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Fluid Mechanics

PHYS 426
The initial growth of salt fingers
In a situation when the saltier but warmer water is overlying the fresher but colder water the so-called "double-diffusive instability" can develop if heat diffuses away faster than salinity. The instability leads to slow mixing taking a form of vertically elongated fluid parcels, called "salt fingers", sinking and rising on a thermal time scale (Fig. 1). This thermohaline mixing has been observed in the ocean, where the solar radiation warms up the surface layers which, at the same time, become saltier because of the water evaporation. A similar phenomenon can also be observed in a kitchen experiment, in which sugar plays the role of heat because it diffuses faster than salt (Fig. 2). With some efforts, comsol can be tuned up to simulate processes in fluid mechanics. As an example, in Fig. 3 we show the animation of our results of 2D numerical simulations of the initial growth of salt fingers obtained with comsol. Some information about thermohaline mixing in stars is given on the research page.
A simple airfoil model
This example shows a comsol simulation of a simple airfoil in a wind tunnel. The simulation finds a stationary solution for the incompressible Navier-Stokes equation in 2D geometry (Fig. 1).
A long bar in a wind tunnel
This comsol simulation is a numerical experiment reproducing Example 4.1 on page 103 in the textbook on Fluid Mechanics by Kundu et al.
Thermal convection
Comsol simulations of thermal convection in 2D using a stream function