Research On Air Supply Flowpath And Casing Heat Transfer Characteristics Of Active Clearance Control System In A High Pressure Turbine

The Active Clearance Control(ACC)technology in High Pressure Turbine(HPT)is one of the most important technologies to improve aero-engine performance,reduce specific fuel consumption and increase aero-engine reliability.The ACC technology in HPT is implemented in engineering by the control of thermal deformation of turbine casing.This leads to two fundamental technologies of ACC system: low resistance,compact air supply flow-path,and concise,efficient heat transfer design of turbine casing.This paper abstracts and modulizes typical flow components according to the characteristics of air supply flow-path.The analytic models for flow components are deduced theoretically.With results from three-dimensional numerical calculation and data collected in engineering application,a fast analysis model suitable for engineering is established and one-dimensional analysis module for ACC system air supply flow-path is implemented on the plantform provided by Flowmaster commercial software.Then,pressure distribution and cooling air matching of air supply flow-path in ACC system,temperature distribution and deformation control of casing are systematically analyzed.The mechanisms of flow in air supply collector and impingement cooling tubes of ACC air supply flow-path are revealed.Design scheme of air supply flow-path and casing structure satisfying design requirements of well-controllable thermal deformation are established for two stage HPT.The calculation and analysis indicate,when the ACC system is working,rows of impingement cooling tube effectively cool temperature controlling area such as casing flanges,and reduce the local temperature significantly.Adjusting the temperature distribution on casing,the radial displacement variations of turbine shroud rings on the first and second stages are controlled well due to apparent contraction of radial displacement caused by cooling.On the base of research on mechanism,a experimental validation plan of ACC system on HPT quasi-component is proposed.A experiment system satisfying high temperature and pressure testing condition is established.Testing parts with ACC system on HPT quasi-component in full scale and real structure are designed and manufactured.Breakthrough is occurred on high accurate testing technique to measure dynamic radial displacement of turbine shroud rings,and technique to measure temperature on feature points in turbine casing parts with full structure,in high temperature and high pressure experimental condition with complex turbine casing structure.In the validation experiment of ACC system on HPT quasi-component in full scale and real structure,specific analysis is conducted on the flow characteristics of ACC air supply flow-path,temperature distribution and thermal respond characteristics of turbine casing,radial displacement respond characteristics of turbine shroud rings in operating ACC system.The experimental result shows that,(1)pressure distribution of air supply collector is very even in ACC air supply flow-path.Although the pressure is increasing in impingement cooling tubes from inlet to the closed end,it is tend to be on the same level with the increase of impingement hole area ratio(ratio of area of tube cross section to total area of impingement holes on tubes)on impingement cooling tubes,as maximum pressure increase in 4 impingement cooling tubes is only 1.7%;(2)With operating ACC system,the maximum relative deviation of single point displacement contraction and circumferential-averaged displacement contraction is 18.3% for first stage and 8.8% for second stage turbine shroud ring;(3)The ACC cooling system could effectively adjust the temperature on characteristic positions of turbine casing,as it shows that temperature of turbine casing reduces rapidly with the increasing of ACC system cooling air Reynolds number.The average absolute temperature drop on any cooling regions of turbine casing is from 100 K to 167 K,and the average relative temperature drop(ratio of absolute temperature drop to temperature in the case without operating ACC system)is from 16% to 37%.With control valves in ACC system are fully open,displacement contractions of the first and second stage turbine shroud rings are 0.59 mm and 0.74 mm,respectively,which is expected.Moreover,as control valves in ACC system are open,closed or transient in-between,respond rates of turbine casing temperature and displacement contraction of the two stage turbine shroud rings are satisfied.