汽轮机排汽系统优化设计与性能分析

本文将试验设计方法、响应面近似建模方法及优化算法与排汽系统参数化造型程序及CFD求解软件相结合,应用于汽轮机排汽系统优化设计与分析.并以300/600 MW汽轮机低压排汽系统模型为研究对象,在两种入口条件下应用该方法对其进行了气动优化设计.与原始排汽系统相比,优化后扩压性能有较大的改善,验证了本文提出的气动优化设计方法的有效性,同时表明排汽系统入口条件和几何参数都会影响优化结果.     

进口漩流对透平排汽缸内部流动的影响

使用CFD软件CFX数值模拟了不同漩流条件下大功率汽轮机低压排汽系统实验模型内部的复杂三维流动,定义了衡量非轴对称流场周向不均匀程度的周向不均匀系数.通过对不同漩流条件下计算得到的总压损失系数、静压恢复系数、周向不均匀系数以及缸内流场的对比分析,发现来流在不同径向位置处的漩流角对排汽缸内流动有不同的影响,在此基础上提出了能改善排汽缸气动性能的来流切向气流角分布并进行了数值验证分析.     

汽液分离器对两相流引射器制冷系统性能的影响

针对汽液分离效果差的问题,重新设计了应用于两相流引射器制冷系统的汽液分离器,将使用新汽液分离器的两相流引射器制冷系统的性能与原系统进行了比较,分析了汽液分离器对引射器性能及制冷系统性能的影响。实验结果表明:重新设计的汽液分离器分离效果大大改善,对于不同的实验工况条件,采用新设计的汽液分离器的两相流引射制冷系统,主蒸发器制冷量由占总制冷量的21.1%~27.8%,提升到82.2%~87.3%,主蒸发器起到了主要作用;在引射器结构参数相同的条件下,引射器的引射比由0.2~0.46提升到0.56~0.64;采用新设计的汽液分离器系统制冷量和COP均与原系统基本相同。     

水平轴风力机动态来流条件下翼型气动特性的数值分析

动态来流条件下,水平轴风力机的功率输出可增加30%～50%.本文通过量纲分析,确定影响水平轴风力机翼型动态来流条件下气动特性的主要参数为特征频率fr和雷诺数Re.运用CFD方法对NREL S825翼型在不同fr数和Re数条件下,进行了气动特性的对比.结果表明在动态来流条件下,低Re数对翼型特性影响较小,而fr数是影响翼型性能的关键.     

来流马赫数波动对扩压叶栅气动性能的影响

准确地掌握来流马赫数的波动(即不确定性)对扩压叶栅的气动性能的影响对于指导压气机设计具有重要意义。采用非嵌入式混沌多项式方法,从统计学的角度评估了随机来流马赫数对扩压叶栅气动性能的影响,并着重对比分析了不同攻角和不同随机来流马赫数工况下来流马赫数的不确定性对扩压叶栅气动性能的整体影响和随之带来的气动性能的波动影响。研究结果表明,来流马赫数的不确定性的确对叶栅气动性能产生影响:来流攻角偏离设计攻角越多,叶栅的气动性能对来流马赫数的不确定性越敏感,且在叶栅通道中反应较敏感区域的范围及位置均随着攻角的变化而变化;随机来流马赫数越高,叶栅的气动性能对来流马赫数的不确定性越敏感。     

封严腔几何特征对涡轮性能的影响

在涡轮转静叶片排之间喷入冷气可以阻止高温燃气进入盘腔,但是冷气与主流的掺混损失对涡轮气动性能不利。本文采用数值计算的方法,研究了转静叶片排之间封严腔轴向位置和轴向间隙的变化对涡轮性能和端区流动的影响。结果表明,封严出流与主流的剪切作用形成了诱导涡,诱导涡随后发展成为通道涡并占据了端区二次流的主导地位。封严腔轴向位置和轴向间隙的改变使等熵效率和封严效率产生了相反的变化,因此在设计时要兼顾气动性能和冷却要求进行综合考虑。     

时间推进通流气动设计方法的探索和分析

本文在时间推进法与风扇气动设计相结合方面进行了探索,初步形成时间推进通流气动设计方法及相应设计程序。该方法根本上克服了流线曲率法不能解决混合型方程组的困难,能适用于超音来流风扇的气动设计。采用该方法对高负荷亚音来流风扇、超音通流风扇和超音来流风扇进行气动设计,证实了该方法相对流线曲率法具有很大的优越性。     

缘线匹配技术在轴流透平设计中的应用探索

缘线匹配技术是叶轮机非定常气动设计技术,它以叶轮机相邻叶排前、后缘线空间相对位置为非定常设计自由度来进一步提升叶轮机性能,这在叶轮机定常设计框架下是不能考虑的。本文以单级蒸汽透平设计为例对缘线匹配非定常设计技术进行数值研究,初步展示了缘线匹配的应用方法及其设计验证,数值计算结果表明缘线匹配技术为叶轮机非定常气动设计提供了有效的设计自由度。     

