Showing papers by "National Aerospace Laboratories published in 2005"

Electroless deposition of Ni–Cu–P, Ni–W–P and Ni–W–Cu–P alloys

Abstract: Interest in electroless plating of nickel-based ternary alloys has increased because of their excellent corrosion, wear, thermal and electrical resistance. They also possess good magnetic properties. In the present investigation, the effect of copper and tungsten in alkaline electroless nickel baths has been studied in depositing Ni–Cu–P and Ni–W–P alloys and also the synergistic effect of ions in depositing Ni–W–Cu–P alloys. Deposits were characterized using XRD, scanning electron microscopy (SEM), energy-dispersive analysis of X-ray (EDX) and atomic force microscopy (AFM) techniques. XRD results revealed that not much variation in structure and grain size has been found in Ni–Cu–P deposit. A decrease in phosphorus content and a marginal increase in grain size have been observed due to the tungsten addition in the Ni–P deposit. Addition of copper in Ni–W–P baths has resulted in a quaternary deposit, Ni–W–Cu–P, with increased crystallinity. SEM studies showed that presence of coarse nodules in ternary Ni–Cu–P and Ni–W–P deposits. Addition of copper in Ni–W–P baths has resulted in a very smooth deposit. Studies by AFM on deposits have proved that the copper has suppressed coarse nodules by inhibiting their growth in quaternary deposit. No considerable change in hardness has been noticed in both as-plated and heat-treated deposits due to the inclusion of copper in Ni–W–P deposit. A marginal improvement in corrosion resistance has been observed in quaternary alloy compared to ternary (Ni–Cu–P or Ni–W–P) alloys.

Density Measurements in an Axisymmetric Underexpanded Jet by Background-Oriented Schlieren Technique

Abstract: The background-oriented schlieren (BOS) technique has been applied to obtain the mean density field of a complex underexpanded jet flow. The measurements were made on an axisymmetric sonic jet operating at ideally expanded and highly underexpanded values of nozzle pressure ratios. The methodology involved two steps: validation of the filtered backprojection tomography used here, by making measurements of a four-jet configuration followed by density measurements on axisymmetric sonic jets. Pitot measurements made on an ideally expanded sonic jet were utilized for validation of BOS. The presented density fields show that meaningful quantitative data can be extracted by using minimal hardware with this technology.

Optical oxygen sensor coating based on the fluorescence quenching of a new pyrene derivative

Abstract: A new pyrene derivative 1-decyl-4-(1-pyrenyl) butanoate (DPB) was synthesized by the esterification reaction of 1-pyrene butyric acid with n-decanol. The photophysical properties of this pyrene ester were studied in toluene and in silicone polymers. The emission spectra of DPB exhibited excimer emission in solution and in silicone polymer coatings and the emission was effectively quenched by oxygen. A comparison of the oxygen sensor performance of DPB was made with that of pyrene and 1-pyrene butyric acid in silicone polymer coatings. The effect of different silicone resins on the properties of the DPB-based oxygen sensor coating was studied and the most suitable binder was selected. The new pyrene derivative was found to have potential as a substitute for pyrene in pressure-sensitive paints used for the measurement of surface pressure distribution on wind tunnel models.

A three-dimensional numerical study of mixed mode (I and II) crack tip fields in elastic-plastic solids

Abstract: he stress fields near a crack front in a ductile solid are essentially three-dimensional (3D) in nature. The objective of this paper is to investigate the structure of these fields and to establish the validity of two-dimensional (2D) plane stress and plane strain approximations near the crack front under mixed mode (combined modes I and II) loading. To this end, detailed 3D and 2D small strain, elastic–plastic finite element simulations are carried out using a boundary layer (small scale yielding) formulation. The plastic zones and radial, angular and thickness variations of the stresses are studied corresponding to different levels of remote elastic mode mixity and applied load, as measured by the plastic zone size with respect to the plate thickness. The 3D results are compared with those obtained from 2D simulations and asymptotic solutions. It is found that, in general, plane stress conditions prevail at a distance from the crack front exceeding half the plate thickness, although it could be slightly smaller for mode II predominant loading. The implications of the 3D stress distribution on micro-void growth near the crack front are briefly discussed.

