Effect of the uneven circumferential blade space on the performance of small axial flow fan

Effects of the uneven circumferential blade space on static characteristics and aerodynamic noise of a small axial flow fan are studied in this work.The blade angle modulation is adopted to design a series of unequally spaced fans,which have different maximum of modulation angular displacement.The steady flow is simulated by the calculations of Navier-Stokes equations coupled with RNG k-epsilon turbulence model,while the unsteady flow is computed with large eddy simulation.According to theoretical analysis,a fan with a maximum of modulation angular displacement of 6° is regarded as the optimal unequally spaced fan.The experiment of static characteristic is carried out in a standard wind tunnel and the aerodynamic noise of both fans is tested in a semi-anechoic room.Then,performances of the optimal unequally spaced fan are compared with those of the prototype fan.The results show that there is reasonable agreement between the simulation results and the experimental data.It is found that the discrete noise of the optimal unequally spaced fan is lower than that of the prototype fan at the near field monitoring point.This can be explained that the total pressure fluctuation of the optimal unequally spaced fan is much more regular than that of the prototype fan.     

Numerical and experimental study on aerodynamic performance of small axial flow fan with splitter blades

To improve the aerodynamic performance of small axial flow fan, in this paper the design of a small axial flow fan with splitter blades is studied. The RNG k-ε turbulence model and SIMPLE algorithm were applied to the steady simulation calculation of the flow field, and its result was used as the initial field of the large eddy simulation to calculate the unsteady pressure field. The FW-H noise model was adopted to predict aerodynamic noise in the six monitoring points. Fast Fourier transform algorithm was applied to process the pressure signal. Experiment of noise testing was done to further investigate the aerodynamic noise of fans. And then the results obtained from the numerical simulation and experiment were described and analyzed. The results show that the static characteristics of small axial fan with splitter blades are similar with the prototype fan, and the static characteristics are improved within a certain range of flux. The power spectral density at the six monitoring points of small axial flow fan with splitter blades have decreased to some extent. The experimental results show sound pressure level of new fan has reduced in most frequency bands by comparing with prototype fan. The research results will provide a proof for parameter optimization and noise prediction of small axial flow fans with high performance.     

汽轮机低压缸进汽结构变流量工况气动性能的研究

为了探究传统轴向分流和新型环形空腔两种出口导流形式对一型进汽结构变流量工况下气动性能的影响,采用全三维数值模拟的方法对分别带有两种出口导流形式的进汽结构进行研究,并通过分析出口气动参数变化规律,获得二者的变流量性能特性.结果表明:二者在流动损失方面无明显差别,但带有环形空腔出口导流形式的进汽结构在出口气流角均匀度和马赫...     

Effect of Guide Vanes on the Performance of a Variable Chord Self—Rectifying Air Turbine

INTRODUCTIONWiththeconventionalenergyresourceslikelytogetexhaustedinafewdecades,theinexhaustiblesourcesofenergyhavetotaketheirplace.Alternateenergyfromtheoceanisattractingtheattelltionoftheresearchersinrecentyearsduetoitsperennialavailabilityandminimumhealthhazards.Ofthemanypossibleformsofoceanenergy,waveenergyispromising.Waveenergyisanalternateformenergy,whichispollutantfreeandinnearfutureitislikelytobeeconomicallyviable.Countrieswhicharesurroundedbyseaandpossessremotelysituatedislandcom…     

基于CFD的轴流泵后置导叶水力性能分析

为了解轴流泵后置导叶的水力性能,基于RNG湍流模型,采用计算流体动力学CFD软件Fluent,应用SIMPLIEC算法对轴流泵模型装置全流道进行了数值模拟,分析了四种不同流量下导叶体的内部流动特性,研究了导叶的水力性能。结果表明,导叶的水力损失随流量的增加先减小后增大;在设计流量处导叶水力损失最小,导叶压力转换能力最好;小流量下叶轮进出口处水流流态紊乱,导叶流道内出现漩涡回流,是导致导叶水力损失较大的主要原因;大流量下叶轮出口水流轴向速度较大,水流导叶进口边撞击将导致导叶体水力损失增加,水力性能下降。     

Unsteady flow condition of contra-rotating small-sized axial fan

Small-sized axial fans are used as air cooler for electric equipments.But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices.Therefore,higher rotational speed design is conducted,although,it causes the deterioration of efficiency and the increase of noise.Then,the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of performance.In the case of contra-rotating rotors,it is necessary to design the rotor considering the unsteady flow condition of each front and rear rotor.In the present paper,the fan performance of the contra-rotating small-sized axial fan with 100mm diameter at a designed and a partial flow rates is shown,and the unsteady flow conditions at the inlet and the outlet of each front and rear rotor are clarified with unsteady numerical results.Furthermore,the relation between the performance and the unsteady flow condition of the contra-rotating small-sized axial fan is discussed and the methods to improve the performance are considered.     

