Numerical Simulation of Axial Inflow Characteristics and Aerodynamic Noise in a Large-Scale Adjustable-Blade Fan

Numerical simulation are conducted to explore the characteristics of the axial inflow and related aerodynamic noise for a large-scale adjustable fan with the installation angle changing from−12°to 12°.In such a range the maximum static(gauge)pressure at the inlet changes from−2280 Pa to 382 Pa,and the minimum static pressure decreases from−3389 Pa to−8000 Pa.As for the axial intermediate flow surface,one low pressure zone is located at the junction of the suction surface and the hub,another is located at the suction surface close to the casing position.At the outlet boundary,the low pressure is negative and decreases from−1716 Pa to−4589 Pa.The sound pressure level of the inlet and outlet noise tends to increase monotonously by 11.6 dB and 7.3 dB,respectively.The acoustic energy of discrete noise is always higher than that of broadband noise regardless of whether the inlet or outlet flow surfaces are considered.The acoustic energy ratio of discrete noise at the inlet tends to increase from 0.78 to 0.93,while at the outlet it first decreases from 0.79 to 0.73 and then increases to 0.84.

Unsteady Flow Condition between Front and Rear Rotor of Contra-Rotating Small Sized Axial Fan

Contra-rotating small-sized axial fans are used as cooling fans for electric equipment. In the case of the contra-rotating rotors, the blade row distance between front and rear rotors is a key parameter for the performance and stable operation. The wake and potential interference occur between the front and rear rotors and leakage flow from the front rotor tip influences on the flow condition of the rear rotor near the shroud when the blade row distance is small. Therefore, it is important to clarify the flow condition between front and rear rotors. The fan static pressure curves were obtained by the experimental apparatus and the numerical analysis was also conducted to investigate the internal flow between front and rear rotors. The leakage flow from the front rotor tip reaches the leading edge of the rear rotor when the blade row distance is small as L = 10 mm and the pressure fluctuations at the leading edge of the rear rotor tip becomes larger than those at other radial positions. In the present paper, the vorticity contour between front and rear rotors is shown and pressure fluctuations related to the leakage flow from the front rotor is investigated using the numerical analysis result. Then, suitable blade row distance for the contra-rotating small sized axial fan is discussed based on the internal flow condition.

Design of Half-Ducted Axial Flow Fan Considering Radial Inflow and Outflow

Half-ducted fan and ducted fan have been designed and numerically analyzed for investigating the radial flow effect on the overall performance and the three dimensional flow field in design. Based on quasi-three dimensional flow theory, the meridional flow was calculated by adopting the radial balance equations, while the calculation of the blade to blade flow was obtained by 2D cascade data with the correction by a potential flow theory. Two types of axial flow fan were designed. One is the full ducted case as if it was in the straight pipe and another is the half-ducted case with the radial inflow and outflow. The previous experimental results of authors were used to decide the inclinations of both the inflow and outflow. And the circular arc blade with equal thickness was adopted. The numerical results indicate that both of the designed fans can reach the specified efficiency and also the efficiency surpasses more than 11%. Furthermore, the static pressure characteristic of half-ducted fan is much better than that of ducted fan. In comparison of the three dimensional internal flow of these two fans, the improvement of the flow angle at inlet and outlet, the distributions of velocity in the flow field and the pressure distributions on the blade surfaces can be achieved more successfully in accordance with the design intension on consideration of flow angle in design. The conclusion that half-ducted design with considering radial inflow and outflow is feasible and valid in comparison with ducted design for axial flow fans has been obtained at the end of the paper.

Performance and Internal Flow of Contra-Rotating Small-Sized Cooling Fan

High pressure and large flow rate small-sized cooling fans are used for servers in data centers and there is a strong demand to increase its performance because of increase of quantity of heat from servers. Contra-rotating rotors have been adopted for some of high pressure and large flow rate cooling fans to meet the demand. The performance curve of the contra-rotating small-sized cooling fan with 40 mm square casing was investigated by an experimental apparatus and its internal flow condition was clarified by the numerical analysis. The fan static pressure of the front rotor was extremely low and it increased significantly at the rear rotor. The uniform flow was achieved at the inlet of the rear rotor because of the special shape of the casing between the front and rear rotors. On the other hand, the tip leakage flow was large enough to influence on the main flow of the test cooling fan by the design specification of high pressure with compact rotor diameter.

