Ludwig Prandtl A Biographical Sketch, Remembrances and Documents German original by Johanna Vogel-Prandtl English translation by V. Vasanta Ram Published by The International Centre for Theoretical Physics Trieste, Italy on the occasion of the 100th anniversary of the publication in 1904 of Prantdl’s paper on the boundary layer theory August 14, 2004 1 Ludwig Prandtl 4.2.1875 − 15.8.1953 2 A few words about the translation Ever since I received from Professor Ernst Mueller, now more than ten years ago, a copy of Ludwig Prandtl’s biography, authored in German by his daughter Mrs. Johanna Vogel- Prandtl, I wanted to have the text translated to English. Prandtl was clearly one of the greatest fluid dynamicists ever, but his later life seemed to me to be somewhat tragic for reasons that the readers will soon see. I was especially keen that the contents of Prandtl’s letter of 1941 to Hermann Goering, decrying the outbursts against “Jewish Science”, which had evolved into a political movement in Nazi Germany, should be made public. It must have taken some courage and concern on Prandtl’s part to note that “they [the antagonists of “Jewish Physics”] have poisoned the air with ... disdain for the past...” See also Chapter 21 of this book. This aspect of Prandtl's personality was counter to the notion that was in circulation after the second world-war---that he was a naïve man who had buried his head in the sand. I immediately made some inquiries for translation and publication of the book but the project stalled for a number of reasons, including finances. Both Ernst Mueller and the biographer, with whom he was in contact about the possibility of the translation, passed away sometime thereafter, which slowed the project even further. The occasion of the 100th anniversary of Prandtl’s 1904 paper on boundary layers revived the idea in my mind and I was fortunate that Dr. V. Vasanta Ram readily agreed to translate the biography. For him, as for me, it has been a labor of love. As one of Professor Hermann Schlichting’s Ph.D. students, Vasanta Ram belongs to Prandtl's academic family, is knowledgeable about both German and English, and thus an ideal person to have undertaken the task. He has worked hard on the translation despite his physical handicap and other hurdles that he and I faced during the exercise. He commands my unstinted praise and gratitude. I also wish to thank Professor Roddam Narasimha for being a steady source of encouragement. It is my hope to be able to soon place the translation as a book published by an international publisher. This version is complete but various improvements are possible. It seemed important to use the occasion of the IUTAM meeting to distribute the material in the present form on the CD that you currently have in your possession. I hope that you will find its reading as much of an occasion as I did for reflecting on the vicissitudes of life. One obvious aspect requires specific mention: the author of the German original was not a professionally trained scientific biographer. This book is thus an intimate account of the person she loved and admired. The translator has kept alive the same informal spirit and style everywhere. I have reviewed the translation numerous times but none of my modifications has attempted to alter this feature. Katepalli R. Sreenivasan Trieste, 21 July 2004 3 Author's foreword by Johanna Vogel-Prandtl Translator’s preface by V. Vasanta Ram Chapter 1. Introduction Chapter 2. Childhood Chapter 3. As a student, and an employee at MAN Chapter 4. Engagement and marriage Chapter 5. 1911-1918, daily routine Chapter 6. A day at home Chapter 7. Gliding Chapter 8. 'Call' to Munich Chapter 9. Building up of the Institute and new projects Chapter 10. The new Kaiser-Wilhelm-Institut Chapter 11. Journey to London Chapter 12. Journey to Japan Chapter 13. A day at home again Chapter 14. Journeys on vacation Chapter 15. The year 1933 Chapter 16. Honorary doctorates at Cambridge and Trondheim Chapter 17. The house in the mountains Chapter 18. Pleading for W. Heisenberg Chapter 19. Voices on the situation at that time Chapter 20. Congress in America Chapter 21. Physicists' dispute Chapter 22. Journey to Romania Chapter 23. The last war years Chapter 24. The end of the war Chapter 25. New beginning at the university Chapter 26. The first post-war years Chapter 27. The last years of life Chapter 28. Concluding remarks Appendix Literature cited Glossary 4 Author's foreword By Johanna Vogel-Prandtl In the course of the last few years, I have felt more and more impelled to sketch a biographical study of the personality of my father, Ludwig Prandtl. As his daughter, I could, after all, use