Gas Turbine Exhaust Frame and Diffuser

The exhaust frame assembly (figure here after) consists of the exhaust frame and the exhaust diffuser. The exhaust frame is bolted to the aft flange of the turbine shell.

Structurally, the frame consists of an outer cylinder and inner cylinder interconnected by ten radial struts. On the inner gas path surfaces of the two cylinders are attached the inner and outer diffusers. The no.3 bearing is supported from the inner cylinder.

The exhaust diffuser, located at the extreme aft end of the gas turbine, bolts to, and is supported by, the exhaust frame. The exhaust frame is a fabricated assembly consisting of an Inner cylinder and an outer divergent cylinder that flairs at the exit end at a right angle to the turbine centerline. At the exit end of the diffuser between the two cylinders are five turning vanes mounted at the bend. Gases exhausted from the third turbine stage enter the diffuser where velocity is reduced by diffusion and pressure is recovered. At the exit of the diffuser, turning vanes direct the gases into the exhaust plenum.

Exhaust frame radial struts cross the exhaust gas stream. These struts position the inner cylinder and no.3 bearing in relation to the outer casing of the gas turbine. The struts must be maintained at a uniform temperature in order to control the center position of the rotor in relation to the stator. This temperature stabilization is accomplished by protecting the struts from exhaust gases with a metal fairing fabricated into the diffuser and then forcing cooling air into this space around the struts.

Turbine shell cooling air enters the space between the exhaust frame and the diffuser and flows in two directions. The air flows in one direction into the turbine shell cooling annulus and also down through the space between the struts and the airfoil fairings surrounding the struts and subsequently into the load shaft tunnel and turbine third-stage aft wheelspace.

Exhaust frame assembly 

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