scholarly journals Effect of T-shaped spur dike length on mean flow characteristics along a 180-degree sharp bend

2021 ◽  
Vol 69 (1) ◽  
pp. 98-107
Author(s):  
Maryam Akbari ◽  
Mohammad Vaghefi ◽  
Yee-Meng Chiew
Keyword(s):  
Secondary Flow ◽  
Flow Pattern ◽  
Maximum Velocity ◽  
Primary Objective ◽  
Mean Flow ◽  
Complex Flow ◽  
Flow Strength ◽  
Spur Dike ◽  
Sharp Bend ◽  
The Mean

AbstractAn open channel flume with a central 180-degree bend with a rigid bed is designed to obtain a better understanding of the complex flow pattern around a T-shaped spur dike located in a sharp bend. The 3-dimensional velocities are measured by using an acoustic Doppler velocimetry under clear-water conditions. This study’s primary objective is to compare variations of the mean flow pattern along a 180-degree bend with a variety of T-shaped spur dike lengths. In order to do so, parameters such as streamlines, the maximum velocity distribution, and the secondary flow strength under the influence of three T-shaped spur dike lengths will be analyzed and then compared with the case where no spur dikes are implemented. The results show that with the spur dike placed at the bend apex, the mean secondary flow strength at that range increases by approximately 2.5 times. In addition, a 67% increase in the length of the wing and web of the spur dike leads to a 27% growth in the mean secondary flow strength along the bend.

scholarly journals Influence of Rigid Emerged Vegetation in a Channel Bend on Bed Topography and Flow Velocity Field: Laboratory Experiments

Water ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 118 ◽  
Author(s):  
Hossein Hamidifar ◽  
Alireza Keshavarzi ◽  
Paweł M. Rowiński
Keyword(s):  
Laboratory Experiments ◽  
Flow Characteristics ◽  
Maximum Velocity ◽  
Flow Conditions ◽  
Mean Flow ◽  
Bed Topography ◽  
Channel Bend ◽  
Bed Erosion ◽  
Flow Hydraulics ◽  
The Mean

Trees have been used extensively by river managers for improving the river environment and ecology. The link between flow hydraulics, bed topography, habitat availability, and organic matters is influenced by vegetation. In this study, the effect of trees on the mean flow, bed topography, and bed shear stress were tested under different flow conditions. It was found that each configuration of trees produced particular flow characteristics and bed topography patterns. The SR (single row of trees) model appeared to deflect the maximum velocity downstream of the bend apex toward the inner bank, while leading the velocity to be more uniformly distributed throughout the bend. The entrainment of sediment particles occurred toward the area with higher values of turbulent kinetic energy (TKE). The results showed that both SR and DR (double rows of trees) models are effective in relieving bed erosion in sharp ingoing bends. The volume of the scoured bed was reduced up to 70.4% for tests with trees. This study shows the effectiveness of the SR model in reducing the maximum erosion depth.

A Mapped Finite Difference Study of Noise Propagation in Nonuniform Ducts With Mean Flow

1987 ◽  
Vol 109 (4) ◽  
pp. 372-380 ◽  
Author(s):  
Peter E. Raad ◽  
James W. White
Keyword(s):  
Fluid Flow ◽  
Finite Difference ◽  
Primary Objective ◽  
Mean Flow ◽  
Noise Propagation ◽  
Mapping Procedure ◽  
Soft Wall ◽  
Implicit Finite Difference ◽  
The Mean ◽  
Fully Coupled

The primary objective of this work is to study noise propagation in acoustically lined variable area ducts with mean fluid flow. The method of study is numerical in nature and involves a body-fitted grid mapping procedure in conjunction with a factored-implicit finite difference technique. The mean fluid flow model used is two-dimensional, inviscid, irrotational, incompressible, and nonheat conducting. Fully-coupled solutions of the linearized gas dynamic equations are obtained for both positive and negative Mach numbers as well as for hard and soft wall conditions. The factored-implicit finite difference technqiue used did give rise to short wavelength perturbations, but these were dampened by the introduction of higher order artificial dissipation terms into the scheme. Results compared favorably with available numerical and experimental data.

Turbulent planar wakes under pressure gradient conditions

2017 ◽  
Vol 830 ◽  
Author(s):  
Sina Shamsoddin ◽  
Fernando Porté-Agel
Keyword(s):  
Pressure Gradient ◽  
Maximum Velocity ◽  
Wind Farms ◽  
Parameter Tuning ◽  
Momentum Equation ◽  
Mean Flow ◽  
Self Similarity ◽  
High Lift ◽  
Velocity Deficit ◽  
The Mean

Accurate prediction of the spatial evolution of turbulent wake flows under pressure gradient conditions is required in some engineering applications such as the design of high-lift devices and wind farms over topography. In this paper, we aim to develop an analytical model to predict the evolution of a turbulent planar wake under an arbitrary pressure gradient condition. The model is based on the cross-stream integration of the streamwise momentum equation and uses the self-similarity of the mean flow. We have also made an experimentally supported assumption that the ratio of the maximum velocity deficit to the wake width is independent of the imposed pressure gradient. The asymptotic response of the wake to the pressure gradient is also investigated. After its derivation, the model is successfully validated against experimental data by comparing the evolution of the wake width and maximum velocity deficit. The inputs of the model are the imposed pressure gradient and the wake width under zero pressure gradient. The model does not require any parameter tuning and is deemed to be practical, computationally fast, accurate enough, and therefore useful for the scientific and engineering communities.

