Turbulent plane Poiseuille flow

TL;DR

This paper develops a non-local closure model for turbulent stress in plane Poiseuille flow, analyzing the flow at high Reynolds numbers and revealing complex boundary layer structures including an inner layer near the flow center.

Contribution

It derives a new non-local turbulence closure model for plane Poiseuille flow, extending classical theories and analyzing the flow structure at high Reynolds numbers.

Findings

The turbulent stress is a non-local function of the velocity field.

Identification of an additional inner boundary layer near the flow center.

Asymptotic analysis reveals complex boundary layer interactions.

Abstract

The ultimate goal of a sound theory of turbulence in fluids is to close in a rational way the Reynolds equations, namely to express the time averaged turbulent stress tensor as a function of the time averaged velocity field. This closure problem is a deep and unsolved problem of statistical physics whose solution requires to go beyond the assumption of a homogeneous and isotropic state, as fluctuations in turbulent flows are strongly related to the geometry of this flow. This links the dissipation to the space dependence of the average velocity field. Based on the idea that dissipation in fully developed turbulence is by singular events resulting from an evolution described by the Euler equations, it has been recently observed that the closure problem is strongly restricted, and that it implies that the turbulent stress is a non local function (in space) of the average velocity field, an extension of classical Boussinesq theory of turbulent viscosity. The resulting equations for the turbulent stress are derived here in one of the simplest possible physical situation, the turbulent Poiseuille flow between two parallel plates. In this case the integral kernel giving the turbulent stress, as function of the averaged velocity field, takes a simple form leading to a full analysis of the averaged turbulent flow in the limit of a very large Reynolds number. In this limit one has to match a viscous boundary layer, near the walls bounding the flow, and an outer solution in the bulk of the flow. This asymptotic analysis is non trivial because one has to match solution with logarithms. A non trivial and somewhat unexpected feature of this solution is that, besides the boundary layers close to the walls, there is another "inner" boundary layer near the center plane of the flow.