# Logarithmic-layer turbulence: a view from the wall

## TL;DR

This paper investigates how well turbulent flow structures away from the wall can be reconstructed using only wall measurements, highlighting the potential for wall sensors in turbulence control and defining wall-attached eddies quantitatively.

## Contribution

It demonstrates the effectiveness of linear stochastic estimation in reconstructing flow velocities from wall data and characterizes the observable turbulent structures at different distances from the wall.

## Key findings

- Large wall-attached eddies are well reconstructed from wall data.
- Approximately 40% of kinetic energy and Reynolds stress are captured by observable structures.
- Wall sensors could be used for active turbulence control in the logarithmic layer.

## Abstract

The observability of the flow field away from the wall in turbulent channel flow is studied using only wall observations. Reconstructions are generated from noiseless but limited wall data using linear stochastic estimation, with emphasis on the quality of the reconstruction. All the velocities are well reconstructed in the buffer layer, but only relatively large "wall-attached" eddies are observable farther from the wall. In particular, the large structures accounting for approximately 40% of the total kinetic energy and of the tangential Reynolds stress are captured accurately. It is argued that this should allow the use of wall sensors for the active control of logarithmic-layer turbulence. It also suggests a quantitative definition of "wall-attached" eddies.