Nose Bluntness for Side-Force Control on Circular Cones at High Incidence

Abstract: An experimental investigation has been car ked out to study the effect of nose bluntness on the characteristics of vortex asymmetry and induced side forces on slender cone models at low speeds. Two cone models with semi-apex angles of 8 and 12 deg were utilized, and on each model nose bluntness was varied up to 20% (based on base diameter).Measurements made consisted of six-component balance loads over a Widerange of Reynolds number from 0.4 x 10(6) to 5.4 x 10(6). The results show that the onset of vortex asymmetry with nose blunting correlates with geometrical parameters and is practically independent of Reynolds number. The (maximum) side-force levels decrease initially up to a certain bluntness ratio, then increase, followed by a gradual decrease for large values of bluntness ratios. This decrease or increase inside-force levels with nose blunting is associated with a corresponding increase or decrease, respectively, in the onset of vortex asymmetry.Whereas the increase in side-force level beyond the first minimum is qualitatively similar to that observed in earlier studies, the present data definitely indicate that there is a progressive decrease inside-force levels to relatively low values for large bluntness ratios,which could form an important design input. The bluntness ratio corresponding to the occurrence of the first minimum in (maximum) side force depends on the cone angle and is nearly independent of Reynolds number.

Compression behavior of TaC0.98 under nonhydrostatic and quasi-hydrostatic pressures up to 76 GPa

Abstract: Powder samples of TaC0.98 sandwiched between aluminum disks were placed in a rhenium gasket and compressed in a diamond anvil cell. The X-ray diffraction patterns were recorded under pressures up to 50 GPa using synchrotron radiation. The presence of aluminum in the cell rendered the sample pressure nearly hydrostatic and also served as the pressure standard. In another set experiments,TaC0.98 powder mixed with small quantity of platinum powder was placed in stainless steel gasket and compressed between the anvils. The X-ray diffraction patterns were recorded up to 76 GPa. In absence of any pressure-transmitting medium, the stress state of the sample was expected to be highly nonhydrostatic. The diffraction data were analyzed using lattice strain theory to estimate, the difference between the axial and radial stress components in the sample. The magnitudes of t suggest that the lower limit13; of compressive strength of TaC0.98 increases with increasing pressure and reaches -11 GPa at 76 GPa pressure. No phase transformation was observed up to the highest pressure. The bulk modulus and its pressure derivative derived from the volume-compression-pressure data are 345(9) GPa and 4.0(4), respectively.

Superhard nanocomposite coatings of TiN/a-C prepared by reactive DC magnetron sputtering

Abstract: Single layer TiN coatings were prepared on silicon (111) substrates using a multi-target reactive DC magnetron sputtering process at various nitrogen flow rates and substrate biases. TiN coatings prepared at a nitrogen flow rate of 0.6 sccm, a power density of 5.4 W/cm2 and a substrate bias of −275 V, showed a nanoindentation hardness of 3300 kg/mm2, whereas amorphous carbon (a-C) coatings prepared under similar deposition conditions exhibited a hardness of 800 kg/mm2. Subsequently, nanocomposite coatings of TiN/a-C were prepared on silicon (111) and M3 tool steel substrates by rotating the substrate back and forth between the titanium and the graphite targets. The nanocomposite coatings were prepared at various carbon concentrations. Structural characterization of the coatings was done by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The compositions of the coatings were determined using energy dispersive X-ray analysis (EDAX). The nanocomposite coatings exhibited a broad (111) reflection of cubic TiN phase in XRD data. Nanoindentation data showed that about 1.5-μm-thick TiN/a-C nanocomposite coatings exhibited a maximum hardness of 4800 kg/mm2 at a carbon concentration of approximately 17 at.%. The TEM micrographs showed that TiN nanocrystals were embedded in a-C matrix and the average crystallite size was 78 A. The selected area electron diffraction of the nanocomposite coatings showed the presence of both nanocrystalline (TiN) and amorphous (a-C) phases. This was confirmed by high-resolution TEM studies.

