凝胶推进剂供给管流的压降数值研究

为了探索凝胶推进剂输送数值研究的方法及可行性,在凝胶推进剂直圆管和突变截面管道流动实验的基础上,采用Power-Law与Carreau两种本构模型,建立了非牛顿流体的二维不可压缩稳态流动的求解方法,通过交错网格进行离散求解,开展了基于SIMPLE算法的凝胶推进剂供给管流的压降数值仿真,分析了壁面滑移修正及触变性对管流压降的影响。结果表明:模拟液直圆管流的截面轴向速度的数值解同解析解的误差小于2%;考虑壁面滑移修正的管流压力损失与实验值一致性较好;触变性对突变截面管道流动的局部压降有显著的影响,这对于进一步优化供给管路及喷注器设计具有一定的理论指导意义。     

幂律型凝胶推进剂射流撞击雾化SPH模拟

为研究幂律型本构关系对于凝胶推进剂雾化的影响,应用光滑粒子流体动力学(SPH)方法进行了凝胶推进剂的射流撞击雾化仿真,并与实验结果进行了对比。推导了幂律型本构关系的SPH求解方法,发展了三维隐式SPH算法,克服了凝胶推进剂的高粘度对于时间步长的限制。制备了胶凝剂含量分别为1%,2%的两种水基凝胶推进剂模拟液并进行了6种工况的雾化实验和数值模拟,证明了本文SPH方法可以有效模拟凝胶推进剂的雾化问题。对于本文研究的工况,雾化区内模拟液的表观粘度普遍高于10-2N?s/m2,从撞击点至雾化区下游,模拟液的表观粘度呈震荡上升分布。分析表明,雾化区下游的高表观粘度是造成凝胶推进剂雾化生成液丝及大尺寸液滴的重要原因。     

幂律流体液膜破裂的线性稳定性分析

为对凝胶推进剂撞击式喷嘴产生的液膜的破裂行为进行研究,使用线性稳定性分析方法并结合幂定律本构方程对幂律流体液膜的稳定性进行了研究,并对流体物性参数、流变参数等对液膜流动稳定性的影响规律进行了分析.结果发现:稠度系数、流动指数和表面张力越大,液膜表面扰动波的增长率越小,波长越大.而较高的液膜速度、气液密度比和液膜厚度都使扰动波增长率变大,但波长随液膜速度和气液密度比的增大而减小,而液膜厚度的情况却相反.理论计算与实验值的对比表明,线性稳定性分析能较准确地预测液膜的破碎长度,但预测的表面波长却大于实验值.      

幂律型凝胶推进剂管路中的流动特性

为研究幂律型凝胶推进剂在管路中的流动特性,对直径4~14 mm,长度0.5~2.0 m的一组直圆管和直径6 mm,弯角20°~90,°弯曲半径比1~5的一组弯管,在1~30 m/s的流速下,用3种模拟液进行了实验和仿真。对收缩角10°~50°,收缩比3~1.5的收缩和扩张管,在流速1~30m/s的范围内,用模拟液进行了仿真。结果表明,其它条件相同时,管长、弯角、流速和收缩比增加,流动损失增加;凝胶推进剂在管路中呈"柱塞"形流动,其特性取决于流速、流变指数和稠度系数;管壁附近的剪切速率最大,表观粘度最小;弯管内侧剪切速率小于外侧剪切速率;收缩型截面中,剪切速率逐步增大,粘度逐步降低;突缩和突扩截面存在低速回流区。     

凝胶推进剂管道输送系统流阻特性实验和数值研究

为研究凝胶推进剂的流变特性,建立了两种不同结构的凝胶推进剂管道输送系统模型。在直管流变特性实验基础上,确定了凝胶推进剂的流变参数,采用凝胶推进剂和水对整个凝胶推进剂管道输送系统流动进行了数值模拟,并将结果与输送系统流阻实验的实验值进行了对比分析。结果显示数值计算结果与实验结果吻合较好。     

