Modelling three-dimensional flow structures and patterns of boundary shear stress in a natural pool-riffle sequence

We investigate the early development of instabilities in the oscillatory viscous flow past cylinders with elliptic cross-sections using three-dimensional direct numerical simulations. This is a classical hydrodynamic problem for circular cylinders, but other configurations have received only marginal attention. Computed results for some different aspect ratios ${\it\Lambda}$ from 1 : 1 to 1 : 3, all with the major axis of the ellipse aligned in the main flow direction, show good qualitative agreement with Hall’s stability theory (J. Fluid Mech., vol. 146, 1984, pp. 347–367), which predicts a cusp-shaped curve for the onset of the primary instability. The three-dimensional flow structures for aspect ratios larger than 2 : 3 resemble those of a circular cylinder, whereas the elliptical cross-section with the lowest aspect ratio of 1 : 3 exhibits oblate rather than tubular three-dimensional flow structures as well as a pair of counter-rotating spanwise vortices which emerges near the tips of the ellipse. Contrary to a circular cylinder, instabilities for an elliptic cylinder with sufficiently high eccentricity emerge from four rather than two different locations in accordance with the Hall theory.

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Development of three-dimensional flow structures in the laminar-turbulent transition in a wide spherical layer

Doklady Physics ◽

10.1134/s1028335807050047 ◽

2007 ◽

Vol 52 (5) ◽

pp. 256-260 ◽

Cited By ~ 1

Author(s):

D. Yu. Zhilenko ◽

O. É. Krivonosova ◽

N. V. Nikitin

Keyword(s):

Three Dimensional ◽

Spherical Layer ◽

Flow Structures ◽

Three Dimensional Flow ◽

Dimensional Flow ◽

Turbulent Transition ◽

Laminar Turbulent Transition

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Use of Multidimensional Models to Investigate Boundary Shear Stress through Meandering River Channels

Water ◽

10.3390/w12123506 ◽

2020 ◽

Vol 12 (12) ◽

pp. 3506

Author(s):

Timothy J. Randle

Keyword(s):

Shear Stress ◽

Three Dimensional ◽

Field Studies ◽

River Channels ◽

Meandering River ◽

Boundary Shear ◽

Wide Range ◽

Channel Curvature ◽

Boundary Shear Stress ◽

Multidimensional Models

Three-dimensional hydraulics were simulated through a wide range of synthetically generated meandering river channels to determine how channel curvature and width would correlate with the maximum boundary shear stress. Multidimensional models were applied, similar to a computational flume to simulate a wide range of 72 meandering channels, developed from sine-generated curves. Cannel sinuosity ranged from 1.1 to 3.0 and included five consecutive meander bends. Longitudinal slopes of the various channels spanned four orders of magnitude, while bankfull discharges spanned three orders of magnitude. Using results from one-half of the simulation sets, an empirical correlation was found to predict the maximum boundary shear stress as a function of dimensionless ratios of channel curvature and width. The remaining simulation sets were used for verification. Multidimensional models were used to simulate channel hydraulics to efficiently investigate a wide range of channel sinuosity, width/depth ratios, bankfull discharges, and valley slopes. When simulating such a wide range of channel conditions, multidimensional models offer a more efficiency method of generating consistent datasets than either field studies or physical modeling. This paper demonstrates how multidimensional models can be used to identify important hydraulic relationships that are otherwise difficult to determine.

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