Question

The Reynolds number of a 3-D turbulent flow is 10^4. What is the number of time-steps needed?

(a) 100

(b) 1000

(c) 10^4

(d) 10^5

I have been asked this question in a national level competition.

Asked question is from Direct Numerical Solution for Turbulent Models topic in section Turbulence Modelling of Computational Fluid Dynamics

Answer 1

Correct choice is (a) 100

Best explanation: The number of time steps depends on the ratio of the largest to the smallest time scales. This ratio depends on the Reynolds number. The times steps needed is Re^1/2. Here, it is (10^4)^1/2, which is equal to 100. 100-time steps are needed to solve this problem.