矩形带肋通道中蒸汽与空气换热特性比较试验研究

模拟实际燃气轮机叶片内冷通道几何及传热结构,研究了蒸汽和空气在两面带有肋片的矩形通道中当雷诺数为10000⁸0000时的换热和摩擦特性。试验通道宽高比(肋片在宽面上)为0.5,肋间距p/e为10,通道阻塞比为0.047,试验通道长度L为1000mm。试验结果显示,蒸汽和空气在带肋通道中的平均换热系数,平均摩擦系数和换热性能随雷诺数的变化趋势几乎相同;在相同试验条件下,蒸汽在带肋通道中的平均换热系数比空气高30.2%,平均摩擦系数比空气高18.4%;蒸汽在带肋通道带肋面和光滑面上的换热性能比空气分别高8.4%和7.3%。     

Forced convection heat transfer of steam in a square ribbed channel

An experimental study of heat transfer characteristics of steam in a square channel (simulating a gas turbine blade cooling passage) with two opposite surfaces roughened by 60 deg parallel ribs was performed. The ranges of key governing parameters were: Reynolds numbers (Re) based on the channel hydraulic diameter (30000–140000), entry gauge pressure (0.2Mpa–0.5Mpa), heat flux of heat transfer surface area (5kWm⁻²–20kWm⁻²), and steam superheat (13°C–51°C). The test channel length was 1000mm, while the rib spacing (p/e) was 10, and the ratio of rib height (e) to hydraulic diameter (D) was 0.048. The test channel was heated by passing current through stainless steel walls instrumented with thermocouples. The local heat transfer coefficients on the ribbed wall from the channel entrance to the fully developed regions were measured. The semi-empirical correlation was fitted out by using the average Nusselt numbers in the fully developed region to cover the range of Reynolds number. The correlation can be used in the design of new generation of gas turbine blade cooled by steam.     

Heat transfer and friction characteristics in steam cooled rectangular channels with rib turbulators

We studied the heat transfer and friction characteristics in steam-cooled rectangular channels with rib turbulators on W side or H side walls in the Reynolds number (Re) range of 10000-80000. Each of the test channels was welded by four stainless steel plates to simulate the actual geometry and heat transfer structure of blade/vane internal cooling passage. The length of the channel L was 1000 mm, the cross section of the channel was 40 mm × 80 mm, and the pitch-to-rib height ratio p/e was kept at 10. The channel blockage ratio (W/H) was 0.047. Results showed that the Nusselt number (Nu) distributions displayed different trends at the entrance region with the increase of Re for the rib turbulators on the W side walls. The heat transfer performance of the rib turbulators on the H side walls was about 24-27% higher than that on the W side walls at the same pumping power. In addition, semi-empirical correlations for the two cases, rib turbulators on W side walls and rib turbulators on H side walls, were developed based on the heat transfer results, which could be used in the design of the internal cooling passage of new generation steam-cooled gas turbine blade/vane.     

排尘孔涡轮冷却叶片叶顶流动与传热研究

涡轮叶片叶顶排尘孔用于清除冷气中掺杂的尘粒,以保证气膜孔和冲击孔的可靠工作,但排尘孔射流引起叶顶流动和传热问题。采用参数化方法建立有、无排尘孔涡轮冷却叶片几何模型,基于包含叶片主体、主燃气通道和三腔回流式内冷却通道的全局模型,采用流热耦合数值分析,开展排尘孔对涡轮冷却叶片叶顶流动与传热问题的初步研究。研究结果表明,对比有、无排尘孔叶片,排尘孔射流可降低叶顶平均温度约25 K;冷却通道对流换热作用和叶顶排尘孔射流可使叶顶平面降温400～600 K,冷却效果与冷却通道冷气流量和尘孔结构在叶顶位置相关;排尘孔叶顶射流对叶顶间隙高温燃气泄漏具有阻碍作用,可以提高叶片总压恢复系数约0.5%～1.5%,随着冷气流量的增大,这种作用增强;尘孔结构设计应兼顾射流对叶顶流动与传热的共同影响。     

