叶尖间隙对离心叶轮偏置分流叶片工作机理的影响

采用计算流体力学方法研究了不同叶尖间隙情况下偏置分流叶片提升离心叶轮性能的机理.叶尖间隙较小时,主叶片吸力面附近分离区导致主要损失,分流叶片偏向于主叶片吸力面利于削弱损失、提升叶轮性能;随着叶尖间隙的增加,泄漏流的影响增加以至损失集中于分流叶片和主叶片压力之间的通道,分流叶片宜向主叶片压力面偏置,以减少泄漏流在同一通道的聚集.叶尖间隙和分流叶片周向位置对间隙泄漏流、叶片吸力面分离形成的损失及相互关系有着耦合影响,分流叶片周向位置的改变可以调整通道的横向压力梯度、泄漏流掺混入主流的位置,改善分流叶片两侧通道的损失的分配,分流叶片最佳偏置方向随叶尖间隙的大小而发生改变.      

分流叶片位置对高转速离心压气机性能的影响

运用三维粘性流动数值计算程序FineTM/Turbo对叶顶间隙泄漏存在时带分流叶片的高转速离心压气机模型级内部流动进行了数值模拟,重点分析了分流叶片不同起始位置及不同周向位置对压气机级内三维粘性流场及整级性能的影响.计算中采用Jameson的中心差分格式结合Baldwin-Lomax代数模型使用时间推进法求解雷诺平均N-S方程,计算模拟了模型级内部复杂的三维粘性流动过程及气体参数分布的详细结构和规律.计算结果表明:采用分流叶片在进口段会减少叶片阻塞,从而使更高的质量流量可以流经叶轮;分流叶片起始位置位于Ⅲ时,两个通道叶轮出口处速度分布最均匀;分流叶片越短,长叶片压力面无量纲静压载荷越大.当分流叶片长度达到某一数值后,长叶片载荷变化趋于平缓.分流叶片位于不同周向位置时,IBSA叶轮的模型级效率最高,压气机性能最好.     

楔形涡流发生器影响高负荷叶栅性能的机理研究

为探究楔形涡流发生器流动控制技术的作用机理,对一低来流马赫数高负荷扩压叶栅开展数值模拟研究。提出在叶片前缘安装涡流发生器的方案,并对比分析了采用涡流发生器前后叶栅性能及通道内二次流结构的改变。研究结果表明,楔形涡流发生器诱导的吸/压力面涡类似于叶片前缘的马蹄涡,卷吸附面层低能流体,提高其抗逆压梯度能力,进而削弱横向流动,抑制角区分离;涡流发生器的强漩涡结构改善了叶栅通道二次流,使得损失重新分布,叶栅-3°到7°攻角范围内的气动性能显著提升,设计点-1°攻角时平均总压损失系数下降8.04%,平均静压系数增大7.75%,5°攻角时平均总压损失系数下降15.87%,平均静压系数增大21.79%。     

叶根倒角对微小型离心压气机气动性能的影响

为了研究叶根倒角对微小型离心压气机流场及气动性能的影响,对1个带有分流叶片的微小型离心压气机进行数值模拟及理论分析。结果表明:叶根倒角最小角度对主叶片及分流叶片表面的静压分布影响不大,压气机总压比几乎不变,但效率提高明显,最大可提高0.99%。压气机效率的提高,一方面是由于通道涡的削弱减小了损失;另一方面是主叶片吸力面根部附近低速区减小和流线弯曲程度降低,提高了根部附近的流通能力,减少了横向流动,从而减小了二次流的损失。另外,叶根倒角最小角度变大,降低了叶片出口处气流的不均匀性,从而减小了损失。     

传热对微型离心叶轮间隙泄漏流动影响的数值研究

针对某微型燃气轮机的微型离心叶轮,采用三维数值模拟方法,将绝热壁面情况和考虑传热影响情况下的叶轮性能和内部流场进行对比研究,重点分析壁面传热情况对微型离心叶轮间隙泄漏流动的影响.研究发现:传热对叶轮性能的影响主要集中在其对间隙泄漏流的作用上.绝热条件下间隙泄漏流轨迹沿叶片吸力面向下游发展,传热则使得间隙泄漏流动迹向相邻叶片压力面偏转,增强间隙泄漏流与主流的掺混导致间隙泄漏流损失增大.与绝热情况相比,传热虽然在一定程度上减弱了叶片通道内的压力梯度,但由于热量的传入会导致间隙泄漏流初始堵塞增大,最终仍会在叶片通道内造成更大的间隙泄漏流堵塞.     