轴流式对旋除尘风机的结构优化与性能研究

为了提高轴流式对旋除尘风机的除尘性能,研究各个参数相互之间的干扰,对其一级叶轮叶片数量、二级叶轮叶片数量、一二级叶轮距离、风筒直径和叶轮至进口距离这5个主要的结构参数进行优化改进和参数匹配。采取正交试验法,通过FLUENT对各结构参数下的风机除尘过程进行模拟仿真试验,分析风机除尘作业时内部流场和进出口速度、压力分布情况,给出综合评价风机除尘性能公式,得到轴流式对旋除尘风机各个参数的影响程度由大到小分别为一级叶轮叶片数量、风筒直径、二级叶轮叶片数量、一二级叶轮距离、叶轮至进口距离,并通过计算分析得到风机结构的最佳参数组合。

基于热负荷均匀分配原则的直接空冷系统轴流风机转速灵活调节策略

在直接空冷电站中,轴流风机功耗占厂用电比例较高。为获得更为高效的风机运行调整策略,以某典型2´600 MW直接空冷机组为例,基于热负荷均匀分配原则,采用数值模拟方法,研究轴流风机转速灵活调节策略。获得不同环境温度和风速条件下,各轴流风机转速分布规律以及通过空冷凝汽器单元的冷却空气质量流量分布规律。最终,计算得到不同环境气象条件下不同轴流风机转速调节策略风机总功耗变化规律。结果表明,基于热负荷均匀分配原则的轴流风机转速灵活调整策略明显优于轴流风机转速整体调节策略,结果可为直接空冷机组优化运行和深层次节能提供参考。

对旋轴流通风机叶轮内不可逆能量损失机理

随着节能降耗成为当今世界的迫切需要,提高通风机能量转换效率越来越受到重视,已成为通风领域内关键问题。掌握叶轮内不可逆能量损失演化机制是实现能量高效转化的前提与基础,但目前尚缺乏针对叶轮内不可逆能量损失机理方面的研究。为此,以对旋轴流通风机为研究对象,采用数值模拟和实验方法获得了不同流量工况下通风机内部流场。基于熵产理论,建立了通风机叶轮内不可逆能量损失理论模型,明确了叶轮内不可逆能量损失与空间流场参数的内在关系,实现了叶轮内不同类型能量损失的定量分析,结合叶轮内流动特征,明确了能量损失空间演化规律和产生原因。研究结果表明,熵产方法计算叶轮内不可逆能量损失是可靠的,直接黏性耗散损失和壁面摩擦损失是能量损失的重要组成部分,而湍流耗散则是引起能量损失的主要原因,达到总能量损失的60%~80%;对于前级叶轮,湍流耗散引起的能量损失在1.0Q_(BEP)流量工况(Q_(BEP)为最优工况流量)达到最小,而后级叶轮能量损失随流量的降低而增大。能量损失主要集中在Span=0.6~1.0(Span为叶展方向轮毂至机壳的无量纲距离)区域,在1.0Q_(BEP)工况达到总能量损失的70%;叶顶间隙泄漏流和叶片前缘溢流引起的螺旋旋涡、叶轮内回流、叶片压力面和吸力面流动分离以及叶片后缘尾迹都将导致能量损失产生,其中流动分离和尾迹引起的高能量损失区域较小,能量损失相对有限,而旋涡和回流显著影响叶轮内流体流动,最终导致叶顶附近区域出现大量能量损失。

