Disclosed is a fuel injector device having a body with a leading edge and a trailing edge and defining a streamwise direction from the leading edge to the trailing edge, the fuel injector device body having a first wall and a second wall opposite the first wall, each wall extending between and including the leading edge and the trailing edge and the walls conjoining each other at the leading edge and the trailing edge, each wall having a streamwise extent and a crosswise extent, the walls further enclosing an internal space, at least one fluid plenum being provided within the internal space, the fluid plenum at least at one of an upstream end and/or a downstream end being delimited by an internal wall structure, wherein at least one surface of the wall structure is an inclined surface which forms an angle with the streamwise direction which is smaller than or equal to a maximum angle, wherein the maximum angle is 60°.