Abstract:
In the thesis we present a study on the unsteady aerodynamics of insect flight. Motivation
for the study is to establish the rational for adopting unsteady aerodynamics principles in
the design of Micro Air Vehicles (MAV) and to develop engineering design guidance for
the same. Unlike an aircraft with fixed wing or a propeller, birds and insects reciprocate
their wings changing the wing direction and the pitch twice in each stroke. Birds and
insects generate lift based on unsteady aerodynamic principles. Birds in flight, unlike
many insects, not only change their wing direction and pitch but also change the wing
area and wing porosity during a stroke. Thus an insect flight is an order less complex for
adaptation to a MAV application compared to the bird flight and hence we restrict our
discussion here only to insect flight.
Study of insect flight is challenging as it involves measurement of small forces cycling at
high frequency. Typical forces in the case of a tiny insect like fruit fly will be a fraction
of mg cycling at 2()0Hz or more and at the other end of spectrum, for big insects, like
butterfly and dragonfly forces will be in the range of 1-2 gm cycling at 5-40Hz. Study of
wing kinematics is also challenging as we need to get at least two simultaneous-views of
a flying-insect at high frame rate (frame rate has to be at least 10 to 15 times more than
the wing beat frequency). From these two views, we have to workout actual orientations
of the wing and its variation in time. Keeping these factors in mind, we have developed a
two-pronged approach for the study of insect flight dynamics. In one approach, we make
a mechanical model, to mimic some salient features of insect flight and carryout flow
visualization. In the second approach we are developing tools to study the wing
kinematics of an insect while in flight.
The thesis has following outline. In the first chapter, we describe some salient features of
unsteady aerodynamics principles, low Reynolds number flight, how insect uses unsteady
aerodynamics principles for its flight, desirability of adopting insect flight for MAV
design. In this chapter we also give scope of the present work In the second chapter we present the design of one-degree freedom model, mimicking
insect flight, control system used to drive this model, design of flow visualization setup,
test section, flow visualization pictures and discussion based on the flow visualization
results.
In the third chapter we present some of the preliminary arrangements developed to get
wing-kinematics of an insect while in flight. This includes camera system for getting
simultaneous front and top view of a flying insect in a wind-tunnel. As the actual flight
speed of insect is about I m/s, we have to keep low wind speeds in the wind tunnel and in
this chapter we present a procedure for cahbrating anemometer in low wind speed
regime.
In the fourth chapter we present conclusions and scope for future work.