  We computationally study the kinematics of a simple model reciprocal swimmer
(asymmetric dumbbell) as a function of the Reynolds number (Re) and investigate
how the onset and gradual increase of inertia impacts the swimming behavior: a
reversal in the swim direction, flow directions, and the swim stroke. We divide
the swim stroke into the expansion and compression of the two spheres and
relate them to power and recovery strokes. We find that the switch in swim
direction also corresponds to a switch in power and recovery strokes. We obtain
expressions for the mean swimming velocity by collapsing the net displacement
during expansion and compression under power law relationships with respect to
Re, the swimmer's amplitude, and the distance between the two spheres.
Analyzing the fluid flows, we see the averaged flow field during expansion
always resembles a pusher and compression always a puller, but when averaged
over the whole cycle, the flow that dominates is the one that occurs during the
power stroke. We also relate the power and recovery strokes to the swimming
efficiency during times of expansion and compression, and we find that the
power stroke is, surprisingly, not always more efficient than the recovery
stroke. Our results may have important implications for biology and ultimately
the design of artificial swimmers.
