Investigations Of Particle Deposition Mechanism On The Flat Plate Wall With Film Cooling Holes

When aero-engine works in particle environment such as sand dust and fly ash,particles will deposit on the surface of turbine blade with film cooling holes,and gradually form certain deposition morphology as deposition time goes on.Particle deposition not only affects the aerodynamic efficiency of turbine blades,but also changes heat transfer characteristics.Moreover,the deposits may block film cooling holes,and directly reduce the service life of turbine blades.Considering film cooling is still the most common and important cooling method applied to turbine blades at present stage,therefore,particle deposition mechanism on the film cooling wall is investigated in this dissertation,which has great significance to avoiding particle deposition on the surface of turbine blades,improving the service life of turbine blades under the complicated particle environment,and enhancing the survival ability of aero-engine.In this dissertation,steady deposition of particles was studied firstly.Considering near-wall flow field treatment,particle/wall interaction and particle force,a steady deposition analysis method applied to dilute two-phase flow was proposed based on Euler-Lagrangian system,which mainly included particle motion model and particle/air one-way coupling method.On the basis of verifying the rationality of the calculation method,calculating study on particle deposition characteristics on the film cooling wall of high-temperature flat plate was carried out.By analyzing the effects of working condition and film cooling structure to particle deposition rate,the particle deposition mechanism on the film cooling wall was revealed preliminarily.Then,taking into account the complexity of the unsteady deposition of sand dust under the turbine environment and on the basis of summarizing particle deposition phenomena,the actual engine turbine guide vane parameters were combined with the low temperature film cooling flat plate model through similarity and modeling analysis,and designed the low-temperature research model with relative simple structure and the deposition experimental platform.After that,considering the calculation efficiency and research emphasis,a complete analysis method applied to unsteady particle deposition on the film cooling wall was established based on Euler-Euler system,which mainly contained dispersed multiphase method and liquid-solid film model.And the reliability of calculation method was verified also.Finally,calculation study of unsteady particle deposition mechanism on the film cooling wall of the designed low temperature flat plate was conducted.On the one hand,the two-phase flow field structure near film cooling holes and the evolution of particle unsteady deposition were studied.On the other hand,the dimensionless factors affecting the particle deposition were explored,mainly including working condition factors(mainstream Reynolds number,particle concentration,particle stokes number,blowing ratio and attack angle of plate)and film cooling structure factors(film hole angle,hole spacing,trenched hole depth and film hole arrangement),which ulteriorly revealed the particle deposition distribution mechanism on the film cooling wall.The following main conclusions have been drawn in the present thesis:(1)The particle force in the near-wall region has been calculated,and results show that the drag force is more sensitive to the particle diameter and the average velocity of mainstream,the Saffman force is more sensitive to the average velocity of mainstream,while the thermophoresis force is more sensitive to the particle diameter and environment temperature.Under different working conditions,the influence of each force on the particle deposition is consistent with the force analysis.At the same time,the drag force and Saffman force cannot be neglected when using the Euler-Lagrangian method by comparing the magnitude of force.(2)Particle deposition characteristics on the film cooling wall of high-temperature flat plate have been calculated,which is concluded that the degree of jet closing to wall,the flow field uniformity along the exhibition direction and the disturbance intensity of vortex are the main reasons that affect the deposition of particles on the film cooling wall.The better the degree of jet closing to wall and the uniformity of flow field are,the smaller the disturbance intensity of vortex is,the more unfavorable is to particle deposition.In addition,blowing ratio mainly changes the disturbance intensity of vortex,film hole angle and trenched hole depth mainly change the degree of jet closing to wall,and film hole arrangement mainly change the flow field uniformity along the exhibition direction.(3)The calculation of the two-phase flow field distribution and particle unsteady deposition characteristics in the vicinity of film cooling holes has been carried out,and results show that the near-wall high-concentration band and local low-concentration region of particle phase will appear near film cooling flat plate due to the inertia of particles and the particle drag force,and the injection of cold air flow will directly affect the particle distribution in the downstream of film cooling hole.During the deposition simulation of 600 s,the particle deposition thickness at the same position increases with the increasing of deposition time.The deposition thickness in the leading edge region is at least one order of magnitude higher than that of the wall near the film cooling hole.In addition,the change of deposition morphology in the leading edge region with deposition time will affect the flow field near the flat plate and film cooling efficiency to a certain extent.(4)The calculation of the influence of dimensionless working condition factors on the particle deposition shows that mainstream Reynolds number,particle concentration and attack angle of plate all change the deposition morphology from the accumulation of deposition amount,so the change trends of deposition morphology in different conditions are basically similar.While particle stokes number and blowing ratio influence the particle deposition trend by changing the particle inertia and jet momentum respectively,and the change trends of deposition morphology in different conditions no longer have the similarity.The particle deposition tendency is determined by the interaction between particle inertia and jet through comprehensive analysis.(5)The calculation of the influence of dimensionless structure factors on the particle deposition shows that the change of structure factors changes the distribution of cooling jet,which affects the particle deposition distribution.For example,film hole angle changes the spraying direction of cooling jet,hole spacing changes the influence range of cooling jet,trenched hole depth can change the degree of flow field closing to wall in the downstream of film cooling hole and the flow field uniformity along the exhibition direction,and aligned and staggered arrangements of multiple rows of film cooling holes can change the flow field uniformity along the exhibition direction and the disturbance intensity of vortex.