Mechanisms of Secondary Flows in a Straight Square Duct under the Effect of Rotation

Large eddy simulation with a dynamic kinetic energy subgrid-scale model is employed to simulate three dimensional incompressible fully developed turbulent flows through the non-rotating and rotating straight square ducts at the fixed friction Reynolds number of 300 with various spanwise friction rotation numbers. The study of secondary flows in the duct using the mean streamwise vorticity transport equation is extended up to the friction rotation number of 20. As the duct is rotated, the contribution of streamwise vorticity terms remain the same role for each terms. The reciprocal contributions of streamwise vorticity terms are discovered over the duct cross-sectional area as the duct is rotated. The reciprocal contribution of the convection and rotation terms are found in the upper bottom corner and the lower top corner. On the lateral wall, the diffusion and rotation terms are balanced by each other. The equivalent exchangeable contribution of convection and diffusion terms is also found at upper top corner. The consistent contribution ratio between turbulence to rotation terms is found at reattachment points of small secondary flow cells. Furthermore, the rotational effects tend to drive the turbulent flows to be neutralized into the directional preference along the rotational axis.