Effect of Pre-Swirling Flow on Performance and Flow Fields in Semi-Opened Axial Fan

In this study, we tried to improve the performance by giving a pre-swirling flow to the radial inflow that occurred in the semi-opened axial fan. In addition, the flow fields of rotor outlet were clarified experimentally, and the effect of pre-swirling flow was considered. The experiment was carried out using a performance test wind tunnel with a square cross section of 880 mm. Three types of casings were prepared, in which the blade tip protruded 0%, 20%, and 40% of the meridional chord length. They were called R25, R15, and R05, respectively, in the casing bellmouth model code. Guide blades for generating a pre-swirling flow were installed on the vertical wall surface of the casing. In addition, a vertical wall was installed 60% upstream of the meridional chord length as an obstacle to prevent axial inflow. The velocity fields of the rotor outlet were measured using a hot-wire anemometer. From the results, the pre-swirling flow did not significantly affect the fan performance. When there was no obstacles wall upstream, there was a partial increase in efficiency, but the difference was not so large. When there was an obstacle wall upstream, the efficiency increased overall in the case of R15, but in the case of R05, the efficiency increased only in the low flow rate region, and conversely decreased in the high flow rate region. By observing the blade outlet flow fields when the performance was improved, it was confirmed that the influence of the tip leakage vortex was weakened.

Effects of Four Types of Pre-swirls on the Leakage, Flow Field, and Fluid-Induced Force of the Rotary Straight-through Labyrinth Gas Seal

The labyrinth seal in turbomachinery is a key element that restricts leakage flow among rotor-stator clearances from high-pressure regions to low-pressure regions. The fluid-induced forces on the rotor from seals during machine operation must be accurately quantified to predict their dynamic behavior effectively. To understand the fluid-induced force characteristics of the labyrinth seal more fully, the effects of four types of pre-swirls on the leakage, flow field, and fluid-induced force of a rotary straight-through labyrinth gas seal (RSTLGS) were numerically investigated using the proposed steady computational fluid dynamics (CFD) method based on the three-dimensional models of the RSTLGS. The leakage, flow field, and fluid-induced force of the RSTLGS for six axial pre-swirl velocities, four radial preswirl angles, four circumferential positive pre-swirl angles, and four circumferential negative pre-swirl angles were computed under the same geometrical parameters and operational conditions. Mesh analysis ensures the accuracy of the present steady CFD method. The numerical results show that the four types of pre-swirls influence the leakage, flow field, and fluid-induced force of the RSTLGS. The axial pre-swirl velocity remarkably inhibits the fluid-induced force, and the circumferential positive pre-swirl angle and circumferential negative pre-swirl angle remarkably promote the fluid-induced force. The effects of the radial pre-swirl angle on the fluid-induced force are complicated, and the pressure forces and viscous forces show the maximum or minimum values at a specific radial pre-swirl angle. The pre-swirl has a negligible impact on the leakage. The four types of pre-swirls affect the leakage, flow field, and fluidinduced force of the RSTLGS to varying degrees. The pre-swirl is the influence factor affecting the leakage, flow field, and fluid-induced force of the RSTLGS. The conclusions will help to understand the fluid-induced force of labyrinth seals more fully, by providing helpful suggestions for engineering practices and a theoretical basis to analyze the fluid–structure interaction of the seal-rotor system in future research.

Operating characteristics of a high radius pre-swirl cooling system

An experimental investigation into pre-swirl effectiveness and receiver hole discharge coefficient characteristics for a high radius injection pre-swirl cooling systems was carried out on a physically representative experimental rig with a 450 mm diameter rotor.The receiver holes and pre-swirl nozzle were located at a radius of 181 mm and 180 mm respectively.The experimental work was mainly conducted at 5 000～12 000 r/min,4 bar absolute pressure and 1.132 kg/s air supply.The maximum air supply temperature was 190 ℃.Pressure and temperature distributions in the pre-swirl system were examined with an emphasis on the velocity effectiveness of the pre-swirl system as a whole and on the discharge coefficients of the rotating 'receiver holes' in the rotor.The results showed that the velocity effectiveness increased with increasing swirl ratio resulting in reduced blade cooling flow temperature.Different seal flow configurations caused very different effectiveness at different speeds,but outflow through the inner and outer seals always gave the highest effectiveness compared other configurations.Increasing the seal flow rate reduced the effectiveness.For the coefficient of discharge,except for the low speed range,it increased with increase in swirl ratio for most speeds.

