Experimental analysis of flow characteristics in S-shaped ducts at low speeds

This study investigates the flow characteristics within an S-shaped duct at low speeds and examines the impact of varying lengths of upstream and downstream extensions on the internal flow field. The experimental setup includes an S-shaped duct model and an axial fan, with the fan positioned downstream to regulate flow velocity within the duct. Taking the S-duct throat as the reference point, the velocity range under investigation spans from 0.06 to 0.15 Mach. Measurements are taken in a region between the S-shaped duct and the fan using a traverse system to capture aerodynamic interface plane flow parameters. Additionally, wall static pressure measurements are utilized to characterize the flow field within the duct. Results indicate that although flow velocity has a relatively minor effect on the flow pattern inside the S-duct, it can cause a significant fluctuation of the wall static pressure coefficient. In contrast, the influences of the upstream and downstream extensions on the flow pattern inside the S-duct are more critical. Specifically, the upstream extension directly impacts the stall region at the duct's bottom and significantly increases the inlet boundary thickness, while the downstream extension determines the flow modes of the secondary flow on the exit. When both upstream and downstream extensions are sufficiently long, the influence of flow velocities on the flow pattern inside the S-duct can be almost eliminated.