无源微脉冲射流抑制叶栅气流分离的初步实验

基于一种适用于高负荷压气机的无源微脉冲射流控制技术,在平面叶栅实验平台上开展了低马赫数实验研究,得到了无流动控制时叶栅通道内稳态及动态压力特性.对该分离流场（通道内分离涡主频为478Hz,对应的斯特劳哈尔数Sr约为0.2）进行了无源微脉冲射流控制通道内气流分离的实验研究,并针对148Hz到840Hz频率范围内的无源微脉冲射流控制分离流的效果进行了实验测量分析.实验结果表明:在分离涡主频0.85~1.20频率范围内,控制效果最为明显;相比于开缝吹气等定常射流控制方式,无源微脉冲射流控制方式引气流量小,大幅降低了引气对压力面流动特征及叶栅总体性能的影响.      

脉冲射流控制弯曲扩压管道流动分离的特点

结合弯曲扩压通道的脉冲射流总体控制规律,开展了不同射流频率下通道内流场的稳定及动态特性分析.研究结果表明:定常射流控制状态下,流场内沿径向不同位置流动特性的变化幅度基本相同,定常射流通过压制通道内复杂流动现象达到整体线性地改变通道内流场特性的效果;而在合理脉冲射流控制状态下,脉冲射流对流场的影响主要是通过改变分离涡的脉动时空特性,沿径向逐步增强对流场的影响,从而使得主流区内总压损失降低幅度最为明显,此时扩压通道内占主导地位分离涡的周期性特征有了明显的改善,流场拟序结构更为有序.      

基于POD方法的弯曲扩压通道分离流控制的时空特性分析

为了分析一种运用于压气机内分离流控制的无源脉冲射流控制技术的特点,基于弯曲扩压通道试验模型进行了脉冲射流控制的试验和数值模拟研究,结果均表明当射流频率接近通道内分离涡主频时控制效果最为明显;引入了本征正交分解（POD）技术对无控状态下通道内流场结构进行分析,得到了POD各阶模态的流动结构特征。在此基础上对比分析了定常及非定常控制特点,结果表明：非定常控制方式主要是重分配各阶模态之间的能量,有选择性地强化或削弱某阶模态;定常射流控制则是整体削弱高阶模态,压制通道内复杂流动现象;合理地构建脉冲射流可使能量从高阶模态向平均流模态进行转移,能量的转移通过空间流场结构的重构和模态时间演化特性的序化实现。最后针对POD分析结果进行了验证性试验研究,试验结果部分反映了时空特性的变化规律,提升了POD分析结果的可信度。     

基于合成射流的二维后台阶分离流主动控制

作为一种新的流动控制激励器,合成射流技术在流动分离控制、降低压力脉动和抑制噪声等方面具有广阔的应用前景。实验利用合成射流主动控制技术对二维后台阶湍流分离再附流动控制进行了研究,应用表面测压、粒子图像测速(PIV)和热线等多种实验测试技术对后台阶表面压力分布、流场结构以及剪切层特性进行了测试。结果表明,在台阶前缘施加合成射流可有效减小回流区范围和降低再附长度,当合成射流的动量系数为0.301×10^-3时,可使再附点长度减小25%。合成射流控制使得沿台阶下游的湍动能和雷诺应力增强,提高了台阶下游流场的混合效率。热线动态结果表明频率是后台阶分离流动控制的关键参数,当频率为260 Hz、激励频率与剪切层涡脱落频率之比为1.32、激励频率等同于旋涡脱落频率时,合成射流控制效果最好,仅需消耗较小的能量即可实现流动控制的目的。     

端壁非定常脉冲射流对高速扩压叶栅性能的影响

为探究非定常脉冲振荡射流对高速平面扩压叶栅气动性能、分离流动控制以及流场结构的影响,基于CFX数值模拟方法对平面扩压叶栅进行端壁非定常脉冲射流研究,分析射流效果随射流位置、角度和强度的变化规律。结果表明,通过角区脉冲射流可以显著提高叶栅气动性能,仅采用不足叶栅主流0.3%的射流流量,就能使叶栅出口总压损失系数降低28.66%。当射流位于吸力面侧分离起始位置稍下游时控制效果最佳;射流角度、射流强度和射流频率的最佳值分别为α=20°,C_u=110%和F⁺=0.80;脉冲射流具有较好的适应性,在来流冲角i=-8°～+4°内均能降低叶栅损失。脉冲射流主要通过抑制和推迟通道涡和集中脱落涡的发展,减小其影响范围来改善叶栅内的涡系结构。     

