Experimental Analysis of Turbulent Wake Development Behind a Permeable Cylinder

2019 ◽  
Author(s):  
Yasufumi Horimoto ◽  
Yusuke Suzuki ◽  
Kazuki Hagiwara ◽  
Yasuo Kawaguchi
Keyword(s):  
Particle Image ◽  
Isotropic Turbulence ◽  
Flow Region ◽  
Turbulent Wake ◽  
Grid Turbulence ◽  
Solid Cylinder ◽  
Image Velocimetry ◽  
Permeable Cylinders ◽  
Lower Permeability ◽  
Karman Vortex

Abstract To investigate the effect of permeability on turbulent wake behind a cylinder in uniform flow, we conduct particle image velocimetry on turbulent wake behind permeable cylinders, which are made of mesh sheets, of different permeabilities and compare the results with those for a solid cylinder. For relatively lower permeability, turbulent wake is quite similar to the case for a solid cylinder except for a slight shift in the streamwise direction of the reversed flow region implying turbulent Kármán vortex shedding. On the other hand, for higher permeability, the structure of turbulence is qualitatively different. More concretely, turbulent Kármán vortices disappear. Interestingly, however, the momentum deficit for such flow is comparable with that of a solid cylinder. This considerable momentum deficit can be understood with isotropic turbulence caused by the flow penetrating through the mesh constructing the cylinders. These results imply that turbulent wake behind a permeable cylinder involves dynamics both of wake and grid turbulence and the latter one dominates when permeability is sufficiently high.

Evaluation of multiphase flotation models in grid turbulence via Particle Image Velocimetry

2006 ◽  
Vol 80 (2-4) ◽  
pp. 133-143 ◽  
Author(s):  
Michael R. Brady ◽  
Demetri P. Telionis ◽  
Pavlos P. Vlachos ◽  
Roe-Hoan Yoon
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Grid Turbulence ◽  
Image Velocimetry

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.

Experimental Characterization of the Flow-Field Downstream of an Innovative Ultra Low NOx Injection System

2014 ◽  
Author(s):  
Marco Berrino ◽  
Francesca Satta ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Salvatore Colantuoni ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Coherent Structures ◽  
Particle Image ◽  
Flow Region ◽  
Experimental Results ◽  
Injection System ◽  
Hot Wire ◽  
Mean Velocity ◽  
Image Velocimetry

The present paper is focused on the characterization of the aerodynamics of the nonreacting flow downstream of an innovative Ultra Low NOx (ULN) injection system. The system is aimed at reducing NOx emissions and combustor axial length, to obtain a more compact and lighter low-emission combustor. The flow path downstream of the injection system has been investigated by means of Particle Image Velocimetry (PIV) and Hot Wire Anemometry (HWA). Particle Image Velocimetry measurements have been carried out in the meridional plane and in three frontal planes, in order to measure mean velocity components and their fluctuations, as well as to identify the coherent structures that characterize the time-varying flow. Hot Wire Anemometry has been used to investigate the unsteady behavior of the flow and to detect the presence of velocity fluctuation frequencies at different radial and axial positions downstream of the injection system. The HWA technique allowed the identification of the frequencies associated with the precession motion due to the vortex breakdown and with the coherent structures at the interface between the inverse flow region and the jets. The experimental results show a large reverse flow region at the exit, without any back-flow within the injection system, hence offering the evidence that the injection system may be able to stabilize the flame, without inducing risks of flash-back or auto-ignition phenomena. Moreover, the mean velocity distributions show the injection system ability of keeping separated the two jets coming out from the internal and external swirlers, with the consequent possibility of applying fuel-staging. Furthermore, the experimental results have been compared to CFD RANS calculations and used for the validation of the numerical procedure.

