Study On Flow-Heat Transfer And Heat Load Control Method Of In Clearance Of Shrouded Turbine Blades

Turbine rotor shrouded blade structure is widely used in turbine of gas turbines because of its many advantages,such as good aerodynamic performance and blade vibration reduction characteristics.However,the use of shrouded blade structure will lead to more complex leakage flow and heat transfer in the tip area of the blade.At the same time,turbine blades,especially the first-stage blades of high-pressure turbines,face harsh working conditions of high temperature,fast rotation speed and high pressure.If shrouded blade structure is used,the shrouded blade will suffer high thermal load and stress,which may gradually erode the shrouded blade or even damage it.The phenomenon of shrouded blade falling off also happens from time to time,which seriously threatens the safe operation of gas turbine.Therefore,it is necessary to carry out relevant research on flow and heat transfer distribution of shrouded turbine blades and the change rule of heat load,and to optimize the design of the blade shape and the blade cavity,so as to simultaneously improve the heat transfer distribution on the shroud surface and reduce the heat load on the shroud surface,so as to improve the aerodynamic thermal performance and working reliability of the turbine.Firstly,the GE-E3 rotor blade model with a single labyrinth seal is taken as the research object to analyze the leakage flow and heat transfer distribution in the blade tip area,and to discuss the flow and heat transfer law in the blade tip area under different turbine expansion ratios(1.5 to 3.5)and different turbine speeds(3000r/min to 12000r/min).Then,the optimal design of the structure shape of the shroud and the design of the cooling hole structure were carried out to reduce the heat load of the shroud surface.The results show that the distribution of average heat transfer coefficient on the shroud surface is closely related to the leakage vortex in the canopy cavity and the static pressure distribution on the shrouded surface.The average heat transfer coefficient in the region with high static pressure coefficient is high,and the leakage vortex intensity in the region is also high.Due to the sealing effect of the labyrinth seals,the changes of turbine expansion ratio and turbine speed are mainly through the distribution of average heat transfer coefficient on the leading edge of the labyrinth seals,thus affecting the heat load on the blade shroud surface.Finally,it is found that cutting 10% of the surface area of the trailing edge of the blade can reduce the heat load of the blade surface by19.2%.When cooling jet exists,it will inhibit the mainstream from entering the shroud cavity,which will improve turbine performance to some extent.Moreover,mixing of cooling jet and leakage flow has a good cooling effect on the shroud surface,reducing the thermal load on the shroud surface.Secondly,taking real low-pressure shrouded turbines as the research object,the leakage flow and heat transfer distribution in the shrouded end area were also analyzed,and the flow heat transfer law in the shroud end area was discussed under different turbine output power(50%to 120% in design condition)and different guide vane inlet angles(-30° to +30°).The results show that the output power of different turbines has a great influence on the leakage flow and the heat load on the shroud surface.With the increase of turbine output power,the leakage flow increases,resulting in increased aerodynamic losses and decreased turbine performance.At the same time,the dissipative effect of the leakage flow and the shroud surface is enhanced,resulting in an increase in the heat load on the shroud surface.The influence of different guide vane inlet angles on the leakage flow of the shroud cavity and the heat load of the shroud surface is relatively small,because it mainly affects the flow field between guide blades,but has little influence on the flow field between rotor blades.On this basis,aiming at the problems of uneven heat transfer and high heat load on the shroud surface of real low-pressure shrouded turbine blades under varying working conditions,the optimal design of its shroud cavity and cooling hole structure were carried out.The results show that: Compared with changes in the axial position of the labyrinth seals and changes in the inlet and outlet cavities,the modified width of the inlet and outlet of the blade shrouds has a more obvious sealing effect on the cavity of the blade shrouds,which leads to reduced leakage flow of the cavity of the blade shrouds,reduced aerodynamic loss and improved turbine efficiency to a certain extent.Meanwhile,due to weakened interaction between the leakage flow and the surface of the blade shrouds,the heat load on the surface of the blade shrouds is improved,by as much as 27.2%;When the cooling structure of the blade shroud is designed,the cooling jet can also effectively restrain the mainstream from entering the cavity of the blade shroud,thus improving turbine performance.Moreover,the mixing of cooling jet and leakage flow can effectively improve the heat transfer in the tip zone of the blade shroud and reduce the heat load on the surface of the blade shroud.In this paper,based on the consideration of uneven heat transfer and high heat load on the shroud surface,an optimization design method for the structure of the blade shroud and the cavity structure of the blade shroud is proposed to reduce the heat load on the shroud surface,which provides a reference for future design of new turbine shrouded blades.