# Experimental Study of the Bottleneck in Fully Developed Turbulence

## TL;DR

This study experimentally investigates how the bottleneck effect in turbulence energy spectra diminishes with increasing turbulence intensity, using high-Reynolds-number wind tunnel experiments to extend previous numerical findings.

## Contribution

First experimental measurement of the bottleneck effect's dependence on Reynolds number in high-intensity turbulence using an active grid in a wind tunnel.

## Key findings

- Bottleneck strength decreases with increasing Reynolds number.
- Energy spectra show consistent features across different Reynolds numbers.
- Results align with a power-law decrease of the bottleneck effect.

## Abstract

The energy spectrum of incompressible turbulence is known to reveal a pileup of energy at those high wavenumbers where viscous dissipation begins to act. It is called the bottleneck effect. Based on direct numerical simulations of the incompressible Navier-Stokes equations, results from Donzis & Sreenivasan (2010) pointed to a decrease of the strength of the bottleneck with increasing intensity of the turbulence, measured by the Taylor micro-scale Reynolds number $R_{\lambda}$. Here we report first experimental results on the dependence of the amplitude of the bottleneck as a function of $R_{\lambda}$ in a wind-tunnel flow. We used an active grid in the Variable Density Turbulence Tunnel (VDTT) (see Bodenschatz et al. (2014)) to reach $R_{\lambda}$ > 5000, which is unmatched in laboratory flows of decaying turbulence. The VDTT with the active grid permitted us to measure energy spectra from flows of different $R_{\lambda}$, with the small-scale features appearing always at the same frequencies. We relate those spectra recorded to a common reference spectrum, largely eliminating systematic errors which plague hotwire measurements at high frequencies. The data are consistent with a power law for the decrease of the bottleneck strength for the finite range of $R_{\lambda}$ in the experiment.