# Effect of channel dimensions and Reynolds numbers on the turbulence modulation for particle-laden turbulent channel flows

## TL;DR

This study uses large eddy simulations to analyze how channel size and Reynolds number influence turbulence modulation in particle-laden turbulent flows, revealing key parameters affecting turbulence attenuation and structure.

## Contribution

It identifies system size and fluid bulk Reynolds number as the primary factors influencing turbulence modulation in particle-laden flows, providing scaling insights for industrial design.

## Key findings

- Turbulence attenuation varies with system size and Reynolds number.
- Streamwise structures lengthen and become fewer with increased system size.
- High Reynolds numbers produce smaller, thinner streaks that are more closely spaced.

## Abstract

The addition of particles to turbulent flows changes the underlying mechanism of turbulence and leads to turbulence modulation. Different temporal and spatial scales for both phases make it challenging to understand turbulence modulation via one parameter. The important parameters are particle Stokes number, mass loading, particle Reynolds number, fluid bulk Reynolds number, etc., that act together and affect the fluid phase turbulence intensities. In the present study, we have carried out the large eddy simulations for different system sizes (2{\delta}/dp = 54, 81, and 117) and fluid bulk Reynolds numbers (Re_b = 5600 and 13750) to quantify the extent of turbulence attenuation. Here, {\delta} is the half-channel width, dp is the particle diameter, and Re_b is the fluid Reynolds number based on the fluid bulk velocity and channel width. The point particles are tracked with the Lagrangian approach. The scaling analysis of the feedback force shows that system size and fluid bulk Reynolds number are the two crucial parameters that affect the turbulence modulation more significantly than the other. The streamwise turbulent structures are observed to become lengthier and fewer with an increase in system size for the same volume fraction and fixed bulk Reynolds number. However, the streamwise high-speed streaks are smaller, thinner, and closely spaced for higher Reynolds numbers than the lower ones for the same volume fraction. In particle statistics, it is observed that the scaled particle fluctuations increase with the increase in system size while keeping the Reynolds number fixed. However, the scaled particle fluctuations decrease with the increase in fluid bulk Reynolds number for the same volume fraction and fixed system size. The present study highlights the scaling issue for designing industrial equipment for particle-laden turbulent flows.