矩形带肋通道中脉动流强化换热数值研究

为了提高燃气轮机叶片内部对流冷却,采用脉动蒸汽流取代稳态蒸汽流作为内冷介质。利用数值计算方法研究脉动蒸汽流在矩形带肋通道中的强化换热能力。通过与稳态蒸汽流的对比,分析了非稳态脉动流的脉动频率、脉动幅值和雷诺数对换热效果的影响。计算结果表明,脉动流对换热的影响取决于流体压力梯度的大小,当脉动的蒸汽处于逆压梯度区间,逆压梯度越大瞬态换热更强。而顺压梯度有稳定流体的作用,在顺压梯度时间区间,有瞬时的换热甚至低于稳态流体冷却的情况出现。     

Optimization of a high pressure turbine blade tip cavity with conjugate heat transfer analysis

The current study aims to understand the aero-thermal performance of a cooled cavity tip in a single stage transonic turbine. The squealer tip of the uncooled turbine blade was reduced to an aerodynamic loss with suppressing leakage flow. However, the aerodynamic loss study of the cooled turbine blade tip is rare. It is necessary to study the tip cavity of the cooled turbine blade. Depth, front blend radius and aft blend radius of the cavity were set as design variables, and 30 cases were chosen using design of experiments. These cases were calculated with conjugate heat transfer method. Approximation model was made using the Kriging method, and tip cavity shape was optimized with multidisciplinary design optimization. Average total pressure loss behind the trailing edge and cooling effectiveness of blade tip surface were set to the objective function. The aerodynamic optimization model decreased 1.6 % of total pressure loss, the heat transfer optimization model increased 1.3 % point of cooling effectiveness and aero-thermal optimization model were found. Volume of tip cavity becomes larger when three design variables are grown. Amount of tip leakage flow and its distribution over the tip region increases and total pressure loss and cooling effectiveness increase. In terms of heat transfer, blade tip without cavity is advantageous. Total pressure loss coefficient, however, also increases over 5 %. To improve both aero-thermal characteristics of cooled blade tip, the design using the multidisciplinary design optimization is recommended.

     

The effect of cooling conditions on convective heat transfer and flow in a steam-cooled ribbed duct

This work presents a numerical and experimental investigation on the heat transfer and turbulent flow of cooling steam in a rectangular duct with 90° ribs and studies the effect of cooling conditions on the heat transfer augmentation of steam. In the calculation, the variation range of Reynolds is from 10,000 to 190,000, the inlet temperature varies from 300°C to 500°C and the outlet pressure is from 0.5MPa to 6MPa. The aforementioned wide ranges of flow parameters cover the actual operating condition of coolant used in the gas turbine blades. The computations are carried with four turbulence models (the standard k-?, the renormalized group (RNG) k-?, the Launder-Reece-Rodi (LRR) and the Speziale-Sarkar-Gatski (SSG) turbulence models). The comparison of numerical and experimental results reveals that the SSG turbulence model is suitable for steam flow in the ribbed duct. Therefore, adopting the conjugate calculation technique, further study on the steam heat transfer and flow characteristics is performed with SSG turbulence model. The results show that the variation of cooling condition strongly impacts the forced convection heat transfer of steam in the ribbed duct. The cooling supply condition of a relative low temperature and medium pressure could bring a considerable advantage on steam thermal enhancement. In addition, comparing the heat transfer level between steam flow and air flow, the performance advantage of using steam is also influenced by the cooling supply condition. Changing Reynolds number has little effect on the performance superiority of steam cooling. Increasing pressure would strengthen the advantage, but increasing temperature gives an opposite result.     

