Plenums for bifurcated ducts and bifurcated ducts are provided for stabilizing flow therethrough. The plenum comprises an outer cylindrical body intersected by a pair of exhaust duct stubs that are configured to be coupled to a corresponding pair of exhaust ducts and an inner body. The outer cylindrical body includes an axial rear end portion. The inner body is disposed in the axial rear end portion and increases in diameter in the aft direction. The inner body comprises one of a generally axi-symmetrical inner body or a non-axi-symmetrical inner body. The bifurcated duct comprises the plenum and the pair of exhaust ducts. Exhaust systems are also provided.