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In present work, models that predict contact angle of a droplet with a solid surface, are considered and compared with each other. Two phases were assumed to be Newtonian, incompressible and immiscible fluids. OpenFOAM software is applied to simulate the two phases interface by using Color function VOF (CF-VOF) method. Different models for contact angle of a droplet as Tanner and Yokoi models are implemented in the OpenFOAM. In addition, the dynamics and statics contact angle models were used to compare with recent models in order to choose the best one. The outcome of study shows, even though the static contact angle model is simple to understand, however, it could be the best model to predict the droplet behavior in a wide range of different conditions. The fluid viscosity effect was also considered in different models of the present study. It concluded that the fluid viscosity affects the type of pattern of droplet impact and as viscosity of fluid increases; more energy is needed to uplift the droplet again from the surface. Kelvin-Helmholtz instability (K-H) was also simulated and explained in details which initiates on the interface of two fluids due to velocity differences of droplet and the surrounded air.

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In present study, impact of single bubble on an inclined wall and its movement are investigated by applying volume of fluid method (VOF) in OpenFOAM open source cfd package using a solver called interFoam. Both phases are incompressible and surface tension between two phases is estimated by CSF method. The effect of some parameters such as contact angle, wall slope and Bond and Morton dimensionless numbers on bubble shapes and velocity are studied. The numerical results show bubble velocity along wall increases with the increase of wall slope angle. The maximum bubble velocity happens at 50 degree. Three bubble regimes are recognized and introduced in this study named as: sliding, bouncing, and zigzagging based on wall slope. The bubble regime changes from sliding to bouncing when wall slope changes from 30 to 40 degrees. In constant Morton number, increment of Bond number increases both velocity and amplitude of fluctuations. In addition, an increment of Morton number in constant Bond number, decreases velocity and amplitude of fluctuations. Moreover, by increment of Morton number, the bubble motion will change from an accelerating motion to a constant velocity condition.