# One-Dimensional Flow Spectra and Cumulative Energy from Two Pipe Facilities

## TL;DR

This study analyzes turbulent pipe flow spectra and energy distribution across two facilities, revealing Reynolds-number dependent velocity peaks and large-scale structures, with implications for understanding turbulence dynamics.

## Contribution

It provides new measurements of flow spectra and energy fractions in turbulent pipe flow over a wide Reynolds number range using hot-wire probes.

## Key findings

- Reynolds-number dependent inner peak in velocity fluctuations.
- Large scale structures have wavelengths of approximately 3R and 20R.
- Maximum energy contribution occurs near the outer logarithmic layer.

## Abstract

Experiments have been conducted to assess the sizes and energy fractions of structure in fully developed turbulent pipe flow regime in two pipe facilities, ColaPipe at BTU Cottbus-Senftenberg, and CICLoPE at University of Bologna, for shear Reynolds number in the range $2.5\cdot{10^3}\le{\mathrm{Re_{\tau}}}\le{{3.7\cdot{10^4}}}$, utilizing a single hot-wire probe. Considerations are given to the spectra of the streamwise velocity fluctuations, and to large scale motions and their energy contents from the pipe near-wall to centerline. The analysis of the velocity fluctuations revealed a Reynolds-number dependent inner peak at a fixed wall normal location, however, an outer peak seems not to appear that might be attributed either to low Reynolds number effect or not high enough spatial resolution of hot-wire probe, motivating further study utilizing nanoscale probes. Sizes of the large scale, and very large scale structures were estimated to have wavelengths of 3$R$, and 20$R$ at high Reynolds number, srespectively. The fractional energy contents in wavelengths associated with the large scale motions at various wall normal locations showed maximum contribution to the turbulent kinetic energy near the outer limit of the logarithmic layer.