The subject of turbulence remains and probably will remain as the most exciting one for the mind of researchers in a variety of ?elds. Since publication of the ?rst edition of this book in November 2001 a number of otherbooksonturbulencehaveappeared,forexampleBernardandWallace (2002), Oberlack and Busse (2002), Foias et al. (2001), Biskamp (2003), Davidson(2004),Jovanovich(2004),SagautandCambon(2008)tomention afew. Soonehastoaskagain thequestionwhyasecondeditionofonebook from a ?eld of so many on the same subject? Does it make any di?erence? Thereareadditionalreasonsapartofthosegiveninthe?rstedition. One of thebasic premises of this bookis thatWeabsolutelymustleave roomfor doubtor thereis noprogress and nolearning. Thereis nolearning without posing a question. And a question requires doubt. . . Now the freedom of doubt,whichisabsolutelyessentialforthedevelopmentofscience,wasborn from astruggle with constituted authorities. . . R. Feynmann (1964). This is closely related to the term ‘conceptual ’: the book has now a di?erent title An informal conceptual introduction to turbulence. One of the main f- tures of the ?rst edition was indeed its conceptual orientation. The second edition is an attempt to make this feature dominant. Consequently items whicharesecondaryfromthispointofview werereducedandeven removed in favour of those added which are important conceptually. This required addressing in more detail most common misconceptions, which are con- quencesoftheprofounddi?cultiesofthesubjectandwhichtravel fromone publication to another. Consequently a one page Appendix D listing some of these misconceptions in the ?rst edition became chapter 9 titled Ana- gies,misconceptions and ill de?ned concepts.
This book is a second completely revised edition of An Informal Introduction to Turbulence. The main emphasis is on conceptual and problematic aspects, physical phenomena, observations, misconceptions and unresolved issues rather than on conventional formalistic aspects, models, etc. Apart from the obvious fundamental importance of turbulent flows such an emphasis is a consequence of the view that without corresponding progress in fundamental aspects there is little chance for progress in any applications such as drag reduction, mixing, control and modeling of turbulence. More generally there is a desperate need for physical fundamentals of the technological processes in which turbulence plays a central role.
The conceptual issues are made dominant in this second edition. This required to address in more detail those misconceptions which are the consequence of the profound difficulties of the subject and which travel from one publication to another. A new chapter titled Analogies, misconceptions and ill defined concepts was added along with a number of new sections on such topics as ergodicity, Eulerian versus Lagrangian descriptions, on validation of theories, on anomalous scaling and ill posedness of the concept of inertial range, on the Tennekes and Lumlety balance, and mathematics versus turbulence among others. Many of these are to a large extent a consequence of the series of lectures delivered in the Imperial College London in 2007 and 2008 in the frame of Marie Curie Chair in Fundamental and Conceptual Aspects of Turbulent Flows which was held by the author during the period June 1, 2006 – May 31, 2009.
