Direct numerical simulation of supersonic pipe flow at moderate Reynolds number

TL;DR

This study uses direct numerical simulation to analyze compressible turbulent flow in a pipe at high Reynolds number, examining velocity, temperature, and scalar statistics, and proposing universal transformations for compressible turbulence.

Contribution

It introduces improved compressibility transformations for velocity and passive scalar statistics, validated at Re_τ ≈ 1000, enhancing understanding of compressible pipe flow.

Findings

Huang's transformation yields universal Reynolds stress distributions.

A logarithmic layer is observed at Re_τ ≈ 1000.

Passive scalar spectra resemble canonical incompressible flow patterns.

Abstract

We study compressible turbulent flow in a circular pipe, at computationally high Reynolds number. Classical related issues are addressed and discussed in light of the DNS data, including validity of compressibility transformations, velocity/temperature relations, passive scalar statistics, and size of turbulent eddies.Regarding velocity statistics, we find that Huang's transformation yields excellent universality of the scaled Reynolds stresses distributions, whereas the transformation proposed by Trettel and Larsson (2016) yields better representation of the effects of strong variation of density and viscosity occurring in the buffer layer on the mean velocity distribution. A clear logarithmic layer is recovered in terms of transformed velocity and wall distance coordinates at the higher Reynolds number under scrutiny ($\Rey_{\tau} \approx 1000$), whereas the core part of the flow is found to be characterized by a universal parabolic velocity profile. Based on formal similarity between the streamwise velocity and the passive scalar transport equations, we further propose an extension of the above compressibility transformations to also achieve universality of passive scalar statistics. Analysis of the velocity/temperature relationship provides evidence for quadratic dependence which is very well approximated by the thermal analogy proposed by Zhang et Al.(2014). The azimuthal velocity and scalar spectra show an organization very similar to canonical incompressible flow, with a bump-shaped distribution across the flow scales, whose peak increases with the wall distance. We find that the size growth effect is well accounted for through an effective length scale accounting for the local friction velocity and for the local mean shear.