The exhaust duct for a gas turbine engine is conventionally a circular duct which connects to the turbine stage outlet of the engine. The use of a circular duct is convenient since it can be readily connected to the turbine outlet of the engine. In addition, thermal expansion of the exhaust duct resulting from the heat of the exhaust gas flow may be readily accommodated by the radial growth of the exhaust duct.
However, in many gas turbine engine installations it is desirable for the exit portion of the exhaust duct to be non-circular because this can make the mechanical installation of the exhaust duct into its supporting structure easier and more convenient.
In particular it is advantageous for the exhaust duct to be rectilinear in cross-section to facilitate the mounting of the exhaust duct within its surrounding structure.
Due to the need to accommodate dimensional changes in the exhaust duct resulting from the hot exhaust gases passing through the exhaust duct it is known to provide a duct mounting arrangement that independently accommodates both axial and lateral growth (i.e. two degrees of freedom, shown as 1 and 2 in FIG. 1) of the exhaust duct resulting from thermal expansion of the duct. Such mounting arrangements are required to accommodate movement of the duct both axially and laterally and can be mechanically complicated.
It is an object of the present invention to provide a mounting arrangement for a non-circular cross-section exhaust duct that supports the exhaust duct by means of a simple connection having a single degree of freedom.