Long-tailed probability distributions in turbulent-pipe-flow mixing

Abstract

Exponential-tailed scalar probability density functions (PDF’s) are obtained by high-pass filtering scalar concentration time series measured in turbulent pipe flow. This behavior reflects the scale separation of scalar and velocity fluctuations that develops in this flow, such that the low-wave-number scalar fluctuations act as an imposed scalar gradient stirred by finer-scale wall-generated shear. This observation broadens the class of flows in which long-tailed scalar PDF’s are anticipated to occur. © 1997 The American Physical Society.