Acceleration in turbulent channel flow

Abstract

We use Direct Numerical Simulations of turbulent channel flow to study the acceleration A corresponding to the full fluid velocity u and the acceleration a corresponding to the fluctuating velocity u′≡u−⟨u⟩, where ⟨u⟩ is the mean flow. The mean acceleration ⟨A⟩=⟨a⟩ is not zero, and the fluctuations of the convective and local parts of ⟨A⟩ around their means approximately cancel in the intermediate log-like layer. The motions of stagnation points where u′=0 are controlled by a. In this intermediate layer, the fluctuations of a around its mean predominantly come from the fluctuations of its local part. Stagnation points move with an average velocity, which equals the average fluid velocity at these points. The fluctuations around this average stagnation point motion decrease in the log-like layer with increasing distance from the wall.