Showing papers by "Defence Research and Development Laboratory published in 2015"
TL;DR: In this paper, numerical simulations are performed for full scale scramjet combustor of a hypersonic airbreathing vehicle with ethylene fuel at ground test conditions corresponding to flight Mach number, altitude and stagnation enthalpy of 60, 30,km and 161MJ/kg respectively.
42 citations
TL;DR: In this article, a ternary mixture of various ratios of bisphenol F benzoxazine as a hardener for ER and diglycidal ether of polyethylene glycol (EL) resins was made in order to study the visco elastic and thermo mechanical properties in comparison with homo polymerized polybenzoxazine (F-a). FTIR and DSC were used to characterize the cure characteristic.
Abstract: Ternary mixtures of various ratios of bisphenol F benzoxazine as a hardener for bisphenol F novolac epoxy (ER) and diglycidal ether of polyethylene glycol (EL) resins were made in order to study the visco elastic and thermo mechanical properties in comparison with homo polymerized polybenzoxazine (F-a). FTIR, and DSC were used to characterize the cure characteristic. The dynamic mechanical analyzer and thermo gravimetric analysis were investigated on F-a and ternary samples. An improved Tg of curable ternary mixture with 48.1 and 3.1 wt% of ER and EL respectively with benzoxazine resin was achieved based on trends in the ternary diagram. The ternary samples were thermally stable up to 370 °C when compared to F-a. Investigation of fracture toughness and SEM images showed improved fracture toughness for the samples with 52% binary epoxy mixture in the ternary system. The newly developed ternary mixtures showed improved service temperature, thermal stability, cross linking density, processing window and fracture toughness with minimum brittleness when compared to polybenzoxazine. The applicability of the developed ternary mixture was demonstrated by preparing an S glass fabric reinforced composite with F-f. It was observed that this S glass fabric composite has improved flexural strength, flexural modulus, ILSS, Shore D hardness & hydrolytic stability when compared to the polybenzoxazine composite and was found to be very useful for high performance structural applications.
36 citations
TL;DR: In this paper, the same model is applied for cylindrical port motors with high and moderate mass flux, as well as finocyl grain motors, and it is observed that the computed pressures with the burning time match very well experimental data.
19 citations
TL;DR: In this paper, a C/SiC composite nozzle was fabricated using LSI and characterized for mechanical, thermal, and ablation properties, and the overall mass erosion rate and the linear ablation rate were found to be 0.119 kg/m2s and 0.05 mm/s, respectively.
Abstract: 4D C/SiC composite nozzle was fabricated using LSI and characterized for mechanical, thermal, and ablation properties. Average flexural and compressive strengths in the Z-direction were found to be 119 and 110 MPa, while in the U-, V- and W-directions, they were 99 and 55MPa, respectively. Coefficient of thermal expansion was found to be varied in the range 0–1.5 × 10−6/°C (25–1050°C), while thermal diffusivity was 40–5 mm2/s (25–1200°C). Ablation behavior of the nozzle was evaluated under UH25/N2O4 propulsion system for 30 s. The overall mass erosion rate and the linear ablation rate were found to be 0.119 kg/m2s and 0.05 mm/s, respectively.
17 citations
03 Jan 2015-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the tensile properties of C-103 Nb based alloy were evaluated in the temperature range between room temperature (RT) and 1200°C using Gleeble test system at the strain rate of 10 −2 ǫ s −1.
Abstract: In this study, the tensile properties of C-103 Nb based alloy were evaluated in the temperature range between room temperature (RT) and 1200 °C using Gleeble test system at the strain rate of 10 −2 s −1 . The presence of well-defined serrations and temperature insensitivity of 0.2% yield strength confirmed the occurrence of dynamic strain aging (DSA) from RT to 1200 °C. However, the DSA was found to have predominant effect only up to 900 °C, beyond which dynamic recovery and oxidation influenced the tensile properties. Fractography revealed that the alloy had undergone intergranular fracture, which was attributed to the DSA in the temperature range of 600–900 °C and oxidation in the temperature range of 1000–1200 °C.