Turbulence Modeling for Secondary Flow Prediction in a Turbine Cascade

1992 ◽  
Vol 114 (3) ◽  
pp. 590-598 ◽  
Author(s):  
J. G. E. Cleak ◽  
D. G. Gregory-Smith
Keyword(s):  
Secondary Flow ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Equation Model ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Mixing Length ◽  
Turbine Cascade ◽  
Mean Flow ◽  
Complex Flow

Predictions of secondary flow in an axial turbine cascade have been made using three different turbulence models: mixing length, a one-equation model and a k–ε mixing length hybrid model. The results are compared with results from detailed measurements, not only by looking at mean flow velocities and total pressure loss, but also by assessing how well turbulence quantities are predicted. It is found that the turbulence model can have a big influence on the mean flow results, with the mixing length model giving generally the best mean flow. None of the models give good predictions of the turbulent shear stresses in the vortex region, although the k–ε model gives quite good turbulent kinetic energy values. The one-equation model is the only one to contain a transition criterion. The importance of such a criterion is illustrated, but the present one needs development to give reliable predictions in the complex flow within a blade passage.

Mean flow structure in meanders of the Squamish River, British Columbia

1978 ◽  
Vol 15 (11) ◽  
pp. 1833-1849 ◽  
Author(s):  
Edward J. Hickin
Keyword(s):  
Velocity Field ◽  
Secondary Flow ◽  
Flow Structure ◽  
Maximum Velocity ◽  
Shear Stresses ◽  
Channel Migration ◽  
Mean Flow ◽  
Channel Form ◽  
Collapse Model ◽  
Primary Velocity

The primary velocity field and pattern of secondary flow are described for nine consecutive bends of the Squamish River in southwest British Columbia.The velocity field largely can be explained in terms of variation in channel form, advective acceleration responses, and water transfers by secondary flow.The pattern of secondary flow accords with the general model of spiral flow in meanders. Divergences from this ideal pattern can be explained by bend–flow interaction induced by the variable planform geometry of the channel.The strength of secondary circulation increases rapidly as the ratio of the radius of bend curvature to channel width (rm/w) declines from 4.0 to the data minimum of 1.41. There is no discontinuity phenomenon in the flow structure over the measured range of rm/w; the Bagnold separation–collapse model does not apply to the Squamish River.As rm/w declines to values less than 3.0, the maximum velocity filament shifts from the concave to the convex bank zone. The resulting high shear stresses over the point bar and declining shear stresses at the concave bank markedly reduce the channel migration rate.Separation zones developed at the concave bank of tightly curved bends provide the mechanism for completely halting (and indeed reversing) the process of channel migration.

scholarly journals Large-eddy simulation of three-dimensional dunes in a steady, unidirectional flow. Part 1. Turbulence statistics

2013 ◽  
Vol 721 ◽  
pp. 454-483 ◽  
Author(s):  
Mohammad Omidyeganeh ◽  
Ugo Piomelli
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Wall Stress ◽  
Two Dimensional ◽  
Streamwise Vortices ◽  
Mean Flow ◽  
Form Drag ◽  
Separated Shear Layer ◽  
Large Eddy ◽  
The Mean

AbstractWe performed large-eddy simulations of flow over a series of three-dimensional dunes at laboratory scale (Reynolds number based on the average channel depth and streamwise velocity was 18 900) using the Lagrangian dynamic eddy-viscosity subgrid-scale model. The bedform three-dimensionality was imposed by shifting a standard two-dimensional dune shape in the streamwise direction according to a sine wave. The statistics of the flow are discussed in 10 cases with in-phase and staggered crestlines, different deformation amplitudes and wavelengths. The results are validated qualitatively against experiments. The three-dimensional separation of flow at the crestline alters the distribution of wall pressure, which in turn may cause secondary flow across the stream, which directs low-momentum fluid, near the bed, toward the lobe (the most downstream point on the crestline) and high-momentum fluid, near the top surface, toward the saddle (the most upstream point on the crestline). The mean flow is characterized by a pair of counter-rotating streamwise vortices, with core radius of the order of the flow depth. However, for wavelengths smaller than the flow depth, the secondary flow exists only near the bed and the mean flow away from the bed resembles the two-dimensional case. Staggering the crestlines alters the secondary motion; the fastest flow occurs between the lobe and the saddle planes, and two pairs of streamwise vortices appear (a strong one, centred about the lobe, and a weaker one, coming from the previous dune, centred around the saddle). The distribution of the wall stress and the focal points of separation and attachment on the bed are discussed. The sensitivity of the average reattachment length, depends on the induced secondary flow, the streamwise and spanwise components of the channel resistance (the skin friction and the form drag), and the contribution of the form drag to the total resistance are also studied. Three-dimensionality of the bed increases the drag in the channel; the form drag contributes more than in the two-dimensional case to the resistance, except for the staggered-crest case. Turbulent-kinetic energy is increased in the separated shear layer by the introduction of three-dimensionality, but its value normalized by the plane-averaged wall stress is lower than in the corresponding two-dimensional dunes. The upward flow on the stoss side and higher deceleration of flow on the lee side over the lobe plane lift and broaden the separated shear layer, respectively, affecting the turbulent kinetic energy.

