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Turbulence modulation by dense suspensions in channel flows

Francesco Picano
Department of Mechanics and Aeronautics, "Sapienza" University of Rome, Via Eudossiana 18, 00184 Rome, Italy; KTH, Department of Mechanics SE-100 44 Stockholm, Sweden; Department of Industrial Engineering University of Padova Via Venezia 1, 35131, Padova, Italy

Pedro Costa
Laboratory for Aero and Hydrodynamics, Delft University of Technology, Leeghwaterstraat 21, NL-2628 CA Delft, The Netherlands

Wim-Paul Breugem
Laboratory for Aero- and Hydrodynamics, Department of Mechanical Engineering, Delft University of Technology, Leeghwaterstraat 21, 2628CA Delft, The Netherlands

Luca Brandt
Linné Flow Centre, KTH Mechanics, Osquars backe 18, SE-100 44 Stockholm, Sweden

Sinopsis

Dense suspensions are usually investigated in the laminar limit where inertial effects are insignificant. In this regime, the main effect of the suspended phase is to alter the rheological behavior of the flow which always displays higher effective viscosity with respect to the carrier fluid. When the flow rate is high enough, i.e. at high Reynolds number, the flow may become turbulent and the interaction between solid and liquid phase modifies the turbulent dynamics that we know in single-phase fluids. In the present work, we study turbulent channel flows laden with finite-size particles at high volume fraction (Φ = 0.2) by means of Direct Numerical Simulations. A direct-forcing Immersed Boundary Method has been adopted to couple liquid and solid phases. The two-phase simulations have been performed fixing the bulk Reynolds number at Reb = Ub2h/v = 12000 (Ub bulk velocity, h channel half-width and n the fluid kinematic viscosity). The particle size is relatively large with respect to the viscous length, i.e. 10 and 20 times, but smaller than large scales. We will present a detailed comparison of the statistical behavior of the particle-laden flow and the corresponding single-phase flow. The presence of the solid phase strongly alters the wall turbulence dynamics and its effect cannot be accounted only considering the higher rheological effective viscosity.