Aeroelasticity and Structural Dynamics
Theoretical Aeroelasticity of Fixed-Wing Aircrafts and Missiles
Development of fluid-structure coupling with elsAw
The Aeroelasticity and Structural Dynamics department (DADS)
develops the fluid-structure coupling with a Navier-Stokes fluid
modeling, adopting for the flow computation the elsA software,
developed by the Computational Fluid Dynamics and Aeroacoustics
department (DSNA).
A very general framework of development was adopted for the
implementation of all the aeroelastic simulation functionalities in
elsA. These functionalities include: unsteady forced motion
simulations, static coupling using a reduced flexibility matrix, static
and dynamic coupling using a modal approach, and finally static
and dynamic coupling using the full finite element structural model. An
"Object oriented" approach and programming was used to define an elsA
subsystem dedicated to the structural computation part of
the coupled problem. A concept of aeroelastic interface, storing
the data common to fluid and structural computations, was also defined.
Generic class methods, specialized according to the aeroelastic
simulation type, were finally developed in order to manage the
interactions between fluid and structural calculations, through the
aeroelastic interface (fig. 1).
Figure 1: Concept of aeroelastic interface for fluid-structure coupling with elsA
(bigger image)
In the case of static coupling, the calculation of the deformations is
based on the use of a reduced flexibility matrix, obtained from the
full finite element Nastran model. Grid deformation tools are used to
take into account the displacements of the deformable surfaces of the
structure. They are based either on structural analogy techniques
developed by the DADS department, or on the combination of analytical
and transfinite interpolation techniques developed by Airbus and
Cerfacs. The various types of aeroelastic simulation may also be run in
parallel mode.
Figure 2 displays the result of a three-dimensional Navier-Stokes
static coupling simulation, in the case of an industrial wing / pylons
/ nacelles configuration . The aerodynamic structured grid is made of
approximately 7 million nodes, distributed in 91 blocks. The
computation was carried out in parallel on 15 processors of the CCRT HP
cluster.
Fig. 2a: Wall pressures on the wing/pylons/nacelles configuration
Fig. 2b: Corresponding static deformation
Two-dimensional computations were also carried out in order to
validate the dynamic coupling approach, in the case of the NLR7301
profile equipped with a two degrees of freedom structural model. Cases
exhibiting limit cycle oscillations were experimentally highlighted at
DLR on this profile. The prediction of this LCO phenomenon, here
induced by the flow non-linearities, requires to compute the dynamic
response on a sufficiently long time interval - see Figure 3. The
simulation presented here uses the dual time-stepping technique,
the multi-grid technique, and a "Backward-Euler" time scheme associated
with an implicit Lussor phase.
Figure 3a: Structural model of the NLR7301 profile, used to validate the dynamic coupling
Figure 3b: Computation of limit cycle oscillations for the NLR7301 profile, M=0.754