Automatic efficiency optimization of an axial compressor with adjustable inlet guide vanes

The inlet attack angle of rotor blade reasonably can be adjusted with the change of the stagger angle of inlet guide vane (IGV); so the efficiency of each condition will be affected. For the purpose to improve the efficiency, the DSP (Digital Signal Processor) controller is designed to adjust the stagger angle of IGV automatically in order to optimize the efficiency at any operating condition. The A/D signal collection includes inlet static pressure, outlet static pressure, outlet total pressure, rotor speed and torque signal, the efficiency can be calculated in the DSP, and the angle signal for the stepping motor which control the IGV will be sent out from the D/A. Experimental investigations are performed in a three-stage, low-speed axial compressor with variable inlet guide vanes. It is demonstrated that the DSP designed can well adjust the stagger angle of IGV online, the efficiency under different conditions can be optimized. This establishment of DSP online adjustment scheme may provide a practical solution for improving performance of multi-stage axial flow compressor when its operating condition is varied.     

Effect of guide vanes on the performance of a self-rectifying air turbine with constant and variable chord rotors

A Wells turbine is a self-rectifying air flow turbine capable of converting pneumatic power of the periodically reversing air stream in Oscillating Water Column into mechanical energy. The Wells turbine has inherent disadvantages; lower efficiency, poorer starting characteristics, higher axial force and low tangential force in comparison with conventional turbines. Guide vanes before and after the rotor suggest a means to improve the tangential force, hence its efficiency. Experimental investigations are carried out on a Wells turbine with the constant chord and variable chord blade rotors fitted with inlet and outlet guide vanes to understand the aerodynamics. Experiments were also conducted for the above said rotors with various stagger angles to validate the design stagger angle. In addition, the starting and running characteristics of the rotors have been studied and compared with the case without guide vanes. Studies were done at various flow coefficients covering the entire range of flow coefficients over which the turbine is operable. The efficiency, starting characteristics of the turbines with guide vanes have improved when compared with the respective turbines without guide vanes.     

Simulation and experiment research of aerodynamic performance of small axial fans with struts

Interaction between rotor and struts has great effect on the performance of small axial fan systems.The small axial fan systems are selected as the studied objects in this paper,and four square struts are downstream of the rotor.The cross section of the struts is changed to the cylindrical shapes for the investigation:one is in the same hydraulic diameter as the square struts and another one is in the same cross section as the square struts.Influence of the shape of the struts on the static pressure characteristics,the internal flow and the sound emission of the small axial fans are studied.Standard K-ε turbulence model and SIMPLE algorithm are applied in the calculation of the steady fluid field,and the curves of the pressure rising against the flow rate are obtained,which demonstrates that the simulation results are in nice consistence with the experimental data.The steady calculation results are set as the initial field in the unsteady calculation.Large eddy simulation and PISO algorithm are used in the transient calculation,and the Ffowcs Williams-Hawkings model is introduced to predict the sound level at the eight monitoring points.The research results show that:the static pressure coefficients of the fan with cylindrical struts increase by about 25%compared to the fan with square struts,and the efficiencies increase by about 28.6%.The research provides a theoretical guide for shape optimization and noise reduction of small axial fan with struts.     