固体火箭内流场的时均和大涡模拟技术对比研究

分别采用时均RNG湍流模拟和大涡模拟(LES)方法对某型固体火箭发动机内流场进行了瞬态数值模拟研究,建模过程中针对推进剂燃烧以及燃面边界采用了修正壁面通量的方法,并使用了动网格技术。结果表明:大涡模拟技术可以得到发动机内湍流流场中详细拟序结构,时均湍流模拟对于火箭发动机内流场时均量的模拟仍有较好的工程精度。     

非对称喷管超声速流场的PIV实验与数值模拟

选取了跟随性能以及散射性能都上佳的二氧化钛粒子,利用了粒子图像测速仪(particle image velocimetry,PIV)对不同落压比下的非对称喷管(single expansion ramp nozzle,SERN)流场进行了测量,成功获取了相应流动结构,以及沿程上壁面压力分布和速度场等.在测得的图像中,可以清晰地观察到由于过膨胀产生的激波与膨胀波系,并进一步获得出口速度分布.运用计算流体动力学数值模拟方法,对实验状态下的非对称喷管进行了模拟.对比结果发现:PIV实验测得流场结构能很好地与其吻合,这互相验证了CFD计算和PIV实验的正确性及可靠性.      

SSG模型在压缩拐角激波/湍流边界层干扰模拟中的应用

采用非线性方案模化雷诺应力再分配项的二阶矩雷诺应力输运模型——SSG模型和两方程线性涡粘模型SST模型,对24°高雷诺数二维压缩拐角激波/湍流边界层相互干扰流动进行数值模拟。通过在壁面压力分布、壁面摩擦阻力系数分布、截面速度分布及分离区大小等方面与实验数据比较,综合评估了上述两种模型模拟该问题的能力。结果表明:两种湍流模型在上述各方面都取得了与实验较为一致的结果,但相比较而言,除SST模型在流动再附后对壁面摩擦阻力系数分布的模拟更接近实验值外,SSG模型结果在上述其他方面均更接近实验值。本文工作为压缩拐角激波/湍流边界层干扰这类流动数值模拟的湍流模型选择提供了参考。     

基于旋转爆震三维流场结构分析的计算模型对比研究

为了研究不同计算模型对三维旋转爆震数值模拟的影响,分别基于Euler方程、N-S方程、RANS方法和IDDES方法并结合滑移、无滑移壁面边界条件,耦合氢气/空气的有限化学反应速率模型（7组分8基元反应）,采用高分辨率的五阶有限差分格式WENO-PPM5离散对流项,对圆环筒型燃烧室内的三维旋转爆震波进行数值模拟,得到了不同模型下旋转爆震波的流场结构、传播特性和推力性能。对比了不同计算模型对流场结构的影响。当采用滑移壁面边界条件时,Euler方程和N-S方程的计算结果较为一致。当使用无滑移壁面边界条件时,边界层的存在会导致可燃混气与燃烧产物之间接触面上的爆燃燃烧区域沿壁面向上游渗透,增大爆燃区域的范围;且爆震波锋面非受限侧变窄、严重变形,不同计算方法计算的变形程度有所不同。     

跨声速条件下轴对称收扩喷管内外流场的数值研究

采用有限体积法,二阶精度插值的Roe格式对三维流场N-S方程进行空间离散;采用LUSGS隐式时间推进法和多重网格技术加快计算收敛速度;采用不同湍流模型、壁面函数对轴对称喷管内外流场进行三维数值模拟.计算结果与实验数据对比表明,采用涡粘修正的RNG模型,内流场使用增强壁面函数,外流场使用标准壁面函数可以得到准确的计算结果.研究表明:在亚声速条件下,喷管外壁面压力分布随落压比的变化不大;超声速条件下,喷管外壁面激波随着落压比的增大前移.      

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.