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In this chapter，the CFD mode was first used to study the influence of the fluid stabilizing cover on the flow field in the printer cavity. After the uniformity and stability of the flow field in the area above the workbench have been improved，the coupled CFD-DPM mode combined with the UDF of the released particles is used to study the influence of the fluid stabilizing cover on the removing rate of particles at different initial speeds. Firstly，simulate until the gas flow above the workbench is sufficiently stable，and then set three particle release paths through UDF to simulate the movement and adsorption of particles. Setting three particle release paths can reflect the movement of particles in different areas of the workbench，which is closer to the actual working conditions of the printer. Result of a model using the fluid stabilizing cover are compared with the result of the model without the fluid stabilizing cover to research the impact of the cover in the chamber. The influence of the fluid stabilizing cover on the flow field and particle removing rate were investigated numerically. The major conclusions are listed as follows:
（1） The fluid stabilizing cover improves the stability and uniformity of the flow field above the workbench，because the fluid stabilizing cover can reduce the influence of the messy gas flow in the cavity on the flow field above the workbench.After using the fluid stabilizing cover，the uniformity of the flow field above the workbench is greatly improved，and the laminar flow height is increased from 30 mm to 40 mm，with an increase of 33.33%.
（2） After using the fluid stabilizing cover，the removing rate of particles with different initial velocities is increased compared with the model without the fluid stabilizing cover. The removing rate of spatters，which initial velocity is 3 m/s，increases from 60.02% to 73.08% after using the fluid stabilizing cover. While the initial velocity of spatters is 5 m/s，the removing rate increases from 63.91% to 73.04%. The removing rate of spatters increases from 60.37% to 76.15% when initial speed of spatters is 7 m/s.
（3） The fluid stabilizing cover improves the distribution of sputtered particles on the workbench and reduces the adsorption area of the particles on the workbench（as shown in Figure 3-7）. The number of particles adsorbed in the central area of the workbench is greatly reduced compared to the model without the fluid stabilizing cover.
In subsequent research，another fluid stabilizing cover with a better structure will be designed to improve the flow field in the printer and increase the particle removing rate. At the same time，many other factors should be taken into consideration，such as particle diameter，material，and the influence of the heat from the melting pool on the gas flow above the workbench.