Energy transfer mechanisms in adverse pressure gradient turbulent boundary layers

TL;DR

This study investigates energy transfer mechanisms in adverse-pressure-gradient turbulent boundary layers, revealing that core transfer processes remain consistent across different flow conditions, with variations mainly in intensity due to local shear changes.

Contribution

It provides a detailed spectral analysis showing that energy transfer mechanisms are similar in different APG TBLs, despite changes in flow structures and energy spectra.

Findings

Inner layer streak signatures are absent in large defect APG TBLs.

Outer layer structures shift from wall-attached to wall-detached with increasing velocity defect.

Energy transfer mechanisms are consistent across flows, with intensity variations driven by local shear.

Abstract

The energy transfer mechanisms and structures playing a role in these mechanisms in adverse-pressure-gradient (APG) turbulent boundary layers (TBLs) with small and large velocity defects are investigated. We examine the wall-normal and spectral distributions of energy, production and pressure-strain in APG TBLs and compare these distributions with those in canonical flows. It is found that the spectral distributions of production and pressure-strain are not profoundly affected by an increase of the velocity defect, although the energy spectra drastically change in the inner layer of the large defect APG TBL. In the latter, the signature of the inner layer streaks is absent from the energy spectra. However, the production and pressure-strain spectra suggest that the near-wall cycle or another energy transfer mechanism with similar spectral features still exist in large defect TBLs. In the outer layer, energetic, production and pressure-strain structures appear to change from wall-attached to wall-detached structures with increasing velocity defect. Despite this, the 2D spectral distributions have similar shapes and wavelength aspect ratios of the peaks in all these flows. These observations suggest that outer layer energy transfer mechanisms may be the same in wall-bounded flows, no matter if dynamically relevant structures are attached or detached to the wall. Therefore, the conclusion is that the mechanisms responsible for turbulence production and inter-component energy transfer may remain the same within each layer in all these flows. It is the intensity of these mechanisms within one layer that changes with velocity defect, because of the local mean shear variation.