气冷涡轮级气热耦合非定常数值模拟

采用三维非定常气热耦合模拟的数值方法,对具有冷却结构的单级涡轮进行非定常流动和冷却性能进行研究,通过对非定常流场和固体温度场的分析来探讨冷气对叶片排内流场和固体温度场的影响,指出在非定常状态下,不同的动、静叶相对位置对应不同的气膜出流情况。上游周期性不稳定尾流会造成下游动叶片主流掺入气膜保护层,会造成气膜冷却效率降低。尾迹对叶片前缘的撞击引起瞬间的冲角增大,叶片气动负荷以及温度分布存在一定程度的波动,吸力面前缘受到的干扰更为明显。     

叶片前缘表面气膜冷却的实验研究

燃气轮机叶片前缘处有很多高换热区,其中叶片前缘表面处是最先与高温燃气接触的位置,存在承受较高的热负荷的问题,目前较为常见的解决办法是气膜加冲击冷却。通过实验对比不同吹风比、不同曲率位置气膜冷却排孔的温度分布,得出以下结论:冷却效果以出气孔为起点向下游不断减弱,并且在不同的排孔处,下游减弱的趋势不同;当吹风比M1时,吸力面气膜冷却有效度随吹风比的增加而逐渐增加;当吹风比M1时,气膜冷却有效度随吹风比的增加而减小;下游曲率的增加可以有效地增加气膜冷却效果。     

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。     

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。     

汇聚太阳能流体流速对吸热器温度场和应力场影响

为研究高汇聚太阳能流体流速对管式吸热器的温度场、热应变及热应力场的影响,本文采用蒙特卡洛与有限单元相结合的光热力顺序解耦计算法分析了不同流速下管式吸热器的温度场、热应变及热应力场的分布。计算结果表明管式吸热器的温度场、热应变及等效热应力均随着流体流速的增加而降低。与轴向热应力和径向热应力相比,切向热应力对管式吸热器的等效热应力的贡献比例更大,均匀化温度沿管式吸热器的圆周方向分布是热应力抑制的有效手段之一。     

高热流密度回流式圆盘热沉构形设计中的应力-形变分析

采用圆心回流式微通道圆盘热沉三维模型,基于构形理论,考虑粘性耗散,研究在层流流动范围内质量流率、热流密度和微通道分支数对热沉最大热应力和最大热应变的影响。结果表明:随着质量流率的增大,热沉的最大热应力和最大形变均逐渐降低,但降低效果有所减弱;随着热流密度的增大,热沉的最大热应力和最大形变均近似呈线性增长;在相同质量流率和热流密度条件下,均是微通道分支数越多,最大热应力和最大形变越小,但微通道分支数由6增大到8对最大形变的影响相对较小。所得结果可为微通道圆盘热沉的实际热设计提供理论依据。     

燃气轮机叶片前缘气膜冷却的数值模拟

采用数值模拟方法,对燃气轮机叶片前缘气膜冷却问题进行了数值模拟研究。对比分析了在不同吹风比时,叶片吸力面气膜冷却效果的变化规律以及前缘表面不同位置冷却气膜孔排的下游曲率变化对冷却效果的影响。结果表明:不同冷却排孔的冷却效果向下游呈现出逐渐减弱的趋势,每排气膜孔减弱程度各不相同;当吹风比小于1. 0时,吸力面气膜冷却效果随着吹风比的增大而逐渐明显;当吹风比大于1. 0时,吸力面气膜冷却效果随着吹风比的增大而逐渐减弱。     

井筒自循环热交换基本规律实验研究

本文基于井筒自循环采热原理,设计并搭建了井筒自循环换热模拟实验装置,选择常规的水作为携热流体,开展了局部井筒自循环热交换规律实验研究。研究表明,随采热时间增加,套管周围热储温度、压力波动、井口获得的采热量和平均对流换热系数均迅速降低并逐渐保持稳定,热损失率逐渐增大后趋于稳定,温度沿井筒自上而下逐渐升高,但温度分布曲线逐渐降低。不同时间点下,密度和粘度均随水温升高而降低,采热10 min时,沿井筒温度分布最高,密度和粘度最小,因此流速和雷诺数最大。随时间增加,地热储层通过套管管壁向流体传递的热通量逐渐减小,而油管向油套环空传递的热通量逐渐增加。     

