Showing papers by "National Aerospace Laboratories published in 1996"

Viscous Drag Reduction Using Riblets on NACA 0012 Airfoil to Moderate Incidence

Abstract: Results of viscous drag reduction using riblets from 3M on a NACA 0012 airfoil model up to moderate angles of attack are presented. Measurements made consisted of model surface pressure distributions, mean velocity and streamwise turbulence intensity profiles in the boundary layer (just ahead of the trailing edge), and total airfoil drag for two riblet heights of 0.152 and 0.076 mm. Results show significantly higher skin friction drag reduction with incidence compared to plat plate flows; the reduction was as high as 16% at ? = 6 deg. Results of mean velocity profiles show that a larger contribution to drag reduction results from the suction side of the airfoil, indicating increased effectiveness of riblets in adverse pressure gradients. Examination of turbulence intensity profiles in the wall region indicates an appreciable reduction in the presence of riblets; correspondingly, the spectra show reduced energy levels at low frequencies.

Silver as a dopant and as a constituent in AsAgTe glasses: mean atomic volume and Tg

Abstract: The variations of the mean atomic volume, V , the glass transition temperature, T g , and the activation energy for glass transition, E t , with composition have been reported for (As 2 Te 3 ) 1 − x Ag x and (As 2 Te 3 )(Ag 2 Te) glasses; the glasses were prepared by a two-stage melt-quenching method. For the (As 2 Te 3 ) 1− x Ag x glasses, changes in the nature of dependences of V , T g and E t occur at the composition with Ag content of 1 atomic per cent (at.%). Analysis of these results indicates that, for Ag contents ≤ 1 at.%, Ag particles are uniformly dispersed in the network of the As 2 Te 3 glass, without affecting either the short range or the medium range order of the parent glass. For Ag contents ≥ 3.5 at.%, Ag forms AgTe bonds, and the observed variation of the properties can be explained by assuming the resulting three component glasses to be homogeneous mixtures of (As 2 Te 3 ) and (Ag 2 Te) units.

New Technique for Conformational Sampling of Cyclic Molecules Using the AMBER Force Field: Application to 18-Crown-6

Abstract: The results of an exhaustive search of low-energy conformers of the crown ether 18-crown-6 generated by a new approach are presented in this communication. Initial geometries were obtained by local perturbations, which were then minimized using the AMBER force field. The thoroughness of the conformational sampling was ensured by a gradual expansion of the search space from the low to the higher energy regions. The power of this approach in sampling the conformational space is highlighted by the ability to generate the experimentally observed conformations and all the populated conformations visited in a detailed molecular dynamics simulation reported in literature. The new program offers a useful technique for probing the complex conformational behavior of cyclic molecules, which are active at receptors and other biologically active acceptors.

Time-temperature failure analysis of epoxies and unidirectional glass/epoxy composites in compression

Abstract: Time-temperature effects in axial and non-axial compression tests of epoxies of two different formulations and their unidirectional glass fibre-reinforced composites were studied with emphasis on deformation characteristics, macro- and micromechanical aspects of failure, fibre-matrix interfacial failure sequences and comparison between fracture at constant crosshead velocity and constant strain rate. The existing theories and models of Argon, Bowden and Kitagawa for the deformation characteristics of glassy amorphous polymers were compared with the molecular and mechanical deformation of epoxies and their composites. Failure mode transitions and the possibility of a thermodynamical explanation for the crack propagation modes in epoxies were also investigated.

Silver as a dopant and as a constituent in AsAgTe glasses: electrical conductivity

Abstract: Electrical conductivity data (from 200 to 360 K) on fifteen glass compositions of the AsAgTe system are reported and discussed. The glasses were prepared using a two-stage melt-quenching method. For the (As2Te3)1−xAgx glasses, features are seen in the electronic properties, corresponding to a change in the role of Ag from a dopant (for Ag ≤ 1 at.%), to a constituent (for Ag > 1 at.%.). At this composition, step-like changes occur, in the activation energy for electrical conductivity and in the pre-exponential factor. Examination of the data indicate that, as a dopant, Ag acts as neutral scattering centres for charge carriers. As a constituent, Ag enhances the hopping channel for conductivity near the valence band edge.