Reactive hot pressing of titanium nitride-titanium diboride composites at moderate pressures and temperatures

Abstract: Dense composites in the Ti-B-N system have been produced by reactive hot pressing of titanium and BN powders. The effect of the addition of a small amount of nickel (1-3 wt%) on the reaction kinetics and densification of TiN-TiB2 (40 vol %) composite has been studied. Composites of 99% of theoretical density have been produced at 1600DGC under 40 MPa for 30 min with 1% nickel. The hardness and fracture toughness of these composites are 24.5 +/- 0.97 GPa and 6.53 +/- 0.27 MPa (sq rt m), respectively. The microstructural studies on samples produced at lower temperatures indicate the formation of a transient liquid phase, which enhances the kinetics of the reaction and densification of the composite.

Repair Effectiveness Studies on Impact Damaged Sandwich Composite Constructions

Abstract: Experimental studies were carried out using sandwich composite panel specimens, consisting of both polyurethane foam core (PUF) and aramid honeycomb core (Nomex) type constructions. These specimens were subjected to impact damage at energy levels ranging between 7.56 and 15.6J. A ply-drop-patching technique was employed to repair the impact damaged sandwich specimens. The undamaged (virgin), impact damaged, and repaired specimens were then subjected to flexural (four point bending) and edgewise compression tests and strength recoveries were measured to determine the efficiency of the repair technique employed. In flexure, strength recoveries of upto 97% in PUF core and 90% in honeycomb core sandwich specimens were realized after repair, whereeas in compression, the corresponding values were upto 9O% in PUF core and 88% in honeycomb core sandwich specimens. A repair effectiveness factor(Ref)has been conceived and introduced to quantify the efficiency of the repair technique. Further, the repair quality was assessed using a simple NDT method prior to subjecting the sandwich specimens for destructive tests.

Optical Air Flow Measurements for Flight Tests and Flight Testing Optical Air Flow Meters

Abstract: Optical air flow measurements can support the testing of aircraft and can be instrumental to in-flight investigations of the atmosphere or atmospheric phenomena. Furthermore, optical air flow meters potentially contribute as avionics systems to flight safety and as air data systems. The qualification of these instruments for the flight environment is where we encounter the systems in flight testing. An overview is presented of different optical air flow measurement techniques applied in flight and what can be achieved with the techniques for flight test purposes is reviewed. All in-flight optical airflow velocity measurements use light scattering. Light is scattered on both air molecules and aerosols entrained in the air. Basic principles of making optical measurements in flight, some basic optical concepts, electronic concepts, optoelectronic interfaces, and some atmospheric processes associated with natural aerosols are reviewed. Safety aspects in applying the technique are shortly addressed. The different applications of the technique are listed and some typical examples are presented. Recently NASA acquired new data on mountain rotors, mountain induced turbulence, with the ACLAIM system. Rotor position was identified using the lidar system and the potentially hazardous air flow profile was monitored by the ACLAIM system.

Pressure-Sensitive Paint Measurements in a Blowdown Wind Tunnel

Abstract: A methodology to correct for temperature effects on pressure-sensitive paint data in a blowdown wind tunnel has been suggested. PSP measurements using Optrod-B1 paint were made on an aircraft model instrumented with thermocouples and conventional pressure taps. The tests were made at freestream Mach numbers of 0.6 and 0.8 and at model incidences of 6 and 10 deg. The temperature correction is based on a mean model temperature concept for a given blowdown and the corrected PSP data are validated using pressure port data. It has been found that the accuracy of temperature-corrected PSP results is about as good as for those obtained at transonic speeds in other tunnels elsewhere.

