CFDRC has championed the development and application of high-fidelity multidisciplinary and multiphysics computational tools since the mid 1990's. One of our primary application focuses has been on aero-servo-thermo-elastic analysis of aerospace vehicles.

The CFDRC approach emphasizes loose or tight coupling of separate stand-alone fluid dynamics, structure dynamic, flight controls and heat transfer prediction codes (or tools) under a single computational framework. This approach allows technology users to select leading edge and preferred analysis tools, and also allows for the use of existing computational models (geometry and grids).

The computational framework utilized for these analyses is the Multi-Disciplinary Computing Environment (MDICE-C). MDICE-C is a distributed, object-oriented environment for parallel execution of multidisciplinary modules. MDICE-C utilizes conservative-consistent interfacing for the fluid-structure-thermal and controls interaction, and uses advanced grid interpolation algorithms for grid motion and re-meshing due to surface structural and thermal deformations. Several government and industry leading software tools have been integrated into this environment as shown in the graphic below

CFDRC is currently collaborating with several government and industry partners on several projects that involve enhancement and expansion of the MDICE-C environment for various aero-thermo-aero-elastic applications for a wide range of aerospace vehicles and flight regimes. The chart below shows a roadmap for the MDICE-C current and near-future development plans.

Besides developing state-of-the-art multi-disciplinary computational technologies, CFDRC engineers are highly experienced and skilled at applying these technologies to a wide range of industrial applications. We have engineers with significant experience and in-depth knowledge of aero-elasticity applications, especially in the areas of aircraft buffet, flutter, and LCO applications. Some of the examples presented below represent work that was performed by CFDRC engineers in close collaboration with our government and industry partners

Wing flutter occurs as a result of exchange of energy between different modes of the structure because of fluid-structure interactions. Flutter is a growing oscillation of a wing surface leading to large amplitudes and stresses, and which can lead to structural failure.

The MDICE-C environment coupled with the CFD-FASTRAN flow solver has been widely used to analyze wing flutter. A modal solver module based on the mode shapes of the wing or FEMSTRESS module may be used as the structural solver.

CFDRC engineers have performed an aeroelastic analysis of static and dynamic flutter of an AGARD 445 wing. The computed flutter point was observed to be at 0.9 times the experimental flutter point. The following figure shows visualization of actual flow data on the wing surface. The left hand side (reflected wing) shows the pressure, while the right hand side shows deflection (including deflection vectors) on the fluid-structure interface.

The limit cycle oscillations (LCOs) have been a persistent problem and are generally encountered on aircraft carrying external store. Several aircraft models have experienced store-induced LCO for certain attached wing store configurations which result in restricting their intended mission. The LCO characteristics of the fighter aircraft impose safe limits in addition to those defined by structural strength and stability requirements. These limits significantly reduce the effectiveness and maneuverability of fighter aircraft, limit the flight envelope of these aircraft, and risk the aircraft and pilot.

The MDICE-C environment coupled with CFD-FASTRAN flow solver and internally developed nonlinear structural module has been used to study LCO in nonlinear aeroelastic system with fluid nonlinearities, dynamic and kinematics nonlinearities.

CFDRC engineers have performed an aeroelastic analysis of LCO of nonlinear aeroelastic systems. The results were extensively validated against wind tunnel data.

CFDRC engineers used MDICE-C coupled with CFD-FASTRAN and a structural module based on influence coefficients to study aeroelasticity of the F16 wing-body configuration. The computational analysis predicted a wing-tip displacement of 65 mm. The Experimental Displacement is 68mm.

Besides influence coefficients, our structural modules use beam models, linear, and nonlinear FEM models.

In fighter aircraft such as the F/A-18, the leading-edge extension (LEX) of the wing maintains lift at high angles of attack by generating a pair of vortices that trails downstream over the aircraft. At some flight conditions, the leading-edge vortices break down ahead of the vertical tails. In these cases, the breakdown flow impinges upon the vertical tail surfaces, causing severe structural fatigue and premature failure. The buffet characteristics impose limits in addition to those defined by structural strength and stability requirements. The limiting factors may include vibration levels and frequencies at critical airframe locations where items like tracking radar antenna or a gyro might be located.

CFDRC engineers have developed and applied an integrated environment for the prediction of tail buffeting of fighter aircraft. The environment comprises of a CFD fluid dynamics module (CFD-FASTRAN), a structural dynamics module (FEMSTRESS), and a conservative fluid-structure interfacing module. The modules are integrated into the MDICE-C environment for seamless loosely coupled analysis of various aeroelastic phenomena.

Our engineers have predicted the vertical tail buffeting of F/A-18 aircraft over wide range of angles of attack. The results were extensively validated against flight and wind tunnel data.

CFDRC is currently collaborating with several industry partners including aerospace and software companies, under a NASA funded program to develop technologies for aeroelastic ballute aerocapture analysis. Under this NASA contract, The ABAQUS software, NASA Langley CFD research code FUN3D, and NASA Johnson rarified gas dynamics CFD code DAC, will be integrated into MDICE-C, including developing and integration of MDICE-C API's into these software tools. This technology development will allow comprehensive fluid-structure-thermal analysis of many aerospace and other industrial applications involving thin-material configurations.

Demonstration calculations have been performed on a clamped ballute configuration provided by Ball Aerospace Corporation. The figures below show the fluid surface grid, the deformed ballute fabric due to aerodynamic loads, and the Mach number contours in a line of symmetry showing the large usually unstable wake of such a large structure.