Experimental and Numerical Investigations of the 3-D Turbulent Flow Characteristics Around Submerged Permeable Breakwaters

Submerged breakwaters are favored for their design simplicity in projects intended to dissipate wave energy and reduce erosion on coastlines. Despite their popularity, the effects that submerged breakwaters exhibit on the surrounding hydrodynamics are not clearly understood, mainly due to the flow complexity generated from 3-dimensional turbulent structures in the vicinity of the breakwaters that affect the mean flow characteristics and the transport of sediment. The objective of this study was to evaluate the effects that various geometric designs of submerged permeable breakwaters have on the turbulent flow characteristics. To meet the objective of this study, laboratory experiments were performed in a water-recirculating flume, in which the 3-dimensional velocity field was recorded in the vicinity of scaled breakwater models. Breakwaters that were tested include non-permeable, three-hole, and ten-hole models. The experimental data obtained was compared to results obtained from numerical simulations. Results demonstrated that permeable breakwaters exhibit more vertical turbulent strength than their non-permeable counterparts. It was also discovered that three-hole breakwater models produce higher turbulent fluctuations than that of the ten-hole breakwaters. The results from this study will be used eventually to enhance the performance of restoration projects in coastal areas in Louisiana.

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

Water ◽

10.3390/w12010118 ◽

2019 ◽

Vol 12 (1) ◽

pp. 118 ◽

Cited By ~ 3

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.

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PIV Investigation of Turbulent Flow Over a Wavy-Wall in a Horizontal Channel

Volume 2, Fora: Advances in Fluids Engineering Education; Cavitation and Multiphase Flow; Fluid Measurements and Instrumentation ◽

10.1115/fedsm2016-7715 ◽

2016 ◽

Author(s):

Vinicius Martins Segunda ◽

Mark Tachie ◽

Scott Ormiston

Keyword(s):

Turbulent Flow ◽

Reynolds Shear Stress ◽

Flow Characteristics ◽

Wavy Wall ◽

Mean Flow ◽

Particle Image Velocimetry Technique ◽

Turbulent Characteristics ◽

Developing Region ◽

Contour Plots ◽

The Mean

Experimental investigation of turbulent flow in a channel with flat upper wall and wavy lower wall using a particle image velocimetry technique is presented. The mean flow and turbulent characteristics in both the developing region and fully periodic region over the wavy wall were examined. It was observed that the flow characteristics become fully periodic after the eighth wave. The results also showed that the separation and reattachment points within the developing region and fully periodic region are similar. Detailed investigation of the flow field in the fully periodic region was examined using contour plots and one-dimensional profiles of the mean velocities, mean spanwise vorticity, streamwise and wall-normal turbulence intensities and Reynolds shear stress.

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Experimental study on the mean flow characteristics of a supersonic multiple jet configuration

Aerospace Science and Technology ◽

10.1016/j.ast.2020.106377 ◽

2021 ◽

Vol 108 ◽

pp. 106377

Author(s):

Mohammed Faheem ◽

Aqib Khan ◽

Rakesh Kumar ◽

Sher Afghan Khan ◽

Waqar Asrar ◽

...

Keyword(s):

Experimental Study ◽

Flow Characteristics ◽

Mean Flow ◽

The Mean

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Interactions between Tandem Cylinders in an Open Channel: Impact on Mean and Turbulent Flow Characteristics

Water ◽

10.3390/w13131718 ◽

2021 ◽

Vol 13 (13) ◽

pp. 1718

Author(s):

Hasan Zobeyer ◽

Abul B. M. Baki ◽

Saika Nowshin Nowrin

Keyword(s):

Turbulent Flow ◽

Open Channel ◽

Recirculation Zone ◽

Three Dimensional ◽

Flow Characteristics ◽

Flow Recirculation ◽

Tandem Cylinders ◽

Flow Development ◽

The Mean ◽

Recirculation Length

The flow hydrodynamics around a single cylinder differ significantly from the flow fields around two cylinders in a tandem or side-by-side arrangement. In this study, the experimental results on the mean and turbulence characteristics of flow generated by a pair of cylinders placed in tandem in an open-channel flume are presented. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components. This study investigated the effect of cylinder spacing at 3D, 6D, and 9D (center to center) distances on the mean and turbulent flow profiles and the distribution of near-bed shear stress behind the tandem cylinders in the plane of symmetry, where D is the cylinder diameter. The results revealed that the downstream cylinder influenced the flow development between cylinders (i.e., midstream) with 3D, 6D, and 9D spacing. However, the downstream cylinder controlled the flow recirculation length midstream for the 3D distance and showed zero interruption in the 6D and 9D distances. The peak of the turbulent metrics generally occurred near the end of the recirculation zone in all scenarios.