Flight control system of Hypersonic Flight Experiment vehicle

Abstract: This paper describes the flight control system of the Hypersonic Flight Experiment vehicle. The experiment was conducted in early 1996. This paper summarizes the vehicle, sensor, on-board computer, control effectors, navigation, guidance, and control laws. In addition, the actual flight is compared with a simulated flight. The obtained flight data show that the flight control system provided enough stability and control performance to achieve the guidance commands. Some differences are observed between the actual and simulated flight, but they are not serious anomalies. (Author)

Experimental study on rotating cavitation of rocket propellant pump inducers

Abstract: Research on rotating cavitation progressed during the development of a liquid oxygen (LOX) turbopump for the LE-7 engine of the H-II rocket. In some ranges of cavitation numbers, supersynchronous shaft vibrations were observed in the LE-7 LOX main pump inducer. From a comparison with the results of our previous studies it was concluded that such shaft vibrations were caused by rotating cavitation in the inducer. A simple modie cation of the inducer upstream housing almost completely extinguished such shaft vibrations. Some characteristics of rotating cavitation have been fairly well elucidated. However, we were not able to fully explain the mechanism of the ine uence of the simple modie cation of the inducer upstream housing on the rotating cavitation. We thus commenced further experimental studies to investigate rotating cavitation in more detail. In the present study, some visual observations of rotating cavitation were conducted using the same inducer test facility as that used in our previous work.

