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1.
A brief survey is presented of trends in work reported at four International Stirling Engine Conferences held during the 1980s. The discussion covers international participation, publication sources and types, engine types, specialized engines, sponsoring institutions and observed trends 相似文献
2.
In the present survey, various methods for the acoustic design of aeroengine nacelle are first briefly introduced along with the comments on their advantages and disadvantages for practical application, and then detailed analysis and discussion focus on a kind of new method which is called ‘‘transfer element method'(TEM) with emphasis on its application in the following three problems: turbomachinery noise generations, sound transmission in ducts and radiation from the inlet and outlet of ducts, as well as the interaction between them. In the theoretical frame of the TEM, the solution of acoustic field in an infinite duct with stator sound source or liner is extended to that in a finite domain with all knows and unknowns on the interface plane, and the relevant acoustic field is solved by setting up matching equation. In addition, based on combining the TEM with the boundary element method(BEM) by establishing the pressure and its derivative continuum conditions on the inlet and outlet surface, the sound radiation from the inlet and outlet of ducts can also be investigated. Finally, the effects of various interactions between the sound source and acoustic treatment have been discussed in this survey. The numerical examples indicate that it is quite important to consider the effect of such interactions on sound attenuation during the acoustic design of aeroengine nacelle. 相似文献
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The properties of spontaneous reconnection of a current sheet analyzed via direct three-dimensional simulations are presented. In particular the non-linear dynamics of resistive instabilities has been studied in absence or in presence of velocity shears. It is shown that full three-dimensional simulations allow the inclusion of a rich variety of (ideal) secondary instabilities which, depending on the initial equilibrium magnetic field configuration, determine the final fate of the system in the fully non linear regime. In particular in presence of a guide-field the dynamic is similar to what observed in two-dimensional simulations with energy driven toward both smaller and larger scales and energy spectra anisotropy. For different magnetic field configurations, the final state is characterized by the disruption of the coalesced structure created during the resistive phase and the system is characterized by a more chaotic state. A?discussion on the importance of high-order numerical techniques in numerical simulations of magnetic reconnection is also present. 相似文献
5.
This is the second part of a two-part paper which summarizes work pursued by the author in 1967 [2]. The paper describes the application of minimum-variance estimation techniques for in-flight alignment and calibration of an inertial measurement unit (IMU) relative to another IMU and/or some other reference. The first paper [1] formulates the problem, and this paper reports numerical results and analyses. The approach taken is to cast the problem into the framework of Kalman-Bucy estimation theory, where velocity and position differences between the two IMU's are used as observations and the IMU parameters of interest become part of the state vector. Instrument quantization and computer roundoff errors are considered as measurement noise, and environmental induced random accelerations are considered as state noise. In this paper, numerical results for three important IMU error parameter configurations are presented and discussed. The main results of the paper determine the effects of state and observation noise levels and the nominal trajectory on the identifications of the errors for these configurations. A discussion of the minimum number of trajectory maneuvers and of the optimal trajectory maneuvering is given. 相似文献
6.
A survey of current knowledge about Jupiter, Saturn, Uranus, Neptune, Pluto, and their satellites is presented. The best available
numerical values are given for physical parameters, including orbital and body properties, atmospheric composition and structure,
and photometric parameters. The more acceptable current theories of these bodies are outlined with thorough referencing offering
access to the details. The survey attempts to cover the literature through May 1, 1972.
Prepared Under Contract No. NAS7-100 National Aeronautics and Space Administration. 相似文献
7.
《中国航空学报》2021,34(11):48-65
Emissions produced by the aviation industry are currently a severe environmental threat; therefore, aviation agencies and governments have set emission targets and formulated plans to restrict emissions within the next decade. Hybrid aircraft technology is being considered to meet these targets. The importance of these technologies lies in their advancements in terms of aircraft life cycles and environmental benignity. Owing to these advancements, hybrid electric systems with more than one power source have become promising for the aviation industry, considering that the growth of air traffic is projected to double in the next decade. Hybrid technologies have given future hybrid fans and motor-fan engines potential as alternative power generators. Herein, Turboelectric Distributed Propulsion (TeDP) is discussed in terms of power distribution and power sources. The fundamentals of turbofan and turboshaft engines are presented along with their electricity-generation mechanism. TeDP is discussed from a design viewpoint, with a detailed discussion of different types of hybrid electric and turboelectric systems. Examples of proposed TeDP aircraft models and numerical modelling tools used to simulate the performance of TeDP models are reviewed. Finally, innovative turboelectric systems in which electric power savers and mechanical gear changers have been discarded for weight optimisation are presented along with other prospective models, engines, approaches, and architectures. The findings of this review indicate the knowledge gaps in the field of numerical modelling for NASA’s TeDP and its capability to increase the efficiency by up to 24% with a 50% reduction in emissions relative to those of conventional gas turbines. 相似文献
8.