亚声速半开式离心叶轮叶顶间隙的流动特征

针对半开式离心叶轮的间隙泄漏和间隙气流对气动性能的影响,采用数值方法分析了3种叶顶间隙值下叶轮的气动性能、设计工况下的叶片载荷分布、间隙流动气流角以及泄漏涡的分布特征.结果表明:叶轮叶片表面的压力分布规律不受叶顶间隙的影响,但叶片载荷在叶片的中后部有不同程度的减小;间隙处的内泄漏流动本身引起的流动损失较小;与零间隙相比,间隙处的内泄漏气流对流道前半段主流的影响甚微,但在流道中部以后,间隙流扰乱了主气流方向,并在叶顶吸力面附近形成涡流聚集区,造成明显的熵增,带来不可忽视的能量损失.希望所得结果能为建立半开式离心叶轮的间隙气动模型提供参考.      

带分流叶片离心叶轮气动设计及其流场分析

为提高某涡轴发动机的性能,需要对其离心压气机进行改进.本文设计了带分流叶片的离心叶轮,以确保离心压气机在不降低喘振裕度的前提下,设计点总压比提高不低于0.3,效率提高不低于2%.计算结果表明新设计的离心叶轮达到了设计指标.流场分析显示,新设计的叶轮有效地控制了气流分离,减小了出口尾迹的强度与范围;分流叶片的长度对叶轮效率有一定影响,合理的分流叶片长度可以有效地削弱二次流强度,提高叶轮效率.     

具有分流叶片跨声速离心叶轮激波及能量损失分析

对具有分流叶片跨声速离心叶轮,采用激波基本关系式对数值信息进行分析和判定,理论证实了叶轮流道中激波的存在,并确定流道内高速气流易在主叶片前缘、分流叶片前缘以及主叶片的吸力面与分流叶片的压力面通道位置形成激波.进一步对比分析了叶顶间隙和运行工况对激波位置分布特征的影响及引起的能量损失.结果表明:固定叶顶间隙下,随着流量减小,激波位置向流道上游移动;叶顶间隙导致激波线位置向流道下游偏移;分流叶片前缘处有最强激波并引起较明显能量损失.      

斜流扩压器任意中弧线造型3维弯扭叶片设计

为了改善扩压器与叶轮之间的气动匹配,针对斜流/离心叶轮出口复杂的3维流动,以及扩压器叶片不同展向位置气动 负荷分布特征,提出基于任意中弧线造型的扩压器3维弯扭叶片设计方法。该方法在根据叶轮出口流场优化扩压器叶片攻角的 同时,通过对造型截面中弧线任意调整实现扩压器叶片载荷分布和局部流场细节的优化。以某高压比斜流压气机为平台,采用上 述方法完成了对其斜流扩压器的改进设计。3维数值模拟结果表明：与原方案相比,扩压器改进后斜流压气机设计点至近喘点范 围内效率提升约0.3个百分点,设计点流量基本不变,设计转速喘振裕度增大1.0个百分点,在设计点及近喘点状态下扩压器通道 流场均得到了改善,同时改进后扩压器的叶片数由21片减少至19片。     

低雷诺数下离心压气机性能及流动影响的数值研究

对高空低雷诺数条件下低压离心压气机进行了全三维数值模拟,分析了雷诺数对其内部流场的影响.结果表明:随着雷诺数降低,离心压气机的效率、裕度和流通能力下降;影响叶片表面负荷分布,使得转子叶片的做功能力下降;叶片前缘分离区范围增大,二次流增强,分流叶片叶尖泄漏损失增大,主叶片吸力面通道的低速区明显增大,起始位置也向前移动,对展向的影响区域也随之增加.      

