ±20% with present experimental results and also with the published literature. Thus, the obtained results will be useful in cooling miniaturized electronic devices.     

Numerical Investigations of the Influence of Unsteady Vane Trailing Edge Shock Wave on Film Cooling Effectiveness of Rotor Blade Leading Edge

Unsteady numerical simulations of a high-load transonic turbine stage have been carried out to study the influences of vane trailing edge outer-extending shockwave on rotor blade leading edge film cooling performance. The turbine stage used in this paper is composed of a vane section and a rotor one which are both near the root section of a transonic high-load turbine stage. The Mach number is 0.94 at vane outlet, and the relative Mach number is above 1.10 at rotor outlet. Various positions and oblique angles of film cooling holes were investigated in this research. Results show that the cooling efficiency on the blade surface of rotor near leading edge is significantly affected by vane trailing edge outer-extending shockwave in some cases. In the cases that film holes are close to leading edge, cooling performance suffers more from the sweeping vane trailing edge outer-extending shockwave. In addition, coolant flow ejected from oblique film holes is harder to separate from the blade surface of rotor, and can cover more blade area even under the effects of sweeping vane trailing edge shockwave. As a result, oblique film holes can provide better film cooling performance than vertical film holes do near the leading edge on turbine blade which is swept by shockwaves.     

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…     

传热对增压器径流涡轮叶片温度分布的影响

采用共轭传热计算方法,对某柴油发动机废气涡轮增压器径流涡轮流场进行了数值模拟,对比了叶轮在绝热和传热条件下温度分布的差别,研究了传热边界对叶轮温度分布的影响。结果表明,绝热条件下,叶片两侧的温度存在显著的温差,并且从叶轮进口到出口也有明显的温降;而传热条件下,相同叶高下的叶片表面温度分布近乎于一条直线,压力面和吸力面的温度几乎相同;在热平衡条件下,叶轮实体内的温度范围很小,不超过10 K,温度梯度较小表明由温差引起的热应力很小。     

带有冷气掺混的三级透平气动性能数值研究

借助NUMECA数值仿真软件,以某型燃气轮机的三级透平作为计算模型,对其在冷却气体掺混前后的流场进行了数值模拟。考虑到工质物性的影响,采用了变比热高温燃气作为计算工质。同时,针对燃气轮机透平进口的变工况问题,选取不同的透平进口总压值进行数值计算。结果表明,冷却气体的加入使得级损失增大,每列叶片流道出口速度或相对速度减小,下游叶片进口气流角减小;在三级透平冷气掺混时改变进口总压值,每列叶片流道的进口气流角几乎不变,除第三级动叶的激波损失与尾迹损失增大外,其余叶片流道的能量损失变化不明显。     

Effect of the Chevron Angle on Cooling Heat Transfer Characteristics of Supercritical Pressure Fluids in Plate Heat Exchangers

ABSTRACT

For the development of industrial heat pump systems supplying a high-temperature heat source over 130°C, the authors have studied on cooling heat transfer of supercritical pressure fluids flowing in chevron-type plate heat exchangers (PHEs). In this study, to examine the effect of chevron angle on cooling heat transfer of supercritical pressure refrigerants, experiments were conducted for HFC134a and HFO1234ze(E) flowing in the PHEs with the chevron angles from 30° to 65°. In the experiments, cooling heat transfer coefficients were obtained in the wide range of bulk fluid enthalpy from vapor-like high temperature to liquid-like low temperature, changing the pressure in the reduced pressure range from 1.01 to 1.2 at the mass flow rates of 7 and 11 kg/min. Especially for the enthalpy region of the pseudo critical point and its vicinity in which good heat transfer appeared, the effect of chevron angle on heat transfer of supercritical pressure fluids was clarified based on the measurements. Furthermore, the effect of chevron angle was examined for the wide angle range from 0° to 90° with estimating the heat transfer coefficient for the angles 0° and 90° from appropriate correlations. Besides, the present data were compared with some conventional heat transfer correlations.     

Influence of blade outlet angle on performance of low-specific-speed centrifugal pump

In order to analyze the influence of blade outlet angle on inner flow field and performance of low-specific-speed centrifugal pump, the flow field in the pump with different blade outlet angles 32.5° and 39° was numerically calculated. The external performance experiment was also carried out on the pump. Based on SIMPLEC algorithm, time-average N-S equation and the rectified k-? turbulent model were adopted during the process of computation. The distributions of velocity and pressure in pumps with different blade outlet angles were obtained by calculation. The numerical results show that backflow areas exist in the two impellers, while the inner flow has a little improvement in the impeller with larger blade outlet angle. Blade outlet angle has a certain influence on the static pressure near the long-blade leading edge and tongue, but it has little influence on the distribution of static pressure in the passages of impeller. The experiment results show that the low-specific-speed centrifugal pump with larger blade outlet angle has better hydraulic performance.     

