A turbine includes an inner casing, a rotor extending in a longitudinal direction, and rows of buckets transversely disposed on the rotor. A bearing cone covering a portion of the rotor and a flow guide extending from the inner casing define an annular passage for flow of exhaust gases. Exhaust gas movement is facilitated by a guide cap having a streamlined surface and situated in a downstream direction of the flow guide, a tip leakage flow injection channel to inject exhaust gases at the inner surface of the flow guide, an incline of the casing of the turbine surrounding the last stage buckets relative to the longitudinal axis, or use of a first portion of the annular passage with a substantially constant surface area and a second portion of the annular passage with a progressively increasing surface area.