The effect of inlet conditions on the flow and heat transfer in multiple rotating cavity with axial throughflow

This paper discusses experimental results from two different build configurations of a heated multiple rotating cavity test rig.Measurements of heat transfer from the discs and tangential velocities are presented.The test rig is a 70% full scale version of a high pressure compressor stack of an axial gas turbine engine.Of particular interest are the internal cylindrical cavities formed by adjacent discs and the interaction of these with a central axial throughflow of cooling air.Tests were carried out for a range of non-dimensional parameters representative of high pressure compressor internal air system flows(Re up to 5×106 and Rez up to 2×105).Two different builds have been tested.The most significant difference between these two build configurations is the size of the annular gap between the(non-rotating) drive shaft and the bores of the discs.The heat transfer data were obtained from thermocouple measurements of surface temperature and a conduction solution method.The velocity measurements were made using a two component,LDA system.The heat transfer results from the discs show differences between the two builds.This is attributed to the wider annular gap allowing more of the throughflow to penetrate into the cavity.There are also significant differences between the radial distributions of tangential velocity in the two builds of the test rig.For the narrow annular gap,there is an increase of non-dimensional tangential velocity V/Ωr with radial location to solid body rotation V/Ωr=1.For the wider annular gap,the non-dimensional velocities show a decrease with radial location to solid body rotation.      

Research on Auto-detection for Remainder Particles of Aerospace Relay Based on Wavelet Analysis

Aerospace relay is one kind of electronic components which is used widely in national defense system and aerospace system. The existence of remainder particles induces the reliability declining, which has become a severe problem in the development of aerospace relay. Traditional particle impact noise detection (PIND) method for remainder detection is ineffective for small particles, due to its low precision and involvement of subjective factors. An auto-detection method for PIND output signals is proposed in this paper, which is based on direct wavelet de-noising (DWD), cross-correlation analysis (CCA) and homo-filtering (HF), the method enhances the affectiv-ity of PIND test about the small particles. In the end, some practical PIND output signals are analysed, and the validity of this new method is proved.     

Preparation of Highly Dispersed Antimony-doped Tin Oxide Nano-powder via Ion-exchange Hydrolysis of SnCl4 and SbCl3 and Azeotropic Drying

Antimony-doped tin hydroxide colloid precipitates have been synthesized by hydrolysis of SnCl4 and SbCl3 using: (1) an ion-exchange hydrolysis to remove chlorine ions, and (2) isoamyl acetate as an azeotropic solvent to obviate water. The obtained dried powder is of high dispersivity without any need for further grinding. The size and dispersivity of the final particles are investigated with the aid of TG-DTA, BET, XRD and TEM. After having calcined, the antimony-doped tin oxide nanopowder possesses a tetragonal rutile structure with high dispersivity, uniform particles and low hard agglomeration.     

Effects of Mo on the Microstructure and Hydrogen Sorption Properties of Ti-Mo Getters

The effects of Mo on the microstructure evolution, porosity and hydrogen sorption properties of Ti-Mo getters are investigated in this work. The results show that the addition of Mo prolongs the densification process of Ti-Mo getters and results in a significant amount of sintered pores. With the Mo content increasing, the porosity of getters firstly increases reaching the maximum value as it at- tains about 7.5wt.%, and then drops. At the room temperature, the hydrogen sorption property of getters increases progressively with the Mo content increasing, but the tendency is not very clear before its content lies below 2.5wt.%. When the Mo content achieves about 7.5wt.%, the hydrogen sorption property proves to be the best. The discussion is made about the above mentioned phenomena inclusive of hydrogen sorption properties of getters under different activation conditions (from 500-750 ℃).     

