Structure /
CENTER FOR AEROSPACE SCIENCE AND TECHNOLOGY




RESEARCH


The Centre for Aerospace Science and Technology is concerned with the technology related to the design and integration of aeronautical and space vehicles, from the basic scientific disciplines of flight sciences, atmospheric and space environment, through to the technological developments needed to meet performance, efficiency, environmental and certification requirements.

The purpose of the Centre for Aerospace Science and Technology is to perform research and development in several areas of aeronautical and space science and technology, and their spin-offs, namely:

Aeroelasticity
- Close
Aeroelasticity is a short word for a field of research that studies the interaction between aerodynamic and structural behaviour of an aircraft. Its goal is to predict correctly the differences between a rigid and a deformable aircraft in terms of aerodynamics and performance and structural deformations.

Critical coupled aero-structural instabilities prediction as the occurrence of flutter, aileron reversal and divergence, as well as gust response are the most common features that the field of aeroelasticity addresses.

The required inputs for an aeroelastic analysis include aerodynamic forces, mass distribution and structural deformation. Therefore, research, development and validation of computational tools as means of coupling Aerodynamic-Weights and Balance-Structural analyses is a major effort in this field.

Current research in this field includes:
  • Unsteady aerodynamics analysis as means to calculate the aerodynamic damping in a dynamic situation.
  • Unsteady aerodynamics analysis as means to calculate the aerodynamic damping in a dynamic situation.
  • Time dependant coupled aero-structural analysis as means to simulate the aeroelastic behaviour of the aircraft during prescribed mission profiles.
Multidisciplinary Optimization (MDO)
+ More
All MDO architectures can be classified into two major groups. Those that use a single optimization problem are referred to as monolithic architectures. Those that decompose the optimization problem into a set of smaller problems are referred to as distributed architectures. Examples of monolithic architectures include: All-at-Once (AAO), Simultaneous Analysis and Design (SAND), Individual Discipline Feasible (IDF), Multiple Discipline Feasible (MDF). Examples of distributed architectures include: Concurrent Sub-Space Optimization (CSSO), Bi-Level System Synthesis (BLISS), Collaborative Optimization (CO), Analytical Target Cascading (ATC)

MDO techniques apply various decomposition and coordination methods to facilitate communication between several disciplines while utilizing common optimization solvers to find a solution. Sub-optimization functions can be contained within the subsystems with appropriate coupling variables linking all the systems and subsystems together to ensure a global objective is maintained.

Aircraft design is a task that requires knowledge in a number of disciplines starting in geometry and ending in performance calculations. Aerodynamics, Structures, Propulsion, Weights and Balance, Stability and Control are the other fields of knowledge used by the designer for performing a preliminary design of an aircraft.

The way the design is traditionally performed is conditioned by the designer’s experience and is driven by some optimality criteria or compromise that restricts the aircraft performance in different flight conditions than the design flight condition.

The appearance of research fields as Morphing and Novel Configurations question the efficiency of traditional preliminary design, since the range of near optimum operation is extend (in the case of Morphing) or the a priori knowledge base is limited (in the case of novel configurations).

In both cases, Multidisciplinary Optimization can help the designer by calculating the merit of a configuration or morphing technology in performing one or multiple missions, while integrating the results of the aforementioned design disciplines.

Current research in this field includes:
  • Performance based MDO.
  • Robust, Reliable and Robust and Reliable MDO.

Adaptive Structures
+ More
In the last decade, the technological developments in materials and computational means allowed for the creation of a new field of research, where embed sensors in the structures supply information to external control system, which actuate on the structure, changing its structural characteristics. The success the proposed method depends on the developments in three different fields:
  • Development of adequate materials for the sensors and actuators;
  • Research on the electric circuits, with the main purpose of creating new control and signal processing algorithms;
  • Development of new computational algorithms.
In this field of research, we study the possibility of using piezzo-electric materials as actuators and sensors, embedded in the aeronautical structure, with the main purpose of improving the flutter speed and noise of the aircraft.