空气射流特征对纯氨旋流燃烧火焰影响规律

氨是理想能源,为更好利用纯氨燃料,开发适用纯氨燃料的燃烧器,通过数值模拟对某10 kWth天然气旋流燃烧器进行三维建模,并对其纯氨燃烧和氮氧化物排放性能进行计算及仿真分析,探讨空气射流特性对火焰形态、温度分布、NO生成及排放的影响规律,以优化燃烧器纯氨燃烧能力。燃烧早期,旋流对燃料和空气混合影响大,而燃烧后期湍流强度对该过程影响大。发现通过增大空气射流孔面积(由12.8 mm^(2)增至19.2 mm^(2))、增加空气射流角度(由15°增至30°)均可增强旋流强度,促进燃料和空气混合,促进氨燃料快速着火和稳定燃烧,缩短着火距离。但过大的射流角度可能导致空气和燃料出现短暂分离,推迟混合过程,延长着火距离。此外,减小射流孔面积、增大射流角度还将增强燃烧器喷嘴附近湍流强度,促进氨燃料和空气混合燃耗,产生局部高温区,导致NO生成浓度升高。经对比优化,空气射流孔面积19.2 mm^(2)、射流角度15°、射流速度19.83 m/s时纯氨燃烧器实现稳定低NO燃烧,着火距离0.024 m、火焰长度0.446 m,NO生成峰值浓度和排放浓度分别降至443×10^(-6)和37.7×10^(-6)。

基于CFD法的桨前预旋导流罩设计与分析

为满足现有船舶能效指数(energy efficiency existing ship index,EEXI)要求,达到节能减排的目的,基于水动力学基础理论,设计一种桨前预旋导流罩节能装置。该装置由加速型导管和导叶组成:加速型导管可以使水流紧贴船体,改善流动分离,使进入螺旋桨的水流更加均匀,从而提高螺旋桨的推进效率;导叶可以为螺旋桨提供预旋,减少能量损失。利用计算流体动力学(computational fluid dynamics,CFD)软件对比分析优化前后的船尾流场和伴流分布。通过组合与优化节能装置的设计参数,节能装置的节能效果可达7.96%。与自航试验结果比较,证明了采用CFD软件进行桨前预旋导流罩节能装置设计是切实可行的。

供气孔角度对径向预旋系统特性影响的数值研究

为降低航空发动机径向预旋系统的流阻,增加温降,研究供气孔内的流动特性,建立径向预旋系统三维模型,在不同预旋角和旋转雷诺数条件下,采用数值方法研究不同供气孔角度下预旋系统的特性。结果表明:随着供气孔角度的增加,孔内的旋涡逐渐减小,孔内流通性得到改善;系统温降系数增加,在高旋转雷诺数下增幅较大,最大可提高19.3%;供气孔的流量系数有显著提高,最大可提高64.9%,降低了系统的流阻,从而预旋喷嘴出口流量系数及系统无量纲质量流量均有所提高。

叶孔式预旋喷嘴气动设计及验证策略

基于“功能分析—设计定义—试验验证”的产品开发思路,介绍了叶孔式预旋喷嘴气动设计及验证方面的工作。采用视角分析方法完成了预旋喷嘴功能分析,确定了预旋喷嘴的系统边界、利益攸关者及功能。完成了预旋喷嘴气动设计需求分析,确认了设计需求的完整性和合理性。在设计定义环节,对比了3种常见预旋喷嘴形式,分析了各自的优缺点,确立了采用叶孔式预旋喷嘴的构型。基于二阶贝塞尔曲线,完成了叶孔式预旋喷嘴的气动流道参数化造型。通过预旋喷嘴气动性能相关特征设计失效模式及影响分析(DFMEA),识别出预旋喷嘴气动性能相关的关键特性。建立了零组件—部件—核心机/整机的预旋喷嘴流量验证体系。