Turbulent Multi-Phase Flow Interactions Through Grid Turbulence Measured by Particle Image Velocimetry

Volume 3 ◽  
2004 ◽  
Author(s):  
Michael R. Brady ◽  
Pavlos P. Vlachos ◽  
D. Telionis
Keyword(s):  
Particle Image ◽  
Isotropic Turbulence ◽  
Free Stream ◽  
Great Accuracy ◽  
Solid Particles ◽  
Stream Velocity ◽  
Grid Turbulence ◽  
Basic Features ◽  
Multi Phase ◽  
Three Phases

Industrial processes involving multi-phase flows such as flotation require an understanding of the relationships between bubbles, solid particles and the flow. For decades engineers and researchers based their calculations on algebraic formulas that model these interactions. These formulas were derived either from simple models, or from experimental data. Modern experimental tools are employed in this effort to measure with great accuracy the basic features of the motion of all three phases in turbulent flow. We employed a unique Digital Particle Image Velocimeter (DPIV) that can record with great accuracy and kHz temporal resolution, velocity vectors of all three phases, namely the fluid, the solid particles and the air bubbles. The interaction of these three phases was studied in grid turbulence. Flow was directed through a rectangular grid of circular rods and the resulting homogeneous isotropic turbulence was documented. Particles and bubbles were released and the motion of the three phases was monitored. The particle RMS was in good agreement with a model proposed by Shubert, having an average RMS velocity of about 13% of the free stream velocity in the fully developed region. A theoretical model, derived first by Levins and Glastonbury was found to underpredict the particle RMS. The bubble RMS was about 26% of the free stream in the homogeneous isotropic region, 100% greater than the particle RMS and not consistent with the model predictions.

Some characteristics of thin shear layers in homogeneous turbulent flow

2011 ◽  
Vol 369 (1937) ◽  
pp. 709-722 ◽  
Author(s):  
N. A. Worth ◽  
T. B. Nickels
Keyword(s):  
Particle Image Velocimetry ◽  
Turbulent Flow ◽  
Particle Image ◽  
Isotropic Turbulence ◽  
Shear Layers ◽  
Tomographic Particle Image Velocimetry ◽  
Homogeneous Isotropic Turbulence ◽  
Image Velocimetry ◽  
Large Velocity ◽  
Made In

Tomographic particle image velocimetry measurements of homogeneous isotropic turbulence that have been made in a large mixing tank facility at Cambridge are analysed in order to characterize thin highly sheared regions that have been observed. The results indicate that such regions coincide with regions of high enstrophy, dissipation and stretching. Large velocity jumps are observed across the width of these regions. The thickness of the shear layers seems to scale with the Taylor microscale, as has been suggested previously. The results discussed here concentrate on examining individual realizations rather than statistics of these regions.

scholarly journals Augmenting the Structures in a Swirling Flame via Diffusive Injection

2014 ◽  
Vol 2014 ◽  
pp. 1-16 ◽  
Author(s):  
Jonathan Lewis ◽  
Agustin Valera-Medina ◽  
Richard Marsh ◽  
Steven Morris
Keyword(s):  
Carbon Dioxide ◽  
Recirculation Zone ◽  
Particle Image ◽  
Vortex Breakdown ◽  
Flow Region ◽  
Small Scale ◽  
Flame Stability ◽  
Image Velocimetry ◽  
Swirling Flame ◽  
Opposing Effect

Small scale experimentation using particle image velocimetry investigated the effect of the diffusive injection of methane, air, and carbon dioxide on the coherent structures in a swirling flame. The interaction between the high momentum flow region (HMFR) and central recirculation zone (CRZ) of the flame is a potential cause of combustion induced vortex breakdown (CIVB) and occurs when the HMFR squeezes the CRZ, resulting in upstream propagation. The diffusive introduction of methane or carbon dioxide through a central injector increased the size and velocity of the CRZ relative to the HMFR whilst maintaining flame stability, reducing the likelihood of CIVB occurring. The diffusive injection of air had an opposing effect, reducing the size and velocity of the CRZ prior to eradicating it completely. This would also prevent combustion induced vortex breakdown CIVB occurring as a CRZ is fundamental to the process; however, without recirculation it would create an inherently unstable flame.

