To provide conditioned fluid flows, a base body has a main flow duct formed therein with a bypass duct that is branched off from and led back to the main flow duct. An exchangeable flow conditioning insert includes a flow resistance element and is adapted to be arranged in the main flow duct relative to the bypass duct in an axial installation position such that the flow resistance element generates a pressure difference between ports of the bypass duct at the main flow duct.