The aerodynamics of an impulsively-started insect wing

133 Pages·2009·12.98 MB·English

Master of Science Thesis
The aerodynamics of an
impulsively-started insect wing
An experimental and numerical investigation
F.J. Venneman
June 26, 2009

The aerodynamics of an
impulsively-started insect wing
An experimental and numerical investigation
Master of Science Thesis
For obtaining the degree of Master of Science in Applied Physics
at Delft University of Technology
F.J. Venneman
June 26, 2009
Faculty of Aerospace Engineering Faculty of Applied Sciences
·
Delft University of Technology
Copyright c Aerospace Engineering & Applied Physics, Delft University of Technology
(cid:13)
All rights reserved.
DELFT UNIVERSITY OF TECHNOLOGY
DEPARTMENT OF AERODYNAMICS & APPLIED PHYSICS
The undersigned hereby certify that they have read and recommend to the Faculty of Ap-
pliedSciences foracceptance thethesis entitled “The aerodynamics of an impulsively-
started insect wing”byF.J. Vennemaninfulfillment oftherequirementsforthedegree
of Master of Science.
Dated: June 26, 2009
Supervisors:
Prof.dr. R.F. Mudde
Dr.eng. L.M. Portela
Dr.ir. M. Tummers
Prof.dr.ir.drs. H. Bijl
Dr.ir. B.W. van Oudheusden

Preface
Inthe process of choosing a subject formy graduationproject Iknew for sure thatI wanted
something that I was really passionate for. I also wanted to do something that I could
basically explain on a birthday party. Many fields of applied physics seemed attractive, so
it was a hard choice. Until a morning in the summer of 2008, under the shower, I realized I
had to study the fluid dynamics of insects or birds. Flight of insects and specifically birds
has astonished me for years and fluid dynamics has always been the part of physics that I
felt most confident with.
So I went ’shopping’ at various research groups (Multi-Scale Physics, the Laboratory for
Aero & Hydrodynamics and the Aerodynamics group) and ended in the position that they
all were part of my graduation project. At the start it was difficult to get a grip of the
Aerodynamics vocabulary, but once used to it, you realize all the terms relate to basic
physical transport phenomena. Besides the language, the challenge of graduation for me
was to keep focused on the insects while debugging my corrupt scripts. Luckily once in a
month a bug landed on one of my screens to tell me that he/she was the subject of my
graduation.
I would like to end this preface with some words of gratitude. First of all my girlfriend,
Saskia, for understanding when I was in a ’dip’ and infinite support. Then I would like to
thank, Christian Poelma for providing his piv data, Frank Bos for helping me out when
I got segmentation errors, Bas van Oudheusden for advice and reading my report over
and over again, Rob Mudde for coaching me through my graduation project and of course
Hester Bijl for her enthusiasm and keeping me on schedule.
Freek Venneman
Delft, June 15, 2009
MSc. Thesis F.J.Venneman
vi Preface
F.J.Venneman MSc. Thesis
Abstract
The design of Micro Air Vehicles (mavs) is currently an area of rapid growth. To improve
mavs, a better understanding of bird and insect aerodynamics is very helpful. In this
study the time-dependent three-dimensional flow around an impulsively-started fruit-fly
wing is investigated at a Reynolds number of 256 and a constant angle of attack (α = 50◦).
Both the forces on the wing and the flow-field structure are studied from an experimental
and a computational point of view.
On the experimental part, the work presented in this thesis is a first application of
a new tool to determine fluid dynamic forces in three dimensions. Experimentally
obtained velocity-fields around a dynamically-scaled robotic wing, with the previously
mentioned kinematics, are provided for the purpose of this study. Pressure-fields are
deduced from these velocity-fields, by means of a new tool, called the planar Poisson
approach. The forces on the wing are obtained by the momentum approach, using
both the velocity and the pressure-fields. These forces are in good agreement with the
forces that were directly measured by a sensor mounted on the robotic wing. Excellent
agreement is found in the steady part of the stroke, where the relative difference with the
measurements is within 13%.
For the computational element of this study, the Navier-Stokes equations around
the insect wing are solved using OpenFOAM as a framework. The incompressible flow
is solved on a dynamically moving mesh, which deforms based on Radial Basis Function
interpolation, which is a new mesh deformation tool. The forces obtained from the
computations are also in good agreement with the measurements, in the steady part of
the stroke, the relative difference with the measurements in the steady part of the stroke
is within 22%.
MSc. Thesis F.J.Venneman