Flight control system for the automatic landing flight experiment

Abstract: This paper discusses the flight control system developed for the Automatic Landing FLight Experiment, ALFLEX. ALFLEX is an experimental program conducted by the National Aerospace Laboratory and the National Space Development Agency of Japan in order to investigate the automatic landing technology for a future unmanned reentry space vehicle. The ALFLEX vehicle is a dynamically similar sub-scale model of the planned Japanese HII Orbiting Plane, HOPE. Since the HOPE program is in a preliminary conceptual design phase, the ALFLEX vehicle is a scaled model of one of the proposed configurations from 1992 research. The vehicle bare airframe is statically unstable in the pitch axis. In the lateral-directional axes, it has negative weather cock stability and strong dihedral effect, which introduce severe instability. The airframe's instability and the landing performance requirement drive the flight control system design to be one of the key technologies in the HOPE program. Since the vehicle's maximum L/D is approximately 4, it needs the same landing guidance technique as lifting body research vehicles and the Space Shuttle. This paper discusses the flight control design and the design methods applied to ALFLEX, and discusses lessons learned so far. The results from a preliminary flight test are briefly introduced. The series of automatic landing flights are scheduled for the middle of 1996, at Woomera, Australia, and will verify the guidance, navigation and control design. *Head, Control Qualification Lab., member AIAA Senior research engineer, Flight Research Division *^Research engineer, Control Research Division § Associate senior engineer, Winged Space Vehicle Office ^Engineer, Winged Space Vehicle Office *Asistant manager, Nagoya Aerospace Systems **Asistant manager, Nagoya Aerospace Systems Copyright © 1996 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Introduction Automatic landing technology for reentry space vehicles has a long history starting from the lifting body flight experiment at Edwards, California and the US Space Shuttle which demonstrates excellent technology achievement by NASA, e.g. References 1) to 6). Japan has a plan to develop a reentry space vehicle called HOPE, H II Orbiting Plane. Since the HOPE vehicle is unmanned and autonomous, it depends heavily on recent computer technology for flight control. The development project is still in the research phase, and the National Aerospace Laboratory and the National Space Development Agency of Japan are collaboratively conducting research programs in order to develop key technologies for the unmanned reentry vehicle. Among them, ALFLEX, Automatic Landing FLight Experiment, is a research program for the subsonic flight control and automatic landing technology. 7) Technology to be developed in the program breaks down as follows: (1) Integrated navigation system design for automatic landing (2) Automatic landing guidance system design (3) Subsonic flight control system design (4) Subsonic aerodynamics prediction and verification ALFLEX is a research program to study and evaluate design methods to match up-to-date hardware, such as modern computers, sensors and actuators. In the ALFLEX program, however, special hardware has not been developed. Instead, commercially proven avionics and off-the-shelf components are used. An exception is a pseudo-satellite differential GPS system (DGPS), for which the NASDA Tsukuba Space Center developed an onboard receiver and ground system. The DGPS, however, is not a flight critical component, and mainly gives engineering data for off-line analysis in order to use it for a future mission. ALFLEX is a scale model experiment of a future 15 ton reentry space vehicle, HOPE. The vehicle airframe is designed to be dynamically similar to the planned space vehicle. Also the guidance, navigation and control system for ALFLEX is designed to be as similar as possible. Fig. 1 shows three side views of the vehicle, and Fig. 2 shows the primary onboard equipment. The model's length scale is 37 %. In order for HOPE to land on a standard size runway, the runway length specification for ALFLEX is set as 1000 m. According to the similarity rule, where acceleration and mass density are equal for the real and model vehicles, the model's time scale is 60.8%, and the model's velocity scale is 60.8%. The model vehicle's mass should be 5.07%, corresponding to 760 kg; however, it is actually 796 kg, slightly in excess of this figure. The ALFLEX vehicle is released at an altitude of 1500m from a helicopter with a velocity of 46.3m/s (90kt) EAS, the maximum speed for the helicopter's hanging load flight capability. The release altitude is determined in order to achieve an equilibrium flight condition on the glide slope, where approximately 500m altitude will be lost before accelerating to the glide path speed of 84m/s EAS. Ground facilities support the experiment, such as a flight data monitoring system, laser tracker and tracking radar systems. The laser tracker provides reference data for the vehicle position to evaluate the navigation system. The tracking radar provides position data for flight safety. Japanese aerospace manufacturing companies participate in the ALFLEX program. Mitsubishi Heavy Industries Ltd. supports the development of the guidance, navigation and control (GNC) system for ALFLEX. Fuji Heavy Industries, Kawasaki Heavy Industries and TOSHIBA contribute to other parts of the program. The program commenced in 1992, and will be completed with flight tests at Woomera, Australia during 1996. Guidance, Navigation and Control system Design goal The experiment's design goal is safe automatic landing. Quantitative performance requirements are defined for the GNC system design. Automatic landing performance is evaluated by the following measures. 1) Position of touch down, Xtd, Ytd 2) Attitude at touch down, 4>, 0, *P 3) Velocity at touch down, VEAS, VGND 4) Vertical velocity at touch down, Vsink 5) Side-slip angle to the ground at touch down, 6) Pitch rate at nose gear touch down, Qtd(n) 7) Maximum lateral deviation in the ground roll, Ymax 8) Stop position of ground roll, Xstop Table 1 shows the design requirements for the above parameters. Table 1: Landing performances requirement

Preparation of zirconia and silicon carbide whisker biphasic powder mixtures by carbothermal reduction of zircon powders

Abstract: Carbothermic reduction of zircon powders has been studied under argon and nitrogen gas pressures of 0.15 MPa in order to obtain biphasic composite powder mixtures containing zirconia and silicon carbide whiskers. The reduction has been carried out using different mole ratios of carbon and zircon. Carbon was used in the form of activated charcoal (specific surface area ∼1000 m2g−1) or carbon black (specific surface area ∼300 m2g−1). Whilst complete decomposition to m-ZrO2 was obtained in the argon atmosphere at 1700 °C, under the nitrogen atmosphere the conversion was incomplete even at 1700 °C. However, the extent of conversion to zirconia at 1650 °C under nitrogen was found to be more than that under argon gas. In a few cases, particularly under the nitrogen atmosphere, minor amounts of other forms of zirconia e.g., tetragonal (t)-ZrO2 or orthorhombic (o)-ZrO2 were formed along with the major monoclinic (m)-ZrO2 phase. The rate of reaction was found in general to increase with an increase in the carbon content. The studies particularly indicate that activated charcoal is a better reducing agent than carbon black owing probably to its enormous surface area. Further, it was also noted that cobalt chloride and sodium chloride act as a catalyst and a space forming agent respectively. They aid silicon carbide whisker formation and growth and hence the reaction is appreciably accelerated and reaches completion at 1650 °C in the argon atmosphere.