煤矿对旋轴流通风机的振动响应特性分析

为进一步探究煤矿对旋轴流通风机设备可能的优化路径,从振动响应分析的角度着手,对煤矿轴流通风机流场进行仿真分析,通过分析压力-时间变化情况,探究不同轴向间隙和径向间隙对煤矿对旋轴流通风机的振动响应特征。并根据分析结果,确定了较为合理的轴向间隙与径向间隙取值范围,以期为后续的对旋轴流通风机优化设计提供更多参考借鉴。

径向间隙对煤矿对旋轴流通风机性能的影响分析

为进一步探究煤矿对旋轴流通风机径向间隙对风机性能的影响,以某小型煤矿企业的局部对旋轴流通风机为研究对象,对其进行建模与仿真分析,确定了稳态与非稳态两种情况下,不同径向间隙对风机性能的整体影响作用.结果显示,当降低径向间隙时,有助于增加风机压头和对气流做功,但与此同时,较小的径向间隙也将导致风机的气动噪声问题更为突出,对风机流量也将产生一定的不利影响,由此确定将径向间隙控制在叶片直径的0.8%~1%范围较为合理,以此为后续的煤矿对旋轴流通风机径向间隙优化设计工作提供参考借鉴.

Numerical investigation on the cluster effect of an array of axial flow fans for air-cooled condensers in a power plant

The aerodynamic behavior of tens of axial flow fans incorporated with air-cooled condensers in a power plant is different from that of an individual fan.Investigation of the aerodynamic characteristics of axial flow fan array benefits its design optimization and running regulation.Based on a representative 2600 MW direct-dry cooling power plant,the flow rate of each fan and the overall flow rate of the fan array are obtained in the absence of ambient wind and at various wind speeds and directions,using CFD simulation.The cluster factor of each fan and the average cluster factor of the fan array are calculated and analyzed.Results show that the cluster factors are different from each other and that the cluster effect with ambient wind is significantly different from the cluster effect with no wind.The fan at the periphery of the array or upwind of the ambient wind generally has a small cluster factor.The average cluster factor of the array decreases with the increasing wind speeds and also varies widely with wind direction.The cluster effect of the axial flow fan array can be applied to optimize the design and operation of air-cooled condensers in a power plant.

轴向间距对矿用旋风机旋转失速性能的影响

矿用对旋风机在小流量工况运行时极易出现旋转失速现象,严重影响其运行稳定性。采用SST k-ω湍流模型,对FBCDZ-10-No20型对旋风机在5种轴向间距下全流道内的非定常流动进行数值模拟,研究了轴向间距对矿用对旋风机失速过程的影响,揭示了不同轴向间距时的失速起始与发展机理。结果表明:轴向间距对失速起始扰动的首发位置、表现形式和发展过程都具有显著影响。对于70、100 mm两种轴向间距,失速起始扰动均首发于前级叶顶,随后在两级叶轮之间的动−动干涉作用下,后级叶顶也出现失速起始扰动,但与70 mm的轴向间距相比,当轴向间距为100 mm时,动−动干涉效应相对较弱,使得后级出现失速起始扰动需要更长的时间。对于140、170、225 mm三种轴向间距,失速起始扰动均是首先发生在后级叶根区域,不同的是140 mm间距时,前级叶顶泄漏流不能完全随主流流出通道,而是形成了局部叶顶堵塞区;而对于170、225 mm两种间距,前级叶顶则几乎没有堵塞区,最终仅在后级形成了成熟的失速涡团。随着轴向间距的增大,由前级叶顶泄漏流发生前缘溢流及尾缘反流形成的堵塞区逐渐缩小,而由后级叶根吸力面径向涡流形成的堵塞区则逐渐增大,当前级叶顶泄漏流无法形成堵塞区时,失速类型就由前级叶顶泄漏流诱发的“突尖型”转变为由后级叶根径向涡流诱发的“局部喘振型”。

