Defence Research and Development Laboratory

About: Defence Research and Development Laboratory is a facility organization based out in Hyderabad, India. It is known for research contribution in the topics: Turbulence & Mach number. The organization has 404 authors who have published 420 publications receiving 4183 citations. The organization is also known as: DRDL.

Thermal vibration analysis of monolayer graphene embedded in elastic medium based on nonlocal continuum mechanics

Abstract: This paper presents the thermal vibration analysis of doublelayer graphene sheet embedded in polymer elastic medium, using the plate theory and nonlocal continuum mechanics for small scale effects. The graphene is modeled based on continuum plate theory and the axial stress caused by the thermal effects is also considered. Nonlocal governing equations of motion for this double-layer graphene sheet system are derived from the principle of virtual displacements. The closed form solution for thermal-vibration frequencies of a simply supported rectangular nanoplate has been obtained by using the Navier’s method of solution. Numerical results obtained by the present theory are compared with available solutions in the literature and the molecular dynamics results. The influences of the small scale coefficient, the room or low temperature, the high temperature, the half wave number and the aspect ratio of nanoplate on the natural frequencies are considered and discussed in detail. The thermal vibration analysis of single- and doublelayer graphene sheets are considered for the analysis. The mode shapes of the respective graphene system are also captured in this work. The present analysis results can be used for the design of the next generation of nanodevices that make use of the thermal vibration properties of the double-layer graphene system..

Magnetohydrodynamic Flow Control of a Hypersonic Cruise Vehicle Based on AJAX Concept

Abstract: I N THE history of space exploration, rockets were the only flight vehicles available for transportation such as Earth orbital missions for placing satellites, interplanetary flights, and military missions such as Intermediate Range Ballistic Missiless and Intercontinental Ballistic Missile. Most of these rockets flew a oneway mission of transportation from Earth to the destination and, upon completion of the mission, were either lost in space or fell back to Earth as debris, and hence were nonrecoverable. The cost associated with launching these flight vehicles and the imposing technological challenges, though considered as highly mature as of the present day, were overwhelmingly large. The U.S. Space Shuttle of and the Russian Buran/Energiya were designed and operated as the only reusable flyingmissions that couldmake several sorties between the Earth and the flight to orbit [1]. However, huge operating andmaintenance costs associated with each of these missions, and the inexorable reliability and safety issues, gradually shelved them as unacceptable due to the present-day design philosophy of “low-cost access to space.”Hence, next-generation space exploration required a different class of flight vehicles that was required to be cost efficient and fully reusable. In this realm, the hypersonic airbreathing propulsion system based on a supersonic combustion ramjet (SCRAMJET) was envisaged as the key technology platform for possible realization of the reusable launch vehicle (RLV) in full mission mode, which could perform orbital flights similar to that of spacecraft flown by a rocket system, although with logistics akin to that of an airliner, as on a day-to-day basis [2]. Active flow control of hypersonic flight vehicles forms a crucial design requirement for hypersonic research and technology development. The futuristic RLV concepts, such as the hypersonic cruise vehicle (HSCV) based on the SCRAMJET engine, require complex active flow control techniques that use new multidisciplinary and evolutionary physical mechanisms, such as electromagnetic and plasma discharge flow control, right from launch phase to touchdown. Hence, there is a need and demand to develop a multidisciplinary numerical tool considering the pertinent multiphysics environment for addressing research and development needs, as well as for analysis of various hypersonic flow control problems. A schematic of the hypersonic cruise vehicle configuration based on the RLV concept is shown in Fig. 1. At hypersonic speeds, since the angle of the nose oblique shock is narrow, the entire forebody can be used for compressing the air, and hence forms part of the scramjet engine intake. Due to this, the intake characteristics are strongly coupled to the forebody shape of the HSCV; hence, the forebody is highly design optimized to provide adequate air ram compression and mass capture at the inlet. The exhaust duct of the HSCV scramjet engine is shaped as a nozzle having a considerable length, and it forms part of the HSCV aftbody. The nozzle provides adequate expansion of the combusted gases, which in turn provides thrust to the vehicle. It can be observed that there is a tight coupling of airframe with the propulsion system, and the flight conditions influence the propulsive performance, which in turn affects the aerodynamic performance of the vehicle as a whole, and hence necessitates an integrated aeropropulsive design approach. One of themain challenges encountered in theHSCVdesign is that an adequatemass flow rate should be captured at the inlet and the inlet should start. During offdesign flight conditions, the air mass captured by the air intake might drastically reduce, which can result in flameout and thrust loss. To counter the technical challenges of the HSCV design, such as the subcritical air-intakemass flow rate, high forebody heat flux rates, active thermal management, onboard power generation, thrust augmentation, etc., Vladimir Freighstadt of the Leninetz Holding Company inRussia proposed a novelAJAXvehicle concept [3] in the late 1980s. The AJAX concept hypersonic cruise aircraft was proposed to fly in the mesosphere (50–80 km altitude range) and incorporated various novel technologies based on plasma generation, magnetohydrodynamics (MHD) flow control systems, MHD power generation for controlling and augmenting the hypersonic flow, as well as for thermal management schemes [4–6]. The concept was conceived to use the existing adverse hypersonic environment around the vehicle toward its advantage. The AJAX concept made extensive utilization of MHD-based flow control techniques, where the fluid that was preionized and made electrically conducting was easily manipulated by an externally applied magnetic field. Hence, the hypersonic flowfield could be easily modified for convenience, even at offdesign flight conditions, by application of a suitable magnetic field. Due to the use of various onboard MHD subsystems, such as the MHD-controlled inlet or MHD generator and MHD accelerator, the hypersonic ramjet engine is referred to as the magnetoplasma chemical engine, or MPCE. The schematic of the AJAX concept HSCV [6,7] is shown in Fig. 2. It has a waverider type of forebody design, followed by a flat upper surface to the body end, and it houses the MPCE along the midsection of the lower surface. The MHD generator shown in the figure inhibits the mass flow rate by application of a suitable magnetic field, thereby generating electric current. The hydrocarbon endothermic fuel is converted into the hydrogenenriched mixture and fed into the plasma-stabilized combustor for thermochemical reaction, and it sets on the combustion process. The exhaust products of combusted gas when entering the nozzle region are further accelerated using the MHD accelerator for providing additional thrust. The power source for theMHDaccelerator is drawn from the electricity produced by the MHD generator at the inlet. Since the oncoming air is preionized at the nose region of the HSCV, the overall drag of the vehicle is also reduced significantly. The ionizer housed at the nose region is a microwave beam generator that gets its power supply fromMHDgenerator. As adequate power is generated within the MPCE to solve the high-energy needs of the Received 26 January 2016; revision received 5 May 2016; accepted for publication 16 May 2016; published online 24 June 2016. Copyright © 2016 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Copies of this paper may be made for personal and internal use, on condition that the copier pay the per-copy fee to the Copyright Clearance Center (CCC). All requests for copying and permission to reprint should be submitted to CCC at www.copyright.com; employ the ISSN 0022-4650 (print) or 1533-6794 (online) to initiate your request. *Directorate of Computational Dynamics; bals.cfd@gmail.com (Corresponding Author). Directorate of Computational Dynamics.