Techno Press
Tp_Editing System.E (TES.E)
Login Search


You have a Free online access.
aas
 
CONTENTS
Volume 5, Number 4, July 2018
 

Abstract
This computational study examines the augmentation of classic 2-D Rayleigh-Bénard convection by the addition of periodically-spaced transverse fins. The fins are attached to the heated base of the cavity and serve to partition the cavity into \'units\'with different aspect ratios. The respective impacts upon heat transfer of the fin configuration parameters – including spacing, height, thickness and thermal conductivity – are systematically examined through numerical simulations for a range of laminar Rayleigh numbers (0 < Ra < 2 x 100000) and reported in terms of an average Nusselt number. The selection of the low Rayleigh number regime is linked to likely scenarios within aerospace applications (e.g. avionics cooling) where the cavity length scale and/or gravitational acceleration is small. The net heat transfer augmentation is found to result from a combination of competing fin effects, most of which are hydrodynamic in nature. Heat transfer enhancement of up to 1.2 x that for a Rayleigh-Bénard cavity without fins was found to occur under favorable fin configurations. Such configurations are generally characterized by short, thin fins with half-spacings somewhat less than the convection cell diameter from classic Rayleigh-Bénard theory. In contrast, for unfavorable configurations, it is found that the introduction of fins can result in a significant reduction in the heat transfer performance.

Key Words
natural convection; Rayleigh-Bénard cells; low Rayleigh number; passive cooling; heat transfer with partitions

Address
Department of Mechanical Engineering, University of Vermont, Burlington, Vermont, USA

Abstract
Numerical simulations have been conducted to study the unstart/restart characteristics of an over-under turbine-based combined-cycle propulsion system (TBCC) inlet during the inlet transition phase. A dual-solution area exists according to the Kantrowitz theory, in which the inlet states may be different even with the same input parameters. The entire transition process was divided into five stages and the unstart/restart hysteresis loop for each stage was also obtained. These loops construct a hysteresis surface which separates the operating space of the engine into three parts: in which a) inlet can maintain a started state; b) inlet keeps an unstarted state; c) inlet state depends on its initial state. During the transition, the operation of the engine follows a certain order with different backpressures and splitter angles, namely control route, which may result in disparate inlet states. Nine control routes with different backpressures and transition stages were designed to illuminate the route-dependent behavior of the inlet. The control routes operating towards the unstart boundary can make the inlet transit from a started state into an unstarted one. But operating backward the same route cannot make the inlet restart, additional effort should be made.

Key Words
inlet mode transition; unstart/restart hysteresis; control route; route-dependent

Address
Nan Li:Science and Technology on Scramjet Laboratory, Hypervelocity Aerodynamics Institute of CARDC, Sichuan, Mianyang 621000, China
Nan Li, Juntao Chang, Jingfeng Tang, Daren Yu, Wen Bao and Yanping Song: Harbin Institute of Technology, Harbin, Heilongjiang 150001, China

Abstract
Turbulent airflow in channels of rectangular cross section with symmetric centerbodies is studied numerically. Shock wave configurations formed in the channel and in front of the entrance are examined. Solutions of the unsteady Reynolds-averaged Navier-Stokes equations are obtained with finite-volume solvers of second-order accuracy. The solutions demonstrate an expulsion/swallowing of the shocks with variations of the free-stream Mach number or angle of attack. Effects of the centerbody length and thickness on the shock wave stability and flow bifurcation are examined. Bands of the Mach number and angle of attack, in which there exist non-unique flow fields, are identified.

Key Words
supersonic intake; shock waves; instability; hysteresis

Address
Department of Fluid Dynamics, St. Petersburg State University, 28 University Avenue, 198504, Russia

Abstract
In the field of aerospace engineering, accurate control of a spacecraft\'s orientation is often very important to mission success. Therefore, attitude control is a technically plentiful and extensively studied subject in controls literature during recent decades. This investigation of spacecraft attitude control is assumed to address two important aspects of the problem solutions. One sliding mode anti-disturbance control for utilization of faulty actuator components and another one disturbance observer based control to improve the pointing accuracy in the absence of anti-vibration equipment for the elastic appendages like a solar panel. Simultaneous occurrence of vibration due to flexible appendages and reaction degradation due to failure in attitude actuators complicates this case. The advantage of this method is acquisition proper control by the combination of disturbance observer and sliding mode compensation that form a fault tolerant control for the concerned satellite attitude control system. Furthermore, the proposed composite method indicates that occurrence the failure in actuators and even elastic solar panel vibration effect may be handled directly without reconfiguring the control components or providing piezoelectric devices. It\'s noteworthy, attitude quaternion and angular velocity commands are robustly tracked via controllers to become inclined to zero.

