膨胀效应对激波/湍流边界层干扰的影响

采用直接数值模拟方法对来流马赫数2.9,30°激波角的入射激波与膨胀角湍流边界层干扰问题进行了数值研究。入射激波在壁面上的名义入射点固定在膨胀角角点,膨胀角角度分别取为0°、2°、5°和10°。通过改变膨胀角角度,考察了膨胀效应对干扰区内复杂流动现象的影响规律和作用机制,如分离泡、物面压力脉动特性、膨胀区湍流边界层和物面剪切应力脉动场等。研究发现,膨胀角角度的增大使得分离区流向长度和法向高度急剧降低,尤其是在强膨胀效应下分离泡形态呈现整体往下游偏移的双峰结构。物面压力脉动功率谱结果表明,膨胀角为2°和5°时,分离激波的非定常运动仍表征为大尺度低频振荡,而膨胀角为10°,强膨胀效应极大地抑制了分离激波的低频振荡,加速了下游再附边界层物面压力脉动的恢复过程。膨胀区湍流边界层雷诺剪切应力各象限事件贡献和出现概率呈现逐步恢复到上游湍流边界层的趋势,Görtler-like流向涡结构展向和法向尺度变化剧烈,同时在近壁区将诱导生成大量小尺度流向涡。此外,物面剪切应力脉动场的本征正交分解分析指出,膨胀效应的影响体现在低阶模态能量的急剧降低从而使得高阶模态的总体贡献相对升高。     

超声速膨胀角入射激波/湍流边界层干扰直接数值模拟

为了揭示膨胀效应对激波/湍流边界层干扰区内复杂流动现象的影响规律,采用直接数值模拟方法对来流马赫数2.9、30°激波角的入射激波与10°膨胀角湍流边界层相互作用问题进行了数值研究。系统地探讨了激波入射点分别位于膨胀角上游、膨胀角角点和膨胀角下游3种工况下膨胀角干扰区内若干基本流动现象,如分离泡、物面压力脉动及激波非定常运动、湍流边界层统计特性和相干结构动力学过程等。结果表明,激波入射点流向位置改变对分离区流向和法向尺度的影响显著,尤其是当激波入射点位于角点及其下游区域。研究发现,膨胀角干扰区内物面压力脉动强度急剧减小,分离区内压力波向下游传播速度将降低而在膨胀区内将升高,膨胀效应极大地抑制了分离激波的低频振荡运动。相较于入射激波与平板湍流边界层干扰,入射激波流向位置改变对膨胀角再附区速度剖面对数区及尾迹区影响显著,将导致其内层结构参数升高而外层降低,近壁区内将呈现远离一组元湍流状态的趋势。此外,流向速度脉动场本征正交分解分析指出,主模态空间结构集中在分离激波及剪切层根部附近而高阶模态以边界层内小尺度正负交替脉动结构为主。低阶重构流场结果表明,前者对应为分离泡低频膨胀/收缩过程而后者表征为分离泡高频脉动。     

混合动理学通量WENO方法拓展

在马赫数2.5来流条件下，开展了高频微秒脉冲放电控制压缩折角激波/边界层干扰非定常性的风洞实验，放电位于压缩折角上游沿流向布局的6对电极之间，所选取的放电频率为14 kHz,接近于来流边界层的特征频率。采用高速纹影成像技术记录流场的动态变化，并基于纹影图像灰度值的时间序列采用平均、均方根、本征正交分解、动态模态分解、傅里叶变换等方法进行处理，对比研究有/无控制情形下激波/边界层干扰的非定常特性。研究发现，对于无控情形的基准流场，流动的低频特性表现为分离激波的振荡及边界层大尺度涡经过激波的脱落行为，中、高频特性表现为边界层小尺度涡与激波的相互作用；对于受控情形，来流边界层内的大涡尺度在放电作用下增大，大尺度涡与分离激波相互作用使得激波的振荡转变为稀疏压缩波的脉动，流经激波的边界层脉动更强，分离激波的低频振荡(10～300 Hz)有所改善。此时，流动的低频特性主要表现为边界层大尺度涡经过激波的脱落行为，而中、高频特性与基准流场相似。     