轴向间距对FBCDZ-10-No20型对旋风机失速过程的影响

对旋风机在小流量工况运行时容易出现失速甚至喘振等不稳定现象,为研究轴向间距对对旋风机失速起始及其发展与传播过程的影响,采用Shear Stress Transport(剪切应力输运)k-ω湍流模型,对一台FBCDZ-10-No20型对旋风机全通道内的非定常流动进行数值模拟,探究了2种轴向间距下对旋风机的失速发展过程。结果表明:轴向间距对对旋风机失速起始及发展过程具有显著影响。在失速起始阶段,当对旋风机两级叶轮的轴向间距为170 mm时,失速起始扰动首先发生于后级叶根吸力面的尾缘区域,之后扰动沿径向从叶根向叶顶发展,沿周向向某个叶片通道聚集,导致该叶片通道堵塞,从而引起对旋风机失速;当轴向间距为70 mm时,失速起始扰动先后发生于前、后级的叶顶区域,之后扰动逐渐增强,最终发生失速。在完全失速阶段,轴向间距对于失速涡团沿周向、轴向及径向的传播都具有显著影响。轴向间距为170 mm时对旋风机进入单涡团全叶高失速,失速涡团沿轴向传播范围限于后级叶轮区域,沿周向以33.3%的后级转速旋转;轴向间距为70 mm时对旋风机进入多涡团部分叶高失速,失速涡团先后在两级叶轮叶顶区域产生,沿轴向向上、下游传播,沿径向分散于各叶片通道的70%叶高以上区域。由于两级叶轮轴向间距的改变,引起了对旋风机的失速起始扰动类型发生了由“局部喘振型”向“突尖型”的转变。

基于液压系统的风机叶片液压自调角系统

为确保冷却塔循环水系统安全可靠地运行,冷却塔风机转速以及叶片安装角度均按照最大换热量设定。但受生产工艺、环境温度等相关因素的影响,冷却塔风机的换热量在时刻变化,因此,冷却塔风机冷却能力与实际需求不匹配,造成大量能源浪费,为此,提出了一种基于液压系统的冷却塔风机叶片自调角的新型节能方法。首先,对自调角系统的工作原理进行了分析,利用Solidworks软件对自调角机构进行了结构设计,并对液压驱动系统工作原理进行了分析;然后,借助风力机气动载荷的计算方法,得到了液压系统提供的驱动力随安装角度变化的曲线;最后,利用AMESim仿真软件探究了多种液压回路自调角的工作特性,分析了调速阀内部元件节流阀开度对液压回路稳定性的影响。研究结果表明:自调角装置可以实现风机在不停机的工况下调节叶片的安装角度;采用PID调速阀液压回路可提高系统工作的精度和稳定性;当调速阀内部节流口的开度K=0.08时,可有效减少振荡时间,减小振荡峰值。

微型高速轴向柱塞泵转子系统力矩损失仿真分析

微型高速轴向柱塞泵转子系统在充满油液的壳体内高速旋转时,产生较大的力矩损失,影响柱塞泵的效率。首先,建立了轴向柱塞泵转子系统力矩损失仿真模型。其次,分析了其力矩损失组成和柱塞泵转速与斜盘倾角对其力矩损失的影响。最后,通过不同切片位置下柱塞泵转子系统油液速度场和压力场分布特点,分析了其力矩损失。结果表明:转子系统压差力矩损失约为其黏性摩擦力矩损失的11倍,其中,柱塞-滑靴压差力矩损失约占70%;随着转角的变化,压差力矩损失波动较大,黏性摩擦力矩损失几乎保持稳定。油液压力呈梯形分布且51.4°周期性剧烈波动,由旋转中心到壳体内壁压力逐渐增大;同时,靠近出油口和下止点位置处,油液压力较小。

