Particle Image Velocimetry for Air Flows Behind Permeable Cylinders

2007 ◽  
Author(s):  
Hirotaka Takeuchi ◽  
Yuji Tasaka ◽  
Yuichi Murai ◽  
Yasushi Takeda ◽  
Hideaki Tezuka ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Reverse Flow ◽  
Near Field ◽  
Water Mist ◽  
Circular Cylinders ◽  
Spatial Density ◽  
Turbulence Energy ◽  
Solid Cylinder ◽  
Image Velocimetry

Particle image velocimetry is applied to measurement of airflows around three types of permeable circular cylinders. The experimental model of the permeable cylinder is made of squared meshed sheet rolled in circle. Water mist smoke is used as air tracer, which is generated with dry ice in a chamber to produce fine spatial density fluctuation for guaranteeing the PIV quality. Since the flow involves fluctuation in a very wide wavenumber from the cylinder size to mesh-dependent eddies, calculating brightness spectrum quantitatively assesses the smoke image quality. The experiment is carried out in an open type wind tunnel. The following results are obtained when the measurement results are compared to those of a solid cylinder. 1: The flow just behind the cylinder has forward velocity due to the permeability while the solid cylinder has reverse flow in the wake. This feature relaxes near field excitation of Karman vortex shedding. 2: The reattachment point behind the cylinder displaces several times as the solid case. As a result of the above two phenomena, the peak potion of the turbulence energy appears in the far downstream region as the permeability of the cylinder increases.

scholarly journals Analysis of Turbulence Energy Spectrum by Using Particle Image Velocimetry

2014 ◽  
Vol 90 ◽  
pp. 320-326 ◽  
Author(s):  
Mohammad Mainul Hoque ◽  
Mayur J. Sathe ◽  
Jyeshtharaj B. Joshi ◽  
Geoffrey M. Evans
Keyword(s):  
Particle Image Velocimetry ◽  
Energy Spectrum ◽  
Particle Image ◽  
Turbulence Energy ◽  
Image Velocimetry

scholarly journals Particle image velocimetry measurements of induced separation at the leading edge of a plate

2016 ◽  
Vol 804 ◽  
pp. 278-297 ◽  
Author(s):  
J. P. J. Stevenson ◽  
K. P. Nolan ◽  
E. J. Walsh
Keyword(s):  
Particle Image Velocimetry ◽  
Shear Layer ◽  
Particle Image ◽  
Reverse Flow ◽  
Leading Edge ◽  
Quadrant Analysis ◽  
Bypass Transition ◽  
Reynolds Stresses ◽  
Free Stream Turbulence ◽  
Image Velocimetry

The free shear layer that separates from the leading edge of a round-nosed plate has been studied under conditions of low (background) and elevated (grid-generated) free stream turbulence (FST) using high-fidelity particle image velocimetry. Transition occurs after separation in each case, followed by reattachment to the flat surface of the plate downstream. A bubble of reverse flow is thereby formed. First, we find that, under elevated (7 %) FST, the time-mean bubble is almost threefold shorter due to an accelerated transition of the shear layer. Quadrant analysis of the Reynolds stresses reveals the presence of slender, highly coherent fluctuations amid the laminar part of the shear layer that are reminiscent of the boundary-layer streaks seen in bypass transition. Instability and the roll-up of vortices then follow near the crest of the shear layer. These vortices are also present under low FST and in both cases are found to make significant contributions to the production of Reynolds stress over the rear of the bubble. But their role in reattachment, whilst important, is not yet fully clear. Instantaneous flow fields from the low-FST case reveal that the bubble of reverse flow often breaks up into two or more parts, thereby complicating the overall reattachment process. We therefore suggest that the downstream end of the ‘separation isoline’ (the locus of zero absolute streamwise velocity that extends unbroken from the leading edge) be used to define the instantaneous reattachment point. A histogram of this point is found to be bimodal: the upstream peak coincides with the location of roll-up, whereas the downstream mode may suggest a ‘flapping’ motion.

scholarly journals Influence of span-wise coherence on the acoustic radiation in a cylinder wake

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Lars Siegel ◽  
Guosheng He ◽  
Arne Henning ◽  
Karen Mulleners
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Acoustic Radiation ◽  
Maximum Flow ◽  
Flow Speed ◽  
Circular Cylinders ◽  
Cylinder Wake ◽  
Sound Waves ◽  
Image Velocimetry ◽  
Nozzle Size

The aim of this study is to detect and visualise the influence of span-wise coherence on propagating sound waves emanating from a flow around circular cylinders with span-wise variations of the local radius. Synchronous particle image velocimetry (PIV) and microphone measurements are performed in a circular wind tunnel with a nozzle size of 0.4 m×0.4 m at a maximum flow speed of U∞ = 43m s−1 . The test section is surrounded by a full anechoic chamber of approximately 9 m×9 m×5 m.

