It is nearly 50
years ago that I published my first version of the eN method for
transition prediction in two-dimensional incompressible flows. Independently and
simultaneously Smith and Gamberoni presented essentially the same method. During
my study for aeronautical engineer at the Technical University of Delft I had
enjoyed lectures on boundary layer theory by Burgers and Timman. In these
lectures the subject of linear stability theory had aroused my interest that led
to the idea for the eN method. I graduated in 1954 and since then
theoretical and experimental boundary layer research has been my favourite
topic.
In the spring of 1955 Timman invited me to join him to attend the conference on
“Boundary Layer Effects in Aerodynamics” held at the National Physical
Laboratory (NPL) at Teddington. UK. Here I had the wonderful experience of
meeting some of the well-known researchers in
the boundary layer community of that time, such as Eichelbrenner, Glauert,
Görtler, Head, Küchemann, Lachmann, Legendre, Lighthill, Lilley, Owen, Pankhurst,
Pearcy, Preston, Raspet, Ross, Schubauer, Stewartson, Stratford, Thwaites,
Trilling, Young, etc. Some of them were already known to me by name, many I
would get to know personally later in my career. Especially impressive to me was
a private discussion with G.B. Schubauer, famous for his experimental proof of
the existence of Tollmien-Schlichting instability waves in a flat plate boundary
layer. To him I could show the preliminary results of my research on what later
would become the eN method. His appreciation for this idea was of
course extremely stimulating for me as a young aeronautical engineer who was
working on what was going to be his first international publication. In later
years I had the pleasure of meeting Schubauer again at other conferences and to
visit him at the National Bureau of Standards in Washington in 1959.
My work on
eN was published in two reports of the Department
of Aeronautical Engineering of Delft University in July and September
1956. In September 1956 I presented the method at the First European
Aeronautical Congress at Scheveningen, the Netherlands. Before I started my
(first ever) presentation before an international forum, somebody pointed out to
me a very special person in the audience, namely the famous Hermann Schlichting.
The fact that he nodded with appreciation during my presentation was of course
very stimulating. Afterwards he told me that A.M.O. Smith had given a similar
presentation at the International Congress for Mechanics at Brussels the week
before. Later I got to know A.M.O. Smith very well. I have always appreciated
his acquaintance and that of his colleague and later successor at the Douglas
Company, Tuncer Cebeci.
The development of the eN method was the start of a
life-long commitment to boundary layer research in which the contacts with many
colleagues and friends have enriched my life.
In 1996 I had the honour to present the Prandtl Memorial Lecture on the combined
invitation of the German GAMM and DGLR. In this lecture I gave an overview:
“Looking back at forty years of teaching and research in Ludwig Prandtl’s
heritage of boundary layer flows”
The eN method remained one of my favourite topics. The present
collection of papers on CD-ROM illustrates the history of work in this field at
the Low Speed Wind Tunnel laboratory of Delft University. The original
presentation is included as an introductory chapter because, although it is
still quoted very often, not many readers will have a copy readily available.
Finally a recent new version of the method for two-dimensional incompressible
flow will be presented. The author is indebted to Jeroen Bongers for invaluable
assistance with the preparation of the final version of this report and for the
design and realisation of the CD-ROM.
Applications of this new method to the design of suction airfoils using the
FORTRAN environment of the XFOIL program are presented in the Masters Thesis by
Jeroen entitled
"Implementation of a new transition prediction method in XFOIL" ( August
2006). The thesis is also included on the CD-ROM.
Also a provision has been made that reading the report on the new version of the
method live illustrative MATLAB programs can be run by means of an
“N_factor_show”. Finally
the CD-ROM contains a recent overview paper by the author “The eN
method for transition prediction. Historical review of work at TU Delft”, ( AIAA
Paper 2008-3830).
The author is indebted to the Dean of Delft Aerospace Prof. B.A.C.
Droste and the Head of the Aerodynamics Group, Prof. P.G. Bakker for
providing the funding to realise the CD-ROM.
The new database method was derived
using a set of linear stability data that were published by Arnal
(D. Arnal: Diagrammes de stabilité des profils de couche limite
auto-semblables, en ecoulement bidimensionnel incompressible, sans
et avec courant de retour. Technical Report OA Nr. 34/5018, ONERA,
1986)
The author is indebted to Dr. Arnal for his permission to include
his tables in the present digital form on the CD-ROM.
I
dedicate this 50 years of eN history to my wife Anne
for
her continuous love and support during
her
50 years of marriage to me and my work.
1956 Delft 2006
J.L.
van Ingen
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