Showing papers by "National Aerospace Laboratories published in 2002"

Combustion synthesis: an update

Abstract: Combustion synthesis has emerged as a facile and economically viable technique for the preparation of advanced ceramics, catalysts and nanomaterials. Recent innovations in the combustion and processing parameters have resulted in a better understanding of combustion phenomena and control of microstructure and property of the products.

Characterization of Cu/Ni multilayer coatings by nanoindentation and atomic force microscopy

Abstract: Cu/Ni multilayer coatings prepared by RF/DC magnetron sputtering process were characterized using x-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) techniques. Films deposited under certain deposition conditions showed the appearance of satellite reflections around the principal reflections in the XRD data, indicating the formation of superlattice structure. Nanohardness measurements were performed on the films prepared under different deposition conditions, e.g. modulation wavelength (x39B;), copper to nickel thickness ratio (tCu/tNi) and substrate temperature (Ts). Nanohardness data revealed that the hardness was enhanced by a factor of 2.5 times that of the rule-of-mixtures value. This enhancement in hardness occurred over a limited range of x39B;. The results indicated that the hardness also depends on the copper to nickel thickness ratio and for tCu/tNi0.30 the films exhibited a maximum hardness. The hardness increased almost linearly with substrate temperature up to 200 xB0;C and got saturated at 250 xB0;C. No considerable change in the hardness was observed after vacuum annealing of the coatings. Imaging of the residual imprints by AFM revealed pile-up formation after indentation. The extent of pile-up, a measure of plastic flow of the material, was dependent on the preparation conditions of the multilayer coatings.

NASA Langley and NLR Research of Distributed Air/Ground Traffic Management

Abstract: Distributed Air/Ground Traffic Management (DAG-TM) is a concept of future air traffic operations that proposes to distribute information, decision-making authority, and responsibility among flight crews, the air traffic service provider, and aeronautical operational control organizations. This paper provides an overview and status of DAG-TM research at NASA Langley Research Center and the National Aerospace Laboratory of The Netherlands. Specific objectives of the research are to evaluate the technical and operational feasibility of the autonomous airborne component of DAG-TM, which is founded on the operational paradigm of free flight. The paper includes an overview of research approaches, the airborne technologies under development, and a summary of experimental investigations and findings to date. Although research is not yet complete, these findings indicate that free flight is feasible and will significantly enhance system capacity and safety. While free flight cannot alone resolve the complex issues faced by those modernizing the global airspace, it should be considered an essential part of a comprehensive air traffic management modernization activity.

Thermal shock and thermal fatigue study of alumina

Abstract: Preliminary results on the thermal shock and thermal fatigue behaviour of alumina studied in a newly designed novel and simple test equipment are reported. The top surface of a test sample was heated by an oxy-hydrogen flame while the opposite surface was cooled to generate temperature and thermal stress gradients. The maximum stressed zone and the effect of the thickness of the sample on critical temperature difference (TC) were studied by conducting actual experiments on plain and indented alumina specimens and also by modelling temperature and thermal stress distribution in the sample using a finite element (FE) software. It was observed that the maximum stress was experienced near the periphery of the top surface and TC was more for thicker samples. Thermal fatigue study was conducted by varying temperature difference of the fatigue cycles and also by inducing different crack lengths in the sample. It was observed that the fatigue life sharply decreased with increase in initial crack length or by increasing the temperature difference of the fatigue cycles. The acoustic emission (AE) signals corresponding to formation and growth of large number of micro-cracks were observed. # 2002 Elsevier Science Ltd. All rights reserved.

Thermally induced structural changes in Nomex fibres

Abstract: Thermally aged Nomex fibres manifest several residual effects viz. reduction in X-ray crystallinity, weight loss and deterioration in tensile characteristics. Surface damages in the form of longitudinal openings, holes, material deposits etc have also been observed. Based on the data from thermally exposed fibres, the time needed for states of zero tensile strength and modulus have been predicted.

Slow mixed convection in rectangular containers

Abstract: We consider the slow motion of viscous fluid completely filling a rectangular container. The motion is generated by the combined action of differential wall temperatures and the linear motion of the lid. If the relevant Reynolds and Peclet numbers and the lid speed are all small enough, the velocity field will be governed by an inhomogeneous biharmonic equation. In this approximation the temperature field, unaffected by the fluid motion, drives, at least in part, the fluid velocity field. Of interest here are the relative effects of buoyancy and lid motion. It is shown that the field, suitably scaled, depends on the dimensionless depth and lid speed alone. The mixed convection problem is solved for two pairs of wall heating protocols by sequentially solving, by an eigenfunction expansion method, up to four biharmonic problems. We present streamline patterns and quantitative data on the relative effects of lid motion on the buoyancy-driven fields in these containers.

A modal method for finite amplitude, nonlinear sloshing

Abstract: A modal method is used to calculate the two-dimensional sloshing motion of an inviscid liquid in a rectangular container. The full nonlinear problem is reduced to the solution of a system of nonlinear ordinary differential equations for the time varying coefficients in the expansions of the interface and the potential. The effects of capillarity are included in the formulation. The simplicity, generality and power of the method are exhibited not only by recovering the earlier results obtained, for example, by Penney and Price [1], Tadjbakhsh and Keller [2] and Faltinsen et al [3], but also by obtaining new and interesting results of the effects of capillarity and shallow depth, which would be difficult to obtain otherwise. For example, it is found that for the initial interface profile considered here, parasitic capillary waves, borne by the higher number wave modes, are generated for moderate capillarity but disappear for larger values of the parameter. The method can be extended to other simple geometries.