The energy cascade in near-field non-homogeneous non-isotropic turbulence

2015 ◽  
Vol 771 ◽  
pp. 676-705 ◽  
Author(s):  
R. Gomes-Fernandes ◽  
B. Ganapathisubramani ◽  
J. C. Vassilicos
Keyword(s):  
Particle Image Velocimetry ◽  
Spectral Properties ◽  
Particle Image ◽  
Isotropic Turbulence ◽  
Near Field ◽  
Streamwise Direction ◽  
Piv Measurements ◽  
Production Region ◽  
Image Velocimetry ◽  
Energy Transfers

We perform particle image velocimetry (PIV) measurements of various terms of the non-homogeneous Kármán–Howarth–Monin equation in the most inhomogeneous and anisotropic region of grid-generated turbulence, the production region which lies between the grid and the peak of turbulence intensity. We use a well-documented fractal grid which is known to magnify the streamwise extent of the production region and abate its turbulence activity. On the centreline around the centre of that region the two-point advection and transport terms are dominant and the production is significant too. It is therefore impossible to apply usual Kolmogorov arguments based on the Kármán–Howarth–Monin equation and resulting dimensional considerations to deduce interscale flux and spectral properties. The interscale energy transfers at this location turn out to be highly anisotropic and consist of a combined forward and inverse cascade in different directions which, when averaged over directions, gives an interscale energy flux that is negative (hence forward cascade on average) and not too far from linear in $r$, the modulus of the separation vector $\boldsymbol{r}$ between two points. The energy spectrum of the streamwise fluctuating component exhibits a well-defined $-5/3$ power law over one decade, even though the streamwise direction is at a small angle to the inverse cascading direction.

scholarly journals Stall Control by Plasma Actuators: Characterization along the Airfoil Span

Energies ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1374 ◽  
Author(s):  
Giulia Zoppini ◽  
Marco Belan ◽  
Alex Zanotti ◽  
Lorenzo Di Vinci ◽  
Giuseppe Campanardi
Keyword(s):  
Particle Image ◽  
Barrier Discharge ◽  
Three Dimensional ◽  
Flow Region ◽  
Plasma Actuators ◽  
Particle Image Velocimetry Technique ◽  
Consumption Data ◽  
Image Velocimetry ◽  
Flow Morphology ◽  
Stall Control

A dielectric barrier discharge actuator (DBD) is considered and studied as a stall recovery device. The DBD is installed on the nose of a NACA0015 airfoil with chord × span 300 × 930 mm. The geometry of the exposed electrode has periodic triangular tips purposely designed for the case under study. Wind tunnel tests have been carried out over a range of airspeeds up to 35 m/s with a Reynolds number of 700 k. The flow morphology has been characterized by means of the particle image velocimetry technique, obtaining velocity fields and pressure coefficients. By exploring different planes along the model span, the three-dimensional effect of the DBD has been reconstructed, identifying the flow region mainly sensitive to the plasma actuation. Finally, the actuator effectiveness has been quantified accounting for the power consumption data, leading to defining further design improvements in view of a better efficiency.

Experimental investigations of turbulent decaying behaviors in the core-flow region of a propeller wake

2019 ◽  
Vol 234 (2) ◽  
pp. 319-329
Author(s):  
Zhenchen Liu ◽  
Peiqing Liu ◽  
Hao Guo ◽  
Tianxiang Hu
Keyword(s):  
Isotropic Turbulence ◽  
Tangential Velocity ◽  
Flow Region ◽  
Experimental Investigations ◽  
Grid Turbulence ◽  
Core Flow ◽  
Velocity Fluctuations ◽  
The Core ◽  
Propeller Wake ◽  
Turbulent Modeling

This work investigates the turbulent decaying behaviors downstream of a propeller in the core-flow region. Both axial and tangential velocity fluctuations behind a two-bladed propeller were measured using a stationary hot-wire probe. Unexpectedly, the complex near-wake core-flow of the propeller is found to show a similar decay characteristic of homogeneous turbulence, such as grid turbulence. The decay of turbulence intensity is found to be dominated by the level of periodic velocity fluctuations, showing a similar behavior of the homogenous and isotropic turbulence. This turbulent decaying behavior of the core-flow can be adopted for future turbulent modeling techniques.

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