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CONTENTS
Volume 7, Number 3, May 2020
 

Abstract
The exhaust nozzle serves back pressure of Pulse detonation combustor, so combustion chamber gets sufficient pressure for propulsion. In this context recent researches are focused on influence of nozzle effect on single cycle detonation wave propagation and propulsion performance of PDE. The effects of various nozzles like convergent-divergent nozzle, convergent nozzle, divergent nozzle and without nozzle at exit section of detonation tubes were computationally investigated to seek the desired propulsion performance. Further the effect of divergent nozzle length and half angle on detonation wave structure was analyzed. The simulations have been done using Ansys 14 Fluent platform. The LES turbulence model was used to simulate the combustion wave reacting flows in combustor with standard wall function. From these numerical simulations among four acquaint nozzles the highest thrust augmentation could be attained in divergent nozzle geometry and detonation wave propagation velocity eventually reaches to 1830 m/s, which is near about C-J velocity. Smaller the divergent nozzle half angle has a significant effect on faster detonation wave propagation.

Key Words
detonation wave; nozzle shape; pulse detonation combustor; computational fluid dynamics

Address
Pinku Debnath: Department of Mechanical Engineering, National Institute of Technology Agartala, 799046, Tripura, India

K. M. Pandey: Department of Mechanical Engineering, National Institute of Technology, Silchar, Assam,788010 India

Abstract
In many applications like the aircraft or the rockets/missiles, the flow from a nozzle needs to be expanded suddenly in an enlarged duct of larger diameter. The enlarged duct is provided after the nozzle to maximize the thrust created by the flow from the nozzle. When the fluid is suddenly expanded in an enlarged duct, the base pressure is generally lower than the atmospheric pressure, which results in base drag. The objective of this research work is to optimize the length to diameter (L/D) ratio of the enlarged duct using the CFD analysis in the flow field from the supersonic nozzle. The flow from the nozzle drained in an enlarged duct, the thrust, and the base pressure are studied. The Mach numbers for the study were 1.5, 2.0 and 2.5. The nozzle pressure ratios (NPR) of the study were 2, 5 and 8. The L/D ratios of the study were 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. Based on the results, it is concluded that the L/D ratio should be increased to an optimum value to reattach the flow to an enlarged duct and to increase the thrust. The supersonic suddenly expanded flow field is wave dominant, and the results cannot be generalized. The optimized L/D ratios for various combinations of flow and geometrical parameters are given in the conclusion section.

Key Words
base pressure; length to diameter ratio; mach number; nozzle pressure ratio; thrust

Address
Khizar A. Pathan: Department of Mechanical Engineering, Trinity College of Engineering and Research, Pune, India

Prakash S. Dabeer: Department of Mechanical Engineering, Acharya Institute of Technology, Bangalore, India

Sher A. Khan: Department of Mechanical Engineering, International Islamic University Malaysia, Kuala Lumpur, Malaysia

Abstract
As is shown in the paper, the Koltunov-Rzhanitsyn singular kernel of heredity (when constructing mathematical models of the dynamics problem of the hereditary theory of viscoelasticity) adequately describes real mechanical processes, best approximates experimental data for a long period of time. A mathematical model of the problem of the flutter of viscoelastic plates moving in a gas with a high supersonic velocity is given. Using the Bubnov-Galerkin method, discrete models of the problem of the flatter of viscoelastic plates flowed over by supersonic gas flow are obtained. A numerical method is developed to solve nonlinear integro-differential equations (IDE) for the problem of the hereditary theory of viscoelasticity with weakly singular kernels. A general computational algorithm and a system of application programs have been developed, which allow one to investigate the nonlinear dynamic problems of the hereditary theory of viscoelasticity with weakly singular kernels. On the basis of the proposed numerical method and algorithm, nonlinear problems of the flutter of viscoelastic plates flowed over in a gas flow at an arbitrary angle are investigated. In a wide range of changes in various parameters of the plate, the critical velocity of the flutter is determined. It is shown that the singularity parameter

Key Words
mathematical model; viscoelasticity; integro-differential equations; flutter; angle of flow

Address
A.G. Sherov, B.A. Khudayarov and J. Aliyarov: Tashkent Institute of Engineers of Irrigation and Mechanization in Agriculture, Tashkent, Uzbekistan

K.Sh. Ruzmetov: Tashkent State Agrarian University, Tashkent region, Kibray district, Uzbekistan

