The ECERTA Project

Open Source Fighter Flowfield at M0.85, Aoa2.12o

The Open Source Fighter configuration, results from the efforts of trying to build a realistic size aeroelastic test case. The geometry is based on publicly available data for the F-16. The F-16 has a documented history of exhibiting LCOs for certain configurations at specific flight conditions. This prompt a significant research effort using this configuration.

Based on published data, the wing geometry was modified to produce similar aerodynamic characteristics to the F-16 (see figures 3 and 4). A structural model was also developed under the same approach: using finite model updating techniques and publicly available data from GVT, it was possible to construct a finite element model resembling specific natural frequencies.

Further details on the files available here are described in the following document (guide to files)

CFD Resources

• IGES File ( Open Source Fighter IGES)
• ICEM CFD HEXA Projects ( ICEM Multiblock)
• Grids ( CGNS, Tecplot)

MSC.Nastran Resources

• Modal Analysis (Nastran Modal Analysis Model)
• Parametric Mode Generator (Matlab script)

Solver Input Files

• Structural and Modal files (Input files)

MSC.Nastran & CFD Results

Fig. 1: CFD Fine Grid	Fig. 2: MSC. Nastran Structural Model
Fig. 3: CP at 59%Span Comparison with F-16	Fig. 4: CP at 85%Span Comparison with F-16

	Mode 1	Mode 2	Mode 3	Mode 4
Updated FE model	3.74h1	5.91p1	8.12y1	11.0hp
GVT	4.07h1	5.35p1	8.12y1	12.25h2

h_i - i^th bending; p₁ - pitch + torsion; y₁ - yaw; hp - bending + pitch
Table 1: Results from structural finite element model updating

Fig. 5: CFD Based Damping Plot (ASCII Data)	Fig. 6: CFD Based Frequency Plot

Variability Study

For the Open Source Fighter, six parameters were used to represent the structural variability. Due to the size of the model, MC analysis is not viable; instead interval analysis was main tool to study the impact of variability on the onset of flutter. The structural model is made up of the fuselage and three regions along the wing span: root, middle (pylon) and tip; all these components have specific material characteristics, obtained from the finite element model updating procedure. To decrease the total number of parameters used in the variability study, a sensitivity analysis was performed and the following parameters were found to have the most significant impact on the onset of flutter:

Parameter	Nominal Value	Allowed Variation
Store Spring Coefficient	2x106	+/-15%
Young's Modulus - Root	157.3 GPa	+/-10%
Young's Modulus - Middle	96.7 GPa	+/-10%
Material Density - Root	5680 kg/m3	+/-10%
Material Density - Middle	3780 kg/m3	+/-10%
Material Density - Tip	3780 kg/m3	+/-10%

Fig. 6: Open Source Fighter CFD Based Interval Analysis - Real Eigenvalue

References

• S. Marques, H. Kodaparast, K. Badcock, J. Mottershead, Transonic Flutter Predictions for a Generic Fighter Configuration, Proceedings of the International Workshop on Fluid-Structure Interaction, Kassel University Press, Germany, 2009
• S. Marques, H. Kodaparast, K. Badcock, J. Mottershead, CFD Based Aeroelastic Stability Predictions Under the Influence of Structural Variability, 50^th Structural Dynamics and Materials Conference, Palm Springs, California, 2009.