两级跨音湿蒸汽离心透平的设计与气动分析

以湿蒸汽为流动工质,利用一维方法,进行了两级跨音湿蒸汽离心透平的气动初步设计,并采用平衡凝结流动模型,对该两级透平进行流道优化设计与性能分析。所设计的离心透平在进汽干度为0.995 kg/kg、压比为10.15的设计工况下,功率为250.62 kW,轮周效率为82.838%。在变工况条件下,通过调节转速、蒸汽干度、进汽压力、进汽温度与出口背压,获得了两级跨音湿蒸汽离心透平的性能变化规律。结果表明:低转速下小膨胀比的透平效率高,高转速下大膨胀比的透平效率高;进汽干度大的透平效率高;随着膨胀比的增大,效率先增大后减小,存在最佳膨胀比对应的极大值。     

两相流引射循环制冷系统性能的数值模拟

文中提出了两相流引射制冷循环系统稳定工作判据,并据此对传统两相流引射制冷循环系统进行了改进,增加了辅助蒸发器以使系统稳定工作.在此基础上,对以R134a为制冷剂的汽液两相流引射制冷循环的系统性能进行了数值模拟,分析了不同工况、不同引射比对系统性能的影响.数值模拟结果表明:在给定冷凝压力和蒸发压力工况下,两相流引射制冷循...     

Experimental investigation of in-duct insertion loss of catalysts in internal combustion engines

Acoustic performance characteristics of catalysts in the exhaust system are important in the development of predictive tools for the breathing system of internal combustion engines. To understand the wave attenuation behavior of these elements with firing engines, dynamometer experiments are conducted on a 3.0L V-6 engine with two different exhaust systems: one with the catalysts on the cross-over pipe, and the other that replaces the catalysts with equal length straight pipes. The instantaneous crank-angle resolved pressure data are acquired at wide open throttle and 500 rpm intervals over the operating range of the engine (from 1000 to 5000 rpm) at various locations in both exhaust systems. The effect of the catalyst is then isolated and discussed in terms of insertion loss at critical locations in the exhaust system. The analysis is presented both in terms of time-domain and order-domain. The predictive capability of a finite-difference based time-domain nonlinear approach is also demonstrated as applied to large amplitude waves in the exhaust system of firing engines.     

大型室内体育场馆火灾烟气充填及排烟措施研究

模拟了大型室内体育场馆火灾烟气的充填过程。对比了不同排烟条件下(自然排烟和机械排烟)烟气沉降过程。数值模拟结果表明,在无排烟情况下,烟气在大空间体育场馆内的温度并不高,但烟气层下降速度很快。对比不同的排烟方式,发现顶棚自然排烟有良好的排烟效果,顶棚机械排烟效果取决于机械排烟速率与自然排烟速率的相对大小。侧壁机械排烟系统只有在烟气蔓延到排烟口以下才有明显的效果,并且在流量大小一定情况下,侧壁排烟口位置和数量对排烟效果没有明显影响。     

三维跨音速压气机叶栅多目标气动优化设计

提出了一种多目标差分进化算法(MDE),典型函数试验结果表明该算法具有优秀的多日标寻优能力,满足多目标气动优化设计的要求.耦合并行多目标差分进化算法、三次B样条曲面造型方法和CFD求解技术,提出了新的轴流式叶轮机械叶栅三维多目标气动优化设计方法.选择等熵效率和总压比为目标函数,完成了NASA Rotor37转子叶栅的多目标气动优化设计.优化后叶栅的气动性能明显提高,表明该方法具有良好的优化性能和应用前景.     

基于进化算法和复合参数化方法的低速翼型优化

针对设计工况为Re=1×106的翼型在2°和8°两种迎角下的气动性能进行综合优化, 提升其在巡航与起飞着陆时的性能。利用气动估算软件Xfoil结合NACA 4位数参数化方法进行翼型初步优化, 缩小优化空间, 减少计算量。通过求解Reynolds平均Navier-Stokes方程的方式进行精确优化, 最后利用Hicks-Henne形函数法对翼型表面施加扰动进行细节优化, 弥补NACA 4位数参数化方法细节表现不足的缺点。实现了2°和8°两种迎角下气动性能普遍提升20%以上的效果, 并发展了一种复合参数化方法下基于改进进化算法的多目标、多步骤气动优化方法。      

The influence of the exhaust system unsteady gas flow and insulation on the performance of a turbocharged diesel engine

