ECCOMAS CFD 2006 – Special Technology Session
Egmond aan Zee, 5 – 8 September 2006
Flow Simulation and Validation in Aeronautics
Environmentally Friendly Aerodynamic and Acoustic Design of Supersonic
Business Jets
Michel Mallet
Dassault Aviation, St. Cloud
Renewed interest in the design of supersonic aircraft is observed both in Europe and in the United States. This is due to strong market demand for shorter travel time, especially for people using business jets. The new aircraft will be designed to have a minimum impact on the environment: reduced sonic boom and low noise are key design drivers. The design will depend on yet to be defined regulations on sonic boom. The reduction of the size of the aircraft compared to the size considered in most studies performed until recently, the lower value of the cruise Mach number and the ambitious (and not yet fully defined) environment goals lead to a rather large and complex design space.
The presentation will focus on a number of key aerodynamic and acoustic issues associated to the design of a SSBJ.
We will first describe the status and developments in progress to allow automatic aerodynamic shape design. Automatic optimization of wing at cruise is rather mature and already has an impact on design, on-going efforts are dedicated to the development of automatic optimization of engine integration.
The accurate prediction of sonic boom is based on a two step approach that couples a CFD computation in the near field and acoustic tools to propagate the pressure signal to the ground. For the CFD part, unusual mesh requirements are identified: the mesh must be fine not only close to the aircraft but also at least one cord-length away. Specific mesh adaptation techniques will be described.
Automatic shape optimization techniques can also be developed to decrease the sonic boom signature. We will describe the specific development in progress following techniques developed for aerodynamic optimization.
A key design issue is to keep the noise at take off and landing at acceptable levels. This is a challenge because a change in bypass ratio will not have a positive impact both on jet noise and on aerodynamic efficiency at supersonic cruise. Innovative solutions are considered, one possibility is to use mixer-ejector devices. The design of these devices is a challenge and involves complex flow physics : one must achieve entrainment in the ejector and efficient mixing to obtain reduced jet velocity at the exit of the mixer -ejector. Evaluation of the acoustic efficiency of the M/E with its broad band liner is also a challenge for noise modelling and will be discussed.
The MDO process will not be described in detail in this STS presentation, the various and strong links between aerodynamics, acoustics and sonic boom and their impact on design will be discussed.