叶栅式预旋喷嘴气动设计与试验研究

合理的预旋喷嘴设计及分析在减小预旋系统的流动损失,改善叶片换热效果扮演着重要角色。基于自研软件首先对典型结构的预旋喷嘴翼型进行气动设计,然后根据设计结果进行三维仿真分析,并开展试验研究。考虑到预旋喷嘴叶片小、高度较低,在实际加工制造时容易超差,采用仿真方法研究了预旋喷嘴叶片高度与安装角的变化对流动特性的影响。试验结果显示,仿真结果与试验结果符合性较好,证实了预旋喷嘴设计结果满足设计要求。

直榫槽和斜榫槽两种出口结构预旋系统流动特性数值研究

采用三维数值计算方法对发动机直榫槽、斜榫槽两种出口结构的预旋系统开展模拟,研究改变预旋系统出口几何结构对叶片供气通道气体流动及压力损失的影响,并与一维工程计算方法对比。结果表明:榫槽结构由直榫槽改成斜榫槽对叶片供气通道压力损失影响较小,两种结构预旋系统进出口流量差异较小,系统出口各腔流量分配略有差异;数值计算与工程计算结果在系统进口、出口无量纲流量差别较小,上封严出口、下封严出口无量纲流量差别较大,相对偏差接近50%,封严区域流动换热复杂,需要进行三维仿真计算,以提高设计精度。

前置预旋定子泵喷推进器辐射噪声数值预报

The requirement of low radiated noise is increasing for underwater propulsors as the noise significantly affecting the comfort and quietness of ships,submarines,and vessels.To broaden the view of noise characteristics of pump-jet propulsors(PJPs),this paper considers the radiated noise of a pre-swirl stator PJP with the effects of the advance coefficient and rotor rotational speed.Radiated noise is obtained by the“hybrid method”approach,which combines a hydrodynamic solver with a hydroacoustic solver.The turbulence flow is obtained through improved delayed detached eddy simulation(IDDES),which show good agreement with the experiment,including the performance and flow field.The solver precision,permeable surface size,and sampling frequency notably affect the noise calculation.The spectra of thrust fluctuation and radiated noise are characterized by the tonal phenomenon around the blade passing frequency and its harmonics.The spectrum of radiated noise and overall sound pressure level(OSPL)are considerably affected by both the advance coefficient and the rotor rotational speed.Overall,the numerical results and analysis given in this paper should be partly helpful in deepening the understanding of the radiated noise characteristics of PJPs.

泵喷推进器水动力性能实验研究

前置定子式泵喷推进器被广泛应用于世界各国的新一代安静型潜艇上,但其水动力性能实验研究目前还比较匮乏。在空泡水筒中,对一型九叶定子七叶转子的前置定子式泵喷推进器进行了实验测试。其中,使用测力装置对敞水状态下泵喷推进器的推力系数和扭矩系数等进行了测试,使用激光粒子测速系统对其尾流场进行了测试。实验结果表明,此型前置定子式泵喷推进器的转子推力系数、定子及导管推力系数、转子扭矩系数均随着进速系数J的增大而减小,但定子及导管的合扭矩系数的绝对值反而随着J的增大而增大。泵喷推进器的效率在J=1.0处达到最大,为61.91%。前置定子式泵喷推进器的推力主要由转子提供。此外,泵喷推进器的尾流场由喷流加速区、轮毂低速区、混合区组成,实验测试得到了不同工况下尾流场中的瞬态速度以及平均速度值。

