Showing papers by "National Aerospace Laboratories published in 1999"

Lattice strains in gold and rhenium under nonhydrostatic compression to 37 GPa

Abstract: Using energy-dispersive x-ray diffraction techniques together with the theory describing lattice strains under nonhydrostatic compression, the behavior of a layered sample of gold and rhenium has been studied at pressures of 14--37 GPa. For gold, the uniaxial stress component t is consistent with earlier studies and can be described by $t=0.06+0.015P$ where P is the pressure in GPa. The estimated single-crystal elastic moduli are in reasonable agreement with trends based on extrapolated low-pressure data. The degree of elastic anisotropy increases as $\ensuremath{\alpha},$ the parameter which characterizes stress-strain continuity across grain boundaries, is reduced from 1.0 to 0.5. For rhenium, the apparent equation of state has been shown to be strongly influenced by nonhydrostatic compression, as evidenced by its dependence on the angle $\ensuremath{\psi}$ between the diffracting plane normal and the stress axis. The bulk modulus obtained by inversion of nonhydrostatic compression data can differ by nearly a factor of 2 at angles of $0\ifmmode^\circ\else\textdegree\fi{}$ and $90\ifmmode^\circ\else\textdegree\fi{}.$ On the other hand, by a proper choice of $\ensuremath{\psi},$ d spacings corresponding to quasihydrostatic compression can be obtained from data obtained under highly nonhydrostatic conditions. The uniaxial stress in rhenium over the pressure range from 14--37 GPa can be described by $t=2.5+0.09P.$ The large discrepancy between x-ray elastic moduli and ultrasonic data and theoretical calculations indicates that additional factors such as texturing or orientation dependence of t need to be incorporated to more fully describe the strain distribution in hexagonal-close-packed metals.

Source Location by Phased Array Measurements in Closed Wind Tunnel Test Sections

Abstract: The feasibility of high frequency phased array measurements on aircraft scale models in a closed wind tunnel test section was investigated. For that purpose, 100 microphones were built in a 0.6x0.5 m’ plate. which was installed in a floor panel of the 8x6 m2 test section of the Large Low-speed Facility of the German Dutch Wind tunnel (DNW-LLF). F or the microphone positions a sparse array design was used that minimises side lobes in the beamforming process. To suppress boundary layer noise, the array could optionally be covered with a 0.5 cm thick layer of acoustic foam and a 5% open perforated plate. To assess the effect of wall reflections, tests without wind were performed with a loudspeaker at several positions in the tunnel section. Furthermore, wind tunnel tests were carried out on an Airbus transport aircraft model. It is shown that location of acoustic sources is indeed possible for frequencies between 2 and 30 kHz, but their levels may differ from those measured in an anechoic environment. For the lower frequencies, application of the layer of foam and the perforated plate is beneficial. Finally, it is shown that filtering out the most dominant source can extend the array potential.

The eduction of structures from flow imagery using wavelets Part I. The mixing layer

Abstract: Using two-dimensional Mexican hat wavelets, digitized imagery from the flow visualization pictures of a mixing layer by Brown and Roshko have been analysed. The objective of the present study is to “calibrate” the proposed wavelet technique for educing structures in a flow whose large-scale organization is well established. It is found that, with appropriate thresholds on wavelet-transform coefficients, considerable insight into the structure of the flow at different scales can be obtained. In particular, the analysis reveals that the small-scale structure within the large-scale vortices is approximately homogeneous, and has characteristic scales that do not vary significantly with downstream distance.

The characterisation of aqueous silicon slips

Abstract: The optimum conditions of aqueous silicon slips for slip casting was achieved by employing various experimental techniques like zeta potential, particle/floc size distribution, sedimentation, viscosity and rheological measurements as a function of pH of the slips in the pH range of 2–11. Silicon suspensions display a maximum in zeta potential values and a minimum in sedimentation height and viscosity in two pH regions of 4–5 and 8. The slips behaved as near-newtonian at these pH values up to a solid loading of 52 wt% and as non-newtonian with thixotropic behaviour above this solid loading. Samples with highest green density (68%) were produced from 72 wt% solid loaded slips which were conditioned at a pH of 8 and milled for 26 h. The cast bodies of these slips were nitrided to obtain reaction bonded silicon nitride products which were also characterised.

Viscous Drag Reduction Using Riblets on a Swept Wing

Abstract: Results of viscous drag reduction using 3M riblets on a swept wing with a general aviation wing (GAV)(2) airfoil section at low speeds are presented. The tests, made at a chord Reynolds number of 0.75 x 10 exp 6, covered an incidence range of 0-6 deg. Measurements consisted of surface-pressure distributions and total drag using wake survey over the range of incidence covered; in addition, mean velocity, streamwise turbulence intensity, and Reynolds shear-stress profiles in the boundary layer were measured just ahead of the trailing edge at zero incidence. Surface flow patterns on the wing were obtained using an oil-flow technique employing titanium dioxide as pigment. The results showed viscous drag reduction of about 8 percent at zero incidence, which decreased progressively to about 1 percent at an incidence of 6 deg. The fall in riblet effectiveness appears to be a result of significant riblet yaw angle effects observed at higher incidence. Some reduction in the turbulence intensity and Reynolds shear stress in the boundary layer on the wing's upper surface have been observed in the presence of riblets, as in two-dimensional flows.