many personal memories as a basis for preparing a sketch that would do justice to the different facets of his personality. Scenes that took place within the innermost circle of the family should not be absent from such a sketch---scenes reflecting Prandtl's nature that I, as the last member of his family, would like to put on record, at least for the sake of my children and of those who knew Prandtl either personally or by name. I must mention that my uncle, Professor Ludwig Föppl, brought up the subject of writing memoirs again and again in conversations with his brother-in-law, trying to impress on him the importance of doing it on reaching the age he had, just as his father August Föppl had done earlier. Prandtl always put him off, saying with a smile: ''Probably later, I still have many other important things to do!'' But I knew Father well enough to realize that he had no intention whatever of reflecting upon his own life and writing about it, then or later. When Father died in 1953, my uncle, Ludwig Föppl, approached me saying: ''Now you should write about him!'' In any case, this first suggestion set me thinking on how I could possibly succeed in such an undertaking. One shortcoming would certainly not escape notice. I would certainly not be in a position to give professionally competent interpretations of his scientific work, and could therefore speak only in very general terms on it. But his scientific output has been extensively documented in his Collected Works (Gesammelte Abhandlungen [50]), and this is accessible to the reader. Besides, there are numerous further references given, which facilitate the interested reader in continuing his or her study of Ludwig Prandtl's work. When I finally began sorting out papers to write this biography, it turned out that I could fall back on many published material in these matters that had appeared in journals, articles and letters. These are often quoted here. It is quite possible that aerodynamicists and readers interested in science would find my commentaries on particular works of Prandtl inadequate. My objective here has only been to make at least a reference to all the work that obviously occupied such a central position in his life. My more important purpose in this book, however, is to describe the ''human being'' in Ludwig Prandtl. This venture owes much to his letters and articles, and to letters by his pupils, so that my account can for the most part claim a certain authenticity. Finally I wish to thank my husband for going through the text and for making corrections. 5 Special thanks are due to Herr Dr. Julius Rotta, whose close participation in my work made him contribute several supplements. He added scientific articles to the book and examined many quotations for their authenticity. The extensive bibliography of Ludwig Prandtl's writings, prepared by him, has added special value to this book. I wish to extend particular thanks to Herr Dr. Julius Rotta also for proof-reading the work. I feel I owe a debt of thanks also to Herr Dr. Walter Tillmann, the administrator of the MPI-Archives, for his obliging help and competent assistance at the stage of the book going into print. 6 Translator's preface By V. Vasanta Ram It is perhaps no exaggeration to state that it is unlikely to find a fluid dynamicist today who is not in some way influenced by works of Prandtl, of which his 1904 paper on boundary layers is seminal. The Translator is no exception. Later, when he was a research student at Prof. Schlichting's Institut für Strömungsmechanik in Braunschweig, he had the occasion to come in contact with people who had worked with Prandtl. During this period and later, he obtained glimpses of Prandtl's personality through occasional and informal narratives of people who knew him in person. These accounts, together with what the Translator had read about Prandtl in published literature, generated in him a keen interest in wishing to learn more about Prandtl's personality. This interest remained unfulfilled for a long time, until Johanna Vogel-Prandtl's biographical sketch of her father, "Ludwig Prandtl---Ein Lebensbild, Erinnerungen, Dokumente", appeared as a report of MPI in 1993, in German. This publication, while meeting the immediate needs of the present Translator, made him feel that its contents ought to be made known to the community of fluid dynamicists in the world as a whole, many of whom today may not be conversant with German. This feeling would have, most probably, merely stayed as an intention within the Translator's person, had his long-standing friend, Professor K.R. Sreenivasan, not given him the impetus for undertaking the translation into English.