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SummaryWe present a fully‐explicit, iteration‐free, weakly‐compressible method to simulate immiscible incompressible two‐phase flows. To update pressure, we circumvent the computationally expensive Poisson equation and use the general pressure equation which is solved explicitly. In addition, a less diffusive algebraic volume‐of‐fluid approach is used as the interface capturing technique and in order to facilitate improved parallel computing scalability, the technique is discretised temporally using the operator‐split methodology. Our method is fully‐explicit and stable with simple local spatial discretization, and hence, it is easy to implement. Several two‐ and three‐dimensional canonical two‐phase flows are simulated. The qualitative and quantitative results prove that our method is capable of accurately handling problems involving a range of density and viscosity ratios and surface tension effects.
SummaryWe present a fully‐explicit, iteration‐free, weakly‐compressible method to simulate immiscible incompressible two‐phase flows. To update pressure, we circumvent the computationally expensive Poisson equation and use the general pressure equation which is solved explicitly. In addition, a less diffusive algebraic volume‐of‐fluid approach is used as the interface capturing technique and in order to facilitate improved parallel computing scalability, the technique is discretised temporally using the operator‐split methodology. Our method is fully‐explicit and stable with simple local spatial discretization, and hence, it is easy to implement. Several two‐ and three‐dimensional canonical two‐phase flows are simulated. The qualitative and quantitative results prove that our method is capable of accurately handling problems involving a range of density and viscosity ratios and surface tension effects.
In this paper, the flow characteristics of the polishing fluid between the polishing pad and the workpiece are studied for the robotic wet polishing process, and the distribution of the polishing fluid radial velocity Ur and the liquid film thickness z at different rotating radii r are revealed. The two-dimensional computational domain consisting of the polishing pad surface, the workpiece wall and the polishing fluid is established. The particle-liquid two-phase flow simulation is carried out in Fluent, and the influence of different rotation rate ω of the polishing pad and different robot swing speeds v2 on the change and distribution of polishing fluid flow rate and temperature are elaborated. The position distribution of the abrasive particles in the wet polishing process and the velocity distribution of particles in the x and y directions impacting on the workpiece surface are simulated and analyzed for polishing fluids with different average abrasive diameters dp. The three-dimensional calculation domain for wet polishing is established; the workpiece surface erosion is simulated in Fluent; the material removal rate MRR and standard deviation of material removal σ on the workpiece surface are calculated considering different combinations of polishing fluid properties Ci and polishing kinematics Pi. Under the same process parameters, the material removal rate test value MRRT and the standard deviation of material removal test value σT are compared with the simulated values, respectively. The results show that under the combination of 64 groups of physical parameters C1-C64 of the polishing fluid, the error between the test value MRRT, σT and the simulationvalue MRR, σ is within 5%. With 64 sets of polishing kinematics parameters P1-P64, the average error between the test value MRRT and the simulated value MRR is 4.19%. However, when the polishing pad rotation rate ω is high, there is an inefficient polishing area in the smaller radius from the polishing pad rotation center, which results in a lower MRRT in some tests than that in simulation, with an maximum error of 8.1%. The average error between the test value σT and the simulation value σ is 3.77%. When the pressure P of the polishing pad is high, the large particles embedded in the polishing pad surface follow its rotation, causing deep scratches on the workpiece surface, which results in a larger σT in some tests, with an maximum error of 7.8%. In conclusion, the material removal principle and the influence of different process parameters in the robotic wet polishing process are revealed in this paper.through modeling and simulation of the particle-liquid two-phase flow, giving an accurate estimation of the material removal rate of the robotic wet polishing process.
A system of three horizontal fluid layers is considered, with two interfaces separating them. When the upper fluids are of higher density, the system is unstable and Rayleigh–Taylor instabilities occur, as interfacial disturbances grow with time and the fluids overturn. A linearized solution is presented for the corresponding inviscid problem. It reveals a neutrally stable situation when the fluid densities decrease with height. However, whenever a high density fluid lies above a less dense one, the linearized solution predicts exponential growth of the interface between them. With two interfaces present, several different flow scenarios are possible, depending on the two density ratios between the three fluids The interfacial waves can occur either in a sinuous or a varicose formation. A semi-numerical spectral method is used to obtain nonlinear solutions for three-layer viscous fluids, using a recently-published “Completed Boussinesq Approximation”. These nonlinear results are compared with the linearized inviscid solution and also with interface shapes obtained from an SPH algorithm. Results are shown for sinuous and varicose solution types, and inversion layer flows are discussed.
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