Lifetime statistics in transitional pipe flow

TL;DR

This study investigates the decay of turbulence in pipe flow near transitional Reynolds numbers through simulations, revealing how initial conditions and pipe length influence turbulence lifetime statistics.

Contribution

It demonstrates that long-term decay rates are unaffected by initial conditions and shows a linear relationship between pipe length and turbulence lifetime, aligning with experimental findings.

Findings

Decay rate independent of initial conditions

Linear increase of lifetime with pipe length

Extrapolation matches experimental puff length

Abstract

Several experimental and numerical studies have shown that turbulent motions in circular pipe flow near transitional Reynolds numbers may not persist forever, but may decay. We study the properties of these decaying states within direct numerical simulations for Reynolds numbers up to 2200 and in pipes with lengths equal to 5, 9 and 15 times the diameter. We show that the choice of the ensemble of initial conditions affects the short time parts of lifetime distributions, but does not change the characteristic decay rate for long times. Comparing lifetimes for pipes of different length we notice a linear increase in the characteristic lifetime with length, which reproduces the experimental results when extrapolated to 30 diameters, the length of an equilibrium turbulent puff at these Reynolds numbers.