16 citations
TL;DR: A computer code has been developed for internal ballistic performance evaluation of solid rocket motors, using minimum distance function (MDF) approach for prediction of geometry evolution, which can handle any complex geometry without the need to define different geometrical shapes and their evolution as used in several existing analytical geometry evolution-based methodologies.
Abstract: A computer code has been developed for internal ballistic performance evaluation of solid rocket motors, using minimum distance function (MDF) approach for prediction of geometry evolution. This method can handle any complex geometry without the need to define different geometrical shapes and their evolution as used in several existing analytical geometry evolution-based methodologies. The code is validated with both experimental results published in literature, as well as for solid rocket motors of tactical and strategic missiles and a very good match is obtained with static test results. The output of the code gives p-t (pressure-time) curve as well as the detailed parameters of the flow along the axial direction, and geometries in the form of mesh file, which can be further used as input to codes for CFD analysis. Defence Science Journal, Vol. 65, No. 3, May 2015, pp.181-188, DOI: http://dx.doi.org/10.14429/dsj.65.8304
12 citations
TL;DR: In this article, computational fluid dynamics simulations are carried out for a complete hypersonic vehicle integrating both external and internal flow together to calculate the scramjet combustor performance and vehicle net thrust minus drag.
Abstract: Computational fluid dynamics simulations are carried out for a complete hypersonic vehicle integrating both external (nonreacting) and internal (reacting) flow together to calculate the scramjet combustor performance and vehicle net thrust minus drag. Simulations are carried out for a flight Mach number of about six. Three-dimensional Navier–Stokes equations are solved along with the shear stress transport k-ω turbulence model and single-step chemical reaction based on fast chemistry. The Lagrangian particle tracking method for droplets is used for combustion of kerosene fuel. Flow is largely nonuniform at the inlet of the combustor. Mass flow of ingested air increases with increase in angle of attack. Because of more combustion of fuel, wall surface pressure is higher for α=6 deg compared with α=0 deg. Combustion efficiency and thrust achieved are found to increase with the increase in angle of attack. Considerable amount of thrust is obtained from a single expansion ram nozzle and achievement of posit...
10 citations
TL;DR: In this paper, a conceptual hypersonic air-breathing scramjet engine integrated with the vehicle (without combustion) has been simulated numerically using ANSYS CFX software with the SST turbulence model.
Abstract: The flow path of a conceptual hypersonic air-breathing scramjet engine integrated with the vehicle (without combustion) has been simulated numerically using ANSYS CFX software with the SST turbulence model. The computations were performed for the free stream Mach number of 6 and angle-of-attack of 5°. A strong separation bubble was observed on the bodyside wall in the internal compression region where the reflected cowl shock impinges on body which in turn increases the static pressure substantially. The external-internal flow field of the hypersonic mixed compression intake, shock-boundary layer interactions, and the shock-shock interactions present in the internal compression region have qualitatively been obtained and analysed. The variation of centreline pressure along the bodyside wall close to the symmetry plane obtained from numerical simulation centreline has been compared with the experimentally measured data. It has been observed that the computed wall pressure matches fairly well with the measured values in the external ramp compression region, internal compression region and in the combustion chamber. The flow patterns and the pressure variations near the middle wall and the fuel injecting strut locations have also been analysed. Defence Science Journal, Vol. 65, No. 4, July 2015, pp. 272-278, DOI: http://dx.doi.org/10.14429/dsj.65.6979
10 citations
TL;DR: In this paper, the performance of prepared propellant grade hydrazine shows it as a promising rocket fuels and the desired combustion was smooth and C* achieved was higher than that of UH-25, N2O4 combination.