Mean characteristics of asymmetric flows: application to flow below ice jams

1981 ◽  
Vol 8 (3) ◽  
pp. 342-350 ◽  
Author(s):  
Mustafa Gogus ◽  
Jean-Claude Tatinclaux
Keyword(s):  
Flow Characteristics ◽  
Maximum Velocity ◽  
Mean Flow ◽  
Ice Jams ◽  
River Bed ◽  
Friction Factors ◽  
Initial Stage ◽  
The Mean ◽  
Asymmetric Flows ◽  
Semi Empirical

Results are presented of a laboratory study on the effect of the introduction of a floating cover at the surface of a channel on the mean flow velocity distribution in the then “closed conduit” flow, and on the bed friction factor. It is pointed out that, contrary to common assumption, the location of the maximum velocity is not a point of zero shear stress when the bed and the cover have different roughness characteristics. Semi-empirical and graphical relationships between bed and cover friction factors, relative location of maximum velocity, and bed and cover roughness sizes are presented which are sufficient to estimate the mean flow characteristics below the cover for a given flow discharge and flow depth below the cover. The results may be of importance in the calculation of the characteristics of river ice jams in their initial stage of formation when their roughness is significantly greater than that of the river bed.

scholarly journals Turbulence Modelling for Secondary Flow Prediction in a Turbine Cascade

1991 ◽  
Author(s):  
J. G. E. Cleak ◽  
D. G. Gregory-Smith
Keyword(s):  
Secondary Flow ◽  
Turbulence Models ◽  
Equation Model ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Mixing Length ◽  
Turbine Cascade ◽  
Mean Flow ◽  
Complex Flow ◽  
The One

Predictions of secondary flow in an axial turbine cascade have been made using three different turbulence models; mixing length, a one equation model and a k-epsilon/mixing length hybrid model. The results are compared with results from detailed measurements, not only by looking at mean flow velocities and total pressure loss, but also by assessing how well turbulence quantities are predicted. It is found that the turbulence model can have a big influence on the mean flow results, with the mixing length model giving generally the best mean flow. None of the models give good predictions of the turbulent shear stresses in the vortex region, although the k-epsilon model gives quite good turbulent kinetic energy values. The one equation model is the only one to contain a transition criterion. The importance of such a criterion is illustrated, but the present one needs development to give reliable predictions in the complex flow within a blade passage.

On strongly nonlinear gravity waves in a vertically sheared atmosphere

2021 ◽  
Author(s):  
Georg Sebastian Voelker ◽  
Mark Schlutow
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Internal Gravity Wave ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Mean Flow ◽  
Flow Strength ◽  
Weakly Nonlinear ◽  
Strongly Nonlinear ◽  
The Mean

<p>Internal gravity waves are a well-known mechanism of energy redistribution in stratified fluids such as the atmosphere. They may propagate from their generation region, typically in the Troposphere, up to high altitudes. During their lifetime internal waves couple to the atmospheric background through various processes. Among the most important interactions are the exertion of wave drag on the horizontal mean-flow, the heat generation upon wave breaking, or the mixing of atmospheric tracers such as aerosols or greenhouse gases.</p><p>Many of the known internal gravity wave properties and interactions are covered by linear or weakly nonlinear theories. However, for the consideration of some of the crucial effects, like a reciprocal wave-mean-flow interaction including the exertion of wave drag on the mean-flow, strongly nonlinear systems are required. That is, there is no assumption on the wave amplitude relative to the mean-flow strength such that they may be of the same order.</p><p>Here, we exploit a strongly nonlinear Boussinesq theory to analyze the stability of a stationary internal gravity wave which is refracted at the vertical edge of a horizontal jet. Thereby we assume that the incident wave is horizontally periodic, non-hydrostatic, and vertically modulated. Performing a linear stability analysis in the vicinity of the jet edge we find necessary and sufficient criteria for instabilities to grow. In particular, the refracted wave becomes unstable if its incident amplitude is large enough and both mean-flow horizontal winds, below and above the edge of the jet, do not exceed particular upper bounds.</p>

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