Problem Description

Solution

The main difference between level set methods and volume of fluid methods is that volume of fluid methods use a discontinuous function (zero in one phase and one in the other) while level set methods represent the interface by a certain contour of a smooth function. Each of these methods have one main advantage and disadvantage: Due to the discontinuity in VOF methods, it can suffer poor accuracy in the determination of the position of the interface and the calculation of the mean curvature, which in turn determines the surface tension force. The advantage is that the mass of each fluid is exactly conserved. Level set methods, on the other hand, use a smooth function, making it possible to get results with better accuracy.

In the original level set method, a signed distance function is used (that is, in each point, the level set function is the closest distance to the interface, with positive or negative sign depending on in which fluid the point is. The zero contour gives the interface). The main drawback of the originally proposed level set method is that mass is not conserved, and significant mass loss may occur. However, in COMSOL Multiphysics, we use a modified version of the level set method, which has significantly better conservation properties. It is in essence a compromise between the original level set method and the VOF method, with high order accuracy, and with good mass conservation. For an example using the Level Set method, see the Inkjet Printer Head model.

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