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Critical layers in accelerating two-layer flows

Journal of Fluid Mechanics ◽

10.1017/s0022112088003313 ◽

1988 ◽

Vol 197 ◽

pp. 429-451 ◽

Cited By ~ 6

Author(s):

Donald B. Altman

Keyword(s):

Laboratory Experiments ◽

Single Mode ◽

Shear Instability ◽

Mean Flow ◽

Velocity Measurements ◽

Interfacial Wave ◽

Flow Acceleration ◽

Critical Layers ◽

The Mean ◽

Processing Software

A series of laboratory experiments on accelerating two-layer shear flows over topography is described. The mean flow reverses at the interface of the layers, forcing a critical layer to occur there. It is found that for a sufficiently thin interface, a slowly growing recirculating region, the ‘acceleration rotor’, develops on the interfacial wave at mean-flow Richardson numbers of O(0.5). This, in turn, can induce a secondary dynamical shear instability on the trailing edge of the wave. A single-mode, linear, two-layer numerical model reproduces many features of the acceleration rotor if mean-flow acceleration and bottom forcing are included. Velocity measurements are obtained from photographs using image processing software developed for the automated reading of particle-streak photographs. Typical results are shown.

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Self-consistent triple decomposition of the turbulent flow over a backward-facing step under finite amplitude harmonic forcing

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2019.0018 ◽

2019 ◽

Vol 475 (2225) ◽

pp. 20190018

Author(s):

E. Yim ◽

P. Meliga ◽

F. Gallaire

Keyword(s):

Turbulent Flow ◽

Finite Amplitude ◽

Navier Stokes ◽

Reynolds Stresses ◽

Mean Flow ◽

Backward Facing Step ◽

Eddy Viscosity Model ◽

Coherent Interaction ◽

Self Consistent ◽

The Mean

We investigate the saturation of harmonically forced disturbances in the turbulent flow over a backward-facing step subjected to a finite amplitude forcing. The analysis relies on a triple decomposition of the unsteady flow into mean, coherent and incoherent components. The coherent–incoherent interaction is lumped into a Reynolds averaged Navier–Stokes (RANS) eddy viscosity model, and the mean–coherent interaction is analysed via a semi-linear resolvent analysis building on the laminar approach by Mantič-Lugo & Gallaire (2016 J. Fluid Mech. 793 , 777–797. ( doi:10.1017/jfm.2016.109 )). This provides a self-consistent modelling of the interaction between all three components, in the sense that the coherent perturbation structures selected by the resolvent analysis are those whose Reynolds stresses force the mean flow in such a way that the mean flow generates exactly the aforementioned perturbations, while also accounting for the effect of the incoherent scale. The model does not require any input from numerical or experimental data, and accurately predicts the saturation of the forced coherent disturbances, as established from comparison to time-averages of unsteady RANS simulation data.

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A Continuous Prediction Method for Fully Developed Laminar, Transitional, and Turbulent Flows in Pipes

Journal of Applied Mechanics ◽

10.1115/1.3423552 ◽

1975 ◽

Vol 42 (1) ◽

pp. 51-54 ◽

Cited By ~ 2

Author(s):

N. W. Wilson ◽

R. S. Azad

Keyword(s):

Turbulent Flows ◽

Flow Characteristics ◽

Prediction Method ◽

Reynolds Numbers ◽

Mean Flow ◽

Number Range ◽

Circular Pipes ◽

The Mean ◽

Single Set ◽

Good Agreement

A single set of equations is developed to predict the mean flow characteristics in long circular pipes operating at laminar, transitional, and turbulent Reynolds numbers. Generally good agreement is obtained with available data in the Reynolds number range 100 < Re < 500,000.

