Showing papers by "Italian Aerospace Research Centre published in 2009"

A Novel SMA-based Concept for Airfoil Structural Morphing

Abstract: The adaptive structures concept is of great interest in the aerospace field because of the several benefits which can be accomplished in the fields including noise reduction, load alleviation, weight reduction, etc., at a level in which they can be considered as compulsory in the design of future aircraft. Improvements in terms of the aerodynamic efficiency, aeroelastic behavior, stability, and manoeuvrability performance have already been proved through many international studies in the past. In the family of the Smart Materials, Shape Memory Alloys (SMA) seem to be a suitable solution for many static applications. Their high structural integrability in conjunction with actuation capabilities and a favorable performance per weight ratio, allows the development of original architectures. In this study, a morphing wing trailing edge concept is presented; morphing ability was introduced with the aim of replacing a conventional flap device. A compliant rib structure was designed, based on SMA actuators exhibiting structural potential (bearing external aerodynamic loads). Numerical results, achieved through a FE approach, are presented in terms of trailing edge induced displacement and morphed shape.

Wing Shape Control through an SMA-Based Device:

Abstract: Based on numerical and experimental analyses, this article proposes an application of the smart structure concept aimed at realizing a bump on an airfoil profile, finalized to reduce transonic drag, through the use of shape memory alloys (SMAs) The ability of morphing the wing profile is functional to maximize the aerodynamic efficiency in different mission conditions The use of the so-called smart materials allows a favorable actuation performance per weight ratio, also leading to simple and integrated devices Currently, to model their mechanical behavior is still an open issue and this work presents some original ideas about this Numerical results and experimental tests herein presented, demonstrate the efficacy of the developed concept device, calling for further studies on real structures; their correlation also validate the implemented simulation procedure

Preliminary Design of Vertical Takeoff Hopper Concept of Future Launchers Preparatory Program

Abstract: This paper deals with the aerodynamic and aerothermodynamic preliminary design activities for the vertical takeoff hopper concept performed in the frame of the Future Launcher Preparatory Programme of the European Space Agency. The reentry scenario with the corresponding loading environment for the proposed vehicle concept is reported and analyzed. The hypersonic aerodynamic and aerothermodynamic characteristics of the vertical takeoff hopper are investigated by means of several engineering analyses and a limited number of computational fluid dynamics simulations in order to assess the accuracy of the simplified design estimations. The results show that the difference between Eulerian computational fluid dynamics and an engineering-based design is smaller than 10% for aerodynamic coefficients, whereas a margin of about 30% has to be taken into account for what concerns the aerothermodynamic results. The final results applicable for the prosecution of the launcher design activity are that, at the condition of peak heating, the vehicle features a nose stagnation point heat flux of about 500 kW=m and an aerodynamic lift-to-drag ratio of about 1.2.

Hypersonic Low-Density Aerothermodynamics of Orion-Like Exploration Vehicle

Abstract: In the framework of Research Task Group 043 of the NATOResearch and Technology Organization, an analysis of the capabilities in prediction of aerothermal loads acting on a crew exploration vehicle at the higher altitudes of its reentry trajectory has been performed. In particular, the focus of this investigation is to provide information where overlap between the continuum approach (i.e., computational fluid dynamics) and particle approach (i.e., direct simulation Monte Carlo) occurs and improves understanding of relevant physics in transitional regime. Computational fluid dynamics calculations with slip flow boundary conditions had shown good predicting capabilities of slip velocity, slip temperature, and pressure, but not the surface heat flux. The analysis of the contributions to the total surface heat flux had exhibited the lack of continuum model in evaluating the convective heat flux in the transitional zone of the Orion reentry trajectory and an underestimation of shock wave thickness.

Thermostructural Design of a Flying Winglet Experimental Structure for the EXPERT Re-entry Test