Enhancement of combined cycle performance using transpiration cooling of gas turbine blades with steam

Gas/steam combined cycle is synergetic combination of Brayton cycle based topping cycle and Rankine cycle based bottoming cycle, which have capability of operating independently too. Combined cycle performance depends on the constituent cycles and it can be reasonably improved by enhancing gas cycle performance using gas turbine blade cooling. Amongst different cooling techniques the transpiration cooling offers effective utilization of coolant as compared to film cooling because of better shrouding of blade surface as the coolant is discharged from entire blade surface. The present work deals with evaluation of performance enhancement of combined cycle by using steam transpiration cooling of gas turbine blades. The combined cycle performance parameters e.g. overall efficiency and specific power output etc. have been compared for air transpiration cooling and steam transpiration cooling. The results revealed that for the specified conditions the steam is superior coolant in comparison to air and the combined cycle performance can be enhanced by applying transpiration cooling in gas turbine blades with steam as coolant. With a turbine inlet temperature of 1800 K and compressor pressure ratio of 23, the combined cycle efficiency with steam transpiration cooling of gas turbine blades is higher by 1.94 percent approximately as compared to the efficiency of combined cycle with air transpiration cooling of gas turbine blades.     

Experimental and numerical investigation of heat transfer characteristics in a square channel with various truncated ribs

Oblique ribs are widely applied to the internal cooling of turbine blades to promote the heat transfer between blade wall and coolant. In this study, the effect of several new types of truncated ribs on the heat transfer characteristics in 45° oblique rib channels is investigated experimentally and numerically. The numerical results obtained by the SST k-ω turbulence model agree well with the experimental data for the Reynolds number ranging from 10000 to 60000. The results indicate a significant entrance effect on the heat transfer in truncated rib channels. The numerical results show that ribs continuously truncated at 3.8 mm gives the best heat transfer performance among the newly truncated ribs. Compared with the original structure, the Nusselt number and heat transfer enhancement factor of newly truncated ribs increased by 24.6 % and 17.8 %, respectively. Concurrently, the friction factor is reduced by 5.1 %.

     

涡轮叶栅通道中的流动显示

在大尺寸低速叶栅传热风洞中对一种高压涡轮导向叶栅的流场进行了流动显示实验研究。分别采用线簇和小球浮动法对五个雷诺数下的叶栅端壁区三维流场、叶片表面和端壁表面的流动进行了显示。实验结果表明 :涡轮叶栅中有强烈的二次流动 ,并存在复杂的涡系 ;三维流动区约占叶栅通道的 40 % ;雷诺数的增大将增强端壁区的三维流动。流场显示图片说明 :叶片吸力面靠近端壁有角涡形成与发展 ,并存在一个三角形区域 ;流场显示的通道涡大小与流场测量结果吻合。本文的实验结果可用于分析端壁表面和叶片表面换热特性的形成机理     

Performance characteristics of a MPCM slurry cooled unit designed for telecommunication equipment

Optimum control of the PCB surface temperature is very important in achieving high performance and operational reliability of telecommunication equipment with high power density and thermal density. In this study, the performance of a liquid cooling unit with MPCM slurries (called as “MPCM cooled unit”) was tested and analyzed. In addition, its performance was compared with that of an air cooled unit and a water cooled unit. The maximum surface temperature and the index of uniform temperature distribution (IUTD) were introduced to analyze cooling performance. The surface temperature in the unit rack of telecommunication equipment can be controlled properly by using an MPCM cooled unit instead of an air cooled unit. The maximum surface temperature and IUTD of the MPCM cooled unit at the inlet temperature of 19°C were lower than those at inlet temperatures of 25°C and 27°C due to the increases of heat capacity and heat transfer rate. The heat capacity of the MPCM cooled unit increased significantly with the increase of mass flow rate due to high specific heat of MPCM particles with latent heat transfer rate. The cooling performance of the MPCM cooled unit was superior to that of the water cooled unit.     