涡轮预旋供气系统跑道型接受孔对性能影响的实验评估

接受孔对于预旋供气系统内流动和换热具有重要的作用。为对比不同形状的接受孔对预旋供气系统性能的影响,通过实验研究直跑道型、长跑道型以及斜跑道型3种典型结构的接受孔在设计点参数下对预旋供气系统温降以及功耗的影响,并主要分析斜跑道型接受孔模型的流动温降特性。结果表明:相较于采用直跑道型和长跑道型接受孔的预旋供气系统,采用斜跑道型接受孔的系统转子部件的流动损失明显减小,设计点工况下系统温降为24.9K,系统功耗为10.04kW,其比直跑道型接受孔温降效率提高3.5%,系统功耗减小4.2%,熵增减小约9.8%。且旋转马赫数一定时,预旋供气系统压比和系统温比均随着流量比的增大而增大;流量比一定时,旋转马赫数对系统压比几乎没有影响,系统温降随旋转马赫数的增加先增大后减小,两者呈现出二次函数的关系。

叶型接受孔耦合叶轮结构优化对涡轮预旋供气系统性能改进研究

预旋供气系统为燃气涡轮转子叶片提供高品质冷气。为改进预旋供气系统温降性能,基于预旋供气系统数学模型的理论推导,揭示出原模型温降性能不显著的影响机制和解决方法,提出一种动叶前缘式进口的叶型接受孔的优化模型,并评估优化前后预旋供气系统的热力学和气动特性。结果表明,预旋腔内转静部件匹配问题是影响系统性能的一个重要限制因素,动叶前缘式接受孔能够解决转静难以匹配的问题。在满足供气流量和供气压力的条件下,采用动叶前缘式接受孔的优化模型预旋腔压力由原模型的640.2kPa降至533.0kPa,降低了16.7%。系统温变由温升转为温降,温降效率由-30%增加至55%,温降变化范围达13.56K。比功耗由6720 J/kg降至3979J/kg,下降了40.8%。

主燃级基于旋流直射式喷嘴的超低排放燃烧室实验研究

为了实现航空发动机超低NOx超低排放的目标,本文提出贫油预混预蒸发低排放燃烧室主燃级采用旋流直射式喷嘴技术,达到主燃级燃油和空气强化混合的效果,获得良好均匀性的油气混合物进行燃烧。在单头部燃烧室试验件上实验研究了LTO循环4个工况(慢车、进场、爬升和起飞)的燃烧性能和污染排放性能。研究结果表明:除慢车工况的燃烧效率接近0.99外,其余工况的燃烧效率均大于0.995;在LTO循环内,CO,UHC和NO_(x)排放均比CAEP/6排放标准降低50%以上,且NOx比CAEP/6低72.5%,达到了超低排放的目标;同时与其他各型低排放燃烧室相比,起飞工况、爬升工况的NOx排放在LTO循环中的占比均有较大幅度的降低。

中心分级预混旋流火焰燃烧噪声的实验研究

针对中心分级旋流燃烧器中预混甲烷火焰在常温常压下的燃烧噪声进行了实验研究,主要关注实验工况和限制域结构对燃烧噪声的影响。用声级计测量了燃烧噪声声压级,用带有CH滤镜的单反相机拍摄火焰的平均图像。实验结果表明,在主、预燃级空气流量恒定时,总当量比与分层比对燃烧噪声产生了显著的影响,氢气掺入对燃烧噪声无明显影响;预燃级当量比对于燃烧噪声的产生起关键作用,预燃级当量比越接近1.00燃烧噪声越大;相同工况下,预燃级空气流量分配越多,产生的燃烧噪声越大。改变火焰限制域的结构,使用锥形火焰筒可以减少燃烧噪声的产生。本研究还结合带有CH滤镜的摄像机拍摄的火焰图像,初步分析了燃烧噪声与火焰宏观结构之间的对应关系。

