Aerodynamics and Design for Ultra-Low Reynolds Number Flight

Chapter 2
14
C d
0.28
0.24
0.20
0.16
0.12
0.08
0.04
0.00
Thom & Swart Experiment
INS2D Results (R.A.F. 6)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
α (deg.)
FIGURE 2.3 Comparison of computed and experimental C d for the R.A.F. 6 and R.A.F. 6a
airfoils.
2.3 Viscous-Inviscid Interaction Methods
Using integral boundary layer formulations in conjunction with inviscid flow field
solutions offers the potential for significant computational savings over full viscous flow
solvers. Many potential flow panel methods prove problematic when attempting to
model very thin airfoils due to the close proximity of singularity elements, but Euler
solvers have no such issues and still represent a significant computational savings. The
common problem for these methods is the unknown extent to which the limitations and
assumptions of integral boundary layer theory may effect the quality of the solution.
The MSES program developed by Drela [16] has been applied in this study with limited
success. This is a two-dimensional Euler solver, coupled with an integral boundary layer
formulation. It appears to give reasonable drag predictions over a narrow range of
angles of attack, but the limitations of the boundary layer formulation cause the solution