A flow control device includes a first axially extending flow control surface, a second axially extending flow control surface radially offset from the first surface to define a gas flow path therebetween, the gas flow path having a downstream flow path exit, and a third axially extending flow control surface radially offset from the first surface and capable of axially translating with respect to the first and second surfaces for modifying the gas flow path and selectively closing the flow path exit. A turbofan engine includes a core flow passage, a fan bypass passage located radially outward from the core flow passage, a third stream bypass passage located radially outward from the fan bypass passage, and a flow control device that dynamically regulates the third stream bypass passage, allowing fluid flowing through the third stream bypass passage to provide thrust to the turbofan engine and reduce afterbody drag.