An intertial particle seperator (IPS) including an intake air duct, a scavenge duct that shares an interior common wall with the intake air duct, a clean air duct, and a splitter. The splitter is configured to split a flow of intake air into a flow of scavenge air to pass through the scavenge duct and a flow of clean air to pass through the clean air duct. The IPS also includes a plurality of valleys on the intake air duct. The plurality of valleys includes a plurality of troughs and peaks along the interior common wall. In addition, each trough of the plurality of valleys extends along a direction of the flow of intake air.