Space structures are very complex, given their three distinct characteristics: (i) they are flexible structures; (ii) they have multiple flexible components, such as antennas and booms; and (ii) it is necessary to predict with high precision their future capacities, still in the design phase. Therefore, the study of structural and thermic deformations has been increasing, in the various phases: design, manufacturing and construction. Since most mission specifications are not viable with the current technology, it is necessary to develop new methodologies in the area of space vehicle control and dynamics, namely in structural vibrations suppression.

Aeroacoustics
+ More
Aeroacoustics has become one of the main disciplines of aeronautics, since noise is subject to ICAO certification standards and local regulations, and is considered from the outset in the design of aircraft and engines. The objective of the EU H2020 and NASA are to reduce noise by 10 dB by 2020 and 20 dB by 2030. To make aircraft operations inaudible outside the airport perimeter would require a noise reduction of 40 dB. For satellite launchers noise can cause structural fatigue and damage the payload, and is again a major design criterion.

The group is one of the most productive in the world in terms of publications in refereed journals, and covers all aspects of aeroacoustics:
  • Sound generation by aircraft propellers, helicopter rotors, jet engine fans, compressors and turbines, combustion and jet noise, buzz-saw and shock waves.
  • Acoustics of ducts, engine inlets, and exhaust nozzles, including variable area nozzles, sheared, swirling, accelerated/declelerated flows, discrete and continuous spectra;
  • Sound propagation in jets and in the atmosphere, effects of stratification, non-uniform flow and turbulence, noise spectra and directivities;
  • Sound absorption including acoustic liners with non-uniform impedance, effects of shear and bias flows;
  • Installation effects, including sound reflection, shielding of noise, diffraction by obstacles, refraction by flows and scattering by irregular and moving surfaces;
  • Acoustic fatigue, fluid-wall coupling, cabin noise, structural vibration, passive and active noise and vibration suppression;
  • Coupling of sound to vortical and entropy modes and chemical reactions, thermoacoustic combustion stability, show waves in multiphase flows.
The implications of aeroacoustics on overall aircraft design are addressed under the heading of flight dynamics.

Flight Dynamics
+ More
The research concerns various aspects of aircraft operations, including airplane design (performance, stability, control and handling qualities), air traffic operations (capacity, collision avoidance, wake separation, atmospheric hazards) and novel aircraft configurations (flying wings, joined wings, V-tails) for low-noise (see Aeroacoustics) and high cruise efficiency. The topics include:
  • Flight performance, including the effect of atmospheric disturbances, either natural (e.g. windshears) or man-made (e.g. wake vortices);
  • Airplane stability and control, including handling qualities and novel aircraft configurations, optimization for minimum drag in cruise, maximum control power in low-speed engine-out conditions;
  • Air traffic management and airport runway capacity, including aircraft separation, air traffic capacity, navigation and position accuracy, and safety (extremely low collision risk);
  • Overall design of cruise-efficient low-noise aircraft configurations, including performance, stability, control, aerodynamics, propulsion and other aspects of MDO.
Rocket and space flight appear together with astrophysics in space science and technology.

Space Science and Technology
+ More
The research concerns rocket trajectories in the atmosphere and satellite missions, plus near earth space environment and astrophysics. Topics include:
  • Rocket trajectories in the atmosphere, including lifting bodies, and payload/launch/trajectory optimization;
  • Aerothermodynamics of hypersonic flight, including fluid-structure interaction and atmospheric re-entry;
  • Satellite orbits and planning of space missions; acoustic fatigue of rocket launchers and payloads; deployement of large flexible space structures;
  • Near-earth space environment, including solar-terrestrial physics, solar wind interaction with the magnetosphere and waves in the solar wind;
  • Physics of the sun and stars, in particular mass and energy processes in the atmosphere, heating, radiation and magneto-acoustic-gravity-inertial waves;
  • Cosmological models of the large scale universe, including relativistic-quantum interactions.
This area like aeroacoustics and flight dynamics uses novel mathematical and physical models including electromechanical interactions, ordinary and partial differential equations, boundary and initial value problems and solutions in terms of special functions and novel extensions.

