激光表面熔凝多相区统一模型及数值分析

建立了移动光源下三维瞬态、对流/扩散固、液、糊状区及相变，多相区统一的激光熔凝数学模型。该模型主要解决了已往模型必须将固态和液态分开计算然后进行耦合且不能计算糊状区的缺陷．这种方法能够反映糊状区的存在及固液相变过程中潜热的吸收和释放的影响且在计算过程中自动跟踪糊状区位置．无须人为划分相区。根据数学模型的特点。建立了一套固定网格的数值求解方法。通过熔池深度的计算与实验值的比较验证了模型的正确性。进一步研究了表面张力、浮力等驱动力与激光熔池形状几何尺寸的关系。计算结果指出，表面张力和浮力驱动熔池内熔体的对流存在一次环流和二次环流。一次环流使熔池变宽、变浅，二次环流使熔池底部出现凹坑。实验印证了计算结果。

Modeling and Simulating on Laser Remelting Considering Diffusion/Convection and Phase Change Process in the Substrate

A transient, moving laser beam, three dimensional laser remelting mathematical model considering convection, diffusion and phase change process in laser melting pools and substrate was developed, which is suitable for the prediction of fluid flows, temperature field, liquid fraction field and phase change in solid, liquid and mash zone. Based on the mathematical mode, this paper developed an fix grid numerical method. This method need not trace the interface between solid and liquid, and can consider the effect of latent heat released during phase change. The agreement of melting pool depth between prediction and experiment validates the model. The simulation shows that the surface tension and buoyancy drive the liquid metal fluid forming two set eddies in the transverse section, i.e. the first order recirculating,and the second order recirculating. The first order recirculating makes the pool wide and shallow and the second order recirculating digs a pit in the bottom of the pool. The experimental results show a good agreement with the model simulation.