
Computational Fluid Dynamics 

Definition:  Computational Fluid Dynamics (CFD) consists in the development, validation, and use of software tools for the numerical simulation of fluid flows past aerodynamic vehicles.
CFD is a discipline necessitating the knowledge of applied mathematics, fluid dynamics and computer sciences. Different levels of modelling are used for solving the governing partial differential equations of fluid flows (incompressible or compressible, inviscid or viscous...). Physical models have to be validated and calibrated by comparison with experimental data. Geometry of flow domain and boundary and initial conditions must be taken into account properly. Discretised equations are solved through numerical schemes and algorithms aiming at accuracy, efficiency and robustness.
The computer codes are run on scalar or parallel computers along the following steps: After the grid generation (or adaptation), the CFD solver is run before postprocessing and visualisation of the results.
CFD is used for understanding physics by flow analysis, for performance prediction of complex aerodynamic configurations and for flow control or optimum design studies.  Subdomains:  1. Physical modelling (turbulent, reactive flows?)
2. Development of numerical schemes and algorithms
3. Development and production of CFD software
4. Validation of CFD software
5. Grid generation and adaptation
6. High Performance computing (vector and parallel processing)
7. Complex CFD applications 
Unsteady Aerodynamics 

Definition:  In aerodynamics, unsteady phenomena occur from shockboundary layer interaction or boundary layer separation, but also are present in the flows around rotating systems. They concern the external aerodynamics of all the vehicles: aircraft, helicopter, projectile and launcher.
To answer the purpose of transport aircraft, the aims of studies are guided by the requirement of non separated flow in cruise and some constraints in the flight envelope: buffeting onset, flutter risk, limit cycle oscillation and level and spectral power of the loads on structures. Unsteadiness is an important parameter on the behaviour and the performances of flexible aircraft.
For fighters at high angle of attack, separated flows are encountered in air intakes on forebody, wings and afterbody. Thus, hysteresis phenomena of lift coefficient is the characteristic of quick manoeuvres in aerial combat. The aircraft behaviour during flight in turbulence is also an important feature for penetration mission.
Airflow around helicopter is of course unsteady due to the relative speed of local flow on the blades during the rotation of the rotor (advancing side and retreating side) and to the cyclic movements of articulated blades. The same kind of unsteady interaction is encountered between propfan and wing of commuters.
The buffeting observed at the base of launchers is created by strong separation of the external flow and interactions with exhaust plume. Internal separation in overexpanded nozzles at the takeoff is unsteady and 3D and causes lateral forces beside the thrust.
The behaviour in gust and during the activation of control surfaces is important data for the control of the vehicles.
Unsteady flows are also encountered in turbomachinery due to the rotation and interactions between the stages.  Subdomains:  1. Computational Fluid Dynamics
2. Wind tunnel testing; Aeroelasticity
3. Flow separation
4. Rotor aerodynamics
5. Buffeting
6. Flutter
7. Shock waveboundary layer interaction
8. Buzz
9. Surging
10. Rotating stall 
Aeronautical Propulsion Integration 

Definition:  1. For aircraft, the design of powerplant installation aims to minimise the installation drag by avoiding the separation on the pylon or on the wing in all the flight envelope, particularly at low lift coefficient.New installations are studied in order to reduce the noise, for example by engine location on the upper side of the wing or with semiburied engines.Experimental tests on models in wind tunnels need to use TPS techniques for simulating the mass flow rate into the nacelle and its effect on the flow around the wing.
2. For rotorcraft, the aims of the studies are to minimise the hub drag and the interaction drag and to reduce the aerodynamic noise. Some works concern the design of air intakes in relation to airflow through the rotor and of the nozzle in order to reduce the heat transfer on the rear part of the fuselage (infrared signature).
3. For airbreathing missile, the air intakes are optimised to take in account some constraints of furtivity (RCS) and assume a good efficiency at high angle of attack. Some devices are necessary to prevent the separation of the flow on thin lips or in the Sshape diffuser.  Subdomains:  1. Computational Fluid Dynamics
2. Wind Tunnel Testing
3. Air intake
4. Nozzle
5. Drag reduction
6. Flow separation
7. Air flow control
8. Infrared Signature
9. Radar signature
10. Noise reduction 
Airflow control 