Five-Hole Flow Angle Probe Calibration from Dynamic and Tower Flyby Maneuvers

Abstract: Flight-test and data analysis techniques applied to calibrate the static pressure measured by pitot static systems and the flow angles measured by a five-hole probe mounted on a noseboom are described.13; Dynamic maneuvers with rapid variations in the aircraft motion are analyzed by application of parameter estimation techniques based on he output error method to calibrate the angle of attack and angle of sideslip. A complementary approach based on the Kalman filter technique is applied to a wind-box maneuver to calibrate the flow variables. The tower flyby maneuvers are analyzed using the classical approach of altitude determination through geometrical evaluation of photographs,and accurate information is derived from redundant sources to calibrate the pitot static system. The investigations showed that the static pressure measured by aircraft-installed pitot13; static system is accurate, sufficiently whereas that measured by an additional sensor mounted on the noseboom required speed-dependent correction. The flight estimated sensitivity factors for the flow angles measured by the five-hole probe agreed reasonably well with the manufacturer's specifications subject to corrections for biases resulting from misalignment and time delays caused by the recording equipment.

Computational Analysis of Inlet Aerodynamics for a Hypersonic Research Vehicle

Abstract: The aim of the present work is to carry out Reynolds-averaged Navier-Stokes computations of flow through the inlet of a hypersonic research vehicle with a view to accomplish detailed aerodynamic analysis Three inlet configurations that differ in the inlet-duct height are considered in this study The results of this study are13; presented in the form of detailed computational flow visualization through density contours, variation of flow parameters at various desired sections, and inlet performance in each case

An Improved Roe Scheme for Real Gas Flows

Abstract: During reentry and hypersonic igh t of space vehicles through atmosphere real gas eects come into play. The analysis of such hypersonic o ws is critical for proper aerothermal design of these vehicles. The present work emphasises numerical simulation of hypersonic o w with chemical non-equilibrium. A Reynolds Averaged Navier-Stokes code has been developed for this purpose employing an improved Roe scheme which is very robust and does not require any entropy x. To the best knowledge of the authors, such a formulation for real gas o w has not been reported earlier. A circular cylinder test case for which experimental data is available has been used to validate the code. Nomenclature _ !s mass rate of production of the species s s molar concentration of species s coecien t of thermal conductivity s thermal conductivity of the species s i

Structural health monitoring of co-cured composite structures using FBG sensors

Abstract: Structural Health Monitoring (SHM) of aircraft structures, especially composite structures, has assumed increased significance on considerations of safety and costs. With the advent of co-cured structures, wherein bonded joints are replacing bolted joints there is a concern regarding skin-stiffener separation, which might not be detected unless a rigorous non-destructive testing (NDT) is done. It would hence be necessary to be able to detect and assess skin-stiffener separation in composite structures before it reaches the critical size. One of the health monitoring strategies is through strain monitoring using fibre optic strain sensors such as Fibre Bragg Grating (FBG) sensors. The first aspect that needs to be addressed is the characterization of the FBG sensors. Issues of embedment in composites have also to be addressed. Before evolving a damage detection strategy, the sensitivity of the structural strain to skin-stiffener separations must be clearly understood and quantified. This paper presents the analysis and experiments done with a composite test box to study the effect of skin-stiffener separation on the strain behaviour. The box consists of two skins stiffened with spars made of Bi-Directional (BD) glass-epoxy prepreg material. The spars are bolted to the skins and removing suitable number of bolts simulates 'de-bonds'. The strains of the healthy box are compared with the unhealthy box. The strains in the experiments are monitored using both strain gauges and Fibre Bragg Grating (FBG) sensors. The experimental results show that there is significant change in the measured strain near and away from the debond location. The finite element analysis of the box is done using ABAQUS and the analysis is validated with the experimental results. A neural network based methodology is developed here to detect skin-stiffener debonds in structures. A multi-layer perceptron (MLP) neural network with a feed forward back propagation algorithm is used to determine the size/severity of damage. The FE model is used to generate the neural network training data for various sizes of debonds. The results show that the network is able to predict the damage size well. The network is implemented for a specified load. However, it is seen that the damage size predicted is independent of the applied load and the network performance is dependent on the fidelity of the finite element model used to train the network.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Analytical solution for an orthotropic elastic plate containing cracks

Abstract: The problem of estimating the bending stress distribution in the neighborhood of a crack located on a single line in an orthotropic elastic plate of constant thickness subjected to bending moment or twisting moment is examined. Using classical plate theory and integral transform techniques, the general formulae for the bending moment and twisting moment in an elastic plate containing cracks located on a single line are derived. The solution is obtained in a closed form for the case in which there is a single crack in an infinite plate and the results are compared with those obtained from the literature.

