Showing papers by "Defence Research and Development Laboratory published in 2021"

Heat Management in Supersonic/Hypersonic Vehicles Using Endothermic Fuel: Perspective and Challenges.

Abstract: In this study, an in-depth analysis has been performed on various technoengineering aspects of hydrocarbon cracking under supercritical conditions toward developing an endothermic fuel. The paper is segregated into several sections with specific emphasis. The major areas covered in this work include physicochemical characteristics of different endothermic fuels, supercritical pyrolysis of hydrocarbon fuels, phenomena of coking, and its suppression from an application viewpoint. The influence of various parameters (e.g., temperature, pressure, catalysts, space-time, etc.) on fuel conversion, endothermicity, and coke propensity has been emphasized in detail. The typical value of endothermic heat sink capacity for different fuels consisting of C8 to C15 hydrocarbons ranges from 500 to 1150 kJ/kg over temperature and pressure ranges of 550-750 °C and 25-55 bar, respectively. The effectiveness of various additives/initiators in improving endothermicity has been screened for wide ranges of temperature and pressure. Physicochemical properties like distillation characteristics, hydrocarbon composition, °API gravity, and sulfur content of different hydrocarbon fuels are compared in a single window. Most of the findings are abridged meticulously with relevant tables and plots. Toward the end, we have highlighted the critical issues/challenges on the experimental findings and prospective.

Microelectrochemical sparks machining: a modern approach for fabrication of microcomponents from nonconductive materials

Abstract: Microelectro-chemical spark machining (micro-ECSM) is a novel hybrid unconventional machining process which has the capability to fabricate sophisticated and intrinsic microcomponents with high-dimensional accuracy. It is based on the principle which combines the microelectrochemical and microelectric discharge machining process. This process has potential to machine both conductive as well as nonconductive material with high precession without any physical contact, which makes it a unique machining process and raises its demand in different fields starting from aviation to medical sector. The present article describes the mechanism of spark formation and material removal process. The tool feed mechanism and the variants of the micro-ECSM process are elaborated. This article also outlines the various material machined by micro-ECSM process and the enhancements of the machining potential by its hybrid variant and provides new prospect in technological advancement of micro-ECSM process.

Investigation of High-Temperature Stability and Thermal Endurance of Silicone Potting Compound by Thermo-Gravimetric Analysis

Abstract: The high-temperature stability and thermal life of silicone resin-based potting compound (SC-3), used in the aerospace application for electrical insulation, is investigated Thermo-Gravimetry Analysis (TGA) in an inert environment. Nonisothermal TGA is performed in the temperature range of 30 °C to 900 °C at 10, 20, and 30 °C / min heating rates. The kinetic parameters such as activation energy and pre-exponential factor are obtained by the model-free method proposed by Kissinger-Akahira-Sunose (KAS) and Flynn Wall Ozawa (FWO) at various degree of conversion. The thermal degradation of the SC-3 compound is observed in the temperature range of 350 °C to 580 °C, and thermal endurance or time of failure of potting compound SC-3 is estimated as per ASTM E1877 standard. The results reveal that the potting compound SC-3 can be safely used continuously at 100 °C and for ~3.6 min at 350 °C. Experimental results are also useful to understand the degradation mechanism of the SC-3 compound.

Thermoelastic damping in nonlocal rod using three-phase lag heat conduction model

Abstract: This manuscript studies thermoelastic damping of a longitudinally vibrating nanorod at small-scale. The heat conduction in the present work is constructed based on the three phase-lag heat conducti...

Investigation of Slender Bodies at Hypersonic Mach Numbers

Abstract: Tests were carried in a shock tunnel to determine the heating rate and the wall pressure on a test model flying at hypersonic velocity. The experiments were performed at Mach M = 6.5 and a total enthalpy of 1.2 MJ/kg. Helium was used as the driver gas and air as the driven gas. The effective test time during the tunnel testing was 3.5 ms. The vacuum sputtered gages were used to evaluate the heating rate on the test model. The evaluated heating rate agrees well with numerical simulation. The experimentally measured pressure also agrees with computational fluid dynamics

Influence of Filler Content on Thermo-Physical Properties of Hollow Glass Microsphere- Silicone Matrix Composite

Abstract: Thermo-physical properties of hollow glass microsphere (HGM) filled silicone resin are analyzed by various mathematical models to optimize the formulation for a low-density high-temperature resistant composite. The study involves analyzing effective thermal conductivity, specific heat, and density for a two-phase particulate composite system by using the most popular expressions available in the literature at various volume fractions of HGM in the silicone resin matrix. Experiments are performed to compare theoretical results with the experimental data and identified the preferred composition with a density as low as 0.39 g/cc and thermal conductivity 0.116 W/m-K. The microstructural studies by SEM are done to explain the deviation in experimental and theoretical results. FEM analysis is done to understand the heat flow phenomenon in HGM filled silicone composites.

