Stereo Piv Diagnostics of Flow Structure in Swirling Turbulent Propane Flames

2009 ◽  
Vol 4 (3) ◽  
pp. 30-42
Author(s):  
Vladimir Dulin ◽  
Yuriy Kozorezov ◽  
Dmitriy Markovich ◽  
Mikhail Tokarev
Keyword(s):  
Spatial Distribution ◽  
Flow Structure ◽  
Large Scale ◽  
Particle Image ◽  
Correlation Method ◽  
Velocity Fields ◽  
Instantaneous Velocity ◽  
Mean Velocity ◽  
Wide Range ◽  
Swirling Flame

This paper is devoted to experimental study of the instantaneous and average flow structure in the pre-mixed propaneair swirling flames using optical noncontact PIV (Particle Image Velocimetry) method in stereoscopic configuration. A visualization of the typical regimes of combustion for the swirling and non-swirling flame in a wide range of Reynolds numbers and equivalence ratios is presented. In addition, boundaries of steady combustion are defined. Measurements of instantaneous velocity fields for typical combustion regimes are performed. Instantaneous velocity fields were used to calculate the spatial distribution of the mean velocity and turbulence kinetic energy component. Interaction of the flame with a large-scale vortex structures is studied. It shows significantly different effects of burning on the turbulent structure of twisted jet. The paper describes algorithms of data processing, in particular, adaptive cross-correlation method of calculating the instantaneous velocity fields based on an analysis of the local particle image concentration. This method allows to effectively filtering out the velocity vector outliers, which appear in areas with low concentration of tracers during gas flows diagnostics, and calculate the spatial distribution of such characteristics as the intensity of turbulent pulsations.

Cometary evolution and cryovolcanism 1This article is part of a Special issue that honours the work of Dr. Donald M. Hunten FRSC who passed away in December 2010 after a very illustrious career.

2012 ◽  
Vol 90 (8) ◽  
pp. 807-815 ◽  
Author(s):  
Michael J.S. Belton
Keyword(s):  
Spatial Distribution ◽  
Production Rate ◽  
Large Scale ◽  
Special Issue ◽  
Apparent Absence ◽  
Cometary Nuclei ◽  
Evolutionary Hypothesis ◽  
Wide Range ◽  
Show Evidence ◽  
Cometary Activity

Recent space observations of cometary nuclei show evidence of internal (cryovolcanic) activity while retaining aspects of their primitive origins. Using discoveries made during the two most recent cometary encounters: EPOXI at 103P/Hartley 2 and Stardust-NExT at 9P/Tempel 1, we test a hypothesis for their physical evolution, which, if true, could provide a unified basis for understanding the relative ages of their surfaces and the causes of a wide range of cometary activity. We show: (i) that the categorization of 103P/Hartley 2 as hyperactive is not a reflection of the extent of activity over the surface of the nucleus for which we find a normal H2O production rate; (ii) that the heterogeneous spatial distribution of CO2 and H2O in the inner comae of 9P/Tempel 1 and 103P/Hartley 2 is best explained by processes associated with cometary activity rather than the presence of primitive compositional heterogeneities in the nucleus; and (iii) that most of the quasi-circular depressions seen on the surface of 9P/Tempel are the result of outburst activity. The apparent absence of circular depressions and large scale layering on 103P/Hartley 2 present a challenge to the evolutionary hypothesis although the small size of its nucleus may ultimately provide an explanation.

Turbulence Evaluation Within the Secondary Flow Region of a Turbine Cascade

1992 ◽  
Author(s):  
D. G. Gregory-Smith ◽  
Th. Biesinger
Keyword(s):  
Large Scale ◽  
Energy Equation ◽  
Three Dimensional ◽  
Flow Region ◽  
Velocity Fields ◽  
Navier Stokes ◽  
Turbine Cascade ◽  
Mean Velocity ◽  
Turbulent Kinetic Energy Equation ◽  
Transition Modelling

Three-dimensional turbulent and mean velocity fields have been measured within a large-scale axial turbine cascade. The results indicate a complex turbulent flow field especially within the secondary vortex. The turbulence is shown to he significantly non-isotropic, and the production and dissipation terms in the turbulent kinetic energy equation have been evaluated in order to illustrate the unusual turbulence behaviour. Comparisons with a Navier-Stokes computation indicate areas for improvement in turbulence and transition modelling.