基于响应面模型涡轮叶片冷却性能的数值研究

为了给我国自主研发涡轮叶片提供理论基础,基于试验设计和响应面模型对某型叶片的冷却性能进行了数值研究。对某型涡轮叶片的设计参数进行了试验设计,数值研究了主流出口压力、主流进出口压比、冷气与主流温度比及流量比对叶片表面的无量纲温度分布的影响规律,并根据响应面模型拟合得到了叶片平均无量纲温度的经验公式。结果表明：根据试验设计和响应面模型拟合得到的叶片平均无量纲温度的经验公式有较高的精度;在设计参数范围内,涡轮叶片的平均无量纲温度随着主流出口压力(120～140 kPa)和冷气与主流温度比(0.6～0.7)的增大分别提高了0.57%和2.81%,随着主流进出口压比(1.3～1.5)和冷气与主流流量比(3～8)的增大分别降低了1.14%和3.68%。     

柴油机陶瓷燃烧室壁面的传热

1.热损失的意义关于发动机冷却损失的定义及其对性能的影响,因其测量复杂而难以确切说明,因此经常引起实用上的误解。热流密度q表示在单位时间、单位面积燃烧室内燃气和壁面之间的传热量,用下式表示: q=α_g(T_g-T_w) T_g与T_w分别表示瞬时的燃气温度和壁面温度,α_g表示燃气与固体壁面间的传热系数。     

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.     

Numerical study on the effect of jet spacing on the Swirl flow and heat transfer in the turbine airfoil leading edge region

ABSTRACT

In this paper, flow and heat transfer of a swirl chamber that models an internal cooling passage for a gas turbine airfoil leading edge is studied with numerical simulation. The geometry consists of a circular pipe, and rectangular section inlets that lead inlet flow to impinge tangentially on the circular pipe. The effects of the ratio of jet spacing to swirl chamber radius and Reynolds numbers on swirl cooling performance are investigated. The results indicate how the pressure loss and globally averaged Nusselt number on the swirl chamber wall increase with increases of Reynolds number and the ratio of jet spacing to swirl chamber radius. A Nusselt number correlation on these parameters is suggested. Also shown is how Nusselt numbers on the swirl chamber surface increase with the ratio of jet spacing to swirl chamber radius.     

Numerical Study of Film and Regenerative Cooling in a Thrust Chamber at High Pressure

Numerical study of coupled heat transfer of gas flow with film cooling, chamber wall conduction, and regeneration coolant cooling in the thrust chamber of a liquid rocket engine was performed. A one-dimensional model was adopted for regeneration cooling to couple two-dimensional model simulation in the thrust camber. Numerical results show that the method adopted can simulate the gas flow field well, and can calculate the heat flux through the wall, the wall temperature, and the temperature increase of the coolant quickly. In addition, liquid film cooling can reduce the wall temperature greatly, and decrease the heat flux transferred from the hot gas to the chamber wall.     

Effects of Variable Jet Nozzle Angles on Cross-Flow Suppression and Heat Transfer Enhancement of Swirl Chamber

This paper investigated the effects of variable jetting nozzle angles on the cross-flow suppression and heat transfer enhancement of swirl cooling in gas turbine leading edge. The swirl chamber with vertical jet nozzles was set as the baseline, and its flow fields and heat transfer characteristics were analyzed by 3D steady state Reynolds-averaged numerical methods to reveal the mechanism of cross-flow weakening the downstream jets and heat transfer. On this basis, the flow structure on different cross sections and heat transfer characteristics of swirl chamber with variable jetting nozzle angels were compared with the baseline swirl chamber. The results indicated that for the baseline swirl chamber the circumferential velocity gradually decreased and the axial velocity gradually increased, and the cross-flow gradually formed. The cross-flow deflected the downstream jets and drawn them to the center of the chamber, thus weakening the heat transfer. For swirl chamber with variable jetting nozzle angles, the air axial velocity is axial upstream, opposite to the mainstream, so that the impact effects of cross-flow on the jets were reduced, and the heat transfer was enhanced. Furthermore, with the increase of axial velocity along the swirl chamber, the jetting nozzle angle also gradually increased, as well as the effect of cross-flow suppression, which formed a relative balance. For all swirl chambers with variable jet nozzle angles, the thermal performance factors were all larger than 1, which indicated the heat transfer was enhanced with less friction increment.     