激波/湍流边界层干扰物面剪切应力统计特性

为了揭示激波/湍流边界层干扰区内物面剪切应力统计特性的演化规律,采用直接数值模拟方法对来流马赫数2.9、12°激波角的入射激波与平板湍流边界层相互作用问题进行了研究。通过与风洞试验数据的比较分析,验证了计算结果的可靠性。系统地探究了干扰区内物面剪切应力的典型特征,如预乘谱、概率密度分布和相干结构等。研究结果表明,分离激波的低频振荡运动对流向及展向分量的预乘谱均没有实质影响,其脉动仍以高频特征为主,低频能量变化较小。干扰区内流向剪切应力概率密度函数分布变化剧烈,分离泡内对数正态分布规律不再适用,而展向剪切应力在干扰区内与正态分布较为接近。相较于上游湍流边界层,分离泡内物面剪切应力矢量夹角与幅值的联合概率密度变化显著,峰值概率降低,峰值范围增大。此外,流向剪切应力脉动场的本征正交分解分析指出,主能量模态与分离激波的低频振荡以及下游再附边界层内的Görtler-like流向涡结构密切相关。     

超声速压缩拐角激波/边界层干扰动力学模态分解

压缩拐角激波与边界层干扰问题广泛存在于高速飞行器的外部和内部流动中,其非定常复杂流场结构对飞行器气动性能影响显著。动力学模态分析将有助于进一步加深理解激波与边界层干扰流场不同特征频率对应的流动结构及动力学特性,为揭示其复杂流动机理提供参考。本文采用动态模态分解(DMD)方法对来流马赫数为2.9、24°压缩拐角内激波与超声速边界层干扰下的非定常流动进行了模态分析。评估了稀疏改进动态模态分解方法在压缩拐角流动中的适用性,研究了湍流干扰和转捩干扰下典型特征频率对应的动力学模态空间结构差异及其原因,分析了转捩边界层展向非均匀性对低频/高频模态动力学机制的影响规律。研究发现,湍流干扰与转捩干扰下拐角干扰区内均存在两类截然不同的动力学模态:低频模态和高频模态。低频模态结构集中在分离激波及分离泡剪切层的根部,表征为分离泡的大尺度膨胀和收缩运动;高频模态空间分布则以平均声速线附近正负交替结构为主,对应为边界层内不稳定波沿剪切层往下游的传播。转捩边界层的展向结构对低频模态运动特性影响明显,而对高频模态的影响则相对较小。     

展向振荡对激波/湍流边界层干扰的影响

周期振荡作为一种有效的壁面流动控制手段受到广泛关注,而其对激波/湍流边界层干扰的影响目前鲜有研究。本文采用高精度直接数值模拟（DNS）方法对马赫数2.9、12°激波入射角、强振荡下的激波/湍流边界层干扰进行了系统研究。通过与无振荡工况的定量比较,揭示了展向强振荡对干扰区内复杂流动结构的影响规律及作用机制,如分离泡尺度、物面压力脉动非定常特性、物面剪切的非定常特性及统计特征等。研究发现：在展向强振荡作用下,分离点位置提前,间歇区长度增大;同时由于分离泡内强黏性耗散的影响,展向振荡的穿透高度约为分离泡高度的4%,因而对流动结构不会产生实质影响。但展向强振荡会对壁面附近流动造成显著影响,如强振荡诱导的壁面展向速度远大于流向速度,造成流向剪切与展向剪切之间夹角的概率密度函数峰值从0°偏移到80°~90°之间。物面压力及剪切本征正交分解分析表明,展向振荡会导致模态能量从低阶模态向高阶模态转移,降低低频运动的能量占比,增强再附后Görtler涡等壁面附近旋涡结构的强度。     

