燃气轮机燃烧室三维冷态流场数值模拟

本文针对某燃气轮机环管型燃烧室三维冷态流场的数值模拟问题进行了研究。根据该型燃气轮机燃烧室的设计图纸建立真实的三维计算几何模型;在计算中采用SIMPLE算法,k-ε双方程湍流模型,对其进行了冷态空气流场的数值模拟;通过对各处流场分布的分析,特别是对主要区域各关键截面的流动分析,可以判断出燃烧室设计的合理性,为进一步优化燃烧室的结构设计、改善流场结构,并为开展燃烧室热态流场的数值模拟奠定了基础。     

燃气轮机燃烧室流场数值计算研究及分析

对燃气轮机逆流式环形燃烧室,热态三维流场的数值模拟问题进行了研究,建立了三维计算模型,生成了数值计算网格。数值模拟研究表明,改变燃烧室的几个结构参数,可以得到更加合理的流场。通过对关键截面的流动分析,可以判断燃烧室设计的合理性,为进一步优化燃烧室结构设计、改善流场奠定了基础。     

燃气轮机燃烧室内部两相流动数值模拟与结构优化

针对燃气轮机低污染燃烧室内部流动的特殊要求，基于燃烧室完整真实几何结构进行三维的冷态模拟和两相流动模拟，分析内部的流动规律以及原始设计中存在的问题。通过改进燃烧室几何结构，得出更加合理的流场分布，从而指导燃烧室的结构优化设计。改进后的数值模拟结果表明：所采取的改进措施的效果明显，所建立的流动分析系统可以进行燃气轮机燃烧室的优化设计。     

燃气轮机燃烧室内部流场的冷态模拟与优化设计

利用流体分析软件STAR-CD对一个燃气轮机燃烧室的内部流场完整真实的几何结构进行了三维的冷态模拟；得出其内部的流场分布，对其加以分析，找出原设计中存在的问题，并加以改进，得出更加合理的流场分布，从而指导燃烧室的结构设计。改进后的数值模拟结果表明，改进措施的效果是十分明显的，所建立的流动分析系统为燃气轮机燃烧室的优化设计提供了强有力的计算分析工具。     

非下交曲线坐标系数值模拟加力燃烧室湍流两相流燃烧

采用双流体模型对航空发动机加力燃烧室的湍流两相流燃烧过程进行了数值模拟,数值计算方法为非正交曲线坐标下非交错网络的SIMPLE方法,差分网络分区方法生成,计算时对整个流场进行分区迭代直至得到收敛结果。气相化学反应速率用涡旋破碎模型（EBU）,充分考虑两相之间的质量、动量和能量的相互作用,数值模拟结果合理。     

采用热-流耦合方法对火焰筒壁温三维数值模拟

考虑了流场变化对换热的影响,使用热-流耦合方法,对某型燃烧室整个流场、温度场进行完全的数值模拟。该方法对流场和固壁内换热进行耦合计算,得出了三维燃烧室壁温分布。计算中,对完全发展的湍流燃气采用了标准“k-ε”湍流模型,运用DO模型计算了燃气的热辐射,燃烧模型使用涡-耗散模型来计算化学反应速度,固壁材料使用了变比热和变导热系数。数值模拟结果表明流场与固壁相互作用得更充分,能更精确地反映流场和温度场的整个形态,可以模拟出较为合理的流场和温度场分布以及相应的流动换热特性。     

某型涡扇发动机燃烧室三维数值模拟

使用FLUENT对某涡扇发动机环形回流燃烧室进行了冷热态流场的三维数值模拟.比较了Standardk-ε、RNGk-ε、Realizablek-ε三种湍流模型,涡团耗散、平衡PDF两种燃烧模型及两种不同燃油雾化直径的数值模拟结果;比较了考虑火焰筒壁换热、大弯管冷却孔前后的数值模拟结果;分析了燃烧室性能.得出如下结论:R...     

