Numerical and experimental investigations of laminarization via preconditioning in turbulent pipe flows

Abstract This study investigates the potential of passive, orifice-type preconditioners to induce laminarization in turbulent pipe flow. A combined numerical and experimental approach is used for smooth pipes, while pipes with rough walls are explored experimentally. At Re b = 3500, the preconditioner successfully triggers sustained laminarization in smooth pipes, accompanied by a significant drop in the friction coefficient. However, at higher Reynolds number (Re b = 4500) or in the presence of sinusoidal wall roughness mimicking aged pipes, sustained laminarization is not achieved. Still, partial control is observed: in smooth pipes at Re b = 4500, streamwise Reynolds stresses and the friction factor are reduced, and in rough pipes at Re b = 3500, turbulence is suppressed downstream of the preconditioner before recovering farther downstream. At Re b = 4500, fully developed turbulence persists throughout all measured sections of the rough pipe. These results demonstrate that control effectiveness varies systematically with Reynolds number and surface conditions, necessitating design and testing under more realistic conditions.