RESUMO
Suspended particles can alter the properties of fluids and in particular also affect the transition from laminar to turbulent flow. An earlier study [Matas et al., Phys. Rev. Lett. 90, 014501 (2003)PRLTAO0031-900710.1103/PhysRevLett.90.014501] reported how the subcritical (i.e., hysteretic) transition to turbulent puffs is affected by the addition of particles. Here we show that in addition to this known transition, with increasing concentration a supercritical (i.e., continuous) transition to a globally fluctuating state is found. At the same time the Newtonian-type transition to puffs is delayed to larger Reynolds numbers. At even higher concentration only the globally fluctuating state is found. The dynamics of particle laden flows are hence determined by two competing instabilities that give rise to three flow regimes: Newtonian-type turbulence at low, a particle induced globally fluctuating state at high, and a coexistence state at intermediate concentrations.