空冷汽轮机低压级组叶片模化设计与开发

针对空冷汽轮机低压级组叶片设计困难的问题,基于叶片模化设计技术,结合先进的计算流体动力学(CFD)技术,提出了空冷汽轮机低压级组叶片模化和改型优化设计方法.该方法主要是用于将母型低压级组叶片通过模化设计改进为与设计目标总体性能参数相近的低压级组,在此基础上,应用三维气动分析设计优化方法对低压级组进行了改型优化设计,得到了满足设计要求的空冷低压级组叶片;同时,对低压级组进行变工况分析,以保证低压级组在许用范围内具有较好的变工况性能.该方法将多种先进技术相结合,缩短了开发周期,降低了开发成本.研究结果表明,采用该方法开发的低压级组能够很好地继承母型低压级组的优良特性,保证了叶片的安全性和可靠性,具有良好的气动性能和适用范围.     

Purge flow effect on aerodynamics performance in high-pressure turbine cascade

The endwall and blade film cooling systems are the typical solution adopted within gas turbines to allow further increase of turbine inlet temperature, avoiding critical material thermal damages. Due to the complex secondary flow field in the blade passage, endwall is more difficult to be cooled than blade surfaces. In the matter of fact, in endwall film cooling studies, it is necessary to investigate the interaction between coolant air and the secondary flow. In present study, the flow field of high-pressure turbine in linear cascade has been investigated by 5-holes pitot tube to reveal the secondary flows behaviour under the influenced of purge flows through a slot which is located 0.63 C_ax upstream of blade leading edge. Both measurement and numerical simulation presented almost similar trend of aerodynamics performance thus enable the authors to excute the flow visualizations accurately. The presence of newly generated vortical structures was considered to be responsible to the additional loss at higher MFR cases.     

Cooling characteristics on the forced convection of an array of flat-form electronic components in channel flow

Present study is concerned with forced convective heat transfer of the channel flow with line arrays of heated electronic components mounted on a printed circuit board. For the assessment of thermal performance in channel flows, three separate variables are used:channel spacing, row number of the component, and inlet air velocity. The thermal characteristics of a component due to own power and upstream air heated by components were studied. The experimental results were compared with those of numerical solution for various conditions: surface temperature of the components, adiabatic temperature rise, and heat transfer coefficient. The experimental results agree well with the numerical solutions. The study shows that the adiabatic heat transfer coefficient is significantly affected by the inlet velocity in channel flow and less dependent on the channel spacing and row number, except for the case ofH/B=3.3. While reviewing the previous literatures, it is found that a little difference in the correlation between Nu and Re is due to the different geometric ratio of the packaged components.     

Effect of hole shape on the heat transfer in a rectangular duct with perforated blockage walls

Heat transfer coefficients were measured by the improved hue detection based liquid crystal technique in a turbine blade internal cooling passage model with blockage walls. In the experiments, blockages with 9 holes of circular, wide, narrow shapes were used and for the circular shape, the number of hole of 7, 9, and 11 were tested. For all cases, the perforated area was kept same. Results showed that the staggered impingement jets increased heat transfer coefficient, however, pressure drop also increased greatly. Generally, Nusselt number ratio and the thermal performance factor decreased as Reynolds number increased. For all Reynolds numbers tested, the blockage wall with wide holes gave more uniform heat transfer coefficient and higher thermal performance factor. As the number of hole increased from 7 to 11, the distribution of heat transfer coefficient became uniform and the thermal performance factor increased. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

燃气涡轮转子空气冷却的试验研究

本文总结了燃气涡轮转子空气冷却方面的研究成果,它包括：温度场理论计算方法和电热膜拟方法,冷却方案的分析研究以及涡轮叶片热试验等。文中首先扼要地探讨了燃气涡轮冷却问题的主要内容,然后分别阐述了涡轮各个高温零件在稳定工况下温度场的理论解和模拟解,并采用了上述方法对涡轮各种冷却方案进行了分析比较,最后提供了涡轮叶栅放热方面的试验研究成果。     

