Aerospace Propulsion Research Articles

희박기체 및 MEMS 열유동장 해석을 위한 벽면 슬립모델 개발

희박 상태 비행체 외부 및 추진장치 내부 유동이나 MEMS 장치의 기체유동은 높은 열적 비평형성으로 인해 벽면 슬립모델을 필요로 한다. 조절계수와 벽면속도 구배를 바탕으로 하는 Maxwell 조건이 주로 사용되어 왔지만, 조절계수를 자체적으로 정의할 수 없고, 일차 미분 형태로 인해 실제 적용시 수치적 관점에서 효율적이지 못한 어려움이 있었다. 본 연구에서는 이 문제를 해결하고자 Langmuir의 벽면-기체입자 흡착이론을 이용한다. 벽면온도, 벽면-기체입자간 물리적 힘의 함수인 조절계수를 유도하고, 입자형태의 차이를 감안할 수 있는 물리적 슬립모델을 개발하여 기존 Maxwell 모델과 비교하였다. 또한 내부, 외부, 열유체 유동에 관한 슬립모델의 해석적 해를 실험값과 비교하여 그 유용성을 확인하였다. Wall slip models are essential to the study of nonequilibrium gas transport in rarefied and microscale condition that can be found in gas flows associated with aerospace vehicle, propulsion system, and MEMS. The Maxwell slip model has been used for this type of problem, but it has difficulty in defining the so-called accommodation coefficient and has not been very effective in numerical implementation. In the present study, on the basis of Langmuir's theory of the adsorption of gases on metals, a physical slip model is developed. The concept of the accommodation coefficient and the difference of gas particles are clearly explained in the new model. It turned out that the Langmuir model recovers the Maxwell model in the first-order approximation. The new models are also applied to various situations including internal flow in a microchannel. Issues of validation of models are treated by comparing analytic results with experiment.

Analysis of Dual-Mode Hydrocarbon Scramjet Operation at Mach 4-6.5

Reynolds averaged Navier ‐Stokes calculations have been performed for a U.S. Air Force Research Laboratory/ Aerospace Propulsion Ofe ce scramjet combustor designed for Mach 4.0 ‐6.5 e ight. The combustor e owpath is unique in that it is entirely free of e ow obstructions with fuel injection from wall-mounted injection ports and e ameholding established by means of a recessed cavity. Calculations were performed at the minimum (Mach 4.0) andmaximum(Mach6.5)e ightdesign conditions.Thecombustoroperatedin dualmodeattheMach4.0condition. The precombustion shock train formed a region of low-momentum/separated e ow adjacent to the combustor side wall. This proved to be a primary source of e ameholding, with the recessed cavity adding additional e ameholding support. The e ow was notthermally choked at theMach 6.5 condition,resulting in very little upstream interaction. The mixing process at the Mach 4.0 e ight condition was considerably more efe cient than that seen at the Mach 6.5 condition, due primarily to the shock-induced e ow distortion and larger residence time. Even with the reduced mixing levels predicted at the Mach 6.5 condition, the combustion efe ciency was comparable to that achieved at the Mach 4.0 condition. The solutions obtained for dual-mode operation were particularly sensitive to choice of turbulence model and values specie ed for the turbulent Prandtl and Schmidt numbers. Overall, the solution sensitivity to grid resolution was small relative to the solution sensitivity to modeling uncertainties.

SCALAR MIXING AND CHEMICAL REACTION SIMULATIONS USING LATTICE BOLTZMANN METHOD

We simulate scalar mixing and chemical reactions using the lattice Boltzmann method. Simulations of initially non-premixed binary mixtures yield scalar probability distribution functions that are in good agreement with direct numerical simulation (of Navier-Stokes equation) data. One-dimensional chemically-reacting flow simulation of a premixed mixture yields a flame speed that is consistent with experimentally determined value. These results serve to establish the feasibility of the lattice Boltzman method as a viable tool for computing turbulent combustion.

