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CONTENTS
Volume 1, Number 1, January 2014
 

Abstract
Physico-chemical changes of the plasma modified titanium alloy [Ti-6Al-4V] surface were studied with respect to their crystallographic changes by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM).The plasma-treatmentof surface was carried out to enhance adhesion of high performance nano reinforced epoxy adhesive, a phenomenon that was manifested in subsequent experimental results. The enhancement of adhesion as a consequence of improved spreading and wetting on metal surface was studied by contact angle (sessile drop method) and surface energy determination, which shows a distinct increase in polar component of surface energy. The synergism in bond strength was established by analyzing the lap-shear strength of titanium laminate. The extent of enhancement in thermal stability of the dispersed nanosilica particles reinforced epoxy adhesive was studied by Thermo Gravimetric Analysis (TGA), which shows an increase in onset of degradation and high amount of residuals at the high temperature range under study. The fractured surfaces of the joint were examined by Scanning electron microscope (SEM).

Key Words
titanium; plasma; adhesion; XRD; contact angle; SEM

Address
Sabbir Ahmed and Debabrata Chakrabarty: Department of Polymer Science and Technology, University of Calcutta, 92, APC Road, Kolkata-700009, India
Subroto Mukherjee, Alphonsa Joseph and Ghanshyam Jhala: Facilitation Centre for Industrial Plasma Technologies, IPR, A 10-B, G.I.D.C, Sector 25, Gandhinagar-382044, India
Shantanu Bhowmik : Department of Aerospace Engineering, Amrita University, Coimbatore 641112, Tamil Nadu, India Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands

Abstract
The developed concept of smart flow control based on turbulence scale modification was applied to control a flow around a circular cylinder. The concept was realized using arrays of vortex-generators regularly spaced along a cylinder generatrix with a given step. Mechanical and thermal vortex-generators were tested, the latter having been based on the localized surface heating or plasma discharges initiated with microwave radiation near the surface. Thus depending on a particular engineering solution, flow transport properties could be modified in passive or active ways. Matched numerical and experimental investigations showed a possibility to delay flow separation and, accordingly, to improve the aerodynamic performance of blunt bodies.

Key Words
scaled vortices; thermal riblets; aerodynamic performance; multidisciplinary investigations

Address
Nina F. Yurchenko: Department of Thermal & Fluid Dynamic Modeling, Institute of Hydromechanics, National Academy of Sciences of Ukraine, 8/4 Zheliabov St, Kiev 03680, Ukraine

Abstract
An active flow control technique based on \'smart-tabs\' is proposed to delay flow separation on a circular cylinder. The actuators are retractable and orientable multilayer piezoelectric tabs which protrude perpendicularly from the model surface. They are mounted along the spanwise direction with constant spacing. The effectiveness of the control was tested in pre-critical and in post-critical regime by evaluating the effects of several control parameters of the tabs like frequency, amplitude, height, angular position and plate incidence with respect to the local flow. Measurements of the mean static pressure distribution around the cylinder were used to estimate the pressure drag coefficient. The maximum drag reduction achieved in the pre-critical regime was of the order of 30%, whereas in the post-critical regime was about 10%, 3% of which due to active forcing. Furthermore, pressure fluctuation measurements were performed and spectral analysis indicated an almost complete suppression of the vortex shedding in active forcing conditions.

Key Words
flow control; bluff body; cylinder; drag reduction; piezoelectric actuators; smart tabs

Address
Matteo Orazia, Davide Lasagnab and Gaetano Iuso: Dipartimento di Ingegneria Meccanica e Aerospaziale, Politecnico di Torino 24, Corso Duca degli Abruzzi, 10129 Torino, Italy

Abstract
This paper presents a new conceptual design model ACAD (Adaptable Conceptual Aircraft Design), which differs from the other models due to its considerable adaptability to the different classes of aircraft. Another significant feature is the simplicity of the process which leads to the preliminary design outputs and also allowing a substantial autonomy in design choices. The model performs the aircraft design in terms of total weight, weight of aircraft subsystems, airplane and engine performances, and basic aircraft configuration layout. Optimization processes were implemented to calculate the wing aspect ratio and to perform the design requirements fulfillment. In order to evaluate the model outcomes, different test cases are presented: a STOL ultralight airplane, a new commuter with open-rotor engines and a last generation fighter.

Key Words
conceptual design; weight estimation; aircraft performances; design optimization; design requirements

Address
Marco Fioriti: Department Mechanical and Aerospace Engineering, Politecnico di Torino, Turin, Italy

Abstract
Numerical investigations are presented, which show that a back-flow flap can improve the dynamic stall characteristics of oscillating airfoils. The flap was able to weaken the stall vortex and therefore to reduce the peak in the pitching moment. This paper gives a brief insight into the method of function of a back-flow flap. Initial wind tunnel experiments were performed to define the structural requirements for a detailed experimental wind tunnel characterization. A structural integration concept and two different actuation mechanisms of a back-flow flap for a helicopter rotor blade are presented. First a piezoelectric actuation system was investigated, but the analytical model to estimate the performance showed that the displacement generated is too low to enable reliable operation. The seond actuation mechanism is based on magnetic forces to generate an impulse that initiates the opening of the flap. A concept based on two permanent magnets is further detailed and characterized, and this mechanism is shown to generate sufficient impulse for reliable operation in the wind tunnel.

Key Words
back-flow flap; active flap; flow control; solid state hinge; helicopter; rotor blade

Address
Steffen Opitz: German Aerospace Center (DLR), Institute of Composite Structures and Adaptive Systems, Lilienthalplatz, 7, 38108 Braunschweig, Germany
Kurt Kaufmann and Anthony Gardner: German Aerospace Center (DLR), Institute of Aerodynamics and Flow Technology, Bunsenstra

Abstract
A variational asymptotic composite beam model has been developed for thermoelastic analysis. Composite beams, including sandwich structure and laminates, under different boundary conditions are examined. Previously developed beam model, which is based on variational-asymptotic method, is extended to incorporate temperature-dependent materials experiencing large temperature changes. The recovery relations have been derived so that the temperatures, heat fluxes, stresses, and strains can be recovered over the cross-section. The present theory is implemented into the computer program VABS (Variational Asymptotic Beam Sectional analysis). Numerical results are compared with the 3D analysis for the purpose of demonstrating advantages of the present theory and use of VABS.

Key Words
variational asymptotic method; composite beam; finite element method; thermoelasticity; VABS; finite temperature change

Address
Qi Wang: 1Department of Mechanical and Aerospace Engineering, Utah State University, Logan, Utah 84322-4130, USA
Wenbin Yu: School of Aeronautics and Astronautics, Purdue University, West Lafayette, IN, USA


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