Abstract:

Short twisted tape as a modified twisted tape can reduce pressure drop significantly，however, the secondary flow characteristics are unclear. To explore the features of flow induced by short twisted tape in a circular pipe, water in turbulent flow and gas-liquid two-phase flow for the short twisted tape in a pipe was numerically simulated with Fluent software. The effects of helical vortices on the flow and the effects of Reynolds number on helical vortices were investigated by RSM turbulence model and Euler multiphase model. The results showed that the secondary structure induced by the short twisted tape was two central symmetric helical vortices. Helical vortices affected significantly the main flow field. Helical vortices increased the tangential velocity near the pipe wall, while decreased the tangential velocity near the pipe center. Axial velocities near the pipe center and the wall were low, and two high axial velocity areas appeared away from the twisted tape. Reynolds number affected helical vortices, and the pitch of helical vortices decreased with increasing Reynolds number. In the gas-liquid two-phase flow, helical vortices remarkably affected liquid distribution, including droplets and liquid film in full pipe region, and liquid volume fraction was high in the helical vortices region while low far away from the helical vortices. The effects of helical vortices on gas-liquid two-phase flow were different from single phase flow. The axial velocity profile tended towards the parabolic shape of laminar flow, and gas axial velocity significantly increased compared to the smooth pipe. Liquid distribution was not located near helical vortices center.