大型动(静)叶调节轴流风机通用性能数学模型的建立及工程应用实践

基于曲面拟合理论,建立了大型动（静）叶调节轴流风机的通用性能数学模型,使用表明：模型精度高,易收敛,通用性强。对模型在工程中的应用进行了实践,给出模型用于风机流量测量和在线监测,风机喘振故障实时预报的具体方法和思路,并以此为基础建立了风机运行工况在线监测和喘振实时预报。图表1参6     

Z-2350-3.8型轴流风机部分静叶转角度对性能的影响

介绍Z-2350-3．8型轴流风机部分静叶转角度对风机性能的影响。试验证明，部分静叶转角度的应用非常有效地改善风机性能，提高了机组的经济性。     

导叶数目对两级动叶可调轴流风机性能的影响

为研究导叶数目对轴流风机性能的影响,文章以某两级动叶可调轴流风机为研究对象,模拟了第一、二级和两级导叶数目变化时的风机性能,并分析了其对风机性能和流场特征的影响。研究结果表明:导叶数目减少后,风机性能整体高于原风机;导叶数目增加后,风机性能未必高于原风机。其中,两级导叶数目均减至21片时的风机性能最佳,在设计工况下,全压提升119 Pa,效率提升0.4%。在此方案下,第二级动叶做功能力和导叶扩压能力均得到提升,导叶数目变化对下游流场有显著影响,而对上游流场影响较小。     

动叶弯曲对双级轴流风机性能和噪声影响的数值研究

动叶周向弯曲是改善轴流风机气动性能和噪声特性的有效方案。以某600 MW机组配套的两级轴流风机为对象,采用Fluent软件对其进行三维数值计算,分析了动叶弯曲对风机性能和气动噪声的影响,及其内流特征的变化。结果表明：动叶正弯可有效提高风机性能,在设计工况点,动叶上半叶高弯角α₂=40°时全压最高提高232 Pa,α₂=20°时效率最大提高0.16个百分点;动叶弯曲可有效改善叶顶处的流动状态,减小流动损失;动叶弯曲使叶轮区总声压级明显降低,相比原结构,α₂=40°时第1级叶轮处总声压级降低5.87 dB,第2级动叶处总声压级降低2.46 dB,主要为单音噪声的降低;综合动叶弯曲对风机性能和噪声的影响,α₂=20°为最优方案。     

静叶倾斜对双级轴流风机性能和噪声影响的数值研究

以某600 MW机组配套的两级轴流风机为研究对象,采用Fluent软件对其进行三维数值计算,研究了静叶倾斜对风机性能和噪声的影响。结果表明：当正倾斜角度15°时,在设计工况风机效率提高0.09%、全压降低0.36%;静叶正倾斜角度大于25°或反倾斜时,风机效率和全压均降低。静叶正倾斜使两级静叶区的总声压级均有所降低,正倾斜15°时在设计工况点第2级静叶区总声压级降低4.4 dB,且倾斜角度越大降噪效果越显著;静叶反倾斜后,第1级静叶噪声基本不变,第2级静叶区总声压级增大2.5 dB。综合分析静叶倾斜对风机性能和噪声的影响,静叶正倾斜15°为最优方案。     

动叶可调式轴流风机的设计

以动叶安装角的改变来实现轴流式风机大幅度的工况变化并维持较高效率,是近代轴流风机的调节方式.本文阐述了这种风机的气动及结构设计并以上海市黄浦江延安路越江隧道风机的设计为实例进行了介绍.     

动态粗粉分离器结构优化与数值模拟

为提高机组运行的稳定性和经济性,将静态粗粉分离器改造成动态粗粉分离器,采用Fluent软件模拟动态粗粉分离器内部气体流场变化和颗粒运动轨迹,研究分析调节动叶轮转速、静叶转角、入口风速对动态粗粉分离器的出粉细度,分离效率,循环倍率,系统阻力等分离特性的影响变化。结果表明:在入口风速17 m/s~19 m/s,动叶轮转速70 r/min,静叶角度45°时,动态粗粉分离器各项运行指标均较理想,动态粗粉分离器处于最佳运行状态,模拟结果能为实际工程应提供了一定理论依据。在现场试验中,动态粗粉分离器各项运行特性也均优于静态粗粉分离器。     

周向弯叶片对动叶可调轴流风机气动性能影响的数值模拟

为了有效改善轴流风机气动和声学性能,以带后置导叶的OB-84型单级动叶可调轴流风机为对象,利用Fluent软件和Ansys有限元分析模块,对比叶片弯曲前后风机的气动性能和内流特征,分析其静力结构特性并进行了噪声预估。结果表明:叶片弯曲后风机全压提高,大体积流量侧气动性能改善效果明显,设计工况点前弯3.0°性能提升最佳,全压和效率分别提升了3%和0.16%;前弯叶片增大了叶根区轴向速度,延缓了叶根区分离流动的出现,提升了叶片中下部做功能力,减小了叶顶区吸力面与压力面间的压差,有效抑制了叶顶泄漏流的产生;弯曲叶片对降低声功率级影响较小,但可缩小高噪声区分布,从而降低风机噪声。     

