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

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.

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

2017 ◽  
Author(s):  
Caleb Stanley ◽  
Georgios Etsias ◽  
Steven Dabelow ◽  
Dimitrios Dermisis ◽  
Ning Zhang
Keyword(s):  
Turbulent Flow ◽  
Laboratory Experiments ◽  
Flow Characteristics ◽  
Mean Flow ◽  
Turbulent Structures ◽  
3 Dimensional ◽  
The Mean ◽  
Design Simplicity ◽  
Study Laboratory ◽  
Geometric Designs

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.

Experimental Study on the Near Wake Behind Two Staggered Cylinders of Unequal Diameters

2012 ◽  
Author(s):  
Yangyang Gao ◽  
Xikun Wang ◽  
Soon Keat Tan
Keyword(s):  
Reynolds Stress ◽  
Incident Angle ◽  
Reynolds Shear Stress ◽  
Flow Characteristics ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Near Wake ◽  
Particle Image Velocimetry Technique ◽  
Image Velocimetry ◽  
Spacing Ratio

The wake structure behind two staggered circular cylinders with unequal diameters was investigated experimentally using the particle image velocimetry technique (PIV). This investigation was focused on the variations of flow patterns in terms of incident angle at Reynolds number Re = 1200. Comparisons of the time-averaged flow field of two staggered cylinders with unequal diameters at different angles were made to elucidate the mean flow characteristics. The characteristics of Reynolds shear stress contours at different incident angles and spacing ratios were also investigated. The results showed that with increasing of incident angle, the scale of Reynolds stress contours behind the upstream cylinder becomes larger, as well as the effect of spacing ratio on Reynolds stress contours.

LDV Measurements of the Flow Field in the Nozzle Region of a Confined Double Annular Burner

2001 ◽  
Vol 123 (2) ◽  
pp. 228-236 ◽  
Author(s):  
Francois Schmitt ◽  
Birinchi K. Hazarika ◽  
Charles Hirsch
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Turbulence Intensity ◽  
Meridional Plane ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Fine Grid ◽  
Contour Plots ◽  
The Mean ◽  
Grid Points

A database for the complex turbulent flow of a confined double annular burner in cold conditions is presented here. In the region close to the exit of the annular nozzles LDV measurements at 5515 grid points in the meridional plane were conducted. At each measurement position, validated data for 3000–16,000 particles were recorded, and the mean axial and radial velocities, axial and radial turbulence intensity and Reynolds stresses were computed. The resulting mean flow field is axisymmetric within an uncertainty of 2 percent. The contour plots of turbulent quantities on the fine grid, as well as the streamlines based on the mean flow field, are presented for the flow.

Fluid flow analysis of a turbulent offset jet impinging on a wavy wall surface

2019 ◽  
Vol 234 (2) ◽  
pp. 544-563 ◽  
Author(s):  
Tej Pratap Singh ◽  
Amitesh Kumar ◽  
Ashok Kumar Satapathy
Keyword(s):  
Shear Stress ◽  
Fluid Flow ◽  
Reynolds Shear Stress ◽  
Flow Analysis ◽  
Flow Characteristics ◽  
Wavy Wall ◽  
Wall Surface ◽  
Central Difference ◽  
Turbulent Characteristics ◽  
Offset Jet

The fluid flow characteristics of a turbulent offset jet impinging on a wavy wall surface has been investigated numerically. Two-dimensional Reynolds-averaged Navier–Stokes (RANS) equations are solved by the finite volume method. In the governing differential equations, the convective and diffusive terms are discretized by the power law upwind scheme and second-order central difference, respectively. The semi-implicit method for pressure linked equation algorithm is utilized to link the pressure to the velocity. The offset ratio is set to 7.0 and the Reynolds number is fixed to 15,000. The width of the jet is taken as the characteristic length. The amplitude of the wavy wall surface is varied from 0.1 to 0.7 with an interval of 0.1 and the number of cycle is fixed to 10. The results of fluid flow and turbulent characteristics of the offset jet are presented in the form of contours of streamline, velocity vector, turbulent kinetic energy, dissipation rate, pressure, and Reynolds shear stress. The variation in integral constant of momentum flux, wall shear stress, and pressure along the wall is presented and also compared. The decay in the maximum streamwise velocity in the downstream direction and jet half-width along the streamwise direction are also presented and discussed. The wavy surface introduces some remarkable features, which are not present in a normal plane wall case. These features have been discussed in detail.

PIV Study of Turbulent Flow in Asymmetric Converging and Diverging Channels

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
M. K. Shah ◽  
M. F. Tachie
Keyword(s):  
Turbulent Flow ◽  
Pressure Gradient ◽  
Turbulent Flows ◽  
Reynolds Shear Stress ◽  
Lower Boundary ◽  
Adverse Pressure Gradient ◽  
Pressure Gradients ◽  
Mean Flow ◽  
The Mean ◽  
Converging And Diverging Channels

An experimental investigation of turbulent flow subjected to variable adverse and favorable pressure gradients in two-dimensional asymmetric channels is reported. The floors of the diverging and converging channels were flat while the roofs of the channels were curved. Adverse pressure gradient flows at Reh=27,050 and 12,450 and favorable pressure gradient flow at Reh=19,280 were studied. A particle image velocimetry was used to conduct detailed measurements at several planes upstream, within the variable section and within the downstream sections. The boundary layer parameters were obtained in the upper and lower boundary layers to study the effects of pressure gradients on the development of the mean flow on the floor and roof of the channels. The profiles of the mean velocities, turbulence intensities, Reynolds shear stress, mixing length, eddy viscosity, and turbulence production were also obtained to document the salient features of pressure gradient turbulent flows in asymmetric converging and diverging channels.

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

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

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

Water ◽  
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.

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.

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

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.

scholarly journals Measurement of turbulent flow in a narrow open channel

2016 ◽  
Vol 64 (3) ◽  
pp. 273-280 ◽  
Author(s):  
Sankar Sarkar
Keyword(s):  
Turbulent Flow ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Maximum Velocity ◽  
Turbulent Characteristics ◽  
Stress Changes ◽  
Rough Bed ◽  
Median Diameter ◽  
Rough Beds ◽  
Bed Material

Abstract The paper presents the experimental results of turbulent flow over hydraulically smooth and rough beds. Experiments were conducted in a rectangular flume under the aspect ratio b/h = 2 (b = width of the channel 0.5 m, and h = flow depth 0.25 m) for both the bed conditions. For the hydraulically rough bed, the roughness was created by using 3/8″ commercially available angular crushed stone chips; whereas sand of a median diameter d50 = 1.9 mm was used as the bed material for hydraulically smooth bed. The three-dimensional velocity components were captured by using a Vectrino (an acoustic Doppler velocimeter). The study focuses mainly on the turbulent characteristics within the dip that were observed towards the sidewall (corner) of the channel where the maximum velocity occurs below the free-surface. It was also observed that the nondimensional Reynolds shear stress changes its sign from positive to negative within the dip. The quadrant plots for the turbulent bursting shows that the signs of all the bursting events change within the dip. Below the dip, the probability of the occurrence of sweeps and ejections are more than that of inward and outward interactions. On the other hand, within the dip, the probability of the occurrence of the outward and inward interactions is more than that of sweeps and ejections.

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