Heat transfer in internal channel of a blade: Effects of rotation in a trailing edge cooling system

The aerothermal performance of a trailing edge (TE) internal cooling system of a high pressure gas turbine blade was evaluated under stationary and rotating conditions.The investigated geometry consists of a 30:1 scaled model reproducing a typical wedge shaped discharge duct with one row of enlarged pedestals.The airflow pattern inside the device simulates a highly loaded rotor blade cooling scheme with a 90 [deg] turning flow from the radial hub inlet to the tangential TE outlet.Two different tip configurations were tested,the first one with a completely closed section,the second one with a 5 holes outlet surfaces discharging at ambient pressure.In order to assess rotation effects,a rotating test rig,composed of a rotating arm holding both the PMMA TE model and the instru-mentation,was purposely developed and manufactured.A thin Inconel heating foil and wide band Thermo-chromic Liquid Crystals are used to perform steady state heat transfer measurements on the blade pres-sure side.A rotary joint ensures the pneumatic connection between the blower and the rotating apparatus;more-over several slip rings are used for both instrumentation power supply and thermocouple connection.A parallel CFD analysis involving steady-state RANS modeling was conducted to allow an insight of the flow field inside the redirecting channel and the interpedestal ducts to better interpret the developing vortical structures.Low-Reynolds grid clustering permits to integrate up to the wall both the momentum and the thermal boundary layer.Calculations were performed by means of an in-house developed pressure based solver exploiting the k-ω SST turbulence model implemented in the framework of the open-source finite volume discretization toolbox OpenFOAM?.Analyzed flow conditions correspond to Reynolds number of 20000 in the hub inlet section and angular speed varies to obtain rotation numbers in the range from 0 to 0.3.The orientation of the rotation axis is orthogonal to the heated surface as to resemble a 90 [deg] blade metal angle.Results are reported in terms of de-tailed heat transfer coefficient 2D maps on the suction side surface as well as spanwise profiles inside the pedestal ducts.     

Computational investigations of blunt trailing‐edge and twist modifications to the inboard region of the NREL 5 MW rotor

The effects of twist and section shape modifications in the inboard region on the aerodynamic characteristics of the NREL 5 MW rotor have been examined using a Reynolds‐averaged Navier–Stokes method OVERFLOW2. The baseline rotor blade was modified by increasing the trailing‐edge thickness over the inboard region by modifying the sections’ thickness distribution aft of the maximum thickness location. Results when compared with the baseline rotor show that a modest increase of trailing‐edge thickness to 10–20%c increased power capture by 1%. Further increases in trailing‐edge thickness decrease in effectiveness to the point of reducing power capture when thicknesses reach 40%c. Increasing trailing‐edge thicknesses also leads to an increase in thrust, but this load is concentrated in the inboard region, resulting in a small increase in root bending moments. The blunt trailing‐edge concept greatly reduces the spanwise extent of inboard flow separation evident in the baseline NREL 5 MW rotor. The low‐pressure region aft of the trailing edge, created by the geometry, acts to reduce the spanwise spreading of the inboard separation. Rotors with modified twist distributions over the inboard 35%R of span are also compared. Inboard twist angles are varied from + 6° to ? 6° from the baseline twist schedule. Increasing inboard blade twist reduces overall rotor power capture but reduces thrust at a faster rate. Power capture remains constant with decreasing inboard geometry twist, whereas thrust increases approximately linearly by 0.75% for a decrease in thrust of 6°. Copyright © 2012 John Wiley & Sons, Ltd.     

凹槽式叶顶流动换热的数值研究

针对叶尖间隙高度对凹槽式叶顶流动与换热的影响展开数值研究,评估4种湍流模型在叶顶换热方面的预测能力.结果表明：凹槽肩壁顶部、凹槽腔底部近前缘区域和叶顶尾缘为高换热区,凹槽腔底的中部和尾部区域为低换热区;不同湍流模型对叶尖间隙泄漏量预测差别很小,但泄漏流流动状态差异很大,这是造成不同湍流模型对叶顶换热预测存在重大差别的原因;在研究的间隙范围内,叶尖间隙泄漏量和叶顶换热强度随间隙高度的增大而增加;在所选的4种湍流模型中,k-ω模型是叶顶换热数值模拟较好的湍流模型选择.     

Localization of wind turbine noise using a microphone array in wind tunnel measurements

An experimental investigation on scaled wind turbine models in a wind tunnel with a microphone array is presented. Our study focuses on the localization and quantification of aerodynamic noise sources on rotating wind turbine blades with the aim of identifying the contributing factors that have an impact on the source spectra. Therefore, wind tunnel measurements were conducted for three different blade geometries (NACA 4412 shape, Clark-Y shape, and sickle shape), five pitch angles between ?2° and +8° and five wind velocities between 5 and 13 ms^??1. For the localization of rotating sound sources with a microphone array, a rotating beamforming method based on the acoustic ray method is used. The Clean-SC deconvolution method was used to improve the resolution of the acoustic sources, and integrated spectra were calculated for the individual blades. The sound sources were localized at the wind turbine blades and assigned to the leading edge and trailing edge subregions. The results show a high dependency on the sound source distribution and the source strength with regard to the observed one-third octave bands, wind velocity, and blade geometry. Hence, the localization of rotating sound sources with a microphone array is a suitable method for the development of wind turbine blades that emit less noise.