Dispersion, slip casting and reaction nitridation of silicon–silicon carbide mixtures

Abstract: The dispersing behaviour of silicon, silicon carbide and their mixtures in aqueous media were monitored by particle size, sedimentation, viscosity and zeta potential analyses as a function of pH of the slurry. The pH values for optimum dispersion were found to be 4 and 8 for silicon, 10 for SiC and 9 for Si +SiC mixtures. Optimum slips of Si + SiC mixtures were slip cast to obtain green compacts which were nitrided once at 1450xB0;C for 2 or 4h or successively and cumulatively for 8 (2 + 6) and 10 (4 + 6) h in a resistively heated graphite furnace. The binding13; phases in the nitrided products were found to be 13; fbrous/needle like a-Si 3N4 , faky grains of (3-Si3N413; and Si2ON2 . The products containing 19-47% of silicon nitride as bond/matrix possessed fexural strength (three ppoint bending) values of 50-85 MPa. 1999 Elsevier Science Limited. All rights reserved

Synthesis and sintering of SiC under high pressure and high temperature

Abstract: Starting from elemental powders, simultaneous synthesis and compaction of SiC were conducted at 3 GPa pressure and temperatures in the range 2100–2900 K. The sintered compacts were characterized by x-ray diffraction, microhardness measurements, and microscopic studies. The efficiency of formation of SiC was dependent on the particle size of the silicon powder, crystallinity of the reactant carbon, molar ratio of silicon and carbon, and synthesis temperature and time. Carbon in excess of the stoichiometric amount was required to obtain compacts free from residual silicon. The SiC samples, with a Si: C molar ratio 1: 1.05, prepared at 2100 K for 300 s had a density and hardness of 3.21 g/cm3 (98.8% of theoretical density) and 22 GPa, respectively. The crystal structure of the SiC depended on the synthesis temperature. Pure β–SiC in the temperature range 2100–2500 K, and a mixture of α– and β–SiC above 2500 K were obtained. The β–SiC was highly crystalline and nearly defect-free.

Decomposition behaviour of Kevlar 49 fibres: Part I. AtT≈T d

Abstract: The structural changes which accompany decomposition of Kevlar 49 fibres at T= 500xB0;C: and 550xB0;C, respectively, have been elucidated. At both these temperatures, cumulative thermal exposures of specific durations, tcum{T}, are required to result in decomposition. The conspicuous features which characterize isothermal decomposition of the fibres are: (i) progressive reduction and an eventual total loss in fibre crystallinity, (ii) progressive loss in weight, (iii) introduction of surface damages, (iv) introduction of hollowness, and (v) deterioration in tensile properties.

Drag Reduction Due to Riblets on a GAW(2) Airfoil

Abstract: THE study of turbulent drag reduction by use of riblets has been an area of significant research during the past de cade. Riblets with symmetric v grooves with adhesive-backed film manufactured the 3M Company (U.S.) have been widely used in earlier studies. The effectiveness of riblets in reducing the drag of a simple wo-dimensional configuration is fairly we 11 established now. Although there has been some effort to assess the effectiveness riblets on airfoils, the results reported by Sundaram et al on a NACA 0012 airfoils at low speeds have been particularly noteworthy.13; Their studies showed that both total and viscous drag reduction increased monotonically with an angle of attack up to 6 deg; it was also shown3 that the higher drag reduction resulted primarily from airfoil upper (or suction) surface, suggesting increased effectiveness of riblets in adverse pressure gradients. In a subsequent study Subaschandar et al., who extending the work of Sundaram etal to higher angles of attack (by using the same NACA 0012 model13; and the same wind tunnel), it was observed that the drag reduction decreased rapidly beyond a = 6 deg with virtually no drag reduction a =12 deg. The present study is an attempt to assess the total drag reduction that is due to riblets on a cambered airfoil up to high angles of attack low speeds. The 13% thickness General Aviation Wing [GAW(2)]13;

Blowdown tunnel application of pressure sensitive paint

Abstract: A pressure sensitive paint (PSP) and a temperature sensitive paint (TSP) were applied to large blowdowntype supersonic wind tunnel testing of an SST model to expand the paint technique beyond usual continuous wind tunnel application. Bach paint was applied on each side of the wing, and luminescence data of both paints were captured by a CCD-camerabased imaging system at the same time. A PSP/TSP combined calibration which requires no pressure tap information and solves both temperature and pressure simultaneously was applied to compensate for unfavorable temperature sensitivity of the PSP. Even there was continuous drop of the surface temperature which was more than 10K during 40 seconds blow of the tunnel at M=2, the pressure data showed little change among the measurements conducted more than 15 seconds after the uniform flow was established. The paint data clearly captured a complex shockinteractive pressure field around a typical nacelleintegrated SST configuration. However, detailed comparisons with the pressure tap data showed the PSP data had about 0.1 shift in Cp toward a higher pressure direction at M=2. In addition, as the first step of the secondary use of the continuous pressure field data, a hinge-moment of an aileron was computed from the paint data.

