Casing cooling duct

A method for operating a turbine, wherein the turbine comprises an inner casing to which at least a stator vane of a turbine section is mountable and an outer casing, which is arranged around the inner casing in such a way that an outer cooling channel is formed between the inner casing and the outer casing, the method comprising:

• injecting a cooling fluid through a fluid inlet of the outer cooling channel from an outer volume of the turbine into the outer cooling channel, and
• exhausting the cooling fluid through a fluid outlet of the cooling channel into an inner volume of the turbine,
• wherein the fluid inlet is located with respect to the fluid outlet such that the cooling fluid inside the outer cooling channel comprises a flow direction which has a component that is orientated in opposite direction with respect to a main flow direction of a working fluid of the turbine.