This invention relates to a nozzle for a turbojet engine and, more particularly, to such a nozzle that is convergent-divergent, has a variable throat, and is air cooled (i.e., the hot gas stream surface of the nozzle is cooled by air).
The prior art method of cooling the convergent and divergent hot gas stream surface of a nozzle comprised cooling the convergent portion of the nozzle by using a liner, which was suported above the convergent portion of the nozzle, thus forming a passage for the cooling air (i.e., the fan duct air). The convergent cooling liner(s) extended from the end of the augmentor liner to the nozzle throat. The cooling air was then "dumped" onto the divergent section, to "film cool" that section.
There are two principal significant problems with regard to this method, and the structures used to perfom the method. Firstly, the convergent liner(s) warp severely, due to augmentor temperature gradient, thereby creating undesired leakage paths for the cooling air. Secondly, the cooling air boundary layer has difficulty turning around (i.e., going over) the sharp throat radius, thereby resulting in severe warping of the divergent section surface(s), preventing the divergent surface(s) from effectively forming an interface seal to hot gas stream leakage, and thereby creating performance losses and very short life for the convergent section liner(s) and the constituent portions of the divergent surface(s).
Our invention obviates these well known, and long-standing, problems of the prior art; and, therefore, our invention significantly advances the state-of-the-art.