The smoothed particle hydrodynamics (SPH) method is usually expected to be an effi-cient numerical tool for calculating the fluid-structure interactions in compressors; however, an endogenetic restriction is the problem of low-order consistency. A high-order SPH method by intro-ducing inverse kernels, which is quite easy to be implemented but efficient, is proposed for solving this restriction. The basic inverse method and the special treatment near boundary are introduced with also the discussion of the combination of the Least-Square (LS) and Moving-Least-Square (MLS) methods. Then detailed analysis in spectral space is presented for people to better under-stand this method. Finally we show three test examples to verify the method behavior. 相似文献
9.
It is the objective of this survey to review research and development results of flapping-wing propulsors and of vehicles equipped with them. Given the complex and multi-disciplinary character of the problem, a wide range of questions is considered in order to provide a general idea of the state-of-the-art. The main attention is directed at the aerohydrodynamics of flapping-wing propulsors. The major relevant mathematical models and the corresponding numerical results are presented together with the experimental data obtained up to the present time. Also, the physical and the design factors are discussed, which affect the aerohydrodynamic characteristics of flapping wings and that therefore have to be accounted for in the modern mathematical models. Experimental data and numerical modeling results are compared to determine domains of validity of the latter for the aerohydrodynamic design of full-scale air and marine vehicles. Also, existing engineering solutions for vehicles with flapping-wing propulsors are presented and prospective directions for future investigations are outlined. 相似文献
10.
刚体姿态仿真方法研究 总被引:5,自引:0,他引:5
首先论述了姿态描述的四种方法:欧拉角、欧拉轴旋转参数、方向余弦和四元数法,重点介绍了四元数法在飞行器运动学上的应用,它消除了欧拉方程的奇异性,计算效率也远远优于其他三种方法;最后讨论了数值仿真的方法及误差。 相似文献
11.
A Class of TVD Type Combined Numerical Scheme for MHD Equations With a Survey About Numerical Methods in Solar Wind Simulations 总被引:3,自引:0,他引:3
It has been believed that three-dimensional, numerical, magnetohydrodynamic (MHD) modelling must play a crucial role in a
seamless forecasting system. This system refers to space weather originating on the sun; propagation of disturbances through
the solar wind and interplanetary magnetic field (IMF), and thence, transmission into the magnetosphere, ionosphere, and thermosphere.
This role comes as no surprise to numerical modelers that participate in the numerical modelling of atmospheric environments
as well as the meteorological conditions at Earth. Space scientists have paid great attention to operational numerical space
weather prediction models. To this purpose practical progress has been made in the past years. Here first is reviewed the
progress of the numerical methods in solar wind modelling. Then, based on our discussion, a new numerical scheme of total
variation diminishing (TVD) type for magnetohydrodynamic equations in spherical coordinates is proposed by taking into account
convergence, stability and resolution. This new MHD model is established by solving the fluid equations of MHD system with
a modified Lax-Friedrichs scheme and the magnetic induction equations with MacCormack II scheme for the purpose of developing
a combined scheme of quick convergence as well as of TVD property. To verify the validation of the scheme, the propagation
of one-dimensional MHD fast and slow shock problem is discussed with the numerical results conforming to the existing results
obtained by the piece-wise parabolic method (PPM). Finally, some conclusions are made.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
Observations relevant to current models of the solar dynamo are presented, with emphasis on the history of solar magnetic activity and on the location and nature of the solar tachocline. The problems encountered when direct numerical simulation is used to analyse the solar cycle are discussed, and recent progress is reviewed. Mean field dynamo theory is still the basis of most theories of the solar dynamo, so a discussion of its fundamental principles and its underlying assumptions is given. The role of magnetic helicity is discussed. Some of the most popular models based on mean field theory are reviewed briefly. Dynamo models based on severe truncations of the full MHD equations are discussed. 相似文献
13.
