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.

Internal Flow Condition between Front and Rear Rotor of Contra-Rotating Small-Sized Axial Fan at Low Flow Rate

Contra-rotating small-sized fans are used as cooling fans for electric equipment. The internal flow condition between the front and rear rotors of the contra-rotating small-sized fan is not known well especially at the low flow rate. Furthermore, the blade row distance between the front and rear rotors is an important parameter for the contra-rotating small-sized fan and its influence on the internal flow condition is not clarified at the low flow rate. Therefore, the internal flow condition of the contra-rotating small-sized fan at the low flow rate is investigated by the numerical analysis in this research. The numerical analysis results are validated by comparing the fan static pressure curves of the numerical results to the experimental results. The internal flow condition at the low flow rate is clarified using the numerical models of the different blade row distance L = 10 mm and 30 mm. In the present paper, pressure fluctuations phase locked each front and rear rotor’s rotation are shown and the influences of the wake and the potential interference are discussed by the unsteady numerical analysis results at the low flow rate.

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。

小尺寸无静叶对转风扇/压气机气动设计与变工况性能分析研究

无静叶对转风扇/压气机能有效减小发动机陀螺力矩,在轴向长度方面具有优势。然而,无静叶往往导致下游叶片攻角变化较大,变工况性能难以保证,且这一特点随叶尖切线速度的增大而恶化。本文利用小尺寸涡扇发动机风扇叶片根部周向速度较低的特点,尝试对其进行风扇与压气机无静叶对转方案设计。通过速度三角形分析了无静叶对转风扇/压气机的性能特点,开发了无静叶对转风扇/压气机一维设计程序进行参数方案的筛选优化,设计得到小尺寸无静叶对转风扇/压气机构型方案,设计点效率为85.1%,压比为3.16。结果表明,对转压气机的下排叶片相对进口气流角的变化范围较常规转叶+静叶相对进口气流角范围更小,而对转下排叶片的进口速度却将增大1.5~3倍,因此,需要合理选择对转风扇/压气机的轮毂比及转速比,才能保证对转风扇/压气机变转速工况下的设计点效率及失速裕度。减小对转风扇/压气机转速比有利于提高设计点效率和裕度,但本文受发动机总体指标限制,对转速比选择进行了折中。

矿用对旋主通风机周向槽机匣处理扩稳机理研究

为了提高对旋风机的稳定裕度,采用数值模拟方法,将周向单槽机匣处理技术应用于FBCDZ-No20型对旋风机的扩稳,探究了周向槽的轴向位置对风机气动性能和扩稳能力的影响。研究表明:对前级叶轮进行周向单槽机匣处理,可以提高对旋风机的稳定裕度,且周向单槽的轴向位置对风机的气动性能和扩稳能力均具有影响;当周向单槽位于前级叶片的前缘和25%叶顶轴向弦长时,风机可以获得可观的稳定裕度提高量,但峰值效率损失较大;当周向单槽分别位于50%、75%的叶顶轴向弦长和尾缘时,扩稳效果逐渐减弱,相应的效率损失也逐渐减小。周向槽是通过抽吸叶片压力面前缘的低能流体,并将其沿周向输运至叶片吸力面的前缘喷出,从而增大了前级叶轮进口相对气流角及叶顶泄漏流的轴向动量,改变了叶顶泄漏流的轨迹,抑制了前缘溢流与尾缘处的边界层分离,进而减轻叶片通道内的流动堵塞,推迟了失速的发生而实现扩稳。采用前级周向单槽机匣处理并未改变对旋风机的最先失速级和失速起始类型。

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.

煤矿FBD型对旋局部通风机叶片安装角对风机影响分析

为探究通风机叶片安装角对风机性能的影响,以煤矿FBD型对旋局部通风机为研究对象,分析其对风机关键部件叶轮的力学性能和振动特性的影响。结果显示,增大叶片安装角将导致叶轮应力和应变上升,同时对振动特性影响不显著。该研究可为后续的叶片安装工作提供一定的参考借鉴。

局部轴流通风机进风端消声结构设计及流场仿真研究

为进一步探究局部轴流通风机的降噪策略,以某煤矿企业的局部轴流通风机为研究对象,结合该局部轴流通风机进风口的结构,经过综合研究后确定采用径向环形进风的方法予以设计,确定进风端消声结构及模型参数;通过结构参数建立仿真分析模型,对局部轴流通风机进风端消声结构在不同工况下运行时的空气流场特征进行仿真分析,以明确其压力、速度和涡流的特点。根据仿真分析结果予以讨论,结果显示,该进风端消声结构进风端阻力损失相对较小,流场速度分布相对较为均匀,同时空气流场内的涡流也整体处于较小水平,表明此结构具有潜在的应用价值。