Ignition strategy in a model scramjet

Abstract: A model scramjet engine was tested at the NAJLKRC RamJet engine Test Facility (RJTF). The engine had an ignition system consisting of plasma torches, pilot fuel injectors, and backward-facing steps upstream of the main fuel injectors. Tests were conducted under conditions of flight Mach numbers of 4, 6 and 8 at altitudes of 15, 25 and 35 km respectively. Tests results showed that the ignition system had sufficient ability to attain intensive combustion in the engine in the Mach 4 condition, whereas it lacked the ability in the Mach 6 and 8 conditions. The ignition system was thus modified and then tested at the Mach 6 condition. At first, a recess with auxiliary injectors was placed downstream of the step to obtain shorter ignition delay and longer residence time than those in the step-base region. Oxygen was injected through the auxiliary injectors to imprtve the fuel-rich condition within the recess. As a result, intensive pilot flame was attained, but ignition of the main fuel occurred only under limited conditions. To attain higher pressure level around the ignition system, the recess was removed and a short strut was mounted on the top-wall. Consequenty, intensive combustion of the main fuel was achieved over a wide range of operational conditions. Using an ignition parameter, defined as pressure-length products divided by velocity (ph/u), the ignition limit was expressed on a temperature-ignition parameter diagram. Introduction The supersonic combustion ramjet (scramjet) is expected to be the most effective propulsion system for the Single Stage To Orbit (SSTO) transportation vehicles and hypersonic transportation vehicles of the next generation. Many studies on scrramjet components such as inlet, combustor and nozzle, have been carried out to obtain a better understanding of the performances of the individual components. *~4 However, it is expected that intensive interactions among these components will occur in real engines. For example, a rise in pressure due to combustion causes separation which propagates upstream * Researcher, Ramjet Combustion Section, Ramjet Propulsion Division. Member ALAA. t Researcher, Ramjet Control Systems Section, Ramjet Propulsion Division. $ Researcher, Ramjet Performance Section, Ramjet Propulsion Division. § Project Engineer, Engineering Section, Engine & Control Equipment Department. Copyright © 1996 by the American Institute of Aeronautics and Astronautics. Inc. All right reserved. into the inlet and changes the.inlet back pressure, which may result in an unstart condition in the inlet. In the case of such interactions, the total performance of the engine cannot be evaluated based on a linear combination of the obtained performances of the individual components. Thus, tests of the models of whole engine are necessary to elucidate the interactions among these components and the overall performance of the whole engine. Testing of the models of whole engine requires rather big and expensive wind-tunnel facilities. Thus, only a limited number of results on whole engine tests have been reported.^ Using the test facility (denoted as RamJet engine Test Facility, RJTF) at NAL-KRC, we have conducted tests of a model scramjet engine in various flight conditions. In flight conditions of Mach 4, intensive combustion was attained with an installed ignition system.^ However, in flight conditions of Mach 6 and 8, it was found that intensive combustion were not attained in the model with the original ignition system.8>9 To improve ignition ability, supplemental equipment such as a recess with auxiliary injectorsS) or a short strut *-" were installed in the model engine. In the present paper, ignition characteristics of the engine with and without these modifications are reported. Test Facility and Engine Model Test facility The RJTF was designed to ssimulate flight conditions of M4, M6, and M8. The facility is equipped with two heating systems to obtain high enthalpy flow. A storage air heater (denoted as SAB) is used to obtain pure hot air for the M4, M6, and M8 flight condition tests. Two types of vitiation air heaters (VAH) fueled by H2 are used to obtain vitiated hot air for the M6 and M8 flight condition tests, respectively. The M6 flight conditions are achieved with the SAH alone or the VAH alone (denoted as M6S and M6V conditions, respectively), whereas the M8 conditions are achieved with a combination of the SAH and the VAH. Table 1 shows the operational conditions of the RJTF and the simulated flight conditions. The high enthalpy flow obtained at the heaters was accelerated through rectangular nozzles. The exit cross section of the every nozzle was 510 mm x 510 mm. The engine model was set in a low pressure chamber which was connected to a steam ejector system to reduce the pressure within the chamber for simulation of high altitude atmosphere. The engine model was located in such way that it breathed in the boundary layer in the facility nozzle. The displacement thickness of the boundary layer was about 15 mm. (See reference 12 for detailed information on the RJTF.) Table 1 Nominal conditions of RJTF Simulated flight conditions