On the laser ignition and initiation of explosives

Energetic materials are conventionally ignited by the application of heat to some part of an explosive target. This is most often provided by a flame or by electrical heating using a resistive wire. The material responds by thermally heating and starting a burning zone, which spreads out from the ignition point generating gas. In some cases this zone can accelerate (due to the effect of this gas) into a reactive shock wave, termed detonation. Lasers are used in a variety of applications to thermal heat a range of materials, and thus seem an obvious candidate to trigger chemical reaction in energetic ones. A light pulse offers several advantages over an electrical one, since it may be delivered down a path both immune to electrical effects and chemically stable. Thus, the triggering of safety apparatus (such as the firing of bolts on aircraft exits) represents a major thrust in the development of laser–triggered explosive devices. The energy of the pulse may be used in one of two ways to achieve these effects. In the first, the laser is shone directly upon the chemical medium, which absorbs the light at discrete wavelengths. In the second, it is used to vaporize a metallic flyer that is launched to impact on a target creating a high–pressure zone. Either mechanism starts the required reaction. However, when the pulse is delivered directly to the material, detonation is found to proceed immediately with no transition via burning. This makes the process inexplicable using present concepts. This review will address a range of the experiments conducted and theories developed for this novel field. However, it should be emphasized that the fundamental mechanisms remain to be fully explained making the application both academically stimulating as well as industrially important.

Chemical vapor deposition of alpha aluminum oxide for high-temperature aerospace sensors

Thin-film thermocouples and strain gages are being developed for high-temperature application on aerospace propulsion hardware for both development test purposes and as active control sensors. The critical technology necessary in the fabrication of the sensor is an adherent, dense, and homogeneous dielectric to provide electrical isolation at engine operating temperatures. Techniques are being developed to create a crystalline aluminum oxide dielectric formed by a combination of a thermally grown oxide (TGO) from a NiCoCrAlY hardcoating, which is then enhanced with the addition of a chemical vapor deposited (CVD) crystalline aluminum oxide layer. This article will focus on the process development used to deposit the α alumina layer on the TGO using CVD in a coldwall reactor at 1100 °C. The chemistry employed in this process is the pyrolitic decomposition of aluminum tri-isopropoxide. The hexagonal (HCP) α phase is achieved at deposition temperatures of 1000–1100 °C, as confirmed by x-ray diffraction analysis. By eliminating gas phase and hot wall decomposition, this approach minimizes precursor depletion effects, yielding a more dense and uniform film morphology. Conformal coatings up to 10 μm thick with high resistivity and good adhesion and hardness have been observed on complex airfoil geometries. Growth rates up to 10 μm/h are possible, although low growth rates lead to more desirable film properties. The kinetics of the deposition indicate that the reaction proceeds by a mass transport limited mechanism. Uniform temperature control over highly complex geometry is desirable, but not essential for uniform film growth. Results indicate that the gas flow uniformity and the precursor transport rate are the critical variables.

Computational Simulation of Gas Turbines: Part 1—Foundations of Component-Based Models

Designing and developing new aerospace propulsion systems is time-consuming and expensive. Computational simulation is a promising means for alleviating this cost, but requires a flexible software simulation system capable of integrating advanced multidisciplinary and multifidelity analysis methods, dynamically constructing arbitrary simulation models, and distributing computationally complex tasks. To address these issues, we have developed Onyx, a Java-based object-oriented domain framework for aerospace propulsion system simulation. This paper presents the design of a common engineering model formalism for use in Onyx. This approach, which is based on hierarchical decomposition and standardized interfaces, provides a flexible component-based representation for gas turbine systems, subsystems and components. It allows new models to be composed programmatically or visually to form more complex models. Onyx’s common engineering model also supports integration of a hierarchy of models which represent the system at differing levels of abstraction. Selection of a particular model is based on a number of criteria, including the level of detail needed, the objective of the simulation, the available knowledge, and given resources. The common engineering model approach is demonstrated by developing gas turbine component models which will be used to compose a gas turbine engine model in Part 2 of this paper. [S0742-4795(00)02303-6]

WS3-3 小型ターボジェットエンジンを用いた航空推進システムの教育

The performance test of micro turbojet engine has been conducted for Laboratory Experiments at Muroran Institute of Technology. The aim of this program is to understand the sturcture of turbojet engine, Brayton cycle, specific thrust, specific fuel comsumption and so on. The persent paper discribed the summary of this program and the reaction of students. This program is po;ular with the students and get good results for education of aerospace propulsion.

