PIV Investigation of an Open Channel Flow Over a Forward Facing Step

2007 ◽  
Author(s):  
M. K. Shah ◽  
M. F. Tachie
Keyword(s):  
Open Channel ◽  
Particle Image ◽  
Open Channel Flow ◽  
Reynolds Stresses ◽  
Velocity Measurements ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Freestream Velocity ◽  
Image Velocimetry ◽  
Forward Facing Step

The characteristics of an open channel turbulent flow over a forward facing step (FFS) are investigated in the present study. Two step heights, h = 6 and 9 mm, at Reynolds number, Reh, (based on the approach freestream velocity, U0, and step height, h) of 1900 and 2800 respectively were studied. Particle image velocimetry technique (PIV) was used to obtain detailed velocity measurements upstream of the FFS, in the reattachment region (x/h = 0, 1, 2) and in the redevelopment region (x/h = 4, 10, 15 and 50). The boundary layer integral parameters, mean velocity profiles and Reynolds stresses obtained in the reattachment and redevelopment region are used to document some of the salient features of the flow.

Low Reynolds Number Effect on Open Channel Flow Over a Rib

2014 ◽  
Author(s):  
Ebenezer E. Essel ◽  
Kathryn Atamanchuk ◽  
Samuel d’Auteuil ◽  
Mark F. Tachie
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Open Channel ◽  
Low Reynolds Number ◽  
Open Channel Flow ◽  
Recirculation Region ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Freestream Velocity ◽  
Low Reynolds

An experimental study was conducted to investigate low Reynolds number effects on open channel flow over a transverse square rib. Particle image velocimetry technique was used to perform detailed velocity measurement in the upstream and recirculation region of a square rib of height, h = 12 mm. The Reynolds number based on the freestream velocity and rib height, Reh = 1510, 2650 and 3950 and the ratio of the boundary layer thickness to step height, δ/h = 2.5 ± 0.2. The results showed that the reattachment length of Reh = 2650 and 3950 increased by 5.7% compared with corresponding value of Reh = 1510. The mean velocities were independent of Reynolds number in the recirculation region but at the reattachment point, Reh = 3650 reduced the streamwise mean velocity and enhanced the wall-normal mean velocity in the region adjacent to the wall. The turbulent kinetic energy beyond the center of the recirculation region increased with increasing Reynolds number.

Open Channel Flow Over Pairs of Rectangular and Streamlined Cylinders at Incidence

2009 ◽  
Author(s):  
M. Agelinchaab ◽  
J. M. Tsikata ◽  
M. F. Tachie ◽  
C. Katopodis
Keyword(s):  
Open Channel ◽  
Particle Image ◽  
Angle Of Incidence ◽  
Mean Flow ◽  
Velocity Measurements ◽  
Particle Image Velocimetry Technique ◽  
Image Velocimetry ◽  
The Mean ◽  
D 12 ◽  
Rectangular Cylinders

This paper reports an experimental investigation of the mean flow and turbulence characteristics around pairs of identical rectangular and streamlined cylinders in an open channel. The cylinder pairs were inclined at different angles of incidence angles relative to the streamwise direction of the approach flow. The rectangular cylinders and the 12% symmetric airfoils cylinders are made of transparent acrylic plates of length, L = 100 mm and maximum thickness, D = 12 mm. The centre-to-centre spacing between the cylinders was 51 mm. The blockage ratio produced by the cylinder pairs was 0.13 at zero angle of incidence. For each cylinder pair inclination, a high resolution particle image velocimetry technique was used to conduct detailed velocity measurements in the streamwise-spanwise plane. From these measurements, iso-contours and profiles of the mean velocities and turbulence statistics were obtained to study the effects of cylinder geometry and inclination on the flow around the cylinder pairs.

An Experimental Investigation of Turbulent Water Flow in Concentric Annulus Using Particle Image Velocimetry Technique

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
F. E. Rodriguez-Corredor ◽  
Majid Bizhani ◽  
Mohammad Ashrafuzzaman ◽  
Ergun Kuru
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Maximum Velocity ◽  
Viscous Sublayer ◽  
Reynolds Stresses ◽  
Flow Loop ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Number Range ◽  
Image Velocimetry

Fully developed turbulent flow of water through a horizontal flow loop with concentric annular geometry was investigated using high resolution particle image velocimetry (PIV). Reynolds number range varied from 17,700 to 66,900. Axial mean velocity profile was found to be following the universal wall law (u+ = y+) in the viscous sublayer (y+ < 10) and log law away from the wall (y+> 30). Radial position of zero shear stress and maximum velocity were found to be slightly different (2%). Root mean square values of velocity fluctuations velocity, Reynolds stresses, vorticity, and turbulent kinetic energy budget were also analyzed.

Turbulent Flow Over Cavities in an Asymmetric Diverging Channel

2007 ◽  
Author(s):  
M. K. Shah ◽  
M. F. Tachie
Keyword(s):  
Turbulent Flow ◽  
Reynolds Shear Stress ◽  
Adverse Pressure Gradient ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Freestream Velocity ◽  
Aspect Ratios ◽  
Image Velocimetry ◽  
Diverging Channel ◽  
Single Cavity

An experimental investigation of turbulent flow over a single cavity in an asymmetric diverging channel is presented. Cavities of two different aspect ratios, w/h = 1 and 4, of height h = 6 mm were studied. The Reynolds number based on the approach freestream velocity and cavity height was Reh = 5000. Particle image velocimetry technique (PIV) was used to conduct detailed velocity measurements upstream of the cavity, inside the cavity and as far downstream of the cavity as x/h = 50. Mean velocity, turbulent intensities and Reynolds shear stress were obtained to document the effect of the cavity on the flow in the presence of adverse pressure gradient.