Experimental estimation and numerical optimization of ‘cylindricity’ error in flow forming of H30 aluminium alloy tubes

Abstract: The present article analyses the influence of flow forming input parameters on the development of “cylindricity error” in H30 aluminum alloy seamless tubes fabricated by a single pass reverse flow forming process. Measurement and control of geometrical precision in terms of cylindricity encompassing straightness and roundness are critical for the success of component manufacturing by flow forming. The experimental trials with a predefined range of input parameters conforming to the full factorial design of experiments approach have been performed, and corresponding cylindricity data have been recorded as the outcome. An empirical relation has been established between the input parameters and the cylindricity. It has been established that cylindricity value increases sharply with an increase in axial stagger contributing 39% to the outcome, whereas the percentage contributions of in-feed and feed-speed ratio are found to be less than 1%. The adequacy of the proposed model has further been analyzed and validated through the confirmation tests. In order to obtain better control over the overall process towards achieving higher productivity and accuracy, 2 meta-heuristic optimization algorithms namely, teaching and learning-based algorithm and genetic algorithm have been utilized for optimization of input process parameters to minimize cylindricity error. Both the algorithms predict that a combination of higher feed rate and lower value of axial stagger and in-feed parameters is essential to achieve the lowest cylindricity error in H30 Al alloy. Confirmatory experimental trials have been carried out to validate both the regression model and optimization, and have been found to agree well with the model predictions described herein.

Experimental investigation of blunt cone model at hypersonic Mach number 7.25

Abstract: Experiments were carried out in hypersonic shock tunnel in Defence Research and Directorate Laboratory at hypersonic Mach number of 7.25 using an 11.37° apex-angle blunt cone model. Heat flux measurement was carried out on cone model at different angles of attack with angle of rotation ϕ = 0° to 360° in steps of 45° with vacuum sputtered platinum thin film sensors. The measured experimental value of heat transfer data at stagnation point was compared with theoretical value estimated Fay and Riddell correlation. As angle of rotation was increased from ϕ = 0° to ϕ = 180°, the shock wave became closer to model surface due to high density ratio across the shock wave and consequently heat transfer rate became higher.

Studies on Hollow Glass Microsphere Reinforced Silicone Matrix Composite for Use in Fast Curing Low Density Thermal Insulation Coating Applications

Abstract: A low density material coating based on silicone polymer matrix reinforced with hollow glass microspheres is developed for thermal insulation. An organo-platinum compound is added to the resin matrix to make it a fast room temperature curing coating. It has a low density in the order of 0.39–0.34 g/cc with medium Shore A hardness in the order of 60–65. The thermal stability in an inert and oxidative environment was analyzed by the TGA method. The insulative properties are investigated using an infra-red heaters test set up, which showed almost 50 % temperature reduction on the substrate compared to the non-coated substrate. The coating properties, like adhesion, impact resistance, corrosion resistance, etc., are analyzed using various bond promoters and excellent in the class of insulative coatings. The effect of various diluents on the curing is observed and then finalized the suitable diluents for spray coating. The coating forms hard silica char, which in turn protect the surface from further high temperatures. A scheme for painting the metallic and non-metallic articles is also established for ease of application to the user.

Limitations of autopilot design for controlling a statically unstable flexible interceptor

Abstract: The Mach number, angle of attack and altitude of operation for an interceptor vary widely during the course of its trajectory. As a result, the interceptor Center of Pressure (CP) locations move significantly around a given Center of Gravity (CG) location at these operating conditions. This results in an inevitable variation in aerodynamic static stability leading to stable and unstable operating regions. In order to ensure good speed of response during the interceptor homing phase, lesser static stability is desirable. Hence the requirement to handle aerodynamic instability at some other operating conditions in the interceptor envelope become inevitable. Since flexibility has a strong bearing on autopilot design, it becomes necessary to control unstable operating points in the presence of flexibility modes. Despite the static stability variation, aerodynamic design can control the level of maximum instability of the configuration. Hence the maximum static instability the autopilot can handle has to be specified for aerodynamic configuration design. This paper brings out the limitations of autopilot design in controlling an unstable interceptor with low bending mode frequencies in terms of maximum instability the autopilot design can handle, which serves as an important input for aerodynamic design.

Novel Privacy Preserving Authentication Scheme Based on Physical Layer Signatures for Mobile Payments

Abstract: Financial transaction through smart mobile devices is an attractive feature in today’s modern wireless network era. Despite having various advantages, privacy and security are always challenging in such services. A novel hybrid security scheme based on physical layer signature and cryptography has been proposed to provide a secured authentication scheme preserving user’s privacy, for the application of mobile payments. This scheme provides two levels of authentication, privacy preserving location authentication and device authentication. User’s privacy is preserved by encrypting the identity of the user by physical layer encryption based on user’s location. Physical layer signatures such as channel state information and carrier frequency offset are used for physical layer encryption. In conventional techniques, Media Access Control (MAC) address is used for initial authentication and they are shared without encryption. In this proposed technique, MAC is encrypted using the secret key derived from physical layer signatures using Singular Value Decomposition (SVD) to preserve privacy. Since secret key, generated using SVD, is location specific and varies with respect to the location, it is used for the location authentication. User authentication, required for mobile payment, is realised using asymmetric key cryptography technique. Since, physical layer security is used for privacy preserving location authentication in addition to the conventional cryptographic methods, the proposed method provides significant improvement in the security. The performance of the proposed method has been analysed in terms of information leakage to adversary, bit error rate performance, and transaction time in comparison with existing method which uses cryptography and provides only device authentication for mobile payment. The proposed technique gives better performance than existing technique in terms of privacy and authentication for mobile payment.

