Turbulence Intensity Modulation by Micropolar Fluids

George Sofiadis,Ioannis Sarris

doi:10.3390/fluids6060195

Abstract

Fluid microstructure nature has a direct effect on turbulence enhancement or attenuation. Certain classes of fluids, such as polymers, tend to reduce turbulence intensity, while others, like dense suspensions, present the opposite results. In this article, we take into consideration the micropolar class of fluids and investigate turbulence intensity modulation for three different Reynolds numbers, as well as different volume fractions of the micropolar density, in a turbulent channel flow. Our findings support that, for low micropolar volume fractions, turbulence presents a monotonic enhancement as the Reynolds number increases. However, on the other hand, for sufficiently high volume fractions, turbulence intensity drops, along with Reynolds number increment. This result is considered to be due to the effect of the micropolar force term on the flow, suppressing near-wall turbulence and enforcing turbulence activity to move further away from the wall. This is the first time that such an observation is made for the class of micropolar fluid flows, and can further assist our understanding of physical phenomena in the more general non-Newtonian flow regime.

Highlights

The turbulence generation mechanism is known to alter depending on the internal microstructure of the fluid flow
Summarizing, the micropolar fluid model has been employed in order to explore the turbulent regime, as well as turbulence modulation, of channel fluid flows with internal microstructure
Direct numerical simulations have been used for the computational experiments, while constants and material parameters have been based on biological flow values in order to obtain more realistic results [18]

Summary

Introduction

The turbulence generation mechanism is known to alter depending on the internal microstructure of the fluid flow. In the majority of these studies, it has been shown that addition of polymeric particles to a Newtonian fluid flow leads to near-wall turbulence dampening. Another class of fluid that presents an altered behavior in comparison with the classic turbulent Newtonian flow is that of dense suspensions. Our findings support that both the Reynolds number, as well as the ratio of micropolar to total viscosity, affect turbulence modulation, which seems to alter its behavior for sufficiently high values of these parameters. Previous studies have reported modulation of the turbulence activity in dilute suspensions [9,10,14,15], the majority of these studies only considers the effect of particle diameter. They mostly report a turbulence attenuation when the particle diameter is less than the turbulent length scale

Materials and Methods

Results and Discussion

Conclusions