Question

Why are turbulence models used?

(a) Define reynolds stress for closure problems

(b) Model hypersonic flows

(c) Lack of system to accurately find turbulent flow characteristic

(d) Closure of continuity equation

I had been asked this question during an interview.

The question is from Turbulence Modelling topic in section Boundary Layers, Laminar & Turbulent Boundary Layers, Navier Stokes Solutions of Aerodynamics

Answer 1

Right answer is (a) Define reynolds stress for closure problems

For explanation: While solving Navier’s Stokes equation for turbulent flow which governs the velocity, pressure of the fluid, the quantity is decomposed into mean and fluctuating components. While solving these using RANS equation, we get a reynolds stress term that needs to be closed in order to solve it. Hence we make use of turbulence modeling which defines these reynolds stresses in terms of the known averaged quantities.