仿生轴流风机气动噪声特性的实验研究

针对轴流风机工作时产生的气动噪声问题,运用仿生学原理对某轴流风机叶轮进行了仿生改型设计,分别得到了尾缘锯齿式单结构仿生叶轮的轴流风机和前缘波齿、尾缘锯齿及表面脊状三结构耦合仿生叶轮的轴流风机。对两类风机以及原型风机进行了气动与噪声实验,获得了风机的气动性能与辐射噪声的频谱特性。测试结果表明：两类仿生风机的全压在全流量范围内均有不同程度的下降,最高下降达27%,但尾缘锯齿风机可以提高中小流量工况下的效率,而三结构耦合仿生风机效率低于原型风机;两类仿生风机产生的辐射噪声A声级均低于原型光滑叶轮风机,且尾缘锯齿风机降噪效果优于耦合仿生风机,并且比A声级最大降噪值为1.58 dB;尾缘锯齿沿展向的分布长度越长,效率越高,降噪效果也越佳。     

Study of unsteady flow simulation of backward impeller with non-uniform casing

The flow characteristics of the centrifugal fans with different blade outlet angles are basically discussed on steady and unsteady simulations for a rectangular casing fan. The blade outlet angles of the impellers are 35° and 25° respectively. The unsteady flow behavior in the passage of the impeller 35° is quite different from that in the steady flow behavior. The large flow separation occurs in the steady flow field and unsteady flow field of the impeller 35°, the flow distribution in the circumferential direction varies remarkably and the flow separation on the blade occurs only at the back region of the fan; but the steady flow behavior in the impeller 25° is almost consistent with the unsteady flow behavior, the flow distribution of the circumferential direction doesn't vary much and the flow separation on the blade hardly occurs. When the circumferential variation of the flow in the impeller is large, the steady flow simulation is not coincident to the unsteady flow simulation.     

两级动叶可调轴流风机内流特征的数值模拟

采用Fluent软件对某600 MW机组配套的两级动叶可调轴流一次风机进行了全三维定常数值模拟,分析了风机第一、第二级叶轮内流特征和动叶安装角对风机性能的影响.结果表明：第二级叶轮出口总压整体呈现高压区和次高压区交替分布的特征,且比第一级叶轮的对称性差;第一、第二级叶轮叶片压力面、吸力面的总压和静压分布规律相似;第二级叶轮叶片压力面和吸力面相应位置上的静压值均大于第一级叶轮叶片;随着动叶安装角的增大,第一、第二级叶轮的总压升系数和静叶的扩压系数均增大,且第二级叶轮大于第一级叶轮,表明第二级叶轮的做功能力和静叶的扩压能力均比第一级叶轮的大.     

尾流激振对转子叶片振动应力影响试验研究

利用一台单级风扇试验件,通过对零级导叶尾流参数和转子叶片振动应力的测量,研究了尾流激振强度及叶片振动应力的变化特性,分析了零导安装角和零导与转子之间的轴向间距对转子叶片振动应力的影响。试验结果表明:等转速线上随工况点向失速边界移动时,零导总压损失系数急剧上升,转子叶片振动应力不断增大;打开零导安装角或减小零导与转子之间的轴向间距均能增大下游转子叶片的振动应力。     

淮阴抽水站可逆式轴流泵装置性能研究

为了满足泵站抽水发电可逆运行的要求,应用Fluent软件,利用CFD数值模拟技术模拟了不同方案的流道内流场,分析了叶片翼型、叶片个数、轮毂比、导叶数量、导叶距转轮出口距离对水泵性能的影响,得到了最优的水力模型装置,即转轮叶片数为4、最优安放角为0°、轮毂比为0.40、导叶数为5、导叶进口边与转轮出口距离为268mm时,转轮具有更好的做功能力,且装置全流道效率和转轮效率达到最大值。根据数值模拟计算设计出的轴流式水泵水轮机转轮特性与模型试验结果比较接近,具备实际应用价值,不仅可节约新转轮的开发成本,且缩短了研发时间。     

船用燃气轮机变几何动力涡轮大攻角流动特性的三维数值模拟

采用三维数值模拟技术,研究了可调导叶转动导致变几何动力涡轮气动性能变化的流场机理。结果表明,在较小的转角范围内,采用大转折角设计的可调导叶使涡轮处于大攻角运行。在大正攻角或大负攻角下可调导叶级动叶栅流道内的三维分离流场结构及其产生机理有很大差异,而且大正攻角造成的吸力面分离流动更使整个涡轮的效率显著地下降。通过系统的机理分析,提出可调导叶宜采用较小转折角的后部加载叶型,而变几何动力涡轮可调导叶级动叶栅要采用较大负冲角的气动设计原则。     

