Wind tunnel modelling of atmospheric boundary layer flow over hills

353 Pages·2013·7.87 MB·English

Wind tunnel modelling of atmospheric boundary layer flow over hills

Dissertation

Zur Erlangung des Doktorgrades der Naturwissenschaften im
Fachbereich Geowissenschaften der Universität Hamburg

vorgelegt von

Graciana Petersen

aus

Hamburg

Hamburg
2013
(Jahr der Drucklegung)
Als Dissertation angenommen vom Fachbereich Geowissenschaften
der Universität Hamburg

Aufgrund der Gutachten von Prof. Dr. Bernd Leitl
und Prof. Dr. Michael Schatzmann

Hamburg, den 18. Januar 2013.

Tag der Disputation war am 18. Januar 2013.

Prof. Dr. Jürgen Oßenbrügge
Leiter des Fachbereichs Geowissenschaften

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Cover page according to §7.5 of the Doctoral Degree Regulations of the MIN Faculty;
Names of the evaluators:

Prof. Dr. Bernd Leitl
University of Hamburg
Meteorological Institute – EWTL Environmental Wind Tunnel Laboratory
Bundesstrasse 55
D-20146 Hamburg / Germany

Prof. Dr. Michael Schatzmann
University of Hamburg
Meteorological Institute
Bundesstrasse 55
D - 20146 Hamburg

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Declaration according to §7.4 of the Doctoral Degree Regulations of the MIN Faculty:

I hereby declare, on oath, that I have written the present dissertation by my own and
have not used other than the acknowledged resources and aids.

Hamburg, 26/09/2012
(Signature)

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Preface

“What we observe is not nature itself, but nature exposed to our method of questioning.”
Werner Heisenberg

How can wind tunnel modelling be applied to the atmosphere of the earth? What has to
be considered for modelling hilly terrain? What insights can we hope for using wind
tunnel experiments for the improvement of wind energy assessment?

The analysis carried out does not answer the question of whether or not wind tunnel
simulation is useful for wind energy assessment in every-day work of wind consulting
from economical point of view. Instead, the scientific potential and value of wind tunnel
experiments for atmospheric wind flow over hills is investigated. This includes an analysis
of the underlying theories, an analysis of the relation between models and reality and
extensive analyses of the quality and data of the experiments which were carried out.

It is clear that a scientific analysis concerning the potential and value of a scientific
method, such as wind tunnel modelling, is never complete. It is not only a snapshot in
time (since modelling techniques advance) it is also always a matter of the focus of the
author on certain aspects.

This analysis is inspired by the idea that science is not an isolated endeavour: “The
physicist may be satisfied when he has the mathematical scheme and knows how to use it
for the interpretation of the experiments. But he has to speak about his results also to
non-physicists who will not be satisfied unless some explanation is given in plain language.
Even for the physicist the description in plain language will be the criterion of the degree
of understanding that has been reached”, [Heisenberg, 1958]. That is, science is driven by
interaction and communication amongst people with diverse backgrounds.
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Serious problems come along with the complexity in scientific work. This comprises for
example according to William Rehg (with regard to scientific argumentation) the scientific
authority and neutrality, [Rehg 2009, 2011]. His conclusions are that “given that the
multidisciplinary complexity of the technical issues exceeds the expertise of any one
person, the cogency of such arguments must be assessed […] at the level of the
argumentative process […] specifically, assessment must attend to three levels of context:
(1) the report content, (2) the local transactions in which reports are constructed and
evaluated, and (3) the relevant public networks through which the reports legitimately
travel”, [Rehg 2011, pp. 386]. He argues that for a quality assessment of scientific work,
the report content is only one of three levels of the context. The context of production,
the use of results and the preparedness for the public perception has to be assessed as
well. This fits well with Heisenberg’s opinion and the motivation behind this work. The
author of this work believes that multidisciplinary work is not only necessary for quality
assurance of scientific argumentation – above all it is the main potential for development
in science.

As a teaser for the complexity of modern research in fluid dynamics, see Figure 1, p. 14.

The purpose of this work is to be as focused and exhaustive of the available expert
knowledge as necessary whilst being as interdisciplinary und mutually understandable as
possible, since the author wants to deliver a compact and coherent analysis on the issue.
This work is divided into 4 key parts:

 I) Introduction
 II) Fundamental work
 III) Experimental work
 IV) Conclusions and future work

The outline of the chapters is as follows:

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I) Introduction

Chapter 1-3: The motivation for this work and an introduction into atmospheric boundary
layer flow as well as wind tunnel modelling is presented.

II) Fundamental work

Chapter 4: The theoretical foundation of fluid dynamics is analysed. This builds the basis
for the analysis of wind tunnel modelling within atmospheric science. The analysis is
carried out by formal methods of philosophy of science, which are used to structure
building blocks and theories of science (structuralism and conceptual spaces). Both
methods have been widely applied to a number of scientific disciplines in literature. Here,
they are applied to fluid dynamics and target to reveal an innovative point of view for
philosophers of science, physicists and mathematicians dealing with the Navier-Stokes
Equations.

Chapter 5: The relation between models, theories and applicability of wind tunnel
modelling is examined. This will set the stage for what scientifically can be expected of
wind tunnel modelling with application for wind assessment. The term “models” is used
here in the sense of Cartwright, Morgan and Morrison, meaning models as mediators
between reality and theories. In modern philosophy of science it is convenient to believe
that not only one theory can explain the world, but different theories competing with
each other [Cartwright 1983, Morgan and Morrison 1999]. This will be explained in detail.
Also, the analysis links the ideas of modern philosophy of science with an analysis of the
challenges in wind (energy) assessment.

Chapter 6: This chapter is a comprehensive overview of the physics of the atmospheric
boundary layer flows over hills and the challenges which theories, field studies and
numerical or physical modelling face. Whereas preceding chapters are written for a more
general audience, here the fundamental concepts of atmospheric boundary layer flow
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over hills are presented in detail. A literature review and historical overview examines
how wind tunnel modelling has been applied to atmospheric boundary layer flow over
hills. In addition, specific theories for wind flow over hills, e.g. the Linear Theory by
Jackson and Hunt, [1975], are explored and field studies for atmospheric flow over hills
are reviewed.

III) Experimental work

Chapter 7: The challenges for quality assurance in wind tunnel modelling of atmospheric
boundary layer flows are narrowed down further by means of a concrete example. In this
chapter, the pilot study to the main (real) Bolund wind tunnel study is described. In this
pilot study the sensitivity of the geometrical representation of hill shapes as well as the
impact of the geometrical representation on the repeatability of measurements was
examined extensively. The aim of the pilot study was to test the aforementioned
sensitivity of wind tunnel modelling to prepare for the main wind tunnel study of Bolund
in WOTAN.

Chapter 8: In this chapter, the main Bolund wind tunnel experiment in the large wind
tunnel, WOTAN, of the environmental wind tunnel laboratory (EWTL) Hamburg is
described. The selected site is the Bolund hill, an island with steep slopes with an area of
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60 x 150 m in Denmark where a field study was carried out in 2007/2008. The major
point in this chapter is to provide a concrete and detailed analysis of the quality and
uncertainty of the experimental results of Bolund in WOTAN. To maximize accuracy
emphasis was placed on the determination of plausible meteorological inflow conditions
similar to those of the field study area. Secondly, to maximize precision of the experiment
emphasis was placed on the assessment and optimisation of the repeatability of the
experiment. This was based on the lessons learnt from the pilot study. In brief, this
chapter aims to illustrate the key issues of wind tunnel simulation for flow over hills
against the background of the fundamental analyses of the previous chapters.

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