Abstract: Propellant grade hydrazine was prepared with 64 per cent yield and 95.5 per cent purity. Purity of the propellant grade hydrazine was determined using wet chemical, gas chromatographic (GC) and eudiometric methods. It was observed that the compositions containing blends of hydrazine-methyl alcohol-ammonium nitrate and hydrazine-methyl alcohol-ammonium perchlorate were not found to be frozen even after cooling to -65 °C for 30 minutes. Mono and bi-propellant thrusters were designed and developed to demonstrate the performance of prepared propellant grade hydrazine as a promising rocket fuel. Five static tests with 22 N thruster and one static test with 1 N thruster were performed successfully in mono-propellant mode. The hurdles of chamber pressure oscillations were overcome by compact packing of the catalyst. The desired decomposition and chamber pressure were achieved. One static test was performed successfully with 60 N bi-propellant thruster. The desired chamber pressure and thrust were achieved. The combustion was smooth and C* achieved was higher than that of UH-25, N2O4 combination. The performance of prepared propellant grade hydrazine shows it as a promising rocket fuels.Defence Science Journal, Vol. 65, No. 1, January 2015, pp.31-38, DOI:http://dx.doi.org/10.14429/dsj.65.7986
9 citations
TL;DR: In this article, a hybrid finite volume method for simulating compressible turbulence is developed by combining a fourth-order central scheme and a shock-capturing simple low-dissipation advection upstream splitting method.
Abstract: Summary
A simple, explicit, hybrid finite volume method for simulating compressible turbulence is developed by combining a fourth-order central scheme and a shock-capturing simple low-dissipation advection upstream splitting method. The total flux on each of the cell faces is computed as a weighted average of central/nondissipative and upwind/dissipative fluxes. The weights are determined using an unphysical oscillation sensor in addition to a more traditional discontinuity sensor used in earlier studies. Shocks are well captured, but overshoots in density are predicted around contact discontinuities that are normal to the flow. The use of the latter sensor effectively prevents these overshoots from generating spurious oscillations that travel away from the contact lines. The efficacy of the proposed method for direct or large-eddy simulations of supersonic turbulence is established using several canonical test problems. Copyright © 2015 John Wiley & Sons, Ltd.
9 citations
01 Apr 2015
TL;DR: In this article, the authors describe the dynamics of sandwich beams with viscoelastic cores, which are used in aerospace and automotive industries, and demonstrate the need for simple methods describing the dynamic dynamics of these complex structures.
Abstract: Various types of sandwich beams with viscoelastic cores are currently used in aerospace and automotive industries, indicating the need for simple methods describing the dynamics of these complex st...
TL;DR: An improved analytical method of image registration is used which integrates nearest neighbor method and gradient method and presents a framelet based enhanced fusion for choosing the fused framelet co-efficient that provides detailed edges and good spatial information with adequate de-noising.
Abstract: A enhanced fusion algorithm for generating a super resolution image from a sequence of low-resolution images captured from identical scene apparently a video, based on framelet have been designed and analyzed. In this paper an improved analytical method of image registration is used which integrates nearest neighbor method and gradient method. Comparing to Discrete Wavelet Transform (DWT) the Framelet Transform (FrT) have tight frame filter bank that offers symmetry and permits shift in invariance. Therefore using framelet this paper also present a framelet based enhanced fusion for choosing the fused framelet co-efficient that provides detailed edges and good spatial information with adequate de-noising. The proposed algorithm also has high advantage and computationally fast which are most needed for satellite imaging, medical imaging diagnosis, military surveillance, remote sensing etc. Defence Science Journal, Vol. 65, No. 4, July 2015, pp. 292-299, DOI: http://dx.doi.org/10.14429/dsj.65.8265
TL;DR: In this paper, the mixing of two coaxial supersonic dissimilar gases in free jet environment is numerically explored using three dimensional RANS equations with a k-e turbulence model.
TL;DR: In this paper, an enhanced method of choosing the singular values from the SVD domain images to reconstruct a high resolution image using fusion techniques is proposed, which is called as enhanced SVD based fusion.
Abstract: The singular value decomposition (SVD) plays a very important role in the field of image processing for applications such as feature extraction, image compression, etc. The main objective is to enhance the resolution of the image based on Singular Value Decomposition. The original image and the subsequent sub-pixel shifted image, subjected to image registration is transferred to SVD domain. An enhanced method of choosing the singular values from the SVD domain images to reconstruct a high resolution image using fusion techniques is proposesed. This technique is called as enhanced SVD based fusion. Significant improvement in the performance is observed by applying enhanced SVD method preceding the various interpolation methods which are incorporated. The technique has high advantage and computationally fast which is most needed for satellite imaging, high definition television broadcasting, medical imaging diagnosis, military surveillance, remote sensing etc.
