Application of Computational Fluid Dynamics for Modeling of Secondary Flow cells in Trapezoidal Channel

Channel flows have three components of velocity، 1component in flow direction and 2components in spanwise of Channel. Because of heterogeneity of velocity undulations، in the channel section the vortices are formed that are nominated “Secondary Current Cells”. These cells cause the lateral shear stress in the channel walls and introduce the erosion and scour of the channel walls. Heterogeneity of the turbulency is caused due to boundary conditions of the bed، side wall and free surface، the aspect ratio and the geometry of the channel. The mechanism of secondary currents can be expressed by longitudinal vorticity equation. In this research، the flow in trapezoidal channels has been modeled using the “Computational Fluid Dynamics” (CFD) with “ANSYS CFX” soft ware، and additional to investigation of sufficiency of CFD in modeling of secondary flow cells، depth averaged velocity and boundary shear stress distributions are perused. For this purpose، the experimental model of Tominaga، and analytical model of Shiono and knight has been used to verify the numerical results. The numerical results are in agreement with the experimental and analytical models.