Effect of thermal ageing on Nylon 6,6 fibres

Abstract: The residual effects of thermal ageing at various temperatures on fibres of the aliphatic polyamide Nylon 6,6 have been studied. Both crystal and macro structural characteristics manifest the residual effects. The former category includes changes in intensity, 2θ values and half width. The macro changes include introduction of surface damages in the form of holes, material deposits etc. The fibre also undergoes reduction in weight. The structural changes suggest deterioration in the initial tensile characteristics which has been verified experimentally. A direct correlation between the tensile strength and the angular separation of the equatorial reflections has also been observed.

Theory and application of 3‐D LSKUM based on entropy variables

Abstract: This paper describes the theory and application of a grid-free kinetic upwind scheme known as LSKUM.The basic principle in LSKUM is the determination of derivatives occurring in the conservation laws using the least squares method. The grid-free nature of the scheme is obtained because the least squares method can be used on an arbitrary distribution of nodes, i.e. the nodes need not form a structured/unstructured grid.

Hygrothermal Effects on RT-Cured Glass-Epoxy Composites in Immersion Environments. Part A: Moisture Absorption Characteristics

Abstract: A study on the effect of moisture absorption characteristics of RT-cure glass/epoxy composite and epoxy casting specimens immersed in freshly prepared artifi- cial seawater and distilled water maintained at 333o K are presented in this paper. Results showed that the equilibrium moisture absorption value and the diffusion rate (slope of the moisture absorption curve) are higher in specimens immersed in distilled water than those of artificial seawater. The mixture rule for moisture absorption estimates has been verified for specimens immersed in both environments. These theoretically calculated values com- pared well with those experimentally obtained. The time of saturation for specimens immersed in seawater was found to be higher than that for those immersed in distilled water.

Aerodynamic and aero-acoustic effects of flap tip fences

Abstract: The application of winglet or end-plate type devices to the tips of the trailing-edge flap of a wing has, for some time, been suggested as a (potential) means for improving the aerodynamic efficiency during take-off/climb and for decreasing the airframe noise of transport aircraft in the approach/landing configuration. A third aspect of the application of such devices is their possible effect on the wake vortex characteristics. In this paper the main results and conclusions are presented of exploratory CFD simulations and low-speed wind tunnel tests on a half model of a civil transport type of aircraft configuration with trailing-edge flaps extended and with (and without) winglet type “fences” attached to the main wing at the position of the outboard tip of the trailing-edge flap. Both take-off/climb and approach/landing flap settings were tested. The main results of the investigation are that the application of flap tip fences may lead to: a substantial (up to 7 dB) reduction of the sound power level of the flap tip noise source in the approach/landing configuration (about equal for the lower and the upper + lower fence configurations) a (small) improvement of L/D and CLmax in take-off/climb of up to 1% (lower fence only) possibly a small reduction of a few percent of the strength of the wake vortex from the flap tip region

Role of in situ generated tribofilm on the tribological characteristics of monolith and TiB2 reinforced MoSi2 intermetallic

Abstract: Wear experiments performed on steel disc with increasing load for monolithic MoSi2 of different densities and its composite with TiB2 showed three distinct wear regimes The specimens exhibited severe wear rate below the lower and above the upper critical loads and mild wear in between the two critical loads The increase in density of the monolith and the reinforcement of TiB2 were effective in reducing the coefficient of friction and the specific wear rate The wear experiments have been performed in these three regimes (15, 50 and 75 N) The tribofilm formed on the pin surface was found to contain both pin and disc materials The temperature of the pins during the sliding against EN-24 disc was calculated using one dimensional heat transfer equation at different loads for each composition The composite experiences lower temperatures compared to the monoliths (C) 2002 Elsevier Science BV All rights reserved

Mean and fluctuating pressure in boat-tail separated flows at transonic speeds

Abstract: Experiments were carried out investigating the features of mean and unsteady surface pressure fluctuations in boat-tail separated flows relevant to launch vehicle configurations at transonic speeds. The tests were performed on a generic axisymmetric body in the Mach-number range of 0.7-1.2, and the important geometrical parameters, namely, the boat-tail angle and diameter ratio, were varied systematically. The measurements made included primarily the mean and unsteady surface-pressure fluctuations on nine different model configurations. Flow-visualization studies employing a surface oil flow, and schlieren techniques were carried out to infer features like boundary-layer separation, reattachment, and shock waves in the flow. The features of mean and fluctuating surface pressures are discussed in detail including aspects of similarity. It has been observed that, on a generic configuration employed in the present study, the maximum levels of surface-pressure fluctuations in the reattachment zone are appreciably lower than those found on launch vehicle configurations having a bulbous or hammerhead nose shape. A simple correlation is suggested for the maximum value of rms pressure fluctuations in the reattachment zone at different freestream Mach numbers.