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Helical flow structures play an important role in transport processes in engineered and physiological systems, where cur-vature and torsion generate secondary motions that influence momentum transport, mixing, and wall interactions. This study presents a computational investigation of steady helical pipe flows using the curvature-corrected k–ω SST turbulence model combined with an intermittency-based transition formulation to capture transition and laminarization effects. The numeri-cal framework is validated against experimental velocity measurements obtained downstream of a baseline helical con-figuration, showing good agreement at the measurement plane. Following validation, a parametric study is conducted across three helical geometries with physiologically relevant pitch and curvature ratios (r/D = 1.5–3.0, P/D = 6–12) at Reynolds numbers of 1800 and 3000. Helicity-based visualiza-tion and quantitative cross-sectional metrics are used to char-acterize secondary-flow evolution. The configuration with the smallest pitch and curvature ratios consistently exhibits the largest helicity imbalance between counter-rotating vortices while maintaining the lowest turbulent kinetic energy and intermittency across all cross-sections and Reynolds numbers, indicating an inverse relationship between vortex asymmetry and turbulence intensity under transitional conditions. Reynolds-number sensitivity is also shown to depend strongly on the turbulence modeling approach: while fully turbulent SST predictions remain largely Reynolds-number independent, the transitional formulation captures pronounced Reynolds-number effects in the entrance and mid-helix regions. These findings show that vessel geometry governs an inverse relationship between secondary-flow asymmetry and turbulence, which can be used to identify critical regions of uneven mixing and localized wall interactions in physiological flow systems.
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Quantifying small-scale anisotropy in turbulent flows
The verification of whether small-scale turbulence is isotropic remains a grand challenge. The difficulty arises because the presence of small-scale anisotropy is tied to the dissipation tensor, whose components require the full three-dimensional information of the flow field in both high spatial and temporal resolution, a condition rarely satisfied in turbulence experiments, especially during field scale measurement of atmospheric turbulence. To circumvent this issue, an intermittency-anisotropy framework is proposed through which we successfully extract the features of small-scale anisotropy from single-point measurements of turbulent time series by exploiting the properties of small-scale intermittency. Specifically, this framework quantifies anisotropy by studying the contrasting effects of burstlike activities on the scalewise production of turbulence kinetic energy between the horizontal and vertical directions. The veracity of this approach is tested by applying it over a range of datasets covering an unprecedented range in the Reynolds numbers (Re≈10^3–10^6), sampling frequencies (10 kHz to 10 Hz), surface conditions (aerodynamically smooth surfaces to typical grasslands to forest canopies), and flow types (channel flows, boundary-layer flows, atmospheric flows, and flows over forest canopies). For these diverse datasets, the findings indicate that the effects of small-scale anisotropy persists up to the integral scales of the streamwise velocity fluctuations and there exists a universal relationship to predict this anisotropy from the two-component state of the Reynolds stress tensor. This relationship is important towards the development of next-generation closure models of wall turbulence by incorporating the effects of anisotropy at smaller scales of the flow.
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- PAR ID:
- 10523934
- Publisher / Repository:
- APS
- Date Published:
- Journal Name:
- Physical Review Fluids
- Volume:
- 9
- Issue:
- 7
- ISSN:
- 2469-990X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1103/PhysRevFluids.9.074604
