Serpentine diffusers have become a common feature in modern aircraft as they allow for certain benefits that are impossible with a traditional linear configuration. With the benefits, however, come certain disadvantages, namely flow distortions that reduce engine efficiency and decrease engine surge stability margins. These distortions are now being researched comprehensively to determine solutions for mitigating the adverse effects associated with them. This study investigates how varying the freestream turbulence intensity of the flow entering a serpentine diffuser affects the distortion patterns that are produced by the diffuser. Experiments were performed with a model serpentine diffuser on the Annular Cascade Facility of the Air Force Research Laboratory at Wright-Patterson Air Force Base. Hot wire anemometry was used to measure inlet turbulence, while static pressure probes located axially along the upper and lower surface of the model diffuser and total pressure probes located across the aerodynamic interface plane (AIP) were used to measure the distortion patterns of the flow passing through the diffuser. Varying levels of inlet freestream turbulence, ranging from 0 to 4%, were generated using square and round bar turbulence screens in three distinct test configurations. Axial static pressure measurements indicate that increasing turbulence slightly affects flow separation development downstream of the second turn. This effect is also seen at the AIP where the total pressure recovery increases with increasing level of inlet turbulence in the region of flow separation at the upper surface. The total pressure recovery along the lower surface is also seen to be increased with higher inlet turbulence. However, total pressure recovery increase across the entire AIP is almost negligible. Overall, the inlet freestream turbulence has a minor effect on the distortion patterns caused by the serpentine diffuser when compared with proven active inlet flow control methods.



College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering



Date Submitted


Document Type





serpentine diffuser, turbomachinery, freestream turbulence, flow distortion, experimental fluid dynamics