External flows around the various objects have many applications in the different industries such as the flow around the pipes, heat exchangers, offshore equipment and oil pipelines in the seas, cooling towers, and the transverse flows around the automobile, helicopter, and aircraft. Therefore, force calculation in external flows is very important. In general, the external flow solving is done in two ways, one with a complete solution of the Navier-Stokes equation that leads to a numerical solution and another is the approximate methods in which to model the actual fluid flow.

In the present paper, the authors attempted to study the behavior of air flow in the duct with different constant and rotational sections considering various Reynolds values (1, 25, 50, 100, 200, 300, and 1000). In this regards, the effects of various sections (circle, square, and ellipse) on the flow lines, pressure distribution, velocity profiles, drag and lift coefficients are investigated using numerical simulation. Eventually, the simulation results for stationary and rotational states were compared. The results indicated that the variations of drag and lift coefficients decrease by raising the Reynolds value. Moreover, the circular geometry is the best cross-section for a duct in order to have a minimum value for both drag and life forces.

air flow, various cross-sections, stationary and rotational states, Reynolds, drag and lift coefficients, velocity profile, pressure distribution.