Different Modes of Gas Entrainment Through Bottom Discharge Branch by Using Three Dimensional Particle Image Velocimetry System

2007 ◽  
Author(s):  
Wael Fairouz Saleh ◽  
Ibrahim Galal Hassan
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Structure ◽  
Particle Image ◽  
Three Dimensional ◽  
Industrial Applications ◽  
Particle Image Velocimetry System ◽  
Three Dimension ◽  
Two Phase ◽  
Mean Velocity ◽  
Image Velocimetry

The discharge of two-phase flow from a stratified region through single or multiple branches is an important process in many industrial applications including the pumping of fluid from storage tanks, shell-and-tube heat exchangers, and the fluid flow through small breaks in cooling channels of nuclear reactors during loss-of-coolant accidents (LOCA). Knowledge of the flow phenomena involved along with the quality and mass flow rate of the discharging stream(s) is necessary to adequately predict the different phenomena associated with the process. Particle Image Velocimetry (PIV) in three dimension was used to provide detailed measurements of the flow patterns involving distributions of mean velocity, vorticity field, and flow structure. The experimental investigation was carried out to simulate two phase discharge from a stratified region through branches located on a semi-circular wall configuration during LOCA scenarios. The semi-circular test section is in close dimensional resemblance with that of a CANDU header-feeder system, with branches mounted at orientation angles of zero, 45 and 90 degrees from the horizontal. The experimental data for the phase development (mean velocity, flow structure, etc.) was done during single discharge through the bottom branch from an air/water stratified region over a three selected Froude numbers. These measurements were used to describe the effect of outlet flow conditions on phase redistribution in headers and understand the entrainment phenomena.

scholarly journals Spatial Distribution of Crusts in Antarctic and Greenland Snowpacks and Implications for Snow and Firn Studies

2021 ◽  
Vol 9 ◽  
Author(s):  
Alexander H. Weinhart ◽  
Sepp Kipfstuhl ◽  
Maria Hörhold ◽  
Olaf Eisen ◽  
Johannes Freitag
Keyword(s):  
Spatial Distribution ◽  
Large Scale ◽  
Accumulation Rate ◽  
Sampling Site ◽  
Stable Water Isotopes ◽  
High Accumulation ◽  
Surface Mass ◽  
Antarctic Plateau ◽  
Wide Range ◽  
Surface Snow

The occurrence of snowpack features has been used in the past to classify environmental regimes on the polar ice sheets. Among these features are thin crusts with high density, which contribute to firn stratigraphy and can have significant impact on firn ventilation as well as on remotely inferred properties like accumulation rate or surface mass balance. The importance of crusts in polar snowpack has been acknowledged, but nonetheless little is known about their large-scale distribution. From snow profiles measured by means of microfocus X-ray computer tomography we created a unique dataset showing the spatial distribution of crusts in snow on the East Antarctic Plateau as well as in northern Greenland including a measure for their local variability. With this method, we are able to find also weak and oblique crusts, to count their frequency of occurrence and to measure the high-resolution density. Crusts are local features with a small spatial extent in the range of tens of meters. From several profiles per sampling site we are able to show a decreasing number of crusts in surface snow along a traverse on the East Antarctic Plateau. Combining samples from Antarctica and Greenland with a wide range of annual accumulation rate, we find a positive correlation (R2 = 0.89) between the logarithmic accumulation rate and crusts per annual layer in surface snow. By counting crusts in two Antarctic firn cores, we can show the preservation of crusts with depth and discuss their temporal variability as well as the sensitivity to accumulation rate. In local applications we test the robustness of crusts as a seasonal proxy in comparison to chemical records like impurities or stable water isotopes. While in regions with high accumulation rates the occurrence of crusts shows signs of seasonality, in low accumulation areas dating of the snowpack should be done using a combination of volumetric and stratigraphic elements. Our data can bring new insights for the study of firn permeability, improving of remote sensing signals or the development of new proxies in snow and firn core research.

scholarly journals Experimental Study by Optical and Statistical Methods of Large-Scale Velocity Fluctuations in the Flow Past a Cylinder

2019 ◽  
Vol 14 (3) ◽  
pp. 5-14
Author(s):  
S. S. Abdurakipov ◽  
K. G. Dobroselsky
Keyword(s):  
Experimental Study ◽  
Turbulent Flows ◽  
Large Scale ◽  
Particle Image ◽  
Velocity Fields ◽  
Velocity Fluctuations ◽  
Flow Past ◽  
Image Velocimetry ◽  
Flow Past A Cylinder ◽  
Proper Orthogonal

Using an optical method for measuring the velocity fields Particle Image Velocimetry (PIV) and a statistical method for analyzing coherent structures in turbulent flows Proper Orthogonal Decomposition (POD), an experimental study of the spatial structure of large-scale velocity fluctuations in the precavitational and cavitational flow past a circular cylinder with a Reynolds number of 280 000 was carried out.

