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.

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.

Particle Image Velocimetry Measurements of the Mean Flow Characteristics in a Bubble Plume

2007 ◽  
Vol 133 (6) ◽  
pp. 665-676 ◽  
Author(s):  
Dong-Guan Seol ◽  
Tirtharaj Bhaumik ◽  
Christian Bergmann ◽  
Scott A. Socolofsky
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Flow Characteristics ◽  
Bubble Plume ◽  
Mean Flow ◽  
Image Velocimetry ◽  
The Mean

Near-surface particle image velocimetry measurements in a transitionally rough-wall atmospheric boundary layer

2007 ◽  
Vol 580 ◽  
pp. 319-338 ◽  
Author(s):  
SCOTT C. MORRIS ◽  
SCOTT R. STOLPA ◽  
PAUL E. SLABOCH ◽  
JOSEPH C. KLEWICKI
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Environmental Science ◽  
Particle Image ◽  
Shear Velocity ◽  
Mean Flow ◽  
Mean Velocity ◽  
Near Surface ◽  
Image Velocimetry ◽  
The Mean

The Reynolds number dependence of the structure and statistics of wall-layer turbulence remains an open topic of research. This issue is considered in the present work using two-component planar particle image velocimetry (PIV) measurements acquired at the Surface Layer Turbulence and Environmental Science Test (SLTEST) facility in western Utah. The Reynolds number (δuτ/ν) was of the order 106. The surface was flat with an equivalent sand grain roughness k+ = 18. The domain of the measurements was 500 < yuτ/ν < 3000 in viscous units, 0.00081 < y/δ < 0.005 in outer units, with a streamwise extent of 6000ν/uτ. The mean velocity was fitted by a logarithmic equation with a von Kármán constant of 0.41. The profile of u′v′ indicated that the entire measurement domain was within a region of essentially constant stress, from which the wall shear velocity was estimated. The stochastic measurements discussed include mean and RMS profiles as well as two-point velocity correlations. Examination of the instantaneous vector maps indicated that approximately 60% of the realizations could be characterized as having a nearly uniform velocity. The remaining 40% of the images indicated two regions of nearly uniform momentum separated by a thin region of high shear. This shear layer was typically found to be inclined to the mean flow, with an average positive angle of 14.9°.

Multi-Blade Row Interactions in a Transonic Axial Compressor: Part I—Stator Particle Image Velocimetry (PIV) Investigation

2001 ◽  
Vol 124 (1) ◽  
pp. 10-18 ◽  
Author(s):  
A. J. Sanders ◽  
J. Papalia ◽  
S. Fleeter
Keyword(s):  
Particle Image Velocimetry ◽  
Slip Velocity ◽  
Particle Image ◽  
Operating Conditions ◽  
Mean Flow ◽  
Pressure Surface ◽  
Image Velocimetry ◽  
Blade Row ◽  
The Mean ◽  
Transonic Rotor

Multi-blade row interactions in an advanced design 1&1/2 stage axial-flow compressor are experimentally investigated at both subsonic and transonic rotor operating conditions using particle image velocimetry (PIV). Transonic rotor operation had a significant impact on the downstream stator unsteady flow field due to phenomena associated with the intra-stator transport of the chopped rotor wake segments. In the stator reference frame, the rotor wakes have a slip velocity relative to the mean flow that causes the low-momentum wake fluid to migrate across the vane passage and accumulate on the stator pressure surface as the chopped wake segments are transported downstream. This results in the generation of counterrotating vortices on each side of the chopped wake segment that convect downstream with the mean flow and act as an additional source of unsteadiness to the vane pressure surface. These interaction phenomena are not evident in the PIV data at the part-speed compressor operating condition due to the much lower velocity deficit and hence slip velocity associated with the subsonic rotor wakes.

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.

Size and effect on the mean flow of large-scale horizontal coherent structures in open-channel flows: an experimental studyThis paper is one of a selection of papers in this Special Issue in honour of Professor M. Selim Yalin (1925–2007).