多通道逆喷旋流燃烧器不同负荷下煤粉燃烧特性研究

旋流燃烧器煤粉燃烧特性与其结构参数及运行工况密切相关,是工业煤粉锅炉的研究重点。为了研究煤粉在多通道逆喷旋流燃烧器不同负荷下的燃烧特性,以热态试验台架为基础,采用高温热电偶、烟气分析仪和高速摄像机3种手段对预燃室内的温度分布、组分浓度分布及预燃室外的火焰形态进行测量,分析不同负荷下煤粉在预燃室内、外的燃烧过程。试验结果表明:多通道逆喷旋流燃烧器在不同负荷下均可实现煤粉稳定燃烧,负荷最低可至35%;煤粉呈现“风包火、火包粉”的径向分级燃烧状态,其中低温空气层保证预燃室结构长期稳定运行,高温无氧强还原性气氛保证煤粉快速着火稳定燃烧同时抑制燃烧初期NOx生成;低负荷运行时,煤粉燃烧过程集中在预燃室内且燃烧强度较高,温度较高其峰值均值为1204℃,无氧区域较大时强还原性气氛中CO浓度较高,预燃室外无形态稳定火焰;中、高负荷运行时,预燃室内煤粉燃烧强度略低,温度较低时其峰值均值分别为1087℃、1090℃,无氧区域较小时强还原性气氛中CO浓度较低,燃烧过程延伸至预燃室外,形成稳定的旋流火焰,其直径和发散角度分别维持在750 mm和25°左右,而火焰长度则由2627 mm延伸至3216 mm。

预旋角度对预旋孔流动特性的影响

对预旋角度分别为30°,25°,20°和15°的预旋孔在压比1.1～1.9范围内的流量系数进行了实验测量和数值模拟。研究了压比和预旋角度对预旋孔进出口速度和气流角度、流量系数和预旋效率等参数的影响。流量系数的实验结果与计算结果符合良好,数据显示预旋孔流量系数和预旋效率随压比的增大显著增大。预旋角度的减小使流量系数基本保持不变,而预旋效率由于出气角度的减小而显著增大,最大增幅可达10%。

长径比对预旋孔流动特性影响的数值研究

采用数值方法研究了长径比和压比对预旋孔流动特性的影响,所研究的预旋角度为30°,长径比范围为1～5,压比范围为1.1～1.9。计算获得了出气角度、出气面积、出气速度及其周向分量,流量系数和预旋效率等参数随压比和长径比的变化。对长径比1.75和4的预旋孔流量系数进行了实验测量。结果表明预旋效率是一个可以综合反映预旋喷嘴气流偏转、加速和流动损失等主要性能的无量纲参数。预旋效率随长径比的增加先显著增加后微弱减小,最佳长径比为2.5左右。长径比小于2时由于出气角度和实际出气面积都明显偏离设计值,预旋效率显著偏低,在设计中应避免出现。

预旋进气位置对转静盘腔换热影响的数值研究

对具有不同预旋进气位置的转静盘腔内的换热进行了数值模拟.在进气流量恒定的条件下,改变预旋孔在静盘上的径向位置,研究了旋转雷诺数、预旋角、转静盘间距等参数对进出口气流的无量纲总温降和转盘换热效果的影响.研究表明:旋转雷诺数的增大和转静盘间距的减小都能够增强气流对转盘的换热效果;当预旋孔的径向位置增大时,无量纲总温降和转盘表面的平均努塞尔数都是先增大后减小,预旋孔存在一个最优的径向位置.

扩口孔型预旋喷嘴流动与温降特性

分别对预旋角度为20°的直孔和扩口孔型喷嘴进行了数值模拟和实验测量。计算模型包括仅有进气腔、预旋孔和出气腔的单独模型和在此基础上增加了旋转部分的系统模型;研究内容包括速度场、出气速度、出气角度、流量系数、预旋效率和温降,并对单独模型的孔流量系数进行了实验测量。结果表明流量系数的计算结果与实验结果符合良好,扩口孔的流量系数、预旋效率和温降都比直孔显著增大20%以上。数据还显示由单独模型计算得到的流量系数和预旋效率与由系统模型得到的结果比较接近,根据单独模型的预旋效率而推算出的温降可在一定程度上间接反映预旋系统的温降特性。