Deterioration in heat transfer of endothermal hydrocarbon fuel

Numerical studies under supercritical pressure are carried out to study the heat transfer characteristics in a single-root coolant channel of the active regenerative cooling system of the scramjet engine, using actual physical properties of pentane. The relationships between wall temperature and inlet temperature, mass flow rate, wall heat flux, inlet pressure, as well as center stream temperature are obtained. The results suggest that the heat transfer deterioration occurs when the fuel temperature approaches the pseudo-critical temperature, and the wall temperature increases rapidly and heat transfer coefficient decreases sharply. The decrease of wall heat flux, as well as the increase of mass flow rate and inlet pressure makes the starting point of the heat transfer deterioration and the peak point of the wall temperature move backward. The wall temperature increment induced by heat transfer deterioration decreases, which could reduce the severity of the heat transfer deterioration. The relational expression of the heat transfer deterioration critical heat flux derives from the relationship of the mass flow rate and the inlet pressure.     

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.     

叶片锯齿前缘控制流动分离的数值研究

针对锯齿前缘结构调控叶片近壁面流场特性,以NACA0018叶片为对象,采用大涡模拟方法研究不同锯齿前缘结构对叶片近壁面流场的影响机制。获得了来流速度为30 m·s^-1、雷诺数为513 440、0°攻角下叶片近壁面流场分布特性。分析了锯齿前缘和叶片前缘和尾缘处压力脉动及分离涡的影响。数值结果表明：对正弦波齿而言,随着振幅的增大,在波谷处的小涡开始向前缘移动,整体上小尺度涡增多,前缘近壁面压力脉动增大,尾缘近壁面压力脉动减小;对叠加波形齿而言,尾迹涡进一步破碎,厚度变薄,叶片表面出现破碎的小尺度涡,在尾缘处叶片压力脉动幅值下降最为明显,且未出现明显的窄带尖峰。     

Numerical simulation of steady state heat transfer in a ceramic-coated gas turbine blade

As gas turbine entry temperature (TET) increases, thermal loading on first stage blades increases and, therefore, a variety of cooling techniques and thermal barrier coatings (TBCs) are used. In the present work, steady state blade heat transfer mechanisms were studied via numerical simulations. Convection and radiation to the blade external surface were modeled for a super alloy blade with and without a TBC. The effects of surface emissivity changes, partial TBC coatings and uncertainties in external heat transfer coefficient were also simulated. The results show that at 1500 K TET, radiation heat transfer rate from gas to an uncoated blade is 8.4% of total heat transfer rate which decreases to 3.4% in the presence of a TBC. The TBC blocks radiation, suppresses metal temperatures and reduces heat loss to the coolant. These effects are more pronounced at higher TETs. With selective coating, substantial local temperature suppression occurs. In the presence of radiation and/or TBC, the uncertainties in convection heat transfer coefficient do not have a significant effect on metal temperatures.     

Prediction of local heat transfer characteristics of dilute gas‐solid flows through an adiabatic,horizontal pipe

The local heat transfer characteristics of gas‐solid flows through an adiabatic, horizontal pipe are numerically studied using the two‐fluid model of Ansys Fluent 15. First, the model is validated with the experimental results available in the literature for the air temperature and average Nusselt number. Then, the local heat transfer characteristics of gas‐solid flows, such as temperature profiles of gas and solid, gas‐solid Nusselt number, logarithmic mean temperature difference, and effectiveness of gas and solid, are studied by changing different parameters (gas velocities 15‐24 m/s; inlet solid loading ratios 0.1‐1; particle diameters 100‐400 µm). It is observed that increasing the particle diameter and inlet gas velocity increases the gas temperature and decreases the solid temperature, increases the logarithmic mean temperature difference, and decreases the thermal effectiveness of gas and solid. However, increasing the solid loading ratio decreases the gas and solid temperatures, decreases the logarithmic mean temperature difference, and increases the thermal effectiveness of gas and decreases the thermal effectiveness of solid. Moreover, increasing the particle diameter decreases the gas‐solid Nusselt number, whereas increasing the solid loading ratio and inlet gas velocity increase the gas‐solid Nusselt number.