Embedded engines requiring S-duct diffusers as inlets have long experienced flow separation and distortion. This paper presents an investigation of passive flow control with the application on S-duct diffusers. The flow control is in the form of stream-wise tubercles aiming to improve performance through increasing boundary layer momentum and keeping flow attached in previous regions of separation. Tubercles have shown to increase post-stall performance for airfoils and are similarly applied to the suction surface when used in internal aerodynamics. This paper compares results from experimental testing and computational fluid dynamics (CFD) simulations. The experimental results measured surface pressure with static surface ports, and at the exit, total and static pressure measurements were recorded with a 5-hole AeroProbe. The implementation of flow control led to decreased or mitigated separation regions developing into a more uniform pressure at the aerodynamic interface plane. Similar results were evident in the CFD simulation. A k-ω SST model was chosen since it has shown to better predict the separation regions. A high y+ model was used since additional improvement in separation modeling. The same trends were seen in simulated pressure recovery and in swirl when comparing the use of flow control to the baseline duct performance.

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