The Effect Of Particle Deposition On Film Cooling Performance

As an important industrial equipment,gas turbine is widely used in many fields such as aviation,navigation,vehicle and power station to provide thrust or produce electrical energy.In the last fifty years,inlet temperature of gas turbine engines was increased with the requirement of high thermal efficiency.To ensure that the turbine engines are running in a safe and efficient condition,film cooling technology becomes one of commonly used techniques to prevent the blade surfaces from the hot mainstream.A novel combined hole is first proposed in this thesis and compared with the conventional cylindrical hole.It is found that the film cooling effectiveness for the cylindrical hole case decreases with the increase of the blowing ratio,whereas that for the combined hole case increases by increasing the blowing ratio.In the actual working conditions,operating efficiency of equipment is significantly affected by particle deposition.The deposition from the fuel impurities and dust particles in the air is often found inside film holes,which results in partial hole blockage.Based on the above problems,this paper simplifies the hole blockage configurations into hemispherical and tetrahedral shapes,and studies the effect of different blockage ratios,blockage positions and blockage configurations on film cooling performance.It is found that a high blockage ratio causes earlier occurrence of the lift-off and greater reduction of the vortex strength.Moreover,the lateral coverage area of the coolant flow is decreased with an increase in the blockage ratio.For the hemispherical blockage configuration,1% mist injection provides an improvement of the cooling performance by approximately 10%.A smaller size of the droplets provides a higher evaporation rate,which results in higher film cooling effectiveness.In addition,the film cooling effectiveness is significantly affected by the shape of the blockage configuration,and the hemispherical blockage configuration results in more reduction of the lateral film cooling effectiveness than the tetrahedral one.In order to further investigate the deposition mechanism of fine particles on the blade surface,this paper simulates the deposition effectiveness of different particle sizes based on the critical velocity model and particle removal model.The effects of different blowing ratios and inlet angles on the particle impact rate,deposition rate and invasion rate are also studied.It is found that the particles with small size almost don’t impact on the blade surface.It is also found that the impact rate increases with increasing of particle size,andthe collision mainly occurs on the pressure side of the blade.When the particle size increases to 10?m,the particles begin to invade into the film hole,and the invasion rate increases significantly with increasing the particle size.In addition,the impact rate also increases gradually with increasing the particle size,especially on the pressure side of the blade surface.The impact rate on the pressure side and suction side suddenly increases to200% when the particle size is 50?m,which indicates that the particle rebound from the wall and most particles collide with the blade surface more than once.