| A large amount of compressed air and highly sophisticated cooling structure configurations will be used according to the traditional air cooling technology to meet the blade cooling demands of gas turbine,it not only reduces the overall efficiency of system,but also increases the manufacture cost of high-temperature alloy blade.The closed-loop steam cooling can satisfy the turbine blade cooling demands,the cooling structure is thus simplified and the mixing loss is also avoided,but it still faces the disadvantages of superabundant steam consumption and highly sophisticated cooling system.Mist/air phase change cooling is a promising technology to solve the problem.This cooling technology can improve the heat transfer ability of coolant which is attributed to the phase change latent heat absorption,larger specific heat of mist and vapor,droplet's interactions with flow and direct heat conduction between droplet and wall.The application of mist/air cooling to turbine blades can reduce compressed air consumption on the premise of cooling demands,and simplifying the cooling structure in the blade.The Eulerian-Lagrangian particle tracking method is adopted to investigate the mist/air phase change cooling,considering mist secondary breakup,particle collision and particle-wall interaction based on extended development of commercial software.Conjugate heat transfer mechanical model used in turbine of mist/air cooling is three-dimensional multiple combination fluid dynamics which contains aero-thermal,thermo elastic coupling,heat convection,heat conduction and phase change,the heat transfer enhancement mechanism and particle dynamics is very complex.The multiphase flow models are validated by comparing with the experimental data to reduce the numerical errors at most extent.Mathematical model is developed based on the classic heat and mass theory of individual droplet,the theoretical calculation models of droplet evaporation rate,droplet traveling time and distance are provided under the conditions of non-equilibrium and equilibrium process.The effects of various parameters,such as droplet diameter,pressure and temperature of air and slip velocity on droplet evaporation process are investigated,and the heat transfer mechanism of mist/air phase transition which leads to precooling effect of air is analyzed according to the energy conservation equation of individual droplet.Numerical simulations for the flow and heat transfer mechanism of impingement and swirl cooling on the internal channel of blade leading edge are carried out to find better cooling configuration.The influence law of different parameters on impingement and swirl cooling in such aspects as vortex structure,heat transfer enhancement,pressure loss and thermal uniformity are explored,and comparisons are made between these cooling forms on blade leading edge.The results show that the heat transfer is enhanced and the thermal uniformity is improved by the vortex flow created by swirl cooling,the heat transfer performance of swirl cooling is increased by 16%compared to the impingement cooling when the mist ratio is 8%,the pressure loss of swirl cooling is 68%of the impingement cooling under the same conditions,heat transfer non-uniform coefficient of swirl cooling is about 15%lower than impingement cooling.The conjugate heat transfer investigations considering phase transfer are performed on the blade which has the leading edge and downstream film cooling holes to explore heat transfer enhancement mechanism by application of injecting water mist into the air.The effects of various parameters including mist ratio,mist diameter,particle-wall interactions,mist forces and mist injection locations on the improvement of heat transfer characteristics are investigated.The results indicate that increasing the mist ratio can decrease the blade surface temperature and heat transfer coefficient,and the adiabatic film cooling effectiveness is increased on blade surface,the pressure surface has a better cooling effectiveness than the suction surface under the same conditions.The mist/air phase transition cooling technology with distributed cooling characteristics allows controlling the degree and the location of cooling performance by manipulating the different sizes of injected water mist.In addition,mist/air phase transition cooling can decrease the boundary layer temperature without impact on the mainstream temperature and boundary layer thickness.On the basic of previous studies about impingement cooling,swirl cooling and film cooling technology considering coolant phase transfer,the various cooling structures coupling phase transition cooling technology are applied to the high-temperature turbine vanes of actual heavy-duty gas turbine.The mist/air phase transition cooling performance of different composite cooling configurations which include the film cooling combined rib/fin and trailing edge slot,the impingement cooling combined film cooling-rib/fin and trailing edge slot,swirl/impingement cooling combined film cooling-rib/fin and trailing edge slot are investigated,respectively.The results show that the average cooling performance on blade surface will be raised by 18%compared to the film cooling combined rib/fin and trailing edge slot,the average overall cooling effectiveness on blade surface increases by 7.4%,at the same time,the average temperature gradient is increased by 19%on blade surface when the swirl and impingement cooling add to the cooling system.In addition,the average cooling performance on blade surface of suction surface swirl cooling is slightly higher than pressure surface swirl cooing and impingement cooling. |
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