Experimental scaling law for the sub-critical transition to turbulence in plane Poiseuille flow

TL;DR

This study experimentally investigates the transition to turbulence in plane Poiseuille flow, revealing how perturbation amplitude and Reynolds number influence flow states and highlighting the role of coherent structures.

Contribution

It introduces an experimental scaling law showing the minimal perturbation amplitude scales inversely with Reynolds number for transition.

Findings

Transition triggered by perturbations scales as Re^-1.

Four distinct flow states identified based on parameters.

Coherent structures like hairpin vortices are involved in transition.

Abstract

We present an experimental study of transition to turbulence in a plane Poiseuille flow. Using a well-controlled perturbation, we analyse the flow using extensive Particule Image Velocimetry and flow visualisation (using Laser Induced Fluorescence) measurements and use the deformation of the mean velocity profile as a criterion to characterize the state of the flow. From a large parametric study, four different states are defined depending on the values of the Reynolds number and the amplitude of the perturbation. We discuss the role of coherent structures, like hairpin vortices, in the transition. We find that the minimal amplitude of the perturbation triggering transition scales like Re^-1.