Statistical characteristics of a turbulent jet

Abstract

Velocity probability distributions and autocorrelation functions were measured in the self-preserving region of a round free jet at 57 diameters. On-line digital-sampling procedures were used to interpret the signals from a crossed hot-wire probe. Particular attention was paid to the probabilities of the axial and radial velocity components and of the angle between them at radial locations corresponding to the centre-line and the location of maximum shear stress and at an edge location r/x = 0·087. The results show, for example, that the probability of the axial velocity on the centre-line is slightly non-Gaussian and that, in general, the observed deviations of the probabilities of u depend upon the difference in behaviour of the corresponding distributions for positive and negative ν; outward transport (positive ν) is associated with near-Gaussian u distributions whereas inward transport (negative ν) is associated with skewed u distributions. The probability of the fluctuating vector ( u, v ) becomes more asymmetric with increasing radius with the dominant direction corresponding to positive $\overline{uv}$ . The measured auto-and cross-correlations are shown to be largely independent of radius.