Roughness Effect Downstream of Flow Over a Forward Facing Step

2014 ◽  
Author(s):  
Yaw Y. Afriyie ◽  
Ebenezer E. Essel ◽  
Eric W. Thacher ◽  
Mark F. Tachie
Keyword(s):  
Shear Stress ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Reynolds Shear Stress ◽  
Recirculation Region ◽  
Roughness Effects ◽  
Mean Velocity ◽  
Freestream Velocity ◽  
Image Velocimetry ◽  
Forward Facing Step

This paper presents results of an experimental research conducted to study roughness effects downstream of a forward facing step (FFS). A rough surface and a hydraulically smooth surface were used as a rough-FFS and a smooth-FFS, respectively. The upstream condition was kept smooth. Particle image velocimetry (PIV) technique was used for the velocity measurements. The Reynolds number based on the step height (h) and freestream velocity of the approach flow was kept constant at 8685. The results show that the mean reattachment length for the smooth-FFS (SM-SM) is 1.9h. Roughness reduced the peak values of the streamwise mean velocity, Reynolds shear stress and turbulent kinetic energy by 3%, 45% and 16.7% respectively in the recirculation region. In the early redevelopment region, roughness also reduced the peak values of turbulent kinetic energy and the Reynolds shear stress by 41% and 22% respectively.

PIV Study of Separated and Reattached Open Channel Flow Over Surface Mounted Blocks

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
Martin Agelinchaab ◽  
Mark F. Tachie
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Channel Flow ◽  
Open Channel ◽  
Open Channel Flow ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Mean Velocity ◽  
High Background ◽  
The Mean

A particle image velocimetry is used to study the mean and turbulent fields of separated and redeveloping flow over square, rectangular, and semicircular blocks fixed to the bottom wall of an open channel. The open channel flow is characterized by high background turbulence level, and the ratio of the upstream boundary layer thickness to block height is considerably higher than in prior experiments. The variation of the Reynolds stresses along the dividing streamlines is discussed within the context of vortex stretching, longitudinal strain rate, and wall damping. It appears that wall damping is a more dominant mechanism in the vicinity of reattachment. In the recirculation and reattachment regions, profiles of the mean velocity, turbulent quantities, and transport terms are used to document the salient features of block geometry on the flow. The flow characteristics in these regions strongly depend on block geometry. Downstream of reattachment, a new shear layer is formed, and the redevelopment of the shear layer toward the upstream open channel boundary layer is studied using the boundary layer parameters and Reynolds stresses. The results show that the mean flow rapidly redeveloped so that the Clauser parameter recovered to its upstream value at 90 step heights downstream of reattachment. However, the rate of development close to reattachment strongly depends on block geometry.

scholarly journals A new method for extracting spanwise vortex from 2D particle image velocimetry data in open-channel flow

2020 ◽  
Vol 68 (3) ◽  
pp. 242-248
Author(s):  
Peng Zhang ◽  
Shengfa Yang ◽  
Jiang Hu ◽  
Wenjie Li ◽  
Xuhui Fu ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Channel Flow ◽  
Vortex Structure ◽  
Open Channel ◽  
Particle Image ◽  
Open Channel Flow ◽  
New Method ◽  
Two Dimensional ◽  
Image Velocimetry ◽  
Spanwise Vortex

AbstractThe two-dimensional particle image velocimetry (PIV) data are inevitably contaminated by noise due to various imperfections in instrumentation or algorithm, based on which the well-established vortex identification methods often yield noise or incomplete vortex structure with a jagged boundary. To make up this deficiency, a novel method was proposed in this paper and the efficiency of the new method was demonstrated by its applications in extracting the two-dimensional spanwise vortex structures from 2D PIV data in open-channel flows. The new method takes up a single vortex structure by combining model matching and vorticity filtering, and successfully locates the vortex core and draws a streamlined vortex boundary. The new method shows promise as being more effective than commonly used schemes in open-channel flow applications.

Influence of Leading Edge and Spacing on the Near Wake of Cylinder Pairs

2009 ◽  
Author(s):  
Jonathan M. Tsikata ◽  
Samuel S. Paul ◽  
Chris Katopodis ◽  
Mark F. Tachie
Keyword(s):  
Open Channel ◽  
Particle Image ◽  
Leading Edge ◽  
Particle Image Velocimetry System ◽  
Turbulence Level ◽  
Near Wake ◽  
Mean Velocity ◽  
Rectangular Cylinder ◽  
Image Velocimetry ◽  
The Mean

An experimental study of the effects of the shape of rectangular cylinder leading edge and the cylinder spacing on the wake dynamics in an open channel turbulent flow is reported. The shapes of the rectangular cylinder leading edges were square and round with each having a square trailing edge. In each experiment, measurements were conducted for a pair of cylinders that have identical leading edge shape. Three centre-to-centre spacing (b = 30 mm, 50 mm and 75 mm) were investigated for each cylinder leading edge shape. Particle image velocimetry system was used to conduct measurements around each cylinder pair. The results show that the mean velocity and the turbulence level increases with decreasing spacing. The turbulence levels downstream of a cylinder pair with a round leading edge are relatively higher than the corresponding cylinder pair with square leading edge.

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