Numerical Investigation of the Role of the Inlet Swirl Velocity Profile on Decay of Swirl in Pipe Flow

The influence of the inlet swirl velocity profile shape on the decay of swirl in steady-state, incompressible, laminar pipe flows is investigated by means of computational fluid dynamics. The investigation is carried out for a Reynolds number of 2000, which marks the upper limit of the laminar flow behavior for unidirectional pipe flow. Computations are performed for two different mean swirl numbers, namely, for 0.2 and 0.5. As the integral parameter for describing the swirl intensity, the swirl number is used, in contrast to other work relying on the circulation, instead. It is observed that decay of swirl number along the pipe length occurs at different rates for different shapes of the inlet swirl velocity profile, although the inlet value of the swirl number is kept constant when changing profile shapes. Although this result is obtained for the laminar flow, which is not as important as the turbulent one for engineering applications, it implies the possibility of a similar dependency for turbulent flows, and, thus, calls for the further investigations of the phenomena for turbulent flow. Key-Words: Swirling Pipe Flow, Decay of Swirl, CFD. Nomenclature a radial extension of solid body rotation core C empirical parameter D pipe diameter n exponent in empirical correlation r radial coordinate R pipe radius Re Reynolds number (Re=UD/ ν) S swirl number u axial velocity component U constant inlet axial velocity w swirl velocity component Wmax maximum swirl velocity at inlet x axial coordinate Greek symbols κ empirical parameter ν kinematic viscosity Subscripts 0 inlet value Proceedings of the 5th IASME / WSEAS International Conference on Fluid Mechanics and Aerodynamics, Athens, Greece, August 25-27, 2007 238