FBD No8.0/2×55 kW型局部对旋式通风机叶轮的结构分析

为进一步探究局部对旋式通风机叶轮结构的可能优化路径,以FBD No8.0/2×55 k W型对旋通风机为研究对象,通过三维建模和有限元分析方法,对该通风机叶轮进行力学分析与模态分析,根据分析结果确定叶轮结构需要改进的方向,而后采用NACA4415翼型叶片对叶轮结构进行优化,结果显示,优化后的叶轮叶片应力和应变显著降低,且发生共振的风险大大降低,表明本次分析与优化工作具有一定的现实意义。

变叶片安装角对旋风机气固两相流特性研究

针对某实际运行的矿用对旋风机叶片存在的磨损问题,采用SST k-ω湍流模型和Finnie磨损模型,对不同叶片安装角下风机内部气固两相流场进行了数值模拟研究。首先,选择风机静压、功率和效率为评价指标,进行了风机性能试验,对数值计算方法和模型的准确性进行了验证;然后,根据设计的6种叶片安装角方案,对叶片压力面的磨损特征和气固两相流风机流场的分布规律进行了分析;最后,对不同叶片安装角下气固两相流风机的性能进行了对比,确定了具有最佳抗磨效果和最优风机性能的叶片安装角方案。研究结果表明:相比于原始的叶片安装角,增大后级安装角后的叶片面平均磨损率降低了6.0×10^(-8)kg/(m^(2)·s);同时,增大后级安装角能够有效地缓解后级叶片前缘和尾缘处的分离涡现象,提高风机的性能,达到叶片抗磨的目的。

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。

喷雾降尘对旋式轴流风机气动性能研究

为进一步优化喷雾降尘风机的降尘效果,以改变风机结构参数为研究对象,气动性能为评估指标,在单因素变量分析的基础上进行正交试验从而得到对旋式轴流风机优化方案。通过Fluent软件的DPM双向耦合分析对风机的叶轮叶片数、叶轮转速、导流叶数和出口直径进行单因素试验,得到正交试验所需的参数组,再通过极差分析风机综合性能得到结构参数的最优组合。结果表明,以单因素试验为基础的正交试验获得的对旋式轴流风机优化方案较原模型显著增强降尘效果。

矿用对旋风机气固两相流磨损特性

为探索对旋风机在矿井含尘环境中叶片的磨损情况,以及颗粒长久性磨损造成叶片表面粗糙度增加的后果,基于SST k-ω湍流模型和Finnie磨损模型,利用多相流求解技术对FBD No.6.3矿用对旋式局部通风机进行气固两相流数值模拟,分析不同颗粒浓度和粒径条件下叶片磨损分布特征,探究叶片表面粗糙度对风机内部流场和整机性能的影响。结果表明:气固两相流场内颗粒浓度对叶片磨损率的影响较大,磨损率随浓度的增加而增大;叶片表面粗糙度的均匀和非均匀分布形式导致前缘和尾缘不同程度的能量耗散,在进行对旋风机气固两相非定常流动特性的分析时,应采用粗糙度非均匀分布的方法真实反映叶片粗糙度变化的影响;风机性能随叶片粗糙度的增大而降低,大流量工况下的影响更为显著,但随工作时间的增长,叶片表面粗糙度均匀性提高,流场恶化情况减缓。因此,适时修复或更换磨损叶片,有利于风机安全高效运行。

高湿环境下对旋风机内流场及噪声特性研究

为了研究矿井不同湿度环境下对旋风机内流场及气动噪声的影响特性,采用大涡模拟和FW-H声学模型对环境相对湿度分别为0、25%、50%、70%、80%、90%、100%条件下对旋风机流场进行数值模拟,分析内流场涡结构及气动噪声变化规律。结果表明:随着相对湿度增大,风机静压、功率和效率均呈线性趋势降低,风机叶顶泄露涡强度降低,在进出口的监测点上,声压级均有不同程度的降低;相对湿度每升高10%,压升降低2.08%左右,功率降低1.9%左右,效率降低0.57%左右,各监控点A声级降低0.9%。