Finite element analysis and the stress correspondence paradigm

Abstract: The underlying mechanics of the finite element method as applied to structural analysis is explored in paradigmatic terms. It is shown that the stress correspondence paradigm has the most explanatory power and that it can be axiomatized from a very basic principle, the Hu-Washizu theorem, which is a variation of the least action principle. Numerical experiments are presented to show that the predictions based on analytical quantification from the stress correspondence paradigm are verifiable.

Accurate development of leading-edge vortex using an embedded conical grid

Abstract: The vortex formation and its development near the apex of a sharp-edged delta wing are poorly represented on conventional grids because of dissimilar length scales of the flow and the grid. The problem is overcome by having an embedded conical grid surrounding the wing. Computed Euler solutions on such an embedded conical grid and on a conventional H-O grid are presented for a range of incidence for a subsonic freestream. The solutions on the embedded conical grid show that the vortex is well resolved right from the apex, even at a very low incidence. The vortex breakdown is well predicted on the embedded conical grid, including the case where the breakdown has just moved upstream of the trailing edge.

Generation of comprehensive longitudinal aerodynamic data using dynamic wind tunnel simulation

Abstract: A novel method of generating comprehensive longitudinal aerodynamic data of aircraft using dynamic wind-tunnel simulation is presented. The method utilizes the motion and force responses of an aircraft model to control surface inputs to determine trim lift characteristics, longitudinal stability derivatives, and neutral point. In addition, large-amplitude lift and pitching moment responses characterizing the unsteady aerodynamic behavior are also generated using the same experimental setup. The new test method is demonstrated using a generic delta wing aircraft model with one degree of freedom in pitch. The model pitch attitude and lift force responses to elevon dynamic inputs are measured and used to deduce longitudinal aerodynamic data. Comparison of these results with static test data and Datcom estimates shows good agreement. Nomenclature CL = lift coefe cient, L/qS CLa = lift curve slope, rad 21

A computational model for analysing interactive buckling and delamination growth in composite structures

Abstract: In this paper, a unified method is presented: (i) to model delaminated stiffened laminated composite shells; (ii) for synthesising accurate multiple post-buckling solution paths under compressive loading; and (iii) for predicting delamination growth. A multi-domain modelling technique is used for modelling the delaminated stiffened shell structures. Error-free geometrically nonlinear element formulations — a 2-noded curved stiffener element (BEAM2) and a 3-noded shell element (SHELL3) — are used for the finite element analysis. An accurate and simple automated solution strategy based on Newton type iterations is used for predicting the general geometrically nonlinear and postbuckling behaviour of structures. A simple method derived from the 3-dimensionalJ-integral is used for computing the pointwise energy release rate at the delamination front in the plate/shell models. Finally, the influence of post-buckling structural behaviour and the delamination growth on each other has been demonstrated.