Polynomial Guidance Law for Dual-Seeker Interceptors

Abstract: A polynomial-based guidance law is proposed for interception of a stationary target by a dual-seeker interceptor. The guidance law governs the desired look-angle profile as a cubic polynomial of th...

Investigation of the Effect of Booster Attachment Scheme on the Rolling Moment Characteristics of an Asymmetric Vehicle Using CFD

Abstract: The rolling moment characteristics of a launch vehicle (LV) arising out of joining an air-breathing cruise vehicle (CV) and a booster is investigated through CFD to explain experimental observed behaviour. The launch vehicle has a stabilising fin at the rear and is placed on bearing to have free roll with respect to body. The basic and control rolling moment of LV (without stabilising fin, to mimic freely rolling fin), obtained experimentally, is compared with the corresponding experimental data for CV and found that the values differ, contrary to that observed in literature. CFD is used to investigate the reason for this difference. Investigation in two representative Mach numbers 0.8 (subsonic) and 2.0 (supersonic), has revealed that the interstage flare in LV, has significant effect in modifying the rolling moment contribution of the CV fin. Apart from that, the booster attachment arm, launch shoes are also having some impact in modifying the rolling moment. It is evident that for a canard controlled vehicle, even if the stabilising fin is freely rolling, the after-body geometry has significant effect in dictating the aerodynamic characteristics, especially rolling moment.

2 Loop Nonlinear Dynamic Inversion Fuel Flow Controller Design for Air to Air Ducted Ramjet Rocket

Abstract: Fuel Flow controller based ramjet propulsion system have a flexibility to change rocket velocity depending on guidance requirement by controlling the fuel flow rate as a function of atmospheric conditions like altitude, Mach no. and angle of attack. In this paper, Design objectives & requirements of fuel flow controller have been brought out from guidance loop for air-to-air target engagement. 2-loop non-linear dynamic inversion (DI) based controller design has been proposed to track the commanded thrust and to meet the time constant requirement as a function of altitude, Mach no. and angle of attack. The outer thrust loop is to control commanded thrust and to generate the demand for gas generator pressure loop and inner pressure loop is to meet outer loop demand by controlling throttle valve area. The engine state space plant model has been adapted with improvement of existing model. Throttle valve actuator specifications requirement are also brought out.

Higher Order Sliding Mode-Based Guidance for Controlling Statically Unstable Missiles

Abstract: A surface to air missile (SAM) typically operates at a wide range of Mach numbers, angles of attack and altitudes. This leads to an inevitable significant variation in center of pressure (CP) location. In addition, the propulsion burning changes the Center of Gravity (CG) location. The variation in CP and CG locations results in high variation in aerodynamic static stability in the flight envelope. The high variation of static stability makes operating at statically unstable regions inevitable and needs to be tackled through the missile on-board algorithm. The control design poses a requirement of high autopilot bandwidth to tackle the static instability, which leads to unrealistic actuator bandwidth requirements. Here, we propose a novel technique to handle the high static instability outside the purview of control design without burdening the control requirements. In this paper, the highly unstable operating conditions are avoided through judicious design of mid-course guidance. This paper also presents design of this guidance scheme through higher order sliding mode technique.

Tera-Hertz Wave Propagation in Non-classical Beams Using Spectral Finite Element Method

Abstract: Non-classical beams have vast applications in NEMS/MEMS devices where scale effects are predominant, keeping these applications in mind, the present manuscript studies about the wave dispersion behavior of non-classical beam structures. Governing equations and corresponding boundary conditions for the non-classical Euler-Bernoulli & non-classical Timoshenko beam theories are derived to study the wave propagation characteristics. Time domain equations are converted into frequency domain using fast Fourier transform. Spectral finite element method (SFEM) formulation is implemented for non-classical beams to study the dynamic response of these beam structures in frequency domain. Spectrum and dispersion curves are studied with respect to scale coefficients along with the dynamic stiffness variations in the beams. Numerical experiments are conducted to identify the scale effects on dynamic wave propagation behavior of beams with the consideration of asymptotic frequencies of tera-hertz level. Exhaustive results are presented to understand the complete dynamic wave propagation behavior of these non-classical beams. The presented results are very useful in the design of NEMS/MEMS devices where the beam like elements are critical.