In this work, separation due to the interaction of normal shock with wall boundary layers in a supersonic duct flow is studied using schlieren, oil flow visualization, and pressure measurements. This study uses separation control devices on three walls of a rectangular duct and investigates the influence of adding control on one wall and on the other walls. It was found that control on any wall has effect on separation on other walls. This effect was found to be due to the change in the size of corner separations. Pressure recovery was found to be steeper with the introduction of more control devices in the duct. © IMechE 2018.