For the following hypothetical CFD tasks, compare the DNS, LES, and RANS approaches. Discuss which of them is feasible and which is likely to produce acceptable accuracy and level of description.

a) Try to understand how local properties of turbulent fluctuations created in a cup of coffee by spoon movements affect the rate of sugar dissolution.

b) Analyze dynamics of a solar protuberance.

c) Predict flow in a microfluidic device, essentially a network of channels of width \(10 \mu \mathrm{m}\) in which a water-based solution flows with the typical velocity \(1 \mathrm{~mm} / \mathrm{s}\).

d) Predict drag on a submarine moving through water with constant speed of \(50 \mathrm{~km} / \mathrm{h}\). The length and the largest cross-sectional size of the submarine are, respectively, 100 and \(15 \mathrm{~m}\).