  Flapping animal flight is often modeled as a combined pitching and heaving
motion in order to investigate the unsteady flow structures and resulting
forces that could augment the animal's lift and propulsive capabilities. This
work isolates the heaving motion of flapping flight in order to numerically
investigate the flow physics at a Reynolds number of 40,000, a regime typical
for large birds and bats and challenging to simulate due to the added
complexity of laminar to turbulent transition in which boundary layer
separation and reattachment are traditionally more difficult to predict.
Periodic heaving of a thin flat plate at fixed angles of attacks of 1, 5, 9,
13, and 18 degrees are simulated using a large-eddy simulation (LES). The
heaving motion significantly increases the average lift compared with the
steady flow, and also surpasses the quasi-steady predictions due to the
formation of a leading edge vortex (LEV) that persists well into the static
stall region. The progression of the high-lift mechanisms throughout the
heaving cycle is presented over the range of angles of attack. Lift enhancement
compared with the equivalent steady state flow was found to be up to 17%
greater, and up to 24% greater than that predicted by a quasi-steady analysis.
For the range of kinematics explored it is found that maximum lift enhancement
occurs at an angle of attack of 13 degrees, with a maximum lift coefficient of
2.1, a mean lift coefficient of 1.04.
