Based on the theory of turbine tip clearance change

a structure was developed to adjust the choke acreage of the cooling air flow throttle automatically without other drivers

and the cooling air of turbine casing was controlled to regulate the turbine casing diameter. So the turbine tip clearance was limited in a certain range and its trend was controlled effectively. Three cases were simulated for a general turbine with or without turbine tip clearance control structure. The results show that the turbine tip clearance control structure can adjust the cooling air for turbine casing and the change rate of turbine tip clearance is 6.5%

however

the change rate of the turbine tip clearance without the structure is 20%. So the structure is beneficial to control the change of turbine tip clearance.