Flight Testing
+ More
Flight testing means the critical assessment of the performance of an aircraft or its systems, in real conditions, i.e., with the aircraft in flight. Flight tests involve measurement and subsequent analysis of a set of physical parameters inherent to the aircraft, its systems and surrounding environment. The means allowing the realization of flight tests are called instrumentation systems, which have airborne and non-airborne components, with the later ones installed in a monitoring ground station. Typically, airborne components can measure, encode, record and/or transmit, in real time, collected data to the ground station (telemetry). Ground components, directly related to the instrumentation system, allow reception and/or reproduction, decoding, processing and analysis of data collected in the aircraft under test.

Portugal has autonomous capacity for the realization of flight tests, which, in principle, allows the realization of flight tests of any kind and on any aircraft. This ability is associated with the Flight Test Work Group (Grupo de Trabalho de Ensaios em Voo - GTEV), which resulted from cooperation between the Instituto Superior Técnico (Lisbon Tech) and the Portuguese Air Force.

So far the following aircrafts have been instrumented, mainly owned by the Portuguese Air Force:
  • CASA C- 212-200 AVIOCAR - Basic Aircraft for Flight Research (BAFR);
  • AEROSPATIALE SA-330 PUMA;
  • VOUGHT A-7P CORSAIR II - two instrumented aircrafts;
  • LOCKHEED P-3P ORION - two instrumented aircrafts;
  • DORNIER/DASSAULT ALPHA-JET - two instrumented aircrafts;
  • LOCKHEED C-130H HERCULES;
  • AEROSPATIALE SOCATA EPSILON TB-30 - two instrumented aircrafts;
  • DASSAULT FALCON 20;
  • DASSAULT FALCON 50;
  • DASSAULT FALCON 900B.
The existing capacity has been used in various research and development projects, covering several areas:
  • Flight dynamics - several projects (CASA C-212-200 AVIOCAR - BAFR);
  • Air Traffic Management (ATM) - European Flight Experiments on four-Dimensional Approach and Landing (EFEDAL) project with EUROCONTROL (CASA C-212-200 AVIOCAR - BAFR);
  • In flight loads monitoring for assessing the structural Integrity of aircrafts - projects VOUGHT A-7 P CORSAIR II, LOCKHEED P-3P ORION, LOCKHEED C-130H HERCULES, DORNIER/DASSAULT ALPHA-JET and AEROSPATIALE SOCATA EPSILON TB -30;
  • Certification of new flight configurations/flutter analysis - various projects for the Portuguese Air Force (DORNIER/DASSAULT ALPHA-JET);
  • Characterization of operational use of motors –Larzac project for the Portuguese Air Force and Turbomeca (DORNIER/DASSAULT ALPHA-JET);
  • Satellite Navigation Systems - operational evaluation of the EGNOS system, an international collaborative project involving several entities, including EUROCONTROL and NAV Portugal (DASSAULT FALCON 20, DASSAULT FALCON 50 and DASSAULT FALCON 900B); development and operational evaluation of a GBAS system, a collaborative project involving the NAV Portugal, the Portuguese Air Force and VINAIR (DASSAULT FALCON 50);
  • Development of new techniques for in-flight navigators training (DASSAULT FALCON 50).

System integration and Optimal Design
+ More
Engineering in general, and automotive and aerospace in particular, often deal with very complex and multi-disciplinary systems. The proper integration of their constitutive parts dictate the overall performance and, being a very competitive market, the designers aim at obtained the best possible solution.

To this end, two important topics are studied in this area of research, namely (i) Multidisciplinary Design Optimization; and (ii) Stochastic Optimization. While the first deals with the proper decomposition of deterministic optimization problems involving multiple disciplines, the second typically focuses on single disciplinary problems where some uncertainty is present.

Stochastic Optimization
+ More
In all real problems, there are numerous sources of uncertainty in modeling. For instance, in Aeronautics, there are uncertainties in operations (e.g. aerodynamic loads, flight speed, altitude, angle of attack), uncertainties in material properties (e.g. material tensile strength and Young’s modulus), uncertainties in manufacturing processes (e.g. tolerances on dimensions and shapes) and modeling uncertainties (e.g. simplifications of computational models, experimental determination of parameters, fidelity appropriate to the design stage).