超声速燃烧数值模拟中的湍流与化学反应相互作用模型

高精度数值模拟有助于理解超声速湍流燃烧中湍流与化学反应的相互作用,可为发动机燃烧室等工程应用设计提供可靠的预测模型。除直接数值模拟外,目前在湍流燃烧应用中使用的大涡模拟和雷诺平均Navier-Stokes模拟均需要借助模型模化发生在湍流小尺度上的流动与化学反应过程对湍流大尺度运动的影响。现有的湍流与化学反应相互作用模型大致可分为:火焰面类模型和概率密度函数类模型,2类模型在不同的应用中各自具有优势和局限性。此外,现有模型大都基于低马赫数燃烧,而超声速燃烧中通常会伴随快速混合、局部熄火和再着火以及激波等复杂过程,这为发展其中的湍流与化学反应相互作用模型提出了更多的挑战。     

适于低轨卫星IP网络的单核共享树组播算法(英文)

为了解决低轨卫星IP网络中现有典型源组播算法的信道资源浪费问题,本文提出了一套单核共享树组播算法,即核心群合并共享树(CCST)和加权核心群合并共享树(w-CCST)算法。CCST 算法包括动态近似中心(DAC)选核方法和核心群合并组播路径构建方法。DAC方法专为周期、规律运动的低轨卫星网络提出,不需要复杂的星上计算。在核心群合并方法中,以核节点作为初始核心群,通过核心群和剩余组成员的最短路径方法逐步扩展直至整棵组播树构建完成,从而使得组播树的树代价最小,大大提高了网络的带宽利用率和组播传输效率。w-CCST 算法中所提出的加权因子可以调整树代价和端到端传播时延之间的折衷程度,因此,可以通过调整加权因子来适度增大树代价、降低端到端传播时延以支持某些端到端时延要求苛刻的实时组播业务。最后,与低轨卫星 IP 网络中典型算法进行了性能比较,仿真结果说明,CCST 算法的平均树代价比其它算法显著降低,w-CCST 算法的平均端到端传播时延小于 CCST 算法。     

Jet Vectoring Control Using a Novel Synthetic Jet Actuator

A primary air jet vectoring control system with a novel synthetic jet actuator (SJA) is presented and simulated numerically. The results show that, in comparison with an existing traditional synthetic jet actuator, which is able to perform the duty of either “push” or “pull”, one novel synthetic jet actuator can fulfill both “push” and “pull” functions to vector the primary jet by shifting a slide block inside it. Therefore, because the new actuator possesses greater efficiency, it has potentiality to replace the existing one in various appli- cations, such as thrust vectoring and the reduction of thermal signature. Moreover, as the novel actuator can fulfill those functions that the existing one can not, it may well be expected to popularize it into more flow control systems.     

Nonlinear Adaptive Slewing Motion Control of Spacecraft Truss Driven by Synchronous V-gimbaled CMG Precession

The slewing motion control of a truss arm driven by a V-gimbaled control-moment-gyro (CMG) is a nonlinear control problem. The V-gimbaled CMG consists of a pair of gyros that must precess synchronously. The moment of inertia of the system, the angular momentum of the gyros and the external disturbances are not exactly known. With the help of feedback linearization and recursive Lyapunov design method, an adaptive nonlinear controller is designed to deal with the unknown items. Performance of the proposed controller is verified by simulation.     

An SOR Implicit Time-accurate Scheme in Calculating Unsteady Flows

A new time-accurate marching scheme for unsteady flow calculations is proposed in the present work. This method is the combination of classical Successive Over-Relaxation (SOR) iteration method and Jacobian matrix diagonally dominant splitting method of LUSGS. One advantage of this algorithm is the second-order accuracy because of no factorization error. Another advantage is the low computational cost because the Jacobian matrices and fluxes are only calculated once in each physical time step. And, the SOR algorithm has better convergence property than Gauss-Seidel. To investigate its accuracy and convergency, several unsteady flow computa- tional tests are carried out by using the proposed SOR algorithm. Roe’s FDS scheme is used to discritize the inviscid flux terms. Un- steady computational results of SOR are compared with the experiment results and those of Gauss-Seidel. Results reveal that the numerical results agree well with the experimental data and the second-order accuracy can be obtained as the Gauss-Seidel for unsteady flow computations. The impact of SOR factor is investigated for unsteady computations by using different SOR factors in this algorithm to simulate each computational test. Different numbers of inner iterations are needed to converge to the same criterion for different SOR factors and optimal choice of SOR factor can improve the computational efficiency greatly.