中压进汽腔的流场数值模拟比较

通过数值模拟计算,对中压对称进汽和切向进汽两种结构的流场进行了分析比较,结果表明,单一切向进汽腔的总压损失更小,出口汽流角的周向分布均匀度更好。更进一步,为整体评估中压进汽腔的流场以及对叶片级的流动影响,对中压进汽腔及第1级叶片的整体流体域流场情况进行了分析比较,结果表明,采用大几何角静叶的切向进汽腔气动性能最优;当采取切向进汽腔时,需合理选择第1级静叶几何角并耦合计算,才能实现进汽腔的气动优化。     

一级半轴流式透平级内部若干非定常流动现象的试验研究

设计研制了具有亚音速透平高压级气动特性的一级半轴流式试验透平,采用试验方法对时序效应、叶栅壁面非定常静压幅频特性以及动叶出口非定常速度场进行了研究。结果表明:时序效应具有改善轴流式透平气动性能的潜力;动、静叶排压力有势场干涉引发的基频信号和上游静叶尾迹片段引发的两阶倍频信号,构成了第二列静叶壁面静压非定常分量的基本频率特征,其间还伴随高达六阶的倍频信号,主要由动叶尾缘高频脱落的涡街扰动产生;尚未完成掺混的第一列静叶尾迹片段出现在动叶出口,由其引发的负射流显著改变了动叶出口局部位置处的气流偏转角。     

Experimental studies on effect of guide vane shape on performance of impulse turbine for wave energy conversion

This paper presents the experimental results of effect of guide vane shape on performance of an impulse turbine for wave energy conversion. Two types of guide vanes are considered in the present study: two-dimensional (2D) guide vanes and three-dimensional (3D) guide vanes. The previous investigations by the authors revealed that the 2D guide vanes cause large recirculation zones at leading edge of downstream guide vanes, which affect the performance of turbine considerably. In order to improve the performance of turbine, three-dimensional guide vanes are designed based on free-vortex theory. Detailed aerodynamic and performance tests have been conducted on impulse turbine with the two types of guide vanes. The experiments have been conducted under various inlet conditions such as steady, sinusoidal and random (real Sea) flows. From the results, it was proved that the efficiency of impulse turbine has been improved for 4.5% points due to 3D guide vanes. The hysteric characteristic has been noticed from the experimental results of impulse turbine with sinusoidal and random flow inlet conditions. Furthermore, it was investigated that the performance of turbine is considerably more during deceleration of inlet flow than the acceleration in a half cycle of sinusoidal wave.     

A Simple Method of Flow Field Diagnosis in Multistage Axial Flow Compressors

ＡＳｉｍｐｌｅＭｅｔｈｏｄｏｆＦｌｏｗＦｉｅｌｄＤｉａｇｎｏｓｉｓｉｎＭｕｌｔｉｓｔａｇｅＡｘｉａｌＦｌｏｗＣｏｍｐｒｅｓｓｏｒｓＪｉｅＬｉｕ；ＤａｊｕｎＹｅ（ＤｅｐａｒｔｍｅｎｔｏｆＴｈｅｒｍａｌＥｎｇｉｎｅｅｒｉｎｇ，ＴｓｉｎｇｈｕａＵｎｉｖｅｒ...     

Endwall heat transfer and aerodynamic performance of bowed outlet guide vanes (OGVs) with on- and off-design conditions

ABSTRACT

In this study, numerical simulations are conducted to investigate the effects of bowed outlet guide vanes (OGVs) on endwall heat transfer and aerodynamic performance. Both on- and off-design conditions are studied. For bowed vanes, the bowed angle varies from 10° to 40° and the normalized bowed height ranges from 0.1 to 0.3. Results are included for Nusselt number distributions on the endwall, the energy losses, the yaw angles, and near-wall flow structures. For the convenience of comparison, the straight vane is also studied as a baseline. It is found that the bowed vanes can effectively reduce the endwall heat transfer. Among the tested parameters, a bowed angle of 40° and a normalized bowed height of 0.3 provide the best-controlled heat transfer for both the on- and off-design conditions. However, the bowed vanes have different effects on the energy losses and the yaw angles depending on the operating conditions. For the on-design condition with the inlet angle of 30° (the incidence angle is 0°) and the off-design condition with the inlet angle of 0°, the bowed vanes do not significantly increase the energy losses and yaw angles, whereas for the off-design condition with the inlet angle of ?30°, significant changes are observed.