In past experiments, simulations and theoretical analysis,
rotation has been shown to dramatically effect the
characteristics of turbulent flows, such as causing the mean
velocity profile to appear laminar, leading to an overall
drag reduction, as well as affecting the Reynolds stress tensor.
The axially rotating pipe is an exemplary prototypical
model problem that exhibits these complex turbulent flow
physics. For this flow, the rotation of the pipe causes a region
of turbulence suppression which is particularly sensitive
to the rotation rate and Reynolds number. The physical
mechanisms causing turbulence suppression are currently
not well-understood, and a deeper understanding of these
mechanisms is of great value for many practical examples
involving swirling or rotating flows, such as swirl generators,
wing-tip vortices, axial compressors, hurricanes, etc.
In this work, Direct Numerical Simulations (DNS) of
rotating turbulent pipe flows are conducted at moderate
Reynolds numbers (Re=5300, 11,700, and 19,000) and rotation
numbers of N=0 to 3. The main objectives of this
work are to firstly quantify turbulence suppression for rotating
turbulent pipe flows at different Reynolds numbers as
well as study the effects of rotation on turbulence by analyzing
the characteristics of the Reynolds stress tensor and the
production and dissipation terms of the turbulence budgets.
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This content will become publicly available on July 1, 2025
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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- NSF-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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