Infrared radiation signature of exhaust plume from solid propellants with different energy characteristics

The infrared radiation signature of the plume from solid propellants with different energy characteristics is not the same. Three kinds of double-base propellants of different energy characteristics are chosen to measure the infrared spectral radiance from 1000 cm 1 to 4500 cm 1 of their plumes. The radiative spectrum is obtained in the tests. The experimental results indicate that the infrared radiation of the plume is determined by the energy characteristics of the propellant. The radiative transfer calculation models of the exhaust plume for the solid propellants are established. By including the chemical reaction source term and the radiation source term into the energy equation, the plume field and the radiative transfer are solved in a coupled way. The calculated results are consistent with the experimental data, so the reliability of the models is confirmed. The temperature distribution and the extent of the afterburning of the plume are distinct for the propellants of different energy characteristics, therefore the plume radiation varies for different propellants. The temperature of the fluid cell in the plume will increase or decrease to some extent by the influence of the radiation term.     

Numerical study on similarity of plume infrared radiation between reduced-scale solid rocket motors

This study seeks to determine the similarities in plume radiation between reduced and full-scale solid rocket models in ground test conditions through investigation of flow and radiation for a series of scale ratios ranging from 0.1 to 1. The radiative transfer equation(RTE) considering gas and particle radiation in a non-uniform plume has been adopted and solved by the finite volume method(FVM) to compute the three dimensional, spectral and directional radiation of a plume in the infrared waveband 2–6 μm. Conditions at wavelengths 2.7 μm and 4.3 μm are discussed in detail, and ratios of plume radiation for reduced-scale through full-scale models are examined. This work shows that, with increasing scale ratio of a computed rocket motor, area of the hightemperature core increases as a 2 power function of the scale ratio, and the radiation intensity of the plume increases with 2–2.5 power of the scale ratio. The infrared radiation of plume gases shows a strong spectral dependency, while that of Al_2O_3 particles shows spectral continuity of gray media.Spectral radiation intensity of a computed solid rocket plume's high temperature core increases significantly in peak radiation spectra of plume gases CO and CO_2. Al_2O_3 particles are the major radiation component in a rocket plume. There is good similarity between contours of plume spectral radiance from different scale models of computed rockets, and there are two peak spectra of radiation intensity at wavebands 2.7–3.0 μm and 4.2–4.6 μm. Directed radiation intensity of the entire plume volume will rise with increasing elevation angle.     

Effect of an end plate on surface pressure distributions of two swept wings

A series of wind tunnel tests was conducted to examine how an end plate affects the pressure distributions of two wings with leading edge(LE) sweep angles of 23° and 40°. All the experiments were carried out at a midchord Reynolds number of 8×10~5, covering an angle of attack(AOA) range from -2° to 14°. Static pressure distribution measurements were acquired over the upper surfaces of the wings along three chordwise rows and one spanwise direction at the wing quarter-chord line. The results of the tests confirm that at a particular AOA, increasing the sweep angle causes a noticeable decrease in the upper-surface suction pressure. Furthermore, as the sweep angle increases, the development of a laminar separation bubble near the LEs of the wings takes place at higher AOAs. On the other hand, spanwise pressure measurements show that increasing the wing sweep angle results in forming a stronger vortex on the quarter-chord line which has lower sensitivity to AOA variation and remains substantially attached to the wing surface for higher AOAs than that can be achieved in the case of a lower sweep angle. In addition, data obtained indicate that installing an end plate further reinforces the spanwise flow over the wing surface, thus affecting the pressure distribution.     

Nonlinear flutter wind tunnel test and numerical analysis of folding fins with freeplay nonlinearities

The flutter characteristics of folding control fins with freeplay are investigated by numerical simulation and flutter wind tunnel tests. Based on the characteristics of the structures, fins with different freeplay angles are designed. For a 0° angle of attack, wind tunnel tests of these fins are conducted, and vibration is observed by accelerometers and a high-speed camera. By the expansion of the connected relationships, the governing equations of fit for the nonlinear aeroelastic analysis are established by the free-interface component mode synthesis method. Based on the results of the wind tunnel tests, the flutter characteristics of fins with different freeplay angles are analyzed. The results show that the vibration divergent speed is increased, and the divergent speed is higher than the flutter speed of the nominal linear system. The vibration divergent speed is increased along with an increase in the freeplay angle. The developed free-interface component mode synthesis method could be used to establish governing equations and to analyze the characteristics of nonlinear aeroelastic systems. The results of the numerical simulations and the wind tunnel tests indicate the same trends and critical velocities.     