On the β to B2 ordering temperature in a Ti-22Al-26Nb orthorhombic titanium aluminide

The past decade or so has seen considerable research and development activity on the titanium aluminides based on the Ti-Al-Nb system, especially those involving the Ti{sub 3}Al ({alpha}{sub 2}), Ti{sub 2}AlNb (O) and TiAl ({gamma}) compounds, for applications in high temperature aerospace propulsion systems. In the former two compounds, microstructure development often relies on the decomposition of the high temperature {beta} phase (b.c.c. structure). In Ti{sub 3}Al alloys containing Nb, a number of investigators have reported that rapid quenching from the {beta} phase field leads to an ordered b.c.c. or B2 structure. The {beta} to B2 ordering temperature is of interest and some of these studies have reported that this temperature varies with the Nb content. For instance, in alloys containing Nb in the range of 11 to 15 at. %, the ordering temperature is thought to be in the range of 1,100--1,130 C, but appears to rise sharply for Nb concentrations >20 at. %. In alloy compositions of the type Ti-(22--30)Al-(22--30)Nb, this temperature is believed to be around 1400 C, but is not known with certainty. The present work reports on the determination of the disordered {beta} to B2 ordering transition temperature in a Ti-22Al-26Nb orthorhombic alloy.

Advanced instrumentation for next-generation aerospace propulsion control systems

New control concepts for the next generation of advanced air-breathing and rocket engines and hypersonic combined-cycle propulsion systems are analyzed. The analysis provides a database on the instrumentation technologies for advanced control systems and cross matches the available technologies for each type of engine to the control needs and applications of the other two types of engines. Measurement technologies that are considered to be ready for implementation include optical surface temperature sensors, an isotope wear detector, a brushless torquemeter, a fiberoptic deflectometer, an optical absorption leak detector, the nonintrusive speed sensor, and an ultrasonic triducer. It is concluded that all 30 advanced instrumentation technologies considered can be recommended for further development to meet need of the next generation of jet-, rocket-, and hypersonic-engine control systems.

Experimental studies on mixing of two co-axial high-speed streams

Currently, the focus of attention in aerospace propulsion research has been on the development of advanced air-breathing propulsion systems like scramjets, air-augmented rockets, multimode engines for the hyperplane, etc. A crucial technical problem to be tackled in such systems is the enhancement of mixing between two highspeed gaseous streams. Various methods have been tried so far, but the field is still very much an open one. Tests conducted earlier on subsonic flow mixing have shown that large-scale secondary flows, and not viscous diffusion, are the key to quick, low-loss, efficient mixing. In this regard, a lobe-type, convergent-divergent, supersonic nozzle, named the Petal nozzle, was designed, fabricated, and tested. Near-complete mixing with low total momentum loss within a short mixing chamber of length to diameter ratio of 4.35 was achieved.

Aerospace Propulsion Technology—A Fertile Source of Issues in Basic Fluid Mechanics

Aerospace Propulsion Technology—A Fertile Source of Issues in Basic Fluid Mechanics

Probabilistic Material Degradation under High Temperature, Fatigue, and Creep

A methodology has been developed and embodied in two computer codes for quantitatively characterizing the material strength degradation of aerospace propulsion system structural components that are subjected to various random effects over the course of their service lives. The codes, PROMISS and PROMISC, constitute a material-resistance model that is used in the NESSUS aerospace structural-reliability program. NESSUS addresses the service life-reducing effects of high temperature, mechanical fatigue, and creep.

Metal- and intermetallic-matrix composites for aerospace propulsion and power systems

Successful development and deployment of metal-matrix composites and intermetallic- matrix composites are critical to reaching the goals of many advanced aerospace propulsion and power development programs. The material requirements are based on the aerospace propulsion and power system requirements, economics, and other factors. Advanced military and civilian aircraft engines will require higher specific strength materials that operate at higher temperatures, and the civilian engines will also require long lifetimes. The specific space propulsion and power applications require hightemperature, high-thermal-conductivity, and high-strength materials. Metal-matrix composites and intermetallic-matrix composites either fulfill or have the potential of fulfilling these requirements.

Modern Research Topics in Aerospace Propulsion: in Honor of Corrado Casci. Edited by G. Angelino et al. Springer-Verlag, Heidelberger Platz 3, D-1000 Berlin 33, Germany. 1991. 375pp. Illustrated. DM69,00.

