Eur. Phys. J. B 14, 191-200 (2000)
https://doi.org/10.1007/s100510050120

Laser Doppler velocimetry analysis of transitional pipe flow

¹ Dipartimento di Ingegneria e Fisica dell'Ambiente, Univerista della Basilicata, 85100 Potenza, Italy
² Istituto Nazionale di Fisica della Materia, Genova, Italy

Received: 29 March 1999
Revised: 6 September 1999
Published online: 15 March 2000

Abstract

The objective of this study has been to experimentally analyze the correlation structure of the strong temporal intermittency which characterizes pipe flow close to the transition to turbulence. In doing so transitional pipe flow has been analyzed by Laser Doppler velocimetry and the Reynolds number dependence of the covariance function has been studied. The range which has been analyzed covers the transition to turbulence and moderately developed turbulence (Reynolds number from 1 500 to 5 000). The correlation structure which has been evidenced is generally in agreement with the deterministic, dynamical, interpretation of temporal intermittency which explains the intermittent behavior as a result of a saddle node bifurcation. However, the analysis has evidenced fluctuations even before the onset of turbulence. The structure of these fluctuations is perfectly autoregressive which leads us to conclude that the transition to turbulence can be viewed as a transition from linear randomness to (non-linear) homogeneity.