三维贴体坐标系下燃烧室中两相反应流的数值模拟

本文提供了现代航空发动机主燃烧室中三维两相燃烧流场的数值计算方法。气相场在欧拉坐标中用ＳＬＭＰＬＥ算法求解；液相场在拉格朗勒坐标系中用ＰＳＩＣ算法求解。本数值计算程序采用ｋ－ε双方程湍流模型，旋涡破裂湍流燃烧模型，六通量热辐射模型，采用了三维非正交曲线坐标系，压力交错网格。     

燃烧室形状和位置对柴油机缸内空气运动的影响

本文利用多维数值模拟方法，进行了３个柴油机燃烧室方案下缸内三维流场的计算。系统地分析了燃烧室形状和位置对缸内流场的影响。计算表明，挤流和涡流的相互作用将使缸内涡流呈现非对称结构。     

基于数值模拟的燃惰气燃烧室的优化设计研究

惰性气体是一种高效、环保、经济的防、抑爆及消防灭火介质,惰气的来源制约了惰气安全防护技术的研究开发.以一种新型燃惰气燃烧室为研究对象,采用了RNGk-ε双方程模型描述湍流流动,随机颗粒轨道模型追踪燃油颗粒运动,考虑了化学反应动力学机制对燃烧的影响,采用了修正的EBU湍流燃烧模型计算燃烧速率,同时采用了离散坐标法表征辐射传热过程,建立了燃烧室三维气雾两相湍流燃烧模型,对燃烧室流动燃烧特性进行了深入数值模拟研究,模拟结果与实验结果的比较表明了数值模型及数值方法的合理性.在数值模拟的基础上对燃惰气燃烧室进行了优化设计,采用了多种强化燃烧技术.对优化设计燃烧室的数值模拟结果表明设计合理,满足设计要求.研究结果为惰气安全技术的开发设计奠定了基础.     

Reverse flow regions in three-dimensional backward-facing step flow

Laser-Doppler velocity measurements adjacent to the bounding walls of three-dimensional (3-D) backward-facing step flow are performed for the purpose of mapping the boundaries of the reverse flow regions that develop in this geometry (adjacent to the sidewalls, the flat wall and the stepped wall) as a function of the Reynolds number. The backward-facing step geometry is configured by a step height (S) of 1 cm, which is mounted in a rectangular duct having an aspect ratio (AR) of 8:1 and an expansion ratio (ER) of 2.02:1. Results are presented for a Reynolds number range between 100 and 8000, thus covering the laminar, transitional and turbulent flow regimes. The boundaries of the reverse flow regions are identified by locating the streamwise coordinates on a plane adjacent to the bounding walls where the mean streamwise velocity component is zero. The size of the reverse flow regions increases and moves further downstream in the laminar flow regime; decreases and moves upstream in the transitional flow regime; and remains almost constant or diminishes in the turbulent flow regime; as the Reynolds number increases. The spanwise distribution of the boundary line for the reverse flow region adjacent to the stepped wall develops a minimum near the sidewall in the laminar flow regime, but that minimum in the distribution disappears in the turbulent flow regime. Predictions agree well with measurements in the laminar flow regime and reasonably well in the turbulent flow regime.     

Heat transportation by oscillatory flow with steady flow component

This paper deals with heat transportation by an oscillatory flow composed of a sinusoidal oscillatory flow superimposed with a steady flow. Velocity and temperature fields, heat transportation rate, work rate, and heat transportation efficiency were investigated through numerical analysis. Results obtained elucidated that (1) the phase difference between velocity and temperature variation remained the same as that of the sinusoidal reciprocal flow without the use of a steady flow component. (2) In the upstream direction heat was mainly transported by the steady flow component and in the downstream direction transportation was mainly performed by the oscillatory flow component. (3) The heat transportation rate of the present oscillatory flow composed of both steady and oscillatory flow components was less than the arithmetic sum of the rates produced by the steady flow and the sinusoidal oscillatory flow. (4) The heat transportation rate was increased immensely by superimposing the steady flow on the sinusoidal oscillatory flow. (5) Conversely, work done by the present oscillatory flow increased only slightly. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(7): 482–500, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20130     

