Numerical study of helical vortices in a circular pipe

The present paper describes the numerical study of the creation process and mechanism of helical vortices induced by a twisted tape inside a circular pipe. The RNG k-ε and the RSM turbulence model are used, the latter is in better agreement with experimental results, so the RSM turbulence model deserves further investigation. In the region of twisted tape, firstly, as the boundary layer of twisted tape separates, two vortices appeared and strength, they rotate counter relative to the tape twist, due to the conservation law of angular momentum. The two vortices decay as the influence of tangential velocity of the main flow. During their decaying process, another two co-rotating vortices appear due to the boundary layer separation, these four vortices coexist temporarily, then they decay and disappear. As the development of the flow, two co-rotating helical vortices exist as the instability induced by streamlines deformation. Once the twisted tape ends, the co-rotating secondary vortices remain inside the straight pipe. Secondary motion induced by twisted tape inserts is based on wall shear stress, coriolis force and centrifugal force.