Suspension dynamics in transitional pipe flow

Abstract

Particle-induced transition is characterized by a smooth laminar-turbulent transition. For large pipe-to-particle diameter ratios (D/d) even dilute systems exhibit this smooth transition. In this study we use particles with a D/d of 5.7, which represents a ``sweet spot'', allowing the use of particle image velocimetry to study this particular phenomenon. With direct insight to the velocity fields we show that for this type of transition the velocity fluctuations scale proportionally to the Reynolds number and the particle-to-pipe diameter ratio. Furthermore, elongated streamwise structures are observed during the transition.