Power spectrum estimation of complex signals: group delay approach

Abstract: A method for estimating the power spectrum of a complex signal (CS) realised by the group delay (GD) for a CS and the modified GD concept is proposed This extends the performance advantages of the modified GD applicable to a real signal to a complex signal A significant reduction in variance without any compromise in frequency resolution over that of the periodogram is found

Oxidation of MoSi2 and MoSi2-based materials

Abstract: Oxidation experiments, at 500°C, of MoSi2 and MoSi2-based compounds such as Mo(Al,Si)2 and MoSi2+1 wt% C compacts have been carried out. These compacts were prepared byin situ synthesis and a compaction method, starting from the elemental powders. For comparison, commercial MoSi2 and Mo(Al,Si)2 infiltrated into SiC preform were also studied under similar conditions. It was found that the synthesized high density MoSi2 and Mo(Al,Si)2 infiltrated into SiC preform did not show any oxidation even after 100 h of heating in air. The colour of the polished surfaces of commercial MoSi2, Mo(Al,Si)2 and MoSi2+1 wt% C had changed. The SEM of Mo(Al,Si)2 showed open blisters with rods of MoO3 in them whereas MoSi2+1 wt% C surface had MoO3 rods but no blisters and the oxidation was superficial with no penetration into the compact. It is suggested that in compounds, the presence of small amounts of impurities is not as detrimental to pesting as presence of defects like open pores or cracks. Hence, high density of the compact is essential for the prevention of complete disintegration of the compact.

Reactive flow in scramjet external nozzle

Abstract: The combustion and thrust characteristics in the singleexpanded ramp nozzle (SERN) were studied numerically with two-dimensional Navier-Stokes equations and k-o turbulence model. The external nozzle is one of the important parts of the scramjet engine, since the external nozzle gives a major portion of thrust of scrarnjet engine. One of the critical problems of external nozzle is the unburned gas mixture entering the external nozzle from combustor. The mixing and combustion processes in the external nozzle were studied and the effects of entrance condition of unburned gas mixture on the thrust characteristics are estimated.

Hygrothermal Characterization and Diffusion Studies on Carbon/Epoxy Composites

Abstract: Hygrothermal studies were carried out on unidirectional (UD) carbon fiber epoxy (LY 5052) composites at Vf= 0.5 and have been carried out for three different cases viz. 45°C/85% RH, 45°C/95% RH and 45°C/immersion (100% RH) till saturation is reached. In all cases composite specimens of different test configurations [Longitudinal Tensile (LT), Transverse Tensile (TT), Longitudinal Compression (LC), and Transverse Compression (TC)] were subjected to the above conditions and their diffusion behaviour studied. Generally, the specimens under the above conditions exhibited Fickian diffusion behavior.

Propulsion Research for Rocket SSTOs at NAL/KRC

Abstract: The Kakuda Research Center of the National Aerospace Laboratory (NAL/KRC) has historically contributed to the R&D of Japanese launch vehicles, especially with respect to propulsion. Technical research for reusable launch vehicles (RLVs) has been started, specially focusing on the components of reusable rocket engines and light-weight tank at KRC. Two kinds of high performance nozzles, extendible nozzle and aerospike one, and high performance turbopumps have been studied. A long-life combustor and bearings were tested. Light-weight tank material and light-weight nozzle-material were fabricated and under testing in the subscaled model level. The results of these technical studies are expected to be utilized in the concept study of RLVs and the development of an operational RLV. * Head, Senior Member, AIAA, **Head, Non-member, AIAA ***Director, Member, AIAA, +Senior Engineer, Non-member, AIAA, * Senior Engineer, Member, AIAA, Copyright

Simultaneous retrieval of soil, leaf, canopy, and atmospheric parameters from hyperspectral information in the red edge through model inversion

Abstract: In a modeling case study it has been investigated whether it would be possible to retrieve from optical remote sensing data the (bio)physical parameters of the coupled soil-vegetation- atmosphere system that have an effect on spectral radiances detected by spaceborne sensors. For this, optical data on single leaves generated by means of the PROSPECT model have been applied in the integrated optical soil-canopy-atmosphere radiation model OSCAR. The influences of 2 soil parameters, 2 leaf parameters, 4 canopy parameters and 3 atmospheric parameters on hyperspectral directional planetary reflectances have been simulated in a model inversion experiment. The simultaneous retrieval of the 11 parameters has been tested using classical model inversion by means of the Gauss-Newton method of non-linear least squares parameter estimation. Preliminary results indicate that this approach has some potential, as in a number of widely differing cases the retrieval of all model parameters from 10 nm resolution hyperspectral red edge planetary reflectance data under 5 directions was successful.