Experimental Study of the Flow Structure in Fire-Induced Whirlwinds Downwind of a Fire Using Particle Image Velocimetry

2007 ◽  
Author(s):  
Masahiko Shinohara ◽  
Sanae Matsushima
Keyword(s):  
Experimental Study ◽  
Particle Image Velocimetry ◽  
Flow Visualization ◽  
Flow Structure ◽  
Particle Image ◽  
Reverse Flow ◽  
Tangential Velocity ◽  
Visualization Technique ◽  
Image Velocimetry ◽  
In Fire

The flow structure of fire-induced whirlwinds that occur downwind of a 90-cm-diameter methanol flame was investigated using particle image velocimetry (PIV) and a flow visualization technique. The PIV images showed that the whirlwinds occurred as counter-rotating vortices on both sides of a reverse flow downwind of the flame that moved toward it near the floor. The whirlwinds started near the floor and extended upwards, with a lower tangential velocity near the floor. The radius of the forced vortex region in the whirlwinds increased above a height of 11 cm. Whirlwinds downwind of the 90-cm-diameter methanol flame behaved the same as whirlwinds downwind of a 3-cm-diameter flame that were investigated in a previous study.

Separation-Bubble-Transition Measurements on a Low-Re Airfoil Using Particle Image Velocimetry

2005 ◽  
Author(s):  
B. R. McAuliffe ◽  
M. I. Yaras
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Large Scale ◽  
Particle Image ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Low Reynolds Number ◽  
Piv Measurements ◽  
Image Velocimetry ◽  
Low Reynolds

This paper presents experimental results on separation-bubble transition at low Reynolds number and low freestream turbulence, measured on an airfoil using particle image velocimetry (PIV). The two-dimensional PIV measurements have been performed over the suction surface of a low-Reynolds-number airfoil in a water tow-tank facility. Reynolds numbers, based on airfoil chord length and towing speed, of 40,000 and 65,000 have been examined at various angles of incidence, providing a range of streamwise pressure distributions and transitional separation-bubble geometries. The types of bubbles observed range from a short and thick bubble with separation near the leading edge of the airfoil, to a long and thin bubble with separation far downstream of the suction peak. The PIV measurements facilitate visualization of the vortex dynamics associated with separation-bubble transition. The growth of instability waves within the separated shear layer and eventual breakdown into turbulence is documented through the instantaneous vector fields. For all cases examined, large-scale vortex shedding and multiple reverse-flow zones are observed in the reattachment region. A technique for estimating the location of transition onset based on statistical turbulence quantities is presented, and comparisons are made to existing transition models.

Characterization of Pulsating Submerged Jet—A Particle Image Velocimetry Study

2015 ◽  
Vol 8 (1) ◽  
Author(s):  
Harekrishna Yadav ◽  
Atul Srivastava ◽  
Amit Agrawal
Keyword(s):  
Particle Image Velocimetry ◽  
Critical Frequency ◽  
Particle Image ◽  
Near Field ◽  
Reynolds Numbers ◽  
Pulsation Frequency ◽  
Potential Core ◽  
Image Velocimetry ◽  
Pulsating Jet ◽  
Surrounding Fluid

An experimental investigation has been performed to determine the flow characteristics of an axisymmetric submerged water jet with superimposed periodically oscillating flow. The objective of the study is to quantify in detail the near field of a pulsating jet using the particle image velocimetry (PIV) technique. The amplitude and frequency of oscillations are varied separately and the effect of each parameter is determined for a range of Reynolds numbers (ReD = 1602, 2318, and 3600). The experimental results indicate that for a given Reynolds number and amplitude, with an increase in the frequency of pulsation, the vortex formation shifts toward the nozzle exit. The number of vortices also increases with an increase in the jet pulsation frequency. Broadening of the jet and shortening of the potential core length are also observed. This indicates that mixing with the surrounding fluid is higher with pulsating jet even at relatively low Reynolds numbers. It is observed that frequency up to a critical frequency helps increase entrainment of the surrounding fluid. An upper critical frequency beyond which pulsation does not affect the entrainment is also determined. These results should eventually lead to a better understanding of the physical phenomena responsible for enhanced heat transfer rates in the presence of pulsating jets.

Multiphase Digital Particle Image Velocimetry in a Dispersed, Bubbly, Axisymmetric Jet

2002 ◽  
Author(s):  
G. Chaine ◽  
D. E. Nikitopoulos
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Near Field ◽  
Jet Flow ◽  
Mean Flow ◽  
Two Phase ◽  
Flow Modification ◽  
Image Velocimetry ◽  
Bubble Phase ◽  
Bubbly Jet

A particle image velocimetry (PIV) technique developed for application to two-phase flows is presented and validated. The technique is capable of simultaneously measuring carrier and bubble phase velocities on a plane. The validation experiments have been conducted in a vertical upwards, two-phase (water-air) bubbly jet flow at a Reynolds numbers of 5,673 and 11,345 and low bubble concentration matching the experiments of Stanley and Nikitopoulos (1998). Comparisons with measurements obtained by Stanley and Nikitopoulos (1998) using Phase Doppler Analysis (PDA) experiments indicate that the agreement between the two techniques is very satisfactory (deviations of the order of 5%) for both single-phase and two-phase jet carrier-flow velocities. In addition, bubble phase velocity measurements obtained from backlit visualizations of the bubbly jet flow using the bubble-tracking method of Fiedler et al. (2001) are successfully compared to those obtained from PIV. The PIV study confirms that bubbles experience a substantial deceleration in the unmixed core of the jet near field and illustrates carrier-phase mean-flow modification consistent with past point-wise measurements.

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