Statistical interpretation of LDA measurements in naturally developing turbulent drag-reducing flow using invariant theory
•Polymer drag reduction DR mechanism is validated by the invariant theory and LDA.•Small-scale turbulence motions unroll chains to rotation invariant structures.•Consequently, turbulence reaches maximum anisotropy at the wall and relaminarizes.•Maximum DR is when the turbulence time scale at walls m...
Saved in:
| Published in: | The International journal of heat and fluid flow 2022-02, Vol.93, p.108856, Article 108856 |
|---|---|
| Main Authors: | , , , , , , |
| Format: | Article |
| Language: | eng |
| Subjects: | |
| Online Access: | Get full text |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | •Polymer drag reduction DR mechanism is validated by the invariant theory and LDA.•Small-scale turbulence motions unroll chains to rotation invariant structures.•Consequently, turbulence reaches maximum anisotropy at the wall and relaminarizes.•Maximum DR is when the turbulence time scale at walls matches polymer relaxation time.•Results support the unified description of the transition onset mechanism.
Turbulent drag reduction by an extremely diluted aqueous solution of polyacrylamide was studied in a fully developed plane channel flow under non-tripped flow conditions allowing the natural development of turbulence presumably from the initially laminar like a flow state. Using laser-Doppler anemometry, all components of the Reynolds stress tensor were measured. This permitted the determination of the turbulence anisotropy and independent invariants of the anisotropy tensor. Introducing a measure for the departure of the Reynolds stress tensor from the statistically axisymmetric state that ensures laminarity, fundamental insights relating the origin of turbulence and turbulent drag reduction were analyzed in light of the measured results and existing databases of direct numerical simulations. The chief mechanism relevant to the onset of turbulence and turbulent drag reduction deduced from analytic considerations involving only kinematic constraints was confirmed by the experimental data. Parametrization of the drag reduction effect in terms of the Deborah number based on turbulence quantities evaluated at the wall supports the deduction of the polymer-turbulence interaction in terms of the elastic properties of the polymer and the near-wall turbulence structure. |
|---|---|
| ISSN: | 0142-727X 1879-2278 |