一种榫头榫槽啮合间隙流动特性的试验研究

对放大3倍的"S"型榫头榫槽啮合间隙的流量系数和沿程损失系数进行了试验研究,讨论了"S"型通道出口马赫数对流量系数的影响以及沿程损失特性。榫头榫槽啮合间隙是截面为"S"型的不规则通道。通过试验可得:"S"型通道的流量系数不仅跟雷诺数有关系,而且跟通道出口马赫数也有关系。在通道出口马赫数小于0.3情况下,"S"型通道的流量系数随着雷诺数的增加而增加,然后趋于稳定;在出口马赫数大于0.3情况下,"S"型通道的流量系数随着马赫数的增加而增加;"S"型通道沿程损失系数随雷诺数的变化曲线中并不存在明显的层流到湍流的转唳点而只有一个转折点。结果对榫头榫槽啮合间隙在涡轮盘的热分析中有重要意义。     

The effect of ambient air condition on heat transfer of hot steel plate cooled by an impinging water jet

It has been observed that the cooling capacity of an impinging water jet is affected by the seasonal conditions in large-scale steel manufacturing processes. To confirm this phenomenon, cooling experiments utilizing a hot steel plate cooled by a laminar jet were conducted for two initial ambient air temperatures (10°C and 40°C) in a closed chamber, performing an inverse heat conduction method for quantitative comparison. This study reveals that the cooling capacity at an air temperature of 10°C is lower than the heat extracted at 40°C. The amount of total extracted heat at 10°C is 15% less than at 40°C. These results indicate the quantity of water vapor, absorbed until saturation, affects the mechanism of boiling heat transfer.     

Analysis of contoured holes produced using STED process

Recent developments in air engines call for more efficient means of turbine blade cooling to have higher power generation for the same unit size with increased inlet air temperature. To allow the turbine to operate at higher temperature, thousands of cooling holes are drilled in turbine blades. In order to increase heat transfer in cooling holes, the present design demands the wall of the cooling passage should be provided with contoured ribs. These irregularities help in inducing turbulence in the flow of cooling air, thereby increasing the rate of heat transfer. For drilling these kinds of contoured deep holes in a turbine blade made of material such as Inconel, the conventional drilling techniques are not suitable. The shaped tube electrolytic drilling (STED) is used to perform the task of drilling contoured holes in difficult-to-machine materials. In the present case, contoured holes are drilled by using two distinct feed rates f ₁ and f ₂ alternately (f ₁ > f ₂) and two types of workpiece materials, namely stainless steel and Inconel superalloy. Experimentally obtained profiles are compared with the profiles derived theoretically from the basic electrochemical machining equations. Quality performance factor is evaluated for the machined holes to find the best hole profile. From the present study, it has been observed that by varying the process parameters (viz., voltage (V), faster feed rate (f ₁), and slower feed rate (f ₂)) during drilling and fixing different step lengths, various types of hole profiles can be generated using STED process.     

Heat transfer and friction factor enhancement in a square channel having integral inclined discrete ribs on two opposite walls

The influence of a gap provided in integral inclined ribs on heat transfer and friction factor enhancement is investigated. Experiments are conducted to obtain heat transfer and friction factor characteristics in a square channel with two opposite in-line ribbed walls for Reynolds numbers from 5000 to 40000. The test section of square channel composed of integral inclined ribs with a gap and has a length-tohydraulic diameter ratio (L/D _h ) of 20. The rib pitch-to-height ratio (p/e) is 10, the rib height-to-hydraulic diameter ratio (e/D _h ) is 0.060 and rib attack angle (α) varies in the range of 30⁰ to 90⁰ (4 steps). The relative gap position (d/W) and relative gap width (g/e) is varied in the range of 1/5–2/3 (5 steps) and 0.5–2.0 (4 steps), respectively. The enhancement in heat transfer and friction factor of this roughened duct was compared with smooth duct and duct roughened with continuous inclined ribs (with no gap) under similar flow condition. Presence of inclined ribs with a gap yields about 4-fold enhancements in Nusselt number and about 8-fold increase in the friction factor compared with smooth duct and about 1.3 times and 1.4 times higher than the case of continuous ribs (without gaps) for the entire range of parameters investigated. Ribs with relative gap width of 1.0 at relative gap position of 1/3 and attack angle of 60° provides maximum heat transfer and friction factor enhancement.