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Measurements with a pulsed-wire and a hot-wire anemometer in the highly turbulent wake of a normal flat plate

Journal of Fluid Mechanics ◽

10.1017/s0022112076002218 ◽

1976 ◽

Vol 77 (3) ◽

pp. 473-497 ◽

Cited By ~ 71

Author(s):

L. J. S. Bradbury

Keyword(s):

Turbulent Flow ◽

Flat Plate ◽

Flow Direction ◽

Operating Conditions ◽

Turbulent Intensity ◽

Hot Wire ◽

Mean Flow ◽

Mean Velocity ◽

The Mean ◽

Better Than

This paper describes an investigation into the response of both the pulsed-wire anemometer and the hot-wire anemometer in a highly turbulent flow. The first part of the paper is concerned with a theoretical study of some aspects of the response of these instruments in a highly turbulent flow. It is shown that, under normal operating conditions, the pulsed-wire anemometer should give mean velocity and longitudinal turbulent intensity estimates to an accuracy of better than 10% without any restriction on turbulence level. However, to attain this accuracy in measurements of turbulent intensities normal to the mean flow direction, there is a lower limit on the turbulent intensity of about 50%. An analysis is then carried out of the behaviour of the hot-wire anemometer in a highly turbulent flow. It is found that the large errors that are known to develop are very sensitive to the precise structure of the turbulence, so that even qualitative use of hot-wire data in such flows is not feasible. Some brief comments on the possibility of improving the accuracy of the hot-wire anemometer are then given.The second half of the paper describes some comparative measurements in the highly turbulent flow immediately downstream of a normal flat plate. It is shown that, although it is not possible to interpret the hot-wire results on their own, it is possible to calculate the hot-wire response with a surprising degree of accuracy using the results from the pulsed-wire anemometer. This provides a rather indirect but none the less welcome check on the accuracy of the pulsed-wire results, which, in this very highly turbulent flow, have a certain interest in their own right.

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Coherent structures and dominant frequencies in a turbulent three-dimensional diffuser

Journal of Fluid Mechanics ◽

10.1017/jfm.2012.107 ◽

2012 ◽

Vol 699 ◽

pp. 320-351 ◽

Cited By ~ 14

Author(s):

Johan Malm ◽

Philipp Schlatter ◽

Dan S. Henningson

Keyword(s):

Coherent Structures ◽

Large Scale ◽

Three Dimensional ◽

Flow Characteristics ◽

Low Frequency ◽

Bulk Velocity ◽

Time Signal ◽

Mean Flow ◽

The Mean ◽

Dominant Frequencies

AbstractDominant frequencies and coherent structures are investigated in a turbulent, three-dimensional and separated diffuser flow at $\mathit{Re}= 10\hspace{0.167em} 000$ (based on bulk velocity and inflow-duct height), where mean flow characteristics were first studied experimentally by Cherry, Elkins and Eaton (Intl J. Heat Fluid Flow, vol. 29, 2008, pp. 803–811) and later numerically by Ohlsson et al. (J. Fluid Mech., vol. 650, 2010, pp. 307–318). Coherent structures are educed by proper orthogonal decomposition (POD) of the flow, which together with time probes located in the flow domain are used to extract frequency information. The present study shows that the flow contains multiple phenomena, well separated in frequency space. Dominant large-scale frequencies in a narrow band $\mathit{St}\equiv fh/ {u}_{b} \in [0. 0092, 0. 014] $ (where $h$ is the inflow-duct height and ${u}_{b} $ is the bulk velocity), yielding time periods ${T}^{\ensuremath{\ast} } = T{u}_{b} / h\in [70, 110] $, are deduced from the time signal probes in the upper separated part of the diffuser. The associated structures identified by the POD are large streaks arising from a sinusoidal oscillating motion in the diffuser. Their individual contributions to the total kinetic energy, dominated by the mean flow, are, however, small. The reason for the oscillating movement in this low-frequency range is concluded to be the confinement of the flow in this particular geometric set-up in combination with the high Reynolds number and the large separated zone on the top diffuser wall. Based on this analysis, it is shown that the bulk of the streamwise root mean square (r.m.s.) value arises due to large-scale motion, which in turn can explain the appearance of two or more peaks in the streamwise r.m.s. value. The weak secondary flow present in the inflow duct is shown to survive into the diffuser, where it experiences an imbalance with respect to the upper expanding corners, thereby giving rise to the asymmetry of the mean separated region in the diffuser.

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