Abstract
This paper is the logical follow-up of four papers by the author on the subject \"aerodynamics in Mars atmosphere\". The aim of the papers was to evaluate the influence of two Mars atmosphere models (NASA Glenn and GRAM-2001) on aerodynamics of a capsule (Pathfinder) entering the Mars atmosphere and also to verify the feasibility of evaluating experimentally the ambient density and the ambient pressure by means of the methods by McLaughlin and Cassanto respectively, therefore to correct the values provided by the models. The study was carried out computationally by means of: i) a code integrating the equations of dynamics of an entry capsule for the computation of the trajectories, ii) two Direct Simulation Monte Carlo (DSMC) codes for the solution of the 2-D, axial-symmetric and 3-D flow fields around the capsule in the altitude interval 50-100 km. The computations verified that the entry trajectories of Pathfinder from the two models, in terms of the Mach, Reynolds and Knudsen numbers, were very different. The aim of the present paper is to continue this study, considering other aerodynamic problems and then to provide a contribution to a long series of papers on the subject \"aerodynamics in Mars atmosphere\". More specifically, the present paper evaluated and quantified the effects from the two models of: i) chemical reactions on aerodynamic quantities in the shock layer, ii) surface temperature, therefore of the contribution of the re-emitted molecules, on local (pressure, skin friction, etc.) and on global (drag) quantities, iii) surface recombination reactions (catalyticity) on heat flux. The results verified that the models heavily influence the flow field (as per the shock wave structure) but, apart from the surface recombination reactions, the effects of the different conditions on aerodynamics of the capsule are negligible for both models and confirmed what already found in the previous paper that, because of the higher values of density from the NASA Glenn model, the effects on aerodynamics of a entry capsule are stronger than those computed by the GRAM-2001 model.

Key Words
Mars atmosphere models; Mars Pathfinder capsule; entry trajectory; effects of surface temperature; effects of chemistry; effects of surface catalyticity; Direct Simulation Monte Carlo method

Address
Gennaro Zuppardi: Department of Industrial Engineering – Aerospace Division, University of Naples \"Federico II\", Piazzale Tecchio, 80 – 80125 Naples, Italy

Abstract
Euclid is an optical/near-infrared survey mission of the European Space Agency (ESA) to investigate the nature of dark energy, dark matter and gravity by observing the geometry of the Universe and the formation of structures over cosmological timescales. The Euclid spacecraft mechanical architecture comprises the Payload Module (PLM) and the Service Module (SVM) connected by an interface structure designed to maximize thermal and mechanical decoupling. This paper shortly illustrates the mechanical system of the spacecraft and the mechanical verification philosophy which is based on the Structural and Thermal Model (STM), built at flight standard for structure and thermal qualification and the Proto Flight Model (PFM), used to complete the qualification programme. It will be submitted to a proto-flight test approach and it will be suitable for launch and flight operations. Within the overall verification approach crucial mechanical tests have been successfully performed (2018) on the SVM platform and on the sunshield (SSH) subsystem: the SVM platform static test, the SSH structure modal survey test and the SSH sine vibration qualification test. The paper reports the objectives and the main results of these tests.

Key Words
Euclid mission; spacecraft; mechanical verification; mechanical testing; vibration; modal survey test

Address
Adriano Calvi: European Space Agency/ESTEC, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands

Patrizia Bastia: Thales Alenia Space Italy, Strada Antica di Collegno 253, 10146 Torino, Italy

Manuel Perez Suarez: Airbus Defence and Space, Avenida de Aragón 404, 28022 Madrid, Spain

Philipp Neumann: SpaceTech GmbH, Seelbachstr. 13, D-88090 Immenstaad, Germany

Albert Carbonell: RUAG Schweiz AG, Schaffhauserstrasse 580, 8052 Zürich, Switzerland

Abstract
The paper describes the analysis of deployment strategies and trajectories design suitable for executing the inspection of an operative spacecraft in orbit through re-usable CubeSats. Similar missions have been though indeed, and one mission recently flew from the International Space Station. However, it is important to underline that the inspection of an operative spacecraft in orbit features some peculiar characteristics which have not been demonstrated by any mission flown to date. The most critical aspects of the CubeSat inspection mission stem from safety issues and technology availability in the following areas: trajectory design and motion control of the inspector relative to the target, communications architecture, deployment and retrieval of the inspector, and observation needs. The objectives of the present study are 1) the identification of requirements applicable to the deployment of a nanosatellite from the mother-craft, which is also the subject of the inspection, and 2) the identification of solutions for the trajectories to be flown along the mission phases. The mission for the in-situ observation of Space Rider is proposed as reference case, but the conclusions are applicable to other targets such as the ISS, and they might also be useful for missions targeted at debris inspection.

Key Words
CubeSats; in-orbit inspection; mission analysis; formation flight; rendezvous and docking; deployment analysis; simulation

Address
Sabrina Corpino, Fabrizio Stesina, Daniele Calvi and Luca Guerra: Department of Mechanical and Aerospace Engineering (DIMEAS) Politecnico di Torino,Corso Duca degli Abruzzi 24, 10129 Torino, Italy



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