Preface with a personal touch

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 emethod  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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