Key Words
attitude control; actuator failure; disturbance observer based control; sliding mode

Address
Hamed Yadegari:Satellite Research Institute (SRI), Iranian Space Research Center, NO. 74, Shahid Mirhosseini St. (14th St.), Saadat abad Ave, Tehran, Iran
Boulanouar Khouane, Zhu Yukai and Han Chao:School of Astronautics, Beihang University (BUAA), 37 Xueyuan Rd., Beijing, China
Boulanouar Khouane: Centre de Développement des Satellites - Bir Eldjir/Oran - Algeria

Abstract
The main goal of this article is to validate a methodological process in Actran MSC Software, that is based on the Finite Element Method, to evaluate the comfort in the cabin of a regional aircraft and to study the noise and vibrations reduction through the fuselage by the use of innovative materials. In the preliminary work phase, the CAD model of a fuselage section was created representing the typical features and dimensions of an airplane for regional flights. Subsequently, this model has been imported in Actran and the Sound Pressure Level (SPL) inside the cabin has been analyzed; moreover, the noise reduction through the fuselage has been evaluated. An important investigation and data collection has been carried out for the study of the aircraft cabin to make it as close as possible to a real problem, both in geometry and in materials. The mesh of the structure has been built from the CAD model and has been simplified in order to reduce the number of degrees of freedom. Finally, different fuselage configurations in terms of materials are compared: in particular, aluminum, composite and sandwich material with composite skins and poroelastic core are considered.

Key Words
FEM; vibroacoustic analysis; noise reduction; sound pressure level; cabin comfort

Address
Politecnico di Torino, Department of Mechanics and Aerospace Engineering, Italy

Abstract
One of the major problems in glass fiber reinforced epoxy (GFRE) composite pipes is the durability under water absorption. This condition is generally recognized to cause degradations in strength and mechanical properties. Therefore, there is a need for an intelligent system for detecting the absorption rate and computing the mass of water absorption (M%) as a function of absorption time (t). The present work represents a new non-destructive evaluation (NDE) technique for detecting the water absorption rate by evaluating the dielectric properties of glass fiber and epoxy resin composite pipes subjected to internal hydrostatic pressure at room temperature. The variation in the dielectric signatures is employed to design an electrical capacitance sensor (ECS) with high sensitivity to detect such defects. ECS consists of twelve electrodes mounted on the outer surface of the pipe. Radius-electrode ratio is defined as the ratio of inner and outer radius of pipe. A finite element (FE) simulation model is developed to measure the capacitance values and node potential distribution of ECS electrodes on the basis of water absorption rate in the pipe material as a function of absorption time. The arrangements for positioning12-electrode sensor parameters such as capacitance, capacitance change and change rate of capacitance are analyzed by ANSYS and MATLAB to plot the mass of water absorption curve against absorption time (t). An analytical model based on a Fickian diffusion model is conducted to predict the saturation level of water absorption (MS) from the obtained mass of water absorption curve. The FE results are in excellent agreement with the analytical results and experimental results available in the literature, thus, validating the accuracy and reliability of the proposed expert system.

Key Words
electrical capacitance sensor (ECS), composite materials; water absorption rate

Address
Wael A. Altabey:International Institute for Urban Systems Engineering, Southeast University, Nanjing, Jiangsu, China
Nanjing Zhixing Information Technology Co., Ltd., Andemen Street, Nanjing, Jiangsu, China
Department of Mechanical Engineering, Faculty of Engineering, Alexandria University, Alexandria, Egypt
Mohammad Noori: International Institute for Urban Systems Engineering, Southeast University, Nanjing, Jiangsu, China, Department of Mechanical Engineering, California Polytechnic State University, San Luis Obispo, CA, USA


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2018 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: subs@techno-press.com