Numerical simulation of turbulent drag reduction using rigid fibres
J. S. PASCHKEWITZ a1, YVES DUBIEF a2, COSTAS D. DIMITROPOULOS a1a2, ERIC S. G. SHAQFEH a1a3andPARVIZ MOIN a2a3 a1 Department of Chemical Engineering, Stanford University, CA 94305, USA a2 Center for Turbulence Research, Stanford University, CA 94305, USA a3 Department of Mechanical Engineering, Stanford University, CA 94305, USA
We present a study of the drag reduction induced by rigid fibres in a turbulent channel flow using direct numerical simulation. The extra stresses due to the fibres are calculated with the well-known constitutive equation involving the moments of the orientation vector. Drag reductions of up to 26% are calculated, with the largest drag reductions observed using non-Brownian fibres and semi-dilute concentrations. These findings suggest that elasticity is not necessary to achieve turbulent drag reduction. Flow statistics show trends similar to those observed in simulation of polymeric drag reduction: Reynolds stresses are reduced, velocity fluctuations in the wall-normal and spanwise directions are reduced while streamwise fluctuations are increased, and streamwise vorticity is reduced. We observe strong correlations between the fibre stresses and inter-vortex extensional flow regions. Based on these correlations and instantaneous visualizations of the flow field, we propose a mechanism for turbulent drag reduction by rigid fibre additives.