双喷气自循环机匣处理对对转压气机性能的影响

为发展适用于对转压气机变转速比工况下的扩稳技术,基于某两级对转压气机设计出一种新型双喷气自循环机匣处理结构,能够实现在不同转速比下提高对转压气机的失速裕度。在设计转速比下研究了轴向喷气位置对自循环机匣处理扩稳能力的影响,并选取扩稳性能最佳的双喷气自循环机匣处理方案探究其在变转速比工况下的扩稳潜力。研究结果表明,在设计转速下,双喷气自循环机匣处理主要改善后排转子的叶顶流场,失速裕度最大提高8.40%;在非设计转速比下,双喷气自循环机匣处理可将失速裕度提升8.71%~9.74%。双喷气自循环机匣处理的双射流将叶顶泄漏流和主流的交界面推向下游,同时改善了两转子的叶顶流场品质,从而推迟失速的发生。

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 specific speed axial flow pump. In the present paper, the advantage and disadvantage of using contra-rotating rotors are described in comparison with conventional type of rotor-stator, based on theoretical and experimental investigations. The advantages are as follows： （1） The pump is inherently designed as smaller sized and at lower 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 high performance operation is obtained by rear rotor speed control in addition to front rotor speed control. The disadvantages are as follows： （1） The structure of double shaft system becomes complex. （2） The pump performance is inferior at over flow rate as the rear rotor loading is weakened. （3） The blade rows interaction from rear rotor to front rotor more strongly appears. Then the rear rotor design is a key to achieve higher pump performance. Some methods to overcome these disadvantages will be discussed in more details toward wider usage of contra-rotating axial flow pump in various industrial fields.

煤矿轴流通风机的数值模拟研究

为充分掌握FBCDNo14型对旋轴流式通风机的特点,指导实践生产中通风机运行参数的设置,在对FBCDNo14型通风机原理及其结构分析的基础上,基于SolidWorks三维软件和Fluent软件构建数值模拟仿真模型,并通过试验验证了模型的准确性。对不同叶片安装角度下的三种工况对通风机内部气流轨迹、速度矢量以及压力云图进行对比,以期指导今后通风机参数的优化和实践生产。

引风机中低负荷调峰运行提效技术应用实例

本文以国内某300MW火电机组动叶可调式轴流引风机为研究对象,采用引风机变频阶梯式调速运行方式,在不同负荷工况时对风机转速与动叶开度协同调节,实现了引风机中低负荷调峰运行提效改造效果。应用效果表明,动叶可调式轴流引风机变频阶梯式调速运行后,不仅能够避免风机发生共振隐患,而且能够有效发挥动调风机的动叶调节优势,始终保证风机运行在高效区域,运行安全可靠。该引风机变频阶梯式调速方式完全可满足电厂长时间深度调峰的需求,且保持风机在各负荷工况均高效运行,能够实现风机节能效益最大化。

动叶可调轴流风机失速解析

近来随着电力需求紧张,火电机组负荷需要不断增加,很多机组经常在额定工况甚至超额定工况下运行,相应各轴流风机的出力也随之大幅增大,一旦操作不当或调节幅度过大会使得轴流风机发生失速的概率增加。结合昆明电厂锅炉2号锅炉1号引风机近期多次发生失速的情况,依据动叶可调轴流风机失速原理,对照几次失速前后工况的变化对引风机失速原因进行了分析,认为引风机失速的主要原因为引风机的动叶开度突然增大了,并根据实际处理情况总结归纳了引风机失速的处理措施。

动叶可调轴流式通风机叶片安装角异常工况下的气动特性

动叶可调轴流式风机因具有较宽的高效区而得到广泛应用。以OB-84型带后导叶的动叶可调轴流风机为对象,采用Fluent对单个动叶安装角处于3种异常状况下的叶轮内流特征进行了数值模拟,并分析了安装角异常变化对风机全压和效率特性曲线的影响。研究表明:随异常叶片安装角的增大,异常叶片后缘处的尾迹损失增加,压力面压力梯度从前缘到后缘逐渐减小,而吸力面压力梯度增大并在后缘产生旋涡;叶轮出口的低压区范围扩大而总压值减小,异常叶片引起的流动损失主要集中在叶高中部位置;风机全压呈现先增大后减小的趋势,当异常叶片安装角增加为6°、12°和18°时,风机内效率下降分别为2.9%、4.8%和9.1%。