TL;DR: In this article, a computational fluid dynamics methodology was used in characterising jet-vane based thrust vector control systems of tactical missiles, where three-dimensional Reynolds Averaged Navier-Stokes equations were solved along with two-equation turbulence model for different operating conditions.
Abstract: Computational fluid dynamics methodology was used in characterising jet vane based thrust vector control systems of tactical missiles. Three-dimensional Reynolds Averaged Navier-Stokes equations were solved along with two-equation turbulence model for different operating conditions. Nonlinear regression analysis was applied to the detailed CFD database to evolve a mathematical model for the thrust vector control system. The developed model was validated with series of ground based 6-Component static tests. The proven methodology is applied toa new configuration. Defence Science Journal, Vol. 65, No. 4, July 2015, pp. 261-264, DOI: http://dx.doi.org/10.14429/dsj.65.7960
01 Jun 2015
TL;DR: In this article, the behaviour of turbulent Prandtl/Schmidt number is explored through the model-free simulation results and it is observed that compressibility affects the Reynolds scalar flux vectors.
Abstract: The behaviour of turbulent Prandtl/Schmidt number is explored through the model-free simulation results. It has been observed that compressibility affects the Reynolds scalar flux vectors. Reduced peak values are also observed for compressible convective Mach number mixing layer as compared with the incompressible convective Mach number counterpart, indicating a reduction in the mixing of enthalpy and species. Pr-t and Sc-t variations also indicate a reduction in mixing. It is observed that unlike the incompressible case, it is difficult to assign a constant value to these numbers due to their continuous variation in space. Modelling of Pr-t and Sc-t would be necessary to cater for this continuous spatial variation. However, the turbulent Lewis number is evaluated to be near unity for the compressible case, making it necessary to model only one of the Pr-t and Sc-t..
TL;DR: In this paper, the authors presented an insight for the study of transient, compressible, intermittent pulsed detonation engine with one-step overall reaction model to reduce the computational complexity in detonation simulations.
Abstract: This paper presents an insight for the study of transient, compressible, intermittent pulsed detonation engine with one-step overall reaction model to reduce the computational complexity in detonation simulations. Investigations are done on flow field conditions developing inside the tube with the usage of irreversible one-step chemical reactions for detonations. In the present simulations 1-D and 2-D axisymmetric tubes are considered for the investigation. The flow conditions inside the detonation tube are estimated as a function of time and distance. Studies are also performed with different grid sizes which influence the prediction of Von-Neumann spike, CJ Pressure and detonation velocity. The simulation result from the single-cycle reaction model agrees well with the previous published literature of multi-step reaction models. The present studies shows that one-step overall reaction model is sufficient to predict the flow properties with reasonable accuracy. Finally, the results from the present study were compared and validated using NASA CEA. Defence Science Journal, Vol. 65, No. 4, July 2015, pp. 265-271, DOI: http://dx.doi.org/10.14429/dsj.65.8730
01 Dec 2015
TL;DR: In this article, a finite element method is developed and validated for the estimation of loss factors of a viscoelastically damped plate, where a Viscoelastic layer is used as constrained layer and is sandwiched between a...
Abstract: A finite element method is developed and validated for the estimation of loss factors of a viscoelastically damped plate. Viscoelastic layer is used as constrained layer and is sandwiched between a...
TL;DR: In this article, a three dimensional flowsolver is indigenously developed to numerically simulate hypervelocity thermal and chemical non-equilibrium reactive air flow past flight vehicles, which is implemented in a compressible viscous code CERANS and solved in the finite volume framework.
Abstract: In the present study, a three dimensional flowsolver is indigenously developed to numerically simulate hypervelocity thermal and chemical non equilibrium reactive air flow past flight vehicles. The two-temperature, five species, seventeen reactions, thermo-chemical non equilibrium, non-ionizing, air-chemistry model of Park is implemented in a compressible viscous code CERANS and solved in the finite volume framework. The energy relaxation is addressed by a conservation equation for the vibrational energy of the gas mixture resulting in the evaluation of its vibrational temperature. The AUSM-PW+ numerical flux function has been used for modeling the convective fluxes and a central differencing approximation is used for modeling the diffusive fluxes. The flowsolver had been validated for specifically chosen test cases with inherent flow complexities of non-ionizing hypervelocity thermochemical nonequilibrium flows and results obtained are in good agreement with results available in open literature.
