Phase II Final Report - NASA's Institute for Advanced Concepts

Planetary Exploration Using Biomimetics
An Entomopter for Flight on Mars
est was only in one half of the domain using the assumption of symmetry in the flow-field that
corresponds to symmetric flapping motion. During every time step, the entire mesh rotated
along with the wing; and the part of this mesh that was outside the symmetry plane was
“chopped off” with appropriate symmetry boundary conditions being applied to the newly created
boundary between the chopped off mesh cells and the remaining mesh cells.
Forward flight was represented by assigning the corresponding velocity to the oncoming free
stream (14m/s). This far-field velocity was held stationary in the inflow regions of the boundary.
Only one half of the entire wing was used in the simulation, assuming symmetric flapping. The
actual mesh was comprised of both wings on either side of the symmetry plane. This mesh was
subjected to the rotations prescribed above. One side of the mesh was sliced off. This slicing was
done during each time step to remove mesh cells from the “wrong” side of the symmetry plane.
This approach is rather unique and extremely effective.
Two simulations were performed. One was with flapping (and pitching) but no blowing. The
other was with continuous blowing with a jet velocity of 100 m/s.
The unsteady simulations use 80 time steps per flap cycle. Periodic behavior in time is reached
almost from the first cycle, but several cycles were carried out to confirm this behavior. Each
“iteration” represents a time step.
The x-force is along the free stream (along the horizontal from front to back of the wing).
The y-force is the vertical force.
The z-force is the force in the direction of the span. This is not significant because in a symmetric
wing configuration this force will be opposed by a similar force acting on the other wing
leading to zero net force in this direction when considering both wings as a system
In earlier coarse grid studies, cyclic behavior was reached very rapidly, essentially after one
cycle of flapping. Figure 3-99 plots forces for the flapping case using the finer grid, blown flap
geometry definition, and 100 m/sec blowing velocity. Two cycles were performed. Comparison
of animations between the blown flap and the non-blown flap case shows that the blown flap has
similar beneficial effects at the trailing edge as observed in the stationary wing cases, however
the most significant effects appear to come directly from the dynamic movement of the wing
itself. The subjective comparison of 2D slices of the flapping wing in the animations does not
capture the leading edge vortex (LEV) activity except for the brief time that it exists at that station.
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Phase II Final Report