Dispersed flow film boiling of nitrogen with swirl flow

The heat-transfer characteristics of two-phase film boiling of nitrogen in tubes with tape-generated swirl flow are described. The swirl flow substantially augments the heat transfer and minimizes the thermal non-equilibrium, which is responsible for the relatively poor performance of boilers without twisted-tape inserts. Assuming thermal equilibrium, it is possible to formulate a relatively simple superposition correlation for both evaporation and superheat regions of the once-through boiler. The correlation gives good prediction of wall temperatures along the tube for the entire range of test conditions.     

Experimental investigation of stator flow in diagonal flow fan

Experimental investigations were conducted for the internal flow of the stator of the diagonal flow fan. Comer separation near the hub surface and the suction surface of the stator blade are focused on. At the design flow rate, the values of the axial velocity and the total pressure at stator outlet decrease near the suction surface at around the hub surface by the influence of the comer wall. At low flow rate of 80-90 % of the design flow rate, the comer separation between the suction surface and the hub surface can be found, which become widely spread at 80 % of the design flow rate.     

Numerical simulation of steady flow fields in coiled flow inverter

Flatter velocity profiles and more uniform thermal environments are extremely desirous factors for improved performance in flow reactors and heat exchangers. One means of achieving it in laminar flow systems is to use mixers and flow inverters. In the present study a new device is introduced based on the flow inversion by changing the direction of centrifugal force in helically coiled tubes. The objective of the present study is to characterize flow development and temperature fields in the proposed device made up from the configurations of bent coils. The main mechanism generating the flow is the production of spatially chaotic path by changing the direction of flow using a 90° bend in helical coils (alternating Dean flow). If the direction of centrifugal force is rotated by any angle, the plane of vortex formation also rotates with the same angle. Thus in helical flow a 90° shift in the direction of centrifugal force cause a complete flow inversion. Complete flow fields and thermal fields in helical coil and bent coil configuration were studied using computational fluid dynamics software (FLUENT 6.0). The three-dimensional governing equations for momentum and energy under the laminar flow conditions were solved with a control-volume finite difference method (CVFDM) with second-order accuracy. The flow pattern obtained for the helical coil was in good agreement to those observed by the previous investigators [S.W. Jones, O.M. Thomas, H. Aref, Chaotic advection by laminar flow in twisted pipe. J. Fluid Mech. 209 (1989) 335–357; Ch. Duchene, H. Peerhossaini, P.J. Michard, On the velocity field and tracer patterns in a twisted duct flow. Phys. Fluids 7 (1995) 1307–1317]. The comparison of the flow fields and temperature fields in the helical tube and bent coil configuration are discussed. The bent coil configuration shows a 20–30% enhancement in the heat transfer due to chaotic mixing while relative pressure drop is 5–6%. The results of the present study can be used to model transport processes for developing flows in curved tubes such as chromatographic columns (less axial dispersion [A.K. Saxena, K.D.P. Nigam, Coiled configuration for flow inversion and its effect on residence time distribution. AIChE J. 30 (1984) 363–368]), Chemical reactors (narrower RTD), heat transfer devices, and some biomedical devices.     