Postcuring effects on impact behavior of glass/epoxy composite laminates

Abstract: Studies had been undertaken on the effects of different postcure schedules on the impact resistance of RT-cured glass/epoxy laminates, subjected to repeated drop tests using an in-house built uninstrumented drop weight impact tester. The impact resistance was assessed in terms of two parameters, viz, the number of drops to failure (Nf) and the delamination area growth (dA). The specimens were postcured at different time-temperarure combinations and the impact response was studied at three different incident energy levels (10.6, 12.6, and 14.8 J). It was found that, the Nf and dA values increased to a maximum at an optimum postcure schedule of 85degC/4h. The extent of composite cure for the different postcure schedules was ascertained by measuring the glass transition temperatures (Tg), in order to obtain an appreciation for correlation between the impact resistance and the chemical cure status of the composite. Also, single drop impact studies were made at the 25-J energy level using an instrumented impact tester (DYNATUP 8250) and the aforesaid optimum postcure schedule was reconfirmed.

Vented circular cylinder as a vortex generator

Abstract: hese Mach-Zender interferograms show the effect of slot incidence on the near-wake features of a circular cylinder with natural ventilation. When the slot incidence angle is varied in the range 60amp;deg; to 90amp;deg; with respect to the mean flow, dramatic change in the flow features can be observed, as compared to the basic cylinder. Alternate blowing and suction take place across the slot, resulting in the formation of huge vortices accompanied by generation of sound. Due to the very low pressures in the core of the vortex leaving the near wake flow-field, the instantaneous flow remains attached up to 180amp;deg; from the stagnation point. At a = 60amp;deg;, significant difference in the locations of mean separation lines on top and bottom sides was seen, suggesting production of lift. The interferograms were obtained at free-stream conditions of M = 0.31 and Be = 0.47 million at the 0.3 m vacuum wind tunnel at the Max-Planck Institute of Fluid Mechanics, Goettingen, Germany. The cylinder diameter was 50 mm, and the vent slot had dimensions of 4 mm at the entrance and 4 mm at the exit.

Aero-Thermodynamic Model for Digital Simulation of Turbofan Engine

Abstract: The paper deals with the development and validation of an aero-thermodynamic model for a twin-spool mixed flow turbofan engine based on the state variable and control volume approach. Using actual performance data, the engine simulation has been performed for steady state and transient conditions with the help of MATLAB-SIMULINK. The simulation model is developed in a systematic manner. Engine states for different steady state operating conditions have been plotted. The model is fully equipped with capabilities to be integrated with the engine control design software to yield results for closed loop simulation. The results are validated against an independent and widely available modeling software called Gas turbine Simulation Program (GSP).

Superconductivity in dense Mg1 1-x M x B 2 (M = Zr, Nb, Mo; x = 0.05) materials sintered under pressure

Abstract: Dense compacts of superconducting MgB2 material have been produced by sintering under 3 GPa pressure and 900°C using a cubic anvil apparatus. The starting material was produced by the powder in tube (PIT) method at low pressure and in argon atmosphere. The effect of substitution of Mg sites with non-magnetic 4d-transition metals (Zr, Nb, Mo) on the superconducting transition temperature (T inc) has been studied by resistivity and susceptibility measurements. The results indicate that there is a small gradual reduction in the transition temperature as we move from Zr to Mo.