螺旋桨等离子体流动控制的增效实验

实验依托搭建的螺旋桨等离子体流动控制测试平台,基于等离子体附壁射流抑制边界层分离的两种机制,采用等离子体射流与来流方向相同的正向射流方式和与来流方向相反的逆向射流方式,研究了微秒脉冲等离子体射流对螺旋桨三维流动分离的控制效果,对比分析了两种射流方式增效特点.实验结果表明:在螺旋桨转速为300r/min,电压峰值为8.5kV,脉冲频率为10~160Hz范围内,正向射流有利于减小螺旋桨转矩,逆向射流对转矩的效果则相反.两种射流方式均提高了螺旋桨拉力和效率,同时其控制效果受脉冲频率的影响较大;正向和逆向两种射流分别使螺旋桨效率最大提高了11.56%,2.79%.      

合成射流大攻角非对称涡控制的试验研究

利用合成射流对细长旋成体大攻角非对称涡控制进行了研究,基于合成射流激励器设计了一频率高达1kHz的非定常小扰动控制机构,并将其成功应用于大攻角非对称涡主动流动控制。应用天平测力和七孔探针流场测试技术,研究了合成射流非定常小扰动电压和频率对非对称涡的控制特性和规律。结果表明,采用合成射流能够完全消除背涡的非对称性,扰动频率是影响非对称涡控制的一个关键参数,高频扰动下模型背风区非对称涡结构趋于无控制流态。且文中结果发现,当攻角α=57.5°、非定常小扰动频率fs=150Hz时,即可将非对称涡完全控制成为对称涡。     

引入DMD方法研究有/无控气流分离的动态结构

为分析非定常流动控制技术抑制分离流的机理,对弯曲扩压通道的试验模型进行了数值模拟,针对扩压通道在无控和采用最佳射流频率状态下的计算结果引入了动力模态分解(DMD)技术进行分析。通过DMD技术能够将包含时空信息的扩压通道复杂流场进行分解,捕获流场包含的动力信息和对应的拟序流动结构。将无控和有控流场分解的结果进行对比分析后表明:采用有效激励措施时,和脱落涡频率一致的涡系对流场的影响更加突显,流场整体上表现得更加有序;非定常控制抑制了一部分涡的增长,使得各模态整体上更加稳定;而有控流场占主导地位的涡系结构相比无控流场较为有序,且对主流区未形成明显的直接影响。     

带射流冲击的短扰流柱排内流场的实验研究

用五孔针对带射流冲击的单排短扰流柱内的流场作了详细的测量,得到并分析了带射流冲击的短扰流柱排内的速度分布规律及流场内的漩涡分布.在实验中清楚地探测到流动在靠近扰流柱表面附近速度较大,在对称中心区域发现了一大片低速区,并有回流和漩涡产生.实验发现由于端壁效应和扰流柱表面的流动分离造成扰流柱排内有较强的漩涡流动,扰流柱根部有马蹄涡产生,扰流柱后尾迹区有湍流涡的发展,流道内侧向压力分布不均匀可形成通道涡.与无射流情况比较发现扰流柱表面分离点后移,尾迹区明显减小.     

端壁等离子体气动激励抑制高负荷压气机叶栅角区流动分离实验

为揭示端壁等离子体气动激励抑制高负荷压气机叶栅角区流动分离的影响规律和流场特征,在不同流场参数和激励条件下分别开展了微秒脉冲和纳秒脉冲等离子体气动激励抑制叶栅流动分离的实验研究.结果表明:端壁等离子体气动激励可以有效抑制叶栅角区的流动分离,其作用效果在攻角为3°时最佳,随攻角的增大逐渐下降;微秒脉冲激励的流动控制效果随来流速度的增大而降低,随激励电压和占空比的增大而提高,最佳非定常脉冲频率为500Hz;在较高来流速度下,微秒脉冲激励的作用效果十分微弱,但纳秒脉冲激励能够有效抑制角区流动分离;纳秒脉冲激励的流动控制效果随激励电压增大而提高,激励频率对控制效果至关重要,作用效果随激励频率的增大而不断增强,但当激励频率为5kHz时,作用效果有所下降.      

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.