Understanding and prediction of turbulent flow—1996

The title of this paper is also that of a lecture and a journal paper written by the present author 25 years ago (Bradshaw 1972). Note that “understanding” must come before “prediction”—although the order is reversed in the discussion below—because we must know what level of understanding is needed by currently affordable prediction methods. The present paper considers the question, “What progress has the human race made in the subject in the last quarter-century?” As always on these occasions, progress in some directions seems to have been slow, while other branches concerning the subject have advanced—or even come into being—with amazing rapidity. This paper deals mainly with momentum transfer, because (1) we must calculate the velocity field before being able to predict heat or contaminant transfer; and (2) momentum and thermal internal energy are transported by turbulence in roughly the same way.