Effect of pitch angle on initial stage of a transport airplane ditching

Airworthiness regulations require that the transport airplane should be proved to ensure the survivability of the ditching for the passengers. The planned ditching of a transport airplane on the calm water is numerically simulated. The effect of pitch angle on the impact characteristics is especially investigated by a subscaled model. The Reynolds-averaged Navier-Stokes (RANS) equations of unsteady compressible flow are solved and the realizable j-e equations are employed to model the turbulence. The transformation of the air-water interface is tracked by volume of fluid (VOF) model. The motion of the rigid body is modeled by dynamic mesh method. The initial ditching stage of the transport airplane is analyzed in detail. The numerical results show that as the pitching angle increases, the maximal normal force decreases and the pitching motion becomes much gentler. The aft fuselage would be sucked down by the water and lead to pitching up, whereas the low horizontal tail prevents this trend. Consequently, the transport aircraft with low horizontal tail should ditch on the water at an angle between 10 and 12 as a recommendation.     

Thermal shock damage behavior of CVD ZnS by oxygen propane flame：A numerical and experimental study

Chemical vapor deposition zinc sulfide （CVD ZnS） is widely used as an infrared window material to transmit infrared signals, keep the aerodynamic shape and protect its imaging system, which often suffers high temperature and complicated thermal stresses. The purpose of this paper is to investigate the thermal shock damage of CVD ZnS through a finite element method and oxygen propane flame experiments. The finite element model is developed to simulate the temperature and thermal stress fields by an oxygen propane flame. Then, the thermal shock experiments are performed to investigate the thermal shock damage behavior. The results show that the temperature rising rate of the shock surface is fast during the initial heating stage resulting in high thermal stress. After the thermal shock experiment, the scanning electron microscope （SEM） photographs shows that the shock surface of the specimen becomes rough and the microcracks occur in the thermal shock zone. Good agreements are achieved between the numerical solutions and the experimental results.     

Experimental investigation on static/dynamic characteristics of a fast-response pressure sensitive paint

An optical-based technique using Pressure-Sensitive Paint(PSP) is a promising method to measure the distribution of surface pressure on an aerodynamic model. The static and dynamic characteristics of a fast-response PSP that is developed in the Chinese Academy of Sciences(CAS)are analyzed and tested to serve as the basis for experiments on unsteady surface measurement using a fast-response PSP. Two calibration systems used for this study are set up to investigate the temperature dependency, response time, and resolution. A data processing method, used for dynamic data, is analyzed and selected carefully to determine the optimum signal. Results show that the fastresponse PSP can be used normally at temperatures from 25 ℃ to 80 ℃. The effect of temperature on the accuracy of the measurement must be considered when temperatures are beyond the temperature range of 30–40 ℃. The dynamic calibration device with a solenoid valve can achieve a pressure jump within a millisecond order. The resolution is determined by the signal-to-noise ratio of the photo-multiplier tube. Results of the measurement show that the response time of the PSP decreases with a large pressure variation, and the response time is below 0.016 s when the pressure variation is under 40 kPa.     

Numerical Simulation of Rotor-aerodynamic Surface Interaction in Hover Using Moving Chimera Grid

Three-dimensional unsteady Navier-Stokes equations are numerically solved to simulate the aerodynamic interaction of rotor, canard and horizontal tail in hover based on moving chimera grid. The variations of unsteady aerodynamic forces and moments of the canard and horizontal tail with respect to the rotor azimuth are analyzed with the deflection angle set at 0° and 50°, respectively. The pressure map of aerodynamic surfaces and velocity vector distribution of flow field are investigated to get better understanding of the unsteady aerodynamic interaction. The result shows that the canard and horizontal tail present different characteristics under the downwash of the rotor. The canard produces much vertical force loss with low amplitude fluctuation. Contrarily, the horizontal tail, which is within the flow field induced by the down wash of the rotor, produces only less vertical force loss, but the amplitudes of the lift and pitching moment are larger, implying that a potential deflection angle scheme in hover is 50° for the canard and 0° for the horizontal tail.     

Infrared radiation simulation of exhaust system by coupling FVM with narrow band k-distribution

A three-dimensional infrared radiation code for exhaust system was developed by the finite volume method coupled with narrow band k-distribution in non-gray absorbing-emitting media. The final infrared signature had considered the atmosphere effect, and the simulation values were favorably consistent with testing ones. The results indicate that the relative errors considering the effect of atmosphere compared with that of the contrary condition reduce by 31%, it shows that when simulating the infrared radiation of the target which is received by the infrared detectors, even the calculation band is in atmospheric windows 3~5 μm, the effect of atmospheric transmission on infrared signature of the target should not be neglected.      