Definition:  In this recent and promising area, a lot of devices are searched to act on the boundary layer, on shockboundary layer interaction, on separation or on vortex development in order to :
 reduce the drag by active or passive means;
 develop new concepts for improving the behaviour or the control of the aircraft near the limits of the flight envelope or to extend the flight envelope;
 minimise the effect of wake behind large aircraft in takeoff or landing configurations.
The control systems concern civil aircrafts, fighters and rotor blades and can be passive or active. MEMS can also be used.For controlling the boundary layer separation due to shock or adverse pressure gradient, the main devices are vortex generators, bump, cavity (passive control) and fluidic systems (blowing or synthetic jet).
To reduce the friction drag of turbulent boundary layer, riblets or MEMS can be used. The delay of the transition location is obtained through laminar flow control techniques.The vortex control is realised by mechanical (leading edge flaps) or pneumatic device (forebody and wing vortices). Trailing edge vortex control can be made with adapted trailing edge flaps.Optimisation of rotor blades is also searched to get less vibration and less noise by means of active control without diminishing aerodynamic efficiency (mechanical or pneumatic system).For stealth subsonic airbreathing missile, control devices are needed to prevent separation of the airflow in the short S duct.  Subdomains:  1. Computational Fluid Dynamics
2. Wind Tunnel Testing
3. Drag reduction
4. Laminar flow
5. Transition/turbulence
6. MEMS
7. Vortex generator
8. Wing tip device
9. Synthetic jet
10. Blowing flap
11. Bump riblet 
High Lift Devices 

Definition:  Main objectives of the studies related to high lift devices are :
 to reduce takeoff and landing distances ;
 to get simpler and lighter high lift systems (typically 3 airfoils) with the same efficiency than more complex systems ;
 to reduce aerodynamic noise.
The first topic concerns civil transport and military aircraft. Because the high sweep angle of the wing of supersonic transport and combat aircraft, the leading edge and trailing edge flaps have to be efficient at higher angles of attack for the landing.
The multisurface lifting arrangement is very sensitive to viscous effects due to the very closed interactions between wakes and boundary layers.
Specific distributions of the lift along the wing are also studied in order to modify the topology of the vortices in the wake of big aircraft.  Subdomains:  1. Computational Fluid Dynamics
2. Wind Tunnel Testing
3. Multisurface airfoil
4. Leading edge flap; trailing edge flap
5. Noise reduction
6. Wake vortex
7. Air traffic management
8. Certification Requirements 
Wing Design 

Definition:  The main objective of the wing design is the minimisation of the drag in cruise conditions :
 Lift induced drag, through appropriate platform, twist design or through wing tip devices (winglet, wing tip sail, tip turbine,?);
 viscous drag, through airfoil section shaping to avoid separation of turbulent boundary layer;
 Shock wave drag, controlled in order to prevent strong interaction with boundary layer (no separation).
On the other hand, improvements are searched on aerodynamic interactions, in particular wingbody, propulsion installation and static margin in order to reduce the trim drag.
The wing design uses the last improvements of CFD with numerical optimisation tools and now some multidisciplinary constraints are included in the process.
For the design of flexible wing like rotorcraft blade, coupling methods are used where structural deformations are taken in account. In some cases acoustic constraints are also introduced.
On missiles, the design of control surfaces is mainly driven by hinge mome.  Subdomains:  1. Computational Fluid Dynamics
2. Wind Tunnel Testing
3. Drag reduction
4. Wing tip device
5. Multidisciplinary optimization
6. Flexible wing
7. Noise reduction 
Aerodynamics of External and Removable items 

Definition:  The spreading out of landing gears which provokes an increase of the drag and a negative pitching moment which can modify the behaviour of the aircraft and these aerodynamic phenomena have to be taken in account in flight model for the approach phase and takeoff. On the other part, the landing gears increase the aerodynamic noise and some solutions are searched to minimize this nuisance.
Antenna but also mainly pods are also sources of extra drag and possible aeroelastic problems. The external carriage of stores causes a drag penalty for the aircraft. Fuel tanks (and missiles for military aircraft) dramatically reduce the range of the aircraft and induce modifications of the static margin. At transonic speeds, unstable shock waves are located on stores and can cause damages on control surfaces. Store carriage optimisation aims at reducing drag penalty (conformal pack), flow unsteadiness as well as radar signature.
Evaluation of store trajectories during release is needed for flight security.  Subdomains:  1. Computational Fluid Dynamics
2. Wind Tunnel Testing
3. Aerodynamic noise
4. Unsteady flow
5. Radar signature
6. Landing Gear
7. Flight / Ground Tests
8. Pod 
Wind tunnel Testing/Technology 