压缩拐角激波与旁路转捩边界层干扰数值研究

为了研究激波与旁路转捩边界层的干扰机理,采用直接数值模拟(DNS)方法对来流马赫数Ma∞=2.9,24°压缩拐角内激波与转捩边界层的相互作用进行了系统的研究。考察了旁路转捩干扰下压缩拐角内分离区形态和激波波系结构的典型特征。比较了转捩干扰与湍流干扰流动结构的差异,并分析了造成差异的原因。研究了拐角内转捩边界层的演化特性,探讨了转捩干扰下脉动峰值压力和峰值摩阻的分布规律及形成机制。研究结果表明:相较于湍流干扰,两侧发卡涡串的展向挤压使得分离区起始点以V字型分布,且分离激波沿展向以破碎状态为主,激波脚呈现多层结构;拐角内的干扰作用急剧加速了边界层的转捩过程;转捩干扰下的拐角内峰值脉动压力以单峰结构出现在分离区的下游,同时干扰区内的强湍动能和高雷诺剪切应力使得其局部峰值摩阻系数要高于湍流干扰。     

弯曲后掠压缩拐角激波/湍流边界层干扰特性研究

为研究内转式进气道前体压缩激波与机体边界层之间的弯曲后掠压缩拐角激波/湍流边界层干扰现象,对矩形捕获型线、直母线圆锥基准流场生成的内转式进气道压缩型面进行简化,并利用数值仿真方法对简化模型进行计算,分析并对比了非耦合和耦合情况下弯曲后掠压缩拐角激波/湍流边界层干扰特性.结果表明:非耦合模型所形成的分离区呈弯刀形,分离区...     

基于大涡模拟的压缩拐角激波/边界层干扰研究

为了提高对激波/边界层相互干扰的基本理解,采用大涡模拟(LES)对来流马赫数Ma=2.9,转角为24°的压缩拐角激波与湍流边界层相互干扰进行了研究。采用回收/调节方法作为入口湍流生成技术,并在超声速平板湍流边界层上进行了验证。采用涡识别方法和数值纹影图等流动显示方法,研究了干扰区内激波与边界层相互干扰的结构变化特征。通过对比分析湍动能和雷诺正应力在不同流向位置的分布规律,研究表明:经过激波干扰后湍动能主要集中在边界层的外层,并在拐角附近形成一个低湍动能区;雷诺正应力流向分量和法向分量在边界层内的分布呈现为单峰结构,而展向分量呈现为双峰结构。运用间歇因子对分离激波的大尺度流向运动进行研究,发现激波围绕着平均分离点作前后运动,运动的尺度等于进口湍流边界层厚度的72%。证实了拐角下游G?rtler流向涡对的存在,并对其展向分布和空间演化特性进行了详细研究。     

高超声速有攻角锥裙直接数值模拟

采用直接数值模拟方法对有攻角的高超声速7°～34°锥裙开展了数值研究,通过对比0°、90°、180°周向子午面,评估了三维横流效应对激波/边界层干扰的影响规律和作用机制,包括壁面压力、摩阻、热流分布,分离泡非定常运动,再附边界层演化等。研究发现,不同周向站位均出现流动分离,横流区、迎风区内复杂激波结构与边界层相互作用导致壁面压力、摩阻、热流显著升高。热流与压力的比值在干扰区上升后由于再附降低,而热流与摩阻的雷诺比拟关系在分离区则完全失效。分离泡面积脉动的功率谱结果表明,分离泡非定常膨胀/收缩运动呈低频特征,且分离泡呼吸与激波低频振荡在横流区密切相关,在迎风区存在迟滞,而在背风区不相关。速度脉动场的本征正交分解结果表明,分离区的低频特征与低阶模态相应的剪切层附近大尺度结构相关。对下游再附边界层演化分析指出,攻角的存在导致雷诺应力在再附点附近大幅增强,其流向分量的恢复最为迅速,雷诺应力分量的峰值位置在背风区沿流向持续外移,而在迎风区、横流区已迅速向内层恢复。此外,雷诺应力各向异性不变量分布进一步表明干扰下游的近壁区湍流各向异性峰值在背风区弱于迎风区。     

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.