Aerodynamics

Interest is high in laminar flow control to improve flight performances at both subsonic and supersonic speeds. High lift systems and high angle of attack aerodynamics are open problems. The former is of interest in the landing and take-off phase. The latter one is important to improve agility and maneuverability.

At the present state of the art both experimental and computational methods are being used, with emphasis on the calibration of of CFD codes for the prediction of complex flow fields.

High speed flight is a constant preoccupation among specialists, in view of the possible replacement of the Concorde (HSCT projects in several countries). Problems cited include sizing, range, environment, noise levels at all stages (sonic boom loudness, supersonic noise emission at take-off and landing.)

Debate over CFD methods based on the solution of the Navier-Stokes equations continues. Validation and calibration with laboratory measurements is object of large-scale projects. One of the most important debates scientists are facing is structured vs unstructured methods. Furthermore, there is the convergence criteria, steady-state vs time-dependent solutions, grid influence and grid refinement, the effect of turbulent transition and turbulence modeling. On the other side scientists are lured with Lagrangian and particle methods (Boltzmann gas lattice) that have proved to be incredibly robust on problems particularly complex.

The real challenge for the future is a paradigm shift from greater confidence in experimental results to greater confidence in computational results.

The development of theoretical methods for the treatment of complex, disjoint mathematical problems, until recently considered untreatable, has rapidly received recognition in the aeronautical sciences, first for the structural optimization and later for the aerodynamic design. The multi-disciplinary approach recognizes the importance of the interaction between sub-systems.

Typical problems involving aerodynamics include: the design of a swept wing to operate at high angle of attack, where the interaction between structures and aerodynamics is likely to create aeroelastic instability.

MDO has already been applied to a number of conceptual designs (for example, sizing and definition of non- conventional aircraft, supersonic transport aircraft), trade studies with different performance criteria, etc.

MDO is expected to have a strong impact in the development of supersonic and hypersonic vehicles.

Noise emission from aircraft engines continues to be a concern, especially near heavy-traffic airports around the world. Aerodynamic noise is also one of the major concerns in the development of the new supersonic transport aircraft. Other problems of concern are cabin noise (due to propeller interaction), tip noise from helicopter rotors.

Current research focuses on high by-pass ratio engines (ex. Pratt/Witney), that is 15:1 and beyond. (These engines will turn out to be gigantic.)

Investigations are under way with slow tip speeds, blade-vortex interaction (BVI), downwash effects on tilt rotors.

The advancement of electronics and controls has created exciting perspectives in the aeronautics of unmanned vehicles, which can be used for safe reconnaissance operations in military fields, studies of the atmosphere, inspections of inaccessible areas and control of pollution and disaster areas.

Rotorcraft that have been useful to perform a quite large number of civil and freight transport, rescue operations, military service, have now reached the limit of their flight envelope. New studies address the feasibility of hybrid vehicles that can operate as helicopter and aircraft having VSTOL capability.