Definition:  Wind tunnels are essentially used in R&D to study flow phenomena and to simulate on scaled models the aerodynamics of any aircraft or other aerodynamically relevant object. Geometry, Mach number and Reynolds number are, in that order the main similarity conditions for a precise (nearly exact) simulation. Other conditions may apply (e.g. inertia, real gas...). Depending on what needs to be simulated, numerous (>100) techniques have been developed, some common to most tunnels, some more specific to a certain class of facilities.  Subdomains:  1. Model design/manufacturing: concurrent engineering, from CFD to CAD/CAM, quick prototyping systems.
2. Online data acquisition/reduction systems: highsampling rates for unsteady flows, handling of large data bases, standardised data presentation.
3. Wind tunnel flow conditioning flow quality survey/improvement (angularity, turbulence, noise), high Reynolds number simulation (pressure, cryogenics), high enthalpy tunnels.
4. Full or semispan model common techniques: global & local loads, pressures, boundary layer transition checking, aerodynamic coefficients, buffeting boundaries, visualisations, model support and wall interference correction/reduction.
5. Airframe/propulsion integration: air intakes, nozzles/afterbodies, motorised nacelles, propellers, helicopter rotors, stealth.
6. Flow/surface flow survey: by intrusive and/or non intrusive means.
7. Specific techniques such as : Aeroacoustics, Aeroelasticity/flutter, Jettison (free drop & captive trajectory), Ground effect, Dynamic derivatives, Heat 
Wind tunnel Measuring Techniques 

Definition:  Conventional measuring techniques mostly rely upon strain gauges and temperature sensors. Non intrusive optical measuring techniques are able to visualise the flow structure and to provide quantitative data relative to both surface characteristics (pressure distribution, transition detection, etc.) and flow field properties (mainly velocity and turbulence).  Subdomains:  1. Pressure: (un)steady pressures, Pitot/multihole probes, PSP (Pressure Sensitive Paints).
2. Temperature and heat flux: Infrared Thermography, thermocouples, hot wire, hot film.
3. Velocity: LDV (Laser Doppler Velocimetry), PIV (Particle Image Velocimetry), DGV (Doppler Global Velocimetry).
4. Flow visualisation: Schlieren technique, shadowgraphy, laser tomoscopy, Rayleigh scattering, interferometry
5. Surface visualisation: oil film, minitufts, infrared or sublimation transition detection.
6. Forces, moments: straingage balances (6component or local loads).
7. Model attitude/deformation: potentiometers, accelerometers, photogrammetry, moir?. 
Computational Acoustics 

Definition:  Computational methods for the numerical propagation of sound through internal and external flows. Computational predictions are most often split into noise source modelling and numerical simulation of acoustic propagation. Noise source modelling is strongly problemdependent (turbulence, blade loads fluctuations, cavity resonances, combustion, vibrations) and is assumed to be covered by domain 302.
Methods for the numerical propagation of sound through internal and external flows can be split into two categories, (1) integral methods and (2) discretised methods.
1. Integral methods mostly used for external problems in which acoustic propagation is assumed by the analytical Green's function in free field and uniform flow. The sound is computed at any observer point through a surface or volume integral.
2. Discretized methods assume the discretisation of relevant continuous equations over the propagation medium. Flow nonhomogeneities (spatial and temporal) are taken into account from CFD results. Internal and external flows are concerned.  Subdomains:  1. Noise source modelling.
2. Numerical simulation of acoustic propagation. 
External Noise Prediction 

Definition:  Prediction of aircraft noise in view of reducing community annoyance around airports and heliports. This includes jet aeroplanes, propeller aeroplanes, and helicopters. Studies are mainly focussed on transport aviation, but military aircraft and general aviation also are of concern.In each of the following subdomains, one has to deal with three main activities.
 Analytical or numerical simulations.
 Tests in static facilities, in wind tunnels, or in flight.
 Optimisation of novel designs.  Subdomains:  1. Turbofan or turbojet engines
2. Helicopter turboshaft engines
3. Propeller (high speed and general aviation)
4. Helicopter rotors (main rotor, tail rotor)
5. Airframegenerated noise (high lift devices, landing gears)
6. Installation effects of engines
7. Sonic boom of supersonic aircraftincludes ARDEP Sub domain NOIS of ENV domain. 