Abstract: Within the framework of the European Experimental Re-entry Test Bed (EXPERT) Program, aimed at improving the understanding of physical phenomena occurring during the return of space vehicles from space to earth, the design of a flying winged experimental payload has been performed in order to assess the thermomechanical behavior and resistance of ultrahigh temperature ceramics (UHTC) in real flight aerothermal environment. The EXPERT flying winglet article is intended to reproduce such conditions. Particular interest covers the design of the interfaces between the UHTC winglet and the EXPERT capsule thermal protection systems since thermal stresses arise during the re-entry phase. The fixation of the winglet to the capsule is achieved by means of dedicated bolts that must tolerate mechanical loads occurring at the first stages of the flight, that is, lift-off, ascent, and separation stages. The thermostructural design is performed by employing ANSYS/Workbench finite element commercial code; simulations take into account transient thermostructural loading conditions, the elastic-fragile behavior of the ceramic materials, and the temperature dependent elastic-plastic behavior of the capsule thermal protection systems. In the postprocessing phase, UHTC critical areas have been identified by following two different approaches. The first approach is deterministic and consists in applying a maximum stress criterion, the stress at a node is compared with the temperature dependent strength at that node. The second approach, which is commonly employed for elastic-fragile materials, is probabilistic and consists in applying a Weibull-like failure criterion. Thermal and structural analyses simulating the re-entry phase have demonstrated that the maximum stresses and temperatures evaluated do not exceed their corresponding limits. Then, a configuration respecting all the requirements of the design has been identified, and its thermal and mechanical performances are discussed in detail.

Influence of Free-stream Turbulence on Simulations of Laminar Separation Bubbles

Abstract: This paper presents numerical simulations of laminar separation bubbles. The main aim is to investigate the capability of RANS approach to reproduce this important feature of low-Reynolds number flows. The simulations have been performed without an ”a priori” knowledge of a laminar transition point inside the bubble. Two tests are proposed. The first test case considered is a laminar bubble forming over a flat plate subject to an adverse and then favourable pressure gradient. The flow has been studied experimentally and by DNS at University of Stuttgart. The Spalart-Allmaras and the ·-! SST turbulence models have been employed. The second test case is the flow at Reynolds number of 6×10 4 around the SD7003 airfoil. Experimental and numerical data are found in literature. The evolution of the laminar bubble as a function of the angle of attack is discussed. Results are presented in terms of pressure and friction coefficients. The entir e drag polar of the airfoil has been computed by applying the RANS approach. Large eddy simulations have been also performed in order to make a more complete analysis of the results.

Flight Test Results for a Multi Sensor Obstacle Detection and Tracking System for Sense and Avoid Applications

Abstract: This paper presents the development process of an airborne multi-sensor system for autonomous detection and tracking of flying obstacles. The hardware/software prototype integrating Detect, Sense, and Avoid capability, has been designed and realized by the Italian Aerospace Research Center and the Department of Aerospace Engineering of the University of Naples “Federico II”. First of all, system architecture is described. The sensing subsystem is comprised of a Ka-band airborne pulsed radar, a visible panchromatic highresolution camera, a visible color high-resolution camera, two thermal infrared cameras, and a processing unit for sensor data fusion. Estimated performance of radar/electro-optical sensor fusion is reported. Then the ground segment developed to monitor test flight in real time is described and data from preliminary flight tests are presented and discussed.

An optimal 3D analytical solution for collision avoidance between aircraft

Abstract: This paper focuses on an optimal three-dimensional analytical solution for aircraft non-cooperative collision avoidance. Based on a geometric approach, an analytical solution to a proper kinematic optimization problem is here derived, which implies the simultaneous change of all control variables (speed module, track and slope angles), thus this approach resulting very suitable for real-time applications. In a pair-wise non-cooperative collision avoidance, the speed vector of the aircraft implementing the proposed control strategy is continuously changed with the aim of skimming the safety bubble surrounding the other aircraft (considered as an intruder). Under certain hypotheses, the proposed solution can be proved to be optimal with respect to the minimization of aircraft deviation from its nominal trajectory. Proper performance indexes have been defined and challenging conflict scenarios, where the other aircraft be haves even a pursuer, have been analyzed.

Non-destructive testing of a carbon-nanotube-reinforced composite using HTS-SQUID and electromagnetic techniques

Abstract: The correlation between electrical conductivity and magnetic field response, due to multi-walled carbon nanotubes' (MWCNTs) distribution within the polymer matrix, has been demonstrated using a contactless and non-destructive technique. Multi-walled carbon nanotubes, both buckypaper and reinforced epoxy matrix specimens with different nanotube percentages, have been inspected using the eddy current technique based on an HTc SQUID magnetometer. The SQUID magnetic field response, due to the nanotube distribution, has been compared with the thermographic technique results. Moreover, the electrical conductivity of nanotube-reinforced composites and buckypaper has been carried out by using the Van der Pauw method.

Design of an MR Based on Device for the Adaptive Stiffness Control of Tail Shafts

Abstract: Vertical tail design is driven by many elements concerning directional stability and directional control. The overall size of a vertical tail is mainly determined by the stability requirements, whi...