2009 ◽  
Vol 36 (10) ◽  
pp. 1643-1655 ◽  
Author(s):  
Ana Maria Ferreira da Silva ◽  
Habib Ahmari
Keyword(s):  
Flow Velocity ◽  
Coherent Structures ◽  
Large Scale ◽  
Open Channel ◽  
Channel Flows ◽  
Flow Depth ◽  
Mean Flow ◽  
Velocity Measurements ◽  
Open Channel Flows ◽  
The Mean

The size of the largest horizontal coherent structures (HCSs) of turbulence in open-channel flows is investigated experimentally on the basis of three series of flow velocity measurements. These are further used to explore the dynamics and morphological consequences of HCSs. The flow velocity measurements were carried out in a 21 m long and 1 m wide channel, with a bed formed by sand with average grain size of 2 mm. The bed surface was flat. The turbulent and subcritical flow under investigation was uniform, with a flow depth of 4 cm. The bed slope of 0.0015 was such that, for the present flow depth, the bed shear stress acting on the bed was substantially below the threshold for initiation of motion, thus ensuring that the bed remained flat throughout the measurements. To the knowledge of the writers, this work is a first attempt to systematically investigate HCSs in open-channel flows. It should be viewed as an extension to the case of horizontal structures of work previously carried out by a number of authors on large-scale organized turbulence motion in open-channel flows, so far focusing exclusively on vertical coherent structures (VCSs). The horizontal burst length was found to be between five and seven times the flow width. A slight internal meandering of the flow caused by the superimposition of burst sequences on the mean flow was detectable. Both of these findings lend support to the longstanding belief expressed by many prominent researchers that the formation of large-scale river forms is directly related to the large-scale turbulence. In particular, the present measurements for the first time provide some direct evidence in support of hypotheses previously raised by Yalin and da Silva regarding the formation of alternate bars and meanders through the action of HCSs on the mean flow and the mobile bed and banks.

Multi-Blade Row Interactions in a Transonic Axial Compressor: Part I — Stator Particle Image Velocimetry (PIV) Investigation

2001 ◽  
Author(s):  
A. J. Sanders ◽  
J. Papalia ◽  
S. Fleeter
Keyword(s):  
Particle Image Velocimetry ◽  
Slip Velocity ◽  
Particle Image ◽  
Operating Conditions ◽  
Mean Flow ◽  
Pressure Surface ◽  
Image Velocimetry ◽  
Blade Row ◽  
The Mean ◽  
Transonic Rotor

Multi-blade row interactions in an advanced design 1&1/2 stage axial-flow compressor are experimentally investigated at both subsonic and transonic rotor operating conditions using particle image velocimetry (PIV). Transonic rotor operation had a significant impact on the downstream stator unsteady flow field due to phenomena associated with the intra-stator transport of the chopped rotor wake segments. In the stator reference frame, the rotor wakes have a slip velocity relative to the mean flow that causes the low momentum wake fluid to migrate across the vane passage and accumulate on the stator pressure surface as the chopped wake segments are transported downstream. This results in the generation of counter-rotating vortices on each side of the chopped wake segment that convect downstream with the mean flow and act as an additional source of unsteadiness to the vane pressure surface. These interaction phenomena are not evident in the PIV data at the part-speed compressor operating condition due to the much lower velocity deficit and hence slip velocity associated with the subsonic rotor wakes.

Analysis of local velocity gradients in rapid mixer using particle image velocimetry technique

2002 ◽  
Vol 2 (5-6) ◽  
pp. 47-55
Author(s):  
N.-S. Park ◽  
H. Park
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Velocity Fields ◽  
Local Velocity ◽  
Mixing Condition ◽  
Particle Image Velocimetry Technique ◽  
Velocity Gradients ◽  
Image Velocimetry ◽  
Current Design ◽  
G Value

Recognizing the significance of factual velocity fields in a rapid mixer, this study focuses on analyzing local velocity gradients in various mixer geometries with particle image velocimetry (PIV) and comparing the results of the analysis with the conventional G-value, for reviewing the roles of G-value in the current design and operation practices. The results of this study clearly show that many arguments and doubts are possible about the scientific correctness of G-value, and its current use. This is because the G-value attempts to represent the turbulent and complicated factual velocity field in a jar. Also, the results suggest that it is still a good index for representing some aspects of mixing condition, at least, mixing intensity. However, it cannot represent the distribution of velocity gradients in a jar, which is an important factor for mixing. This study as a result suggests developing another index for representing the distribution to be used with the G-value.

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