Thomas, Lambert and Abdul Razak, Norizham and Grigorios, Dimitriadis
(2017)
Vortex Lattice Simulations of Attached and Separated
Flows around Flapping Wings.
Aerospace, 4 (22).
pp. 1-20.
ISSN 2226-4310
Abstract
Flapping flight is an increasingly popular area of research, with applications to
micro-unmanned air vehicles and animal flight biomechanics. Fast, but accurate methods for
predicting the aerodynamic loads acting on flapping wings are of interest for designing such aircraft
and optimizing thrust production. In this work, the unsteady vortex lattice method is used in
conjunction with three load estimation techniques in order to predict the aerodynamic lift and drag
time histories produced by flapping rectangular wings. The load estimation approaches are the Katz,
Joukowski and simplified Leishman–Beddoes techniques. The simulations’ predictions are compared
to experimental measurements from wind tunnel tests of a flapping and pitching wing. Three types
of kinematics are investigated, pitch-leading, pure flapping and pitch lagging. It is found that
pitch-leading tests can be simulated quite accurately using either the Katz or Joukowski approaches
as no measurable flow separation occurs. For the pure flapping tests, the Katz and Joukowski
techniques are accurate as long as the static pitch angle is greater than zero. For zero or negative
static pitch angles, these methods underestimate the amplitude of the drag. The Leishman–Beddoes
approach yields better drag amplitudes, but can introduce a constant negative drag offset. Finally,
for the pitch-lagging tests the Leishman–Beddoes technique is again more representative of the
experimental results, as long as flow separation is not too extensive. Considering the complexity
of the phenomena involved, in the vast majority of cases, the lift time history is predicted with
reasonable accuracy. The drag (or thrust) time history is more challenging.
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