Lattice Boltzmann Simulation Of Swirling And Droplet Dynamics In Separator

Due to the advantages of the simple geometry,small space requirement and low maintenance costs,dynamic pressure type oil-air separators are widely applied in lubrication systems of aero engines to separate the air-oil mixture.In the working process,the flow fields taking place in separator are complex,including many basic problems of hydrodynamics,for instance,the 3D swirling turbulent flow and the air-oil phase interface migration process.We study the flow field in separator in mesoscopic scale,it is an important theoretical supporting for deeply investigation of the basic physical problems in separator.Firstly,the single phase swirling flow in separator is studied by the lattice Boltzmann method based on the advantage of the mesoscopic level,and the applicability of the lattice Boltzmann method to the flow field in separator is discussed.Secondly,the multicomponent multiphase pseudopotential model with large density ratio is applied to the study of droplet collision process,and the influence of different factors on the droplet collision process is analyzed.Then,an improved multicomponent multiphase pseudopotential model for wetting is proposed by considering the fluid-solid interaction,and the droplet displacement on a vertical wall is simulated by this modified model.Finally,based on the improved model,the effects of various factors on the process of droplet impacting liquid film are studied.The results indicated that:the lattice Boltzmann method can simulate the swirling flow and capture the secondary backflow phenomenon and unstable characteristics of the vortex core of the flow field in separator.The distribution of the average tangential and axial velocity obtained by simulation are basically in agreement with the experiment results.In the simulation of the droplet collision process,the distribution schematic of various collision regimes is obtained in the research range by changing We number and collision parameter B,there is a critical We number that causes the droplet to collide and separate when the collision parameter B is constant.Meanwhile,the decrease of the diameter ratio(increase the diameter of large droplet)will inhibit the droplet separation process.A modified pseudopotential-based fluid-solid interaction is adopted in the multicomponent multiphase pseudopotential model.The achievable contact angles can be ranged from 10° to 180° for static wetting process using the proposed model,the density ratios obtained are all larger than 1200,and the maximum spurious current is 0.016,which is smaller than the value(0.033)in literature.Next,the droplet displacement on a vertical wall is simulated,and the length L increases with increasing the fluid-solid interaction strength,the surface tension,the gravitational acceleration and the droplet radius.Increasing the dimensionless obstacle height,the droplet gradually moves to the right until it collides with the right wall.The increase of the dimensionless obstacle width will postpone the droplet displacement process.In the simulation of the process of droplet impacting on the liquid film,the crown's dimensionless height and radius increase with the increase of Re number.With the increase of We number,the dimensionless height increases gradually,and the dimensionless radius decreases.With the increase of the gravitational acceleration,the dimensionless radius remains the same,and the dimensionless height decreases.When the liquid film thickness is 0.3?H*?0.9,the dimensionless height and radius decrease with the increase of the liquid film thickness.When H*=0.1,the dimensionless height and radius are significantly different from the results of others.In the process of droplet impacting on the moving liquid film,the moving liquid film promotes the development of the upstream crown in the height direction,but it inhibits the development of the downstream crown in the height direction,meanwhile,it inhibits the spreading process of the upstream crown,and it promotes the spreading process of the downstream crown.According to the deviation analysis,the influence of the moving liquid film on the downstream crown is greater than the influence on the downstream crown.It should be noted that,increasing the liquid film thickness will weaken the influence of the liquid film velocity on the dimensionless height,and enhance the influence of the liquid film velocity on the dimensionless radius.With the increase of the groove width,the dimensionless height increases and then decrease,and the dimensionless radius decreases gradually.With the increase of the groove height,the dimensionless height and radius both decreases gradually.Increasing the width of the gas outlet can effectively suppress the blocking phenomenon,but the trapping effect of the wall is relatively weakened,and the droplet escape phenomenon occurs.