大型动叶可调轴流风机气动性能数值模拟北大核心

发展了一种1.5D、非定常的计算流体力学(CFD)模型用于快速准确地预测大型动叶可调轴流风机的气动性能。该模型基于求解1.5D的欧拉方程附加源项,其中源项用于模拟叶片排、摩擦和流道变化对气流的影响,并可以通过求解叶片排的进出口速度三角形求得。附面层模型、损失模型和落后角模型用于求解叶片排进出口气动性能参数。根据给定的单级动叶可调风机在设计转速下的实验气动性能曲线,优化模型中的损失系数和落后角系数使得计算结果和实验计算相近。改变动叶可调风机的安装角,本模型预测得到的该风机在安装角变化(+10°,+5°,-5°,-10°)的性能曲线与实验结果误差小于2%,这证明了本模型在经验参数优化后能够较为准确地预测出动叶可调轴流风机的气动性能,具有较强的工程应用价值。     

大型动叶可调轴流风机气动性能数值模拟

发展了一种1.5D、非定常的计算流体力学(CFD)模型用于快速准确地预测大型动叶可调轴流风机的气动性能。该模型基于求解1.5D的欧拉方程附加源项,其中源项用于模拟叶片排、摩擦和流道变化对气流的影响,并可以通过求解叶片排的进出口速度三角形求得。附面层模型、损失模型和落后角模型用于求解叶片排进出口气动性能参数。根据给定的单级动叶可调风机在设计转速下的实验气动性能曲线,优化模型中的损失系数和落后角系数使得计算结果和实验计算相近。改变动叶可调风机的安装角,本模型预测得到的该风机在安装角变化(+10°,+5°,-5°,-10°)的性能曲线与实验结果误差小于2%,这证明了本模型在经验参数优化后能够较为准确地预测出动叶可调轴流风机的气动性能,具有较强的工程应用价值。     

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.     

Influence of tip end-plate on noise of small axial fan

In this work, tip end-plate is used to improve the noise performance of small axial fans. Both numerical simulations and experimental methods were adopted to study the fluid flow and noise level of axial fans. Four modified models and the prototype are simulated. Influences of tip end-plate on static characteristics, internal flow field and noise of small axial fans are analyzed. The results show that on basis of the prototype, the model with the tip end-plate of 2 mm width and changed length achieved best noise performance. The overall sound pressure level of the model with the tip end-plate of 2 mm width and changed length is 2.4 dB less than that of the prototype at the monitoring point in specified far field. It is found that the mechanism of noise reduction is due to the decrease of vorticity variation on the surface of blades caused by the tip end-plate. Compared with the prototype, the static pressure of the model with the tip end-plate of 2 mm width and changed length at design flow rate decreases by 2 Pa and the efficiency decreases by 0.8%. It is concluded that the method of adding tip end-plate to impeller blades has a positive influence on reducing noise, but it may diminish the static characteristics of small axial fan to some extent.     

Effect of cross-flow on the performance of air-cooled heat exchanger fans

In large-scale applications such as arrays of axial fans in air-cooled heat exchanger systems, edge–proximity and wind-induced cross-flow may decrease the flow through some fans by causing the flow to enter them at off-axis angles. In this study, such off-axis inflows were introduced by inserting inlet pipe sections between the plenum chamber of a standard test facility and one of three different scale model test fans of 1542 mm diameter. Fan power consumption turned out to be completely independent of off-axis inflow angle up to 45°. Fan total-to-total pressure rise was found to be independent of off-axis inflow angle, and the decrement in fan pressure rise was equal to the dynamic pressure based on the cross-flow velocity component at the fan inlet. Analysis showed that for model fans to represent the cross-flow behaviour of their prototypes, they should have the same ratio of dynamic pressure to pressure rise, and the same dimensionless characteristic slope at their operating points. The performance of a row of fans operating at off-axis inflow conditions representing a cooling system was well predicted by a simple model assuming that the fans farther from the edges induce cross-flows over the fans closer to the edges.     

An improved prediction model of vortex shedding noise from blades of fans

The main source of the noise of an axial flow fan is the fluctuating pressure field on blade surfaces caused by the shedding of vortices at the trailing edge of blades. An analytical model to predict the vortex shedding noise generated at the trailing edge of blades of axial flow fans was proposed by Lee in 1993. In this model, for mathematical convenience, an idealized vortex street is considered. However, the agreement between the analytical results and the experimental data needs to be improved because of the simplification about the Karman vortex street in the wake of blade. In the present study, a modified model is proposed based on the prediction model by Lee. The boundary layer theory is used to analyze and calculate the boundary layer development on both the pressure and the suction sides of blades. Considering the effect of boundary layer separation on the location of noise source, the predicted overall sound pressure level compares favorably with the experimental data of an axial fan. In the calculation of A-weighted sound pressure level (L_A), considering the effect of static pressure on radiate energy, the predicted broadband noise with the modified model compares favorably with the experimental data of a multiblade centrifugal fan.     

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.     

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.     

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.     

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。     

Computational study of forced air-convection in open-cathode polymer electrolyte fuel cell stacks

A mathematical model for a polymer electrolyte fuel cell (PEFC) stack with an open-cathode manifold, where a fan provides the oxidant as well as cooling, is derived and studied. In short, the model considers two-phase flow and conservation of mass, momentum, species and energy in the ambient and PEFC stack, as well as conservation of charge and a phenomenological membrane and agglomerate model for the PEFC stack. The fan is resolved as an interfacial condition with a polynomial expression for the static pressure increase over the fan as a function of the fan velocity. The results suggest that there is strong correlation between fan power rating, the height of cathode flow-field and stack performance. Further, the placement of the fan - either in blowing or suction mode - does not give rise to a discernable difference in stack performance for the flow-field considered (metal mesh). Finally, it is noted that the model can be extended to incorporate other types of flow-fields and, most importantly, be employed for design and optimization of forced air-convection open-cathode PEFC stacks and adjacent fans.