TL;DR: In this paper, the authors presented formulation and solution of a long range flight vehicle and a tactical air-to-air flight vehicle trajectory optimisation problem under path and terminal constraints.
Abstract: This paper presents formulation and solution of long range flight vehicle and tactical air-to-air flight vehicle trajectory optimisation. The first case study is of a long range flight vehicle. Here an optimum steering program during powered phase has been evolved as control input for achieving maximum range with available propulsions in the presence of path and terminal constraints. The second case study is of a tactical flight vehicle for air-to-air application. Here a minimum flight time trajectory has been generated for covering a specified range pertaining to a specified air-to-air engagement by evolving pitch lateral acceleration as control input. Here also, there are many path and terminal constraints consisting of launch aircraft, pursuer, and evader. The studies have been carried out as part of system design activity of both flight vehicles. Both are real-life optimisation problems under several constraints. Through it is very difficult to solve such practical problems in flight dynamics using classical optimal control theory, it has been solved successfully using direct transcription method based on nonlinear programming. Rapid convergence has been achieved in four passes with minimum grids in first pass, to start with, and increasing the grids in subsequent passes. Solving such a real-life problem with proper convergence subjected to many constraints is claimed as novelty of present research. Defence Science Journal, Vol. 65, No. 2, March 2015, pp.107-118, DOI:http://dx.doi.org/10.14429/dsj.65.8238
TL;DR: In this paper, numerical simulations were carried out to study the unsteady flow in an intake of a hypersonic air-breathing vehicle, and the results indicated that the flow was unstable due to flow separation bubbles inside intake.
Abstract: Numerical simulations were carried out to study the unsteady flow in an intake of hypersonic air-breathing vehicle. Unsteady RANS simulations were performed to examine started flow of the intake when cowl surface is parallel to the ramp surface. Though started, the flow was unsteady due to flow separation bubbles inside intake. Intake with larger cowl opening at which intake unstarted was also simulated. Simulations indicated unstarted flow, with large pressure oscillations. The numerically simulation results match reasonably well with experimental data. Calculated unstarting Mach number was found to be 3.0-3.2 in comparison of wind tunnel data of 3.6 for the same cowl opening angle. Defence Science Journal, Vol. 65, No. 3, May 2015, pp.189-195, DOI: http://dx.doi.org/10.14429/dsj.65.8254
TL;DR: In this paper, the effect of heat treatment on the tensile properties of AA6082 aluminum alloy tube has been investigated and the results reveal that as-flow formed condition (followed by natural aging) gives the best combination of yield strength, UTS and percentage of elongation.
Abstract: The present study reports the effect of the heat treatment on the tensile properties of the reverse flow-formed AA6082 Aluminum alloy tube. Tensile specimens obtained after each forming pass have been subjected to three different heat-treatment conditions viz., as-flow formed (AFF), as-flow formed followed by artificial aging (170°C/6h) and HT (solutionizing + 170°C/6h) treatments. Characterization of the tensile properties reveals that as-flow formed condition (followed by natural aging) gives the best combination of yield strength, UTS and percentage of elongation. The variations in tensile properties are correlated with microstructure of the materials.
23 Feb 2015
TL;DR: In this article, performance analysis of the recently appeared extended-state-observer (ESO)-based roll autopilot design is carried out and the results show that the ESO-based design offers satisfactory performance in controlling roll angle and its rate in the presence of significant disturbances, parameter uncertainties and cross-coupling effects.
Abstract: In this work, performance analysis of the recently appeared extended-state-observer (ESO)-based roll autopilot design is carried out. Firstly, considering a more realistic roll dynamics, performance comparison of the ESO-based design with several classical roll autopilot structures is carried out and the related results are presented. Next, the better performing designs are implemented and validated through a high fidelity nonlinear 6-DOF environment for a typical tactical missile in a realistic engagement scenario. Lastly, performance of the ESO-based design is investigated using Monte Carlo simulations under several subsystem parameter uncertainties. The results show that the ESO-based design offers satisfactory performance in controlling roll angle and its rate in the presence of significant disturbances, parameter uncertainties and cross-coupling effects and thus offers a viable approach towards design of roll autopilot for high performance tactical missiles.