Cross-leakage flow between adjacent flow channels in PEM fuel cells

In polymer electrolyte membrane (PEM) fuel cells, serpentine flow channels are used conventionally for effective water removal. The reactant flows along the flow channel with pressure decrease due to the frictional and minor losses as well as the reactant depletion because of electrochemical reactions in the cells. Because of the short distance between the adjacent flow channels, often in the order of 1 mm or smaller, the pressure gradient between the adjacent flow channels is very large, driving part of reactant to flow through the porous electrode backing layer (or the so-called gas diffusion layer)—this cross-leakage flow between adjacent flow channels in PEM fuel cells has been largely ignored in previous studies. In this study, the effect of cross-flow in an electrode backing layer has been investigated numerically by considering bipolar plates with single-channel serpentine flow field for both the anode and cathode side. It is found that a significant amount of reactant gas flows through the porous electrode structure, due to the pressure difference, and enters the next flow channel, in addition to a portion entering the catalyst layer for reaction. Therefore, mixing occurs between the relatively high concentration reactant stream following the flow channel and the relatively low reactant concentration stream going through the electrode. It is observed that the cross-leakage flow influences the reactant concentration at the interface between the electrode and the catalyst layer, hence the distribution of reaction rate or current density generated. In practice, this cross-leakage flow in the cathode helps drive the liquid water out of the electrode structure for effective water management, partially responsible for the good PEM fuel cell performance using the serpentine flow channels.     

Performance Test and Flow Measurement of Contra-Rotating Axial Flow Pump

An application of contra-rotating rotors has been proposed against a demand for developing higher specificspeed axial flow pump.In the present paper,the advantage and disadvantage of using contra-rotating rotorsare described in comparison with conventional type of rotor-stator,based on theoretical and experimentalinvestigations.The advantages are as follows:(1)The pump is inherently designed as smaller sized and atlower rotational speed.(2)A stable head-characteristic curve for flow rate with negative slope appears.(3)As the rear rotor rotational speed is varied as independent control of front rotor,the wider range of highperformance operation is obtained by rear rotor speed control in addition to front rotor speed control.Thedisadvantages are as follows:(1)The structure of double shaft system becomes complex.(2)The pumpperformance is inferior at over flow rate as the rear rotor loading is weakened.(3)The blade rows interac-tion from rear rotor to front rotor more strongly appears.Then the rear rotor design is a key to achievehigher pump performance.Some methods to overcome these disadvantages will be discussed in more detailstoward wider usage of contra-rotating axial flow pump in various industrial fields.     

Experimental investigation of flow friction for liquid flow in microchannels

In this paper, investigations on the liquid flow in microchannels with different experimental methods are presented. The experiments were carried out in channels with hydraulic diameter ranging from 30 μm to 344 μm at Reynolds number ranging from 20 to 4000. Based on the experimental data collected and those available in the literature, comparisons and analysis have been carried out to evaluate the possible phenomena occurring in the liquid flow in microchannels. Results obtained show that characteristics of flow in microchannels agree with conventional behaviors predicted by Navier-Stokes equations in the region of those dimensions tested. In this paper, the detailed explanations on experimental results are discussed.     

Local flow measurements of vertical upward bubbly flow in an annulus

Local measurements of flow parameters were performed for vertical upward bubbly flows in an annulus. The annulus channel consisted of an inner rod with a diameter of 19.1 mm and an outer round tube with an inner diameter of 38.1 mm, and the hydraulic equivalent diameter was 19.1 mm. Double-sensor conductivity probe was used for measuring void fraction, interfacial area concentration, and interfacial velocity, and laser Doppler anemometer was utilized for measuring liquid velocity and turbulence intensity. A total of 20 data sets for void fraction, interfacial area concentration, and interfacial velocity were acquired consisting of five void fractions, about 0.050, 0.10, 0.15, 0.20, and 0.25, and four superficial liquid velocities, 0.272, 0.516, 1.03, and 2.08 m/s. A total of eight data sets for liquid velocity and turbulence intensity were acquired consisting of two void fractions, about 0.050, and 0.10, and four superficial liquid velocities, 0.272, 0.516, 1.03, and 2.08 m/s. The constitutive equations for distribution parameter and drift velocity in the drift-flux model, and the semi-theoretical correlation for Sauter mean diameter namely interfacial area concentration, which were proposed previously, were validated by local flow parameters obtained in the experiment using the annulus.