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) Find flow rate and drag in a rectangular duct of a residential air-conditioning system. Assume that the duct cross section is a square of side \(25 \mathrm{~cm}\) and the average velocity is \(1 \mathrm{~m} / \mathrm{s}\).

b) Find turbulent drag on a slender body of length \(2 \mathrm{~m}\) moving at zero attack angle in the air with speed \(10 \mathrm{~m} / \mathrm{s}\).

c) Predict motion of a hurricane.

d) Analyze flow around a swimming fish. Assume that the fish is \(20 \mathrm{~cm}\) long and moves with speed of \(40 \mathrm{~cm} / \mathrm{s}\).