Radar Electronic Counter-Countermeasures 总被引:1,自引:0,他引:1
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本文利用静力问题的基本解建立了Hoff型夹层板振动分析的边界积分方程。在数值实现过程中,边界上和区域内的未知函数均釆用线性插值以提高计算精度。数值结果表明本文方法具有未知量少和计算精度高等优点。对于低阶频率,本文结果与精确解的误差不大于1%。 相似文献
15.
《Progress in Aerospace Sciences》2002,38(4-5):389-420
An in-depth review of boundary-layer flow-separation control by a passive method using low-profile vortex generators is presented. The generators are defined as those with a device height between 10% and 50% of the boundary-layer thickness. Key results are presented for several research efforts, all of which were performed within the past decade and a half where the majority of these works emphasize experimentation with some recent efforts on numerical simulations. Topics of discussion consist of both basic fluid dynamics and applied aerodynamics research. The fluid dynamics research includes comparative studies on separation control effectiveness as well as device-induced vortex characterization and correlation. The comparative studies cover the controlling of low-speed separated flows in adverse pressure gradient and supersonic shock-induced separation. The aerodynamics research includes several applications for aircraft performance enhancement and covers a wide range of speeds. Significant performance improvements are achieved through increased lift and/or reduced drag for various airfoils—low-Reynolds number, high-lift, and transonic—as well as highly swept wings. Performance enhancements for non-airfoil applications include aircraft interior noise reduction, inlet flow distortion alleviation inside compact ducts, and a more efficient overwing fairing. The low-profile vortex generators are best for being applied to applications where flow-separation locations are relatively fixed and the generators can be placed reasonably close upstream of the separation. Using the approach of minimal near-wall protuberances through substantially reduced device height, these devices can produce streamwise vortices just strong enough to overcome the separation without unnecessarily persisting within the boundary layer once the flow-control objective is achieved. Practical advantages of low-profile vortex generators, such as their inherent simplicity and low device drag, are demonstrated to be critically important for many applications as well. 相似文献
16.
The numerical simulation of the flow around a 65° delta wing configuration with rounded leading edges is presented. For the numerical simulation the DLR TAU-Code is used which is based on an unstructured hybrid mesh approach. Within this paper several numerical results are shown, solving the steady RANS equations by different turbulence models. The simulations are carried out within the RTO/AVT-113 task group focusing on experimental and numerical research on delta wing configurations with rounded leading edges. Within this paper the focus is related to the flow topology depending on the angle of attack as well as on Reynolds number effects. Finally the results are compared and verified by experimental data. 相似文献
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本文对坑的三维分离流动做了低速粘流与无粘流的相互作用计算。对三维边界层反方法进行了分析和讨论。用数值试验的方法验证了在H和α作为已知量的情况下,三维边界层反方法的积分方程是双曲型的,并提出了一种近似数值特征线法进行求解。无粘流采用低速位流面元法。计算表明所用方法可计算出三维效应很强(即横向变化很大)的三维边界层分离流动。 相似文献
19.
交叉式多股流板翅式换热器数值研究 总被引:2,自引:1,他引:1
借鉴顺逆式板翅式换热器研究成果,分析了交叉式多股流板翅式换热器传热机理,建立了基于有限容积法的多股流板翅式换热器传热数学模型,经过合理假设将翅片间距与单元格尺寸独立,拓展了前人数学模型适用范围.同时,以机载交叉式3股流板翅式换热器为例,对单元格尺寸选取进行了探讨,对同一通道单元格内流体流动横向传热进行了分析,证明了忽略流动横向传热的可行性,从而在保证精度不变条件下提高了计算效率;并在流体变入口参数条件下进行试验,对数值计算方法进行验证,通过与试验数据对比,理论计算误差小于7.9%,证明了数值计算方法的合理性. 相似文献
20.
The rapid neutron-capture process and the synthesis of heavy and neutron-rich elements 总被引:1,自引:0,他引:1
Wolfgang Hillebrandt 《Space Science Reviews》1978,21(6):639-702
Recent developments in theoretical model-calculations for the synthesis of heavy and neutron-rich chemical elements by means of the rapid neutron-capture process are reviewed. Special emphasis is put on a discussion of possible astrophysical sites, e.g. supernova models, and extrapolated nuclear input data as well. Numerical methods to solve complex nuclear reaction-networks are presented. 相似文献