Based on jackets with triangular flow channels

laminar flow characteristics in triangular helical duct were investigated experimentally and numerically. The simulation results were in good agreement with experimental values. Then the main flow velocity

secondary flow

stream function and vorticity were obtained with numerical method. The distribution of local frictional factor on the boundary of the triangular helical duct was analyzed and compared with that of half-coil helical duct. The results show that the structure of secondary flow is steady two vortices in the range of Dean number and dimensionless curvature ratio. The distribution of local frictional factor along the outer walls differs obviously from that along the inner wall. The mean value of the local frictional factors at the outer walls is 1.54—2.72 times that at the inner wall. With the increase of Dean number and dimensionless curvature ratio

the secondary flow is enhanced and the frictional factors on the outer walls and inner wall increase. For triangular helical ducts with small dimensionless torsion and Dean number

the torsion has little effect on the flow resistance. Compared with the semicircle helical duct with the same area of inner wall

curvature radius

pitch and Reynolds number

the flow resistance in the triangular helical duct is smaller.