Thermodynamic Analysis of Turbofan Engine

Abstract: The present work deals with a detailed parametric thermodynamic analysis of all the possible configurations of turbofan engine (two and three spool with or without mixer and/ afterburner) employing transpiration cooling technique for turbine blade cooling. The study is focused on design point performance and is of general nature rather than an application specific parametric study. The analysis has been carried out by selecting/developing models for various components of engine. A computer program has been written which is capable of predicting engine dependent parameters (i.e. specific thrust, thrust specific fuel consumption, propulsive efficiency, efficiency of energy conversion and overall efficiency) at varying independent parameters at any flight condition and for any set of operating parameters. A set of multi-dimensional carpet plots predicting the effect of dependent in terms of independent parameters has been presented considering transpiration cooling for turbine blades and the temperature effect on specific heat of air/gas. Besides giving the comparative design point performance for a class of turbofan engine, these results could also be useful in assessing the relative benefits of extending technology to new engine configurations. Though, for a realistic mission application, the difference in performance at various thrust sizing conditions and at cruise conditions critical for fuel burn is a key characteristic in selecting the appropriate cycle, however this study could be useful in selecting in general the cycle configuration for a particular need with its optimum operating parameters.

Multi Sensor Data Fusion for Sensor Failure Detection and Health Monitoring

Abstract: The German Aerospace Center (DLR) Institute of Flight Systems has developed a demonstrator for enhanced autonomous technologies. Safe operation in civilian airspace of the small scale autonomous helicopter is a long term research aim. The use of low cost micro sensors in ARTIS (Autonomous Rotorcraft Test bed for Intelligent Systems) and the high level of noise make intelligent data fusion a mandatory requirement for health monitoring. In this paper model based magnetometer failure detection for ARTIS is implemented and investigated. Commonly encountered sensor failures are emulated using simulated and real magnetometer data. Failure detection is achieved by residual monitoring. The health monitoring utilizes the model based redundancies present in the established flight path reconstruction model, which is based on two sequential Extended Kalman filter. The results indicate the feasibility of the methodology for this type of rotorcraft vehicle. The work suggests that fusion of additional vision sensor data would not only provide an excellent reconfiguration strategy but also enhance the detection of small magnetometer drift failure types.

The contact angle in inviscid fluid mechanics

Abstract: We show that in general, the specification of a contact angle condition at the contact line in inviscid fluid motions is incompatible with the classical field equations and boundary conditions generally applicable to them. The limited conditions under which such a specification is permissible are derived; however, these include cases where the static meniscus is not flat. In view of this situation, the status of the many `solutions' in the literature which prescribe a contact angle in potential flows comes into question. We suggest that these solutions which attempt to incorporate a phenomenological, but incompatible, condition are in some, imprecise sense `weak-type solutions'; they satisfy or are likely to satisfy, at least in the limit, the governing equations and boundary conditions everywhere except in the neighbourhood of the contact line. We discuss the implications of the result for the analysis of inviscid flows with free surfaces.

The constancy of the contact angle in viscous liquid motions with pinned contact lines

Abstract: Consider motion initiated in a viscous liquid in a smooth walled container. The liquid is initially at rest under uniform pressure from an inert gas of negligible inertia. We show that if the contact line is pinned and the interface is single valued, the contact angle has to remain constant throughout the motion. This is true even for motions of finite amplitude. Some implications of the result are discussed.

Application of PSP To the Study of 3D Shock-Boundary Layer Interaction

Abstract: Experiments have been performed documenting the pressure field using a PSP technique in blunt fin-induced turbulent boundary layer interactions at a freestream Mach number of 1.8. Three blunt fins of different nose diameters have been tested in this study. The PSP measurements were made using the well known Optrod-B1 binary pressure sensitive paint. Excellent agreement of PSP results with conventional static pressure measurements has been observed.

The contact angle in inviscid fluid mechanics

Abstract: We show that in general, the specification of a contact angle condition at the contact line in inviscid fluid motions is incompatible with the classical field equations and boundary conditions generally applicable to them. The limited conditions under which such a specification is permissible are derived; however, these include cases where the static meniscus is not flat. In view of this situation, the status of the many ‘solutions’ in the literature which prescribe a contact angle in potential flows comes into question. We suggest that these solutions which attempt to incorporate a phenomenological, but incompatible, condition are in some, imprecise sense ‘weak-type solutions’; they satisfy or are likely to satisfy, at least in the limit, the governing equations and boundary conditions everywhere except in the neighbourhood of the contact line. We discuss the implications of the result for the analysis of inviscid flows with free surfaces.