Modern Research Topics in Aerospace Propulsion: in Honor of Corrado Casci. Edited by G. Angelino et al. Springer-Verlag, Heidelberger Platz 3, D-1000 Berlin 33, Germany. 1991. 375pp. Illustrated. DM69,00. - Volume 96 Issue 953

An Overview of Potential Titanium Aluminide Composites in Aerospace Applications

ABSTRACTHigh-temperature, light-weight materials represent enabling technology in the continued evolution of high-performance aerospace vehicles and propulsion systems being pursued by the U.S. Air Force. In this regard, titanium aluminide matrix composites appear to offer unique advantages in terms of a variety of weightspecific properties at high temperatures. However, a key requirement for eventual structural use of these materials is a balance of mechanical properties that can be suitably exploited by aircraft and engine designers without compromising reliability. An overview of the current capability of titanium aluminide composites is presented, with an effort to assess the balance of properties offered by this class of materials. Emphasis is given to life-limiting cyclic and monotonic properties and the roles of high-temperature, time-dependent deformation and environmental effects. An attempt is made to assess the limitations of currently available titanium aluminide composites with respect to application needs and to suggest avenues for improvements in key properties.

Probabilistic constitutive relationships for cyclic material strength models

A methodology is developed that provides a probabilistic treatment for the lifetime of structural components of aerospace propulsion systems subjected to fatigue. Material strength degradation models include both a heuristic fatigue strength reduction model and a fatigue crack growth model. Probabilistic analysis is based on simulation, and both maximum entropy and maximum penalized likelihood methods are used for the generation of probability density functions. The resulting constitutive relationships are included in several computer programs. The programs determine the random time for a nickel-base superalloy engine component to reach a given fatigue strength or a given crack size. Results are presented in the form of probability density functions and cumulative distribution functions of the log of mechanical fatigue cycles.

Performance of an aerospace plane propulsion nozzle

A novel inviscid and viscous analysis is provided for a nozzle that is used with a scramjet for thrust generation. The analysis is based on the theory of a two-dimensional minimum length nozzle with a curved inlet surface, where the flow is sonic or supersonic. Inlet conditions are prescribed and the gas is assumed to be perfect. Viscous and inviscid nondimensional parametric results are provided for the thrust, lift, heat transfer, pitching moment, and a variety of boundary-laye r thicknesses. In addition to global results, wall distributions of thrust, heat transfer, etc., are provided. The analysis demonstrates that the nozzle produces a lift force whose magnitude may exceed the thrust and a significant pitching moment. The thrust is sensitive to the inlet Mach number; it rapidly decreases as this Mach number increases. There is little loss in the thrust as the nozzle's downstream wall is truncated while the corresponding decrease in lift and the pitching moment is moderate.

HIGH TEMPERATURE - HIGH PERFORMANCE COMPOSITES

Composites both high temperature and high performance are the subject of the symposium presented in this book continue to be at the forefront of materials research and development, fundamentally as well as with a view toward future generations of aerospace structures, propulsion devices, and energy conversion systems. The aim of this symposium was to bring together researchers from diverse disciplines to compare their latest results concerning the synthesis, structure-property relationships, and mechanics of metal, intermetallic, glass, and ceramic matrix composites.

Numerical Propulsion System Simulation

The cost of implementing new technology in aerospace propulsion systems is becoming prohibitively expensive. One of the major contributors to the high cost is the need to perform many large scale system tests. Extensive testing is used to capture the complex interactions among the multiple disciplines and the multiple components inherent in complex systems. The objective of the Numerical Propulsion System Simulation (NPSS) is to provide insight into these complex interactions through computational simulations. This will allow for comprehensive evaluation of new concepts early in the design phase before a commitment to hardware is made. It will also allow for rapid assessment of field-related problems, particularly in cases where operational problems were encountered during conditions that would be difficult to simulate experimentally. The tremendous progress taking place in computational engineering and the rapid increase in computing power expected through parallel processing make this concept feasible within the near future. However it is critical that the framework for such simulations be put in place now to serve as a focal point for the continued developments in computational engineering and computing hardware and software. The NPSS concept which is described below will provide that framework.

Aerospace propulsion system materials in the next 25 years—composites take off

Although advanced materials are making significant headway, high-performance alloys will remain the materials of choice beyond the turn of the century. Though the markets for advanced materials are growing more rapidly than those for the conventional alloys, a $1 billion to $2 billion market for conventional alloys over the next eleven years still is substantial.