Pipe flow with large particles and their impact on the transition to turbulence

Abstract

The classical transition from laminar to turbulent flow is affected if solid particles are added. The transition behavior is a function of particle size d and solid volume fraction φ and the flow undergoes a smooth transition, as opposed to intermittent, if φ exceeds a certain threshold. In this work we show that, for particle-laden pipe flows with large particle-to-pipe diameter ratios d/D, the φ threshold for altering the transition is much lower than previously reported for smaller particles. Magnetic resonance velocimetry reveals that particles introduce turbulent-like fluid velocity fluctuations in laminar flow. Factors that might control the limits between "classical"and "smooth"transition in the state space spanned by d/D and φ are discussed based on scaling analyses.