A comprehensive digital computer program is used to simulate the unsteady gas flow in the exhaust and inlet systems of a multi-cylinder, turbocharged, medium-high speed, four-stroke diesel engine installed at the authors' laboratory. The simulation assumes one-dimensional, time-varying gas flow in the engine pipes and incorporates numerous realistic fluid dynamic, thermodynamic and heat-transfer features. The characteristic mathematical transformation solution of the gas-flow dynamics partial differential equations is interfaced with First-Law analysis models of the cylinders main chambers and prechambers. The simulation results are compared most favourably against the engine's experimental performance results, which include mean air consumption rate, pressure histories at various locations on the exhaust system, and energy-mean temperature values at the exit of the exhaust system. The simulation results are also utilized for the determination of the various cylinders' exhaust waves intensity, as they are imposed by the design characteristics of the exhaust manifold. The plotting of relevant charts, showing the contour variation of gas pressure, temperature and Mach index against engine crank angle and pipe length, aids the correct interpretation of the observed behaviour. The detailed simulation of the fluid dynamic and heat-transfer fields in the engine exhaust system, permits an interesting parametric study of the influence of the degree of insulation of the exhaust system on the energy and exergy (availability) content of the exhaust gases before the turbocharger turbine, by coupling the above First-Law with Second-Law analysis concepts.     

考虑来流角变化影响的叶栅稳健性优化设计

进、出口边界流动扰动是叶轮机械中一种典型的不确定性因素,对叶片气动性能产生重要影响.开展考虑边界流动扰动影响的叶片稳健性气动优化设计(RADO)研究,对提高叶片的平均气动性能及气动稳健性具有重要意义,首先介绍叶片RADO的基本原理、实现方法及关键问题.之后开展基于自适应非嵌入式多项式混沌模型的某型跨音速涡轮叶栅来流角不...     

A hybrid approach for aeroacoustic analysis of the engine exhaust system

This paper presents a new hybrid approach for prediction of noise radiation from engine exhaust systems. It couples the time domain analysis of the engine and the frequency domain analysis of the muffler, and has the advantages of both. In this approach, cylinder/cavity is analyzed in the time domain to calculate the exhaust mass flux history at the exhaust valve by means of the method of characteristics, avoiding the tedious procedure of interpolation at every mesh point and solving a number of equations simultaneously at every junction. This is done by making use of an interrelationship between progressive wave variables of the linear acoustic theory and those of the method of characteristics. In this approach, nonlinear propagation in the exhaust pipe is neglected and free expansion is assumed at the radiation end of the exhaust pipe. In the case of a muffler proper, expansion from the exhaust pipe into the first chamber is assumed to be a free expansion. Various results of this approach are compared with those of the method of characteristics and the classical acoustic theory, and various peaks and troughs in insertion loss curves are analytically validated.     

Design and Performance Evaluation of Low‐Volume PM2.5 Inlet for Analyzing Chemical Composition

A new PM_2.5 inlet, based on the particle cup impactor configuration, was designed for sampling fine particles smaller than 2.5 μm in aerodynamic diameter and for operating at a flow rate of 5 l/min, as the devices, which are used to analyze the chemical composition of the particles, have good efficiency only at low‐volume flow rates. The performance of the inlet was evaluated in a test chamber, and the optimum dimensions of the particle cup impactor were determined by varying the nozzle‐to‐cup distance. Additional experiments covering flow rates between 3 and 10 l/min with particle sizes between 0.8 and 5.0 μm were carried out in the test chamber. The performance indicated that a nozzle‐to‐cup distance of 1.1 mm would yield a sharp size cutoff. The results from the tests showed that the inlet had a cutoff size of 2.55 μm in aerodynamic diameter at a flow rate of 5 l/min.     

钝尾缘翼型非定常气动特性及机理

钝尾缘翼型气动特性受到尾涡脱落的影响,在翼型DU 91-W2-250的基础上对称加厚得到了新钝尾缘翼型DU91-W2-250_6,利用密网格进行了非定常气动特性的数值研究。在各个攻角下钝尾缘翼型气动特性都具有周期性的特点,具体的波动特征如波动幅值及周期等则受脱落涡的大小、脱落位置及尾迹宽度的影响,而升力系数波峰、波谷则分别出现在顺时针涡及逆时针涡脱落的时刻。     

Expansion-chamber muffler for impulse noise of pneumatic frictional clutch and brake in mechanical presses

A compound expansion-chamber muffler, which consists of a sound absorbing chamber and a switch valve, the chamber integrating structural features of impedance muffler and micropunch plate muffler, is proposed to diminish impulse exhaust noise of pneumatic friction clutch and pneumatic friction brake (PFC/B) in mechanical presses. The structure decreases the impulse exhaust noise of PFC/B over 30 dB(A). A one-dimensional flow model is applied to study the aerodynamic characteristics of compound exhaust process of the single acting cylinder and muffler because the exhaust time is a critical factor for application of muffler in PFC/B. The volume of sound absorbing chamber is found to be an important design parameter to minimize the exhaust resistance of pneumatic cylinder. Experiments are also conducted to validate analytical results. Then the effects of diameter of exhaust ducts and volume of muffler on the exhaust time are discussed in detail. The proposed one-dimensional computational method, which considers the coupling of air-flow field and sound field, gives satisfactory results for the preliminary design of an expansion-chamber muffler. This method has been applied to an existing model HKM3-40MN to reduce its impulse noise.