Analytic estimation and numerical modeling of actively cooled thermal protection systems with nickel alloys

Actively cooled thermal protection system has great influence on the engine of a hypersonic vehicle, and it is significant to obtain the thermal and stress distribution in the system. So an analytic estimation and numerical modeling are performed in this paper to investigate the behavior of an actively cooled thermal protection system. The analytic estimation is based on the electric analogy method and finite element analysis（FEA） is applied to the numerical simulation. Temperature and stress distributions are obtained for the actively cooled channel walls with three kinds of nickel alloys with or with no thermal barrier coating（TBC）. The temperature of the channel wall with coating has no obvious difference from the one with no coating, but the stress with coating on the channel wall is much smaller than that with no coating. Inconel X-750 has the best characteristics among the three Ni-based materials due to its higher thermal conductivity, lower elasticity module and greater allowable stress. Analytic estimation and numerical modeling results are compared with each other and a reasonable agreement is obtained.     

高校廉洁文化教育的载体构建

作为构建反腐倡廉体系的基础性工作之一,高校廉洁文化教育是从源头上防治腐败的根本之策,关系到整个社会廉洁文化的建设。从打造廉洁文化教育教师主体团队,发挥党团组织的战斗堡垒作用,弘扬廉洁校园文化节、占据网络文化教育阵地等方面,对高校廉洁文化教育载体进行研究,旨在为高校廉洁文化教育提供些许参考意见。     

逻辑分析仪部分参数测量结果的不确定度评定

介绍了逻辑分析仪部分参数测量结果的不确定度分析评定方法，评定过程及结论，可应用在对于计量标准进行相应指标的不确定度评定分析上。     

秒表检定的测量不确定度评定

介绍了用标准时间间隔发生器检定秒表时，测量结果不确定度分析和评定过程；讨论了测量不确定度的几个主要来源；通过一组实例，给出了秒表检定不确定度的分析和评定结果，该过程和结论可应用在对于计量标准进行相应指标的不确定度分析上，也可用于估计秒表检定本身的不确定度。     

高校图书馆期刊管理服务创新举措

高校图书馆期刊管理工作需立足本校实际情况,提高期刊信息服务意识及采购质量,建立合理的馆藏期刊结构,创新期刊管理服务措施,拓展期刊服务内涵。高效发挥期刊信息的作用,提高期刊资源利用率,更好地为读者服务。     

方波幅度的测量不确定度

介绍了用众数法评价方波幅度时的不确定度分析和评价过程；讨论了主要的不确定度来源，包括众数判别区间的影响、波形测量系统幅度测量误差的影响等等；给出了减小不确定度的主要措施，并结合一个实例，给出了方波幅度的不确定度评价结果。     

电磁辐射干扰试验的测量不确定度评定

详细地分析了利用吉赫兹横电磁波室进行小体积受试设备(EUT)电磁场抗扰度测试的不确定度。     

非线性方程迭代算法收敛性分析

从几何上分析了迭代格式xn+ 1=φ(xn)所产生的序列收敛于方程根的收敛条件 ,导出了不依赖函数可导性判断迭代序列收敛的收敛定理 ,给出了产生收敛的迭代序列的技巧。     

粗糙表面偏振二向反射特性建模方法研究

针对地面目标光学偏振特性预测对基础材质粗糙表面偏振二向反射特性建模的需求,对比分析国内外常用的经验、物理和半经验等3种偏振二向反射分布模型的优缺点及其适用范围,得出半经验模型更适用于地面目标光学偏振特性预测.在此基础上,研究基于半经验Priest-Gemer模型的参数反演方法,并提出相应的测试方法,设计试验测试验证平台.最后,对模型中的影响因子进行仿真分析,分析结果表明：目标表面偏振二向反射特性与表面纹理特征、复折射率、入射光角度、探测方位角、天顶角等因素相关,且复折射率对目标表面反射率及反射光的偏振度影响较大,粗糙度会影响遮蔽与阻挡效应,使其产生突变效应.     

某型直升机旋翼轴载荷测试方法研究

某型直升机旋翼轴是驱动旋翼旋转的关键疲劳部件,本文主要介绍了对该型直升机主旋翼轴载荷的测试方法:应变片的选择及测点布置,测试原理,测试结果及分析.     

数显测高仪示值误差的测量不确定度评定

针对数显测高仪各校准点示值误差的校准方法,给出了示值误差的数学模型,并以某校准点为例,对该校准点示值误差的合成标准不确定度和扩展不确定度进行了评定.