01 Sep 2015
TL;DR: The limits for use of mobile phones during Handling, Assembly and Integration of Rocket motors and also during Flight trials are recommended and safe distances have been arrived at and reported in the present work.
Abstract: Electromagnetic waves produced by radio-frequency (RF) transmitters (e.g. radio, television, cell phone and radar) will induce electric currents and voltages in any conducting structure on which they impinge. If this happens in a location where a potentially flammable atmosphere is present, a hazardous situation can occur. However, the possibility of ignition will depend on many factors, particularly whether the spark can deliver sufficient energy to ignite a particular flammable atmosphere. In this paper, an attempt has been made to present the likelihood of ignition of fuel and solvent vapors due to the presence of RF transmitters, inadvertent ignition of Electro Explosive Devices (EEDs), explosives and to recommend the limits for use of mobile phones during Handling, Assembly and Integration of Rocket motors and also during Flight trials. The frequency range covered is 9 KHz to 60 GHz. Ignition of flammable atmosphere has been assessed as per British Standard BS 6656:2002. Inadvertent ignition of EEDs is also assessed as per US Army “Explosives Safety Standard”. As a result, safe distances have been arrived at and reported in the present work.
TL;DR: In this article, a new class of E glass fabric reinforced polybenzoxazine titanate composites (EBTA) were made with bisphenol F benzoxazine (BZ) and in situ generating reactive multi branched n-butoxy triethanol amine titanate (TEA) chelate in various ratios.
Abstract: A new class of E glass fabric reinforced polybenzoxazine titanate composites (EBTA) were made with bisphenol F benzoxazine (BZ) and in situ generating reactive multi branched n-butoxy triethanol amine titanate (TEA) chelate in various ratios. The incorporation of TEA into a polybenzoxazine matrix could cause uniform dispersion within the polymer matrix and ring opening of oxazine at lower temperature, which result in an increase of the cross link density, stiffness and hindered network structures responsible for enhancing the thermal and water resistance. The hypothetical chemical reaction between BZ and TEA was understood by studying the reaction between model compounds such as phenol, tetra isobutyl titanate and triethanol amine. FTIR and DSC studies were utilized to optimize the curing studies and the final cure temperature was established for EBTA composites. The DMA analysis carried out on EBTA composites showed improved stiffness, crosslink density and service temperatures (Tg) with uniform phase distribution when compared to the E glass fabric reinforced polybenzoxazine composite. The thermal stability and char yield with TGA analysis, interfacial adhesion with SEM and hydrolytic stability for the EBTA composites using up to 23% of TEA were found to be improved when compared to the polybenzoxazine composite. The flame retardancy of EBTA composites were found to be retained for the V1 class of polybenzoxazine composite. The EBTA composites showed low maximum cure temperature, improved service temperature, cross link density, stiffness, water absorption resistance, thermal stability and char yield when compared to the E glass fabric polybenzoxazine composite.
01 Jul 2015
TL;DR: In this paper, the authors examined the issue of growth rate reduction of high speed mixing layer with convective Mach number for similar and dissimilar gases using Reynolds averaged Navier-Stokes (RANS) methodology with k- turbulence model.
Abstract: The issue of growth rate reduction of high speed mixing layer with convective Mach number is examined for similar and dissimilar gases using Reynolds averaged Navier-Stokes (RANS) methodology with k- turbulence model. It is observed that the growth rate predicted using RANS simulations closely matches with that predicted using model free simulations. Velocity profiles do not depend on the modelled value of Pr-t and Sc-t; while the temperature and species mass fraction distributions depend heavily on them. Although basic k- turbulence model could not capture the reduced growth rate for the mixing layer formed between similar gases, it predicts very well the reduced growth rate for the mixing layer for the dissimilar gases. It appears that density ratio changes caused by temperature changes for the dissimilar gases have profound effect on the growth rate reduction.