Comparison Between a Slot Jet and Round Jets Impinging a Curved Wall

2003 ◽  
Author(s):  
V. Gilard ◽  
L.-E. Brizzi
Keyword(s):  
Data Processing ◽  
Flow Structure ◽  
Statistical Data ◽  
Velocity Fields ◽  
Reynolds Stresses ◽  
Velocity Measurements ◽  
Mean Velocity ◽  
Statistical Data Processing ◽  
Round Jets ◽  
The Mean

Velocity measurements by PIV are realized in order to compare a slot jet and round jets impinging a curved surface. A statistical data processing allows us to obtain the mean velocity fields and the Reynolds stresses. For the two jet geometries, the flow structure is described. Some velocity distributions according to different axis are extracted of the mean velocity fields and are also described.

Measurement Errors and Uncertainty Quantification of a 2D-PIV Experimental Setup for Jet Flow Characterization

2020 ◽  
Author(s):  
Flavia Barbosa ◽  
Carlos Costa ◽  
Senhorinha Teixeira ◽  
Jose Carlos Teixeira
Keyword(s):  
Heat Transfer ◽  
Uncertainty Quantification ◽  
Measurement Errors ◽  
Jet Impingement ◽  
Velocity Fields ◽  
Mean Velocity ◽  
Air Jets ◽  
Air Jet ◽  
High Heat Transfer ◽  
Wide Range

Abstract The study of the flow interaction and the heat transfer between air jets and a surface is of paramount importance in industrial processes that apply air jet impingement. To ensure a good performance of the process, high heat transfer rates and uniformization of the flow over the target plate are required. To perform this analysis, a PIV technique was implemented for the measurement of the flow velocity fields. However, as any real experiment, the values recorded by the PIV method are subjected to several errors that compromise the reliability and accuracy of the measurements. These errors can have different sources, from the installation and alignment to the particles seeding and calibration procedure. To maximize the accuracy of the experimental results, this paper focus on the identification of measurement errors and uncertainty quantification of an experimental set up specially built for the analysis of the interaction between air jets and a target surface. This work presents an analysis of the system, and the source of errors are identified, quantified and, when possible, corrected. The particle seeding is characterized and its efficiency for the flow tracking is analyzed. The setup was tested to fully characterize the flow field in terms of mean velocity profile and turbulence intensity over a wide range of Reynolds numbers and temperature. Several velocity fields are then measured until convergence of the flow quantities is reached. The combination of these measurements with high spatial resolution and low measurement errors allow to obtain accurate and precise measurements.

scholarly journals Time-resolved particle image velocimetry measurements of a tandem jet array in a cross flow at low velocity ratios

2020 ◽  
Author(s):  
Paul Kristo ◽  
Mark L. Kimber
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Velocity Fields ◽  
Instantaneous Velocity ◽  
Low Velocity ◽  
Time Resolved ◽  
Turbulent Statistics ◽  
Image Velocimetry

Investigation of the near field dynamics of a single and tandem array of three jets are provided by 2-D time-resolved particle image velocimetry (TR-PIV) measurements. Instantaneous velocity fields are examined in the transverse and spanwise planes with jet to cross flow velocity ratios in the range from 0.9 to 1.7. Previous studies have shown that for high ratios (≥2), the leading jet provides sufficient shielding to ensure that all jets downstream exhibit nearly identical flow characteristics. The current transverse plane measurements exhibit more unique and localized features as a result of the competing effects of pressure gradients and vortex mechanisms assessed via the jet exit profiles, first and second order turbulent statistics, streamline trajectories, recirculation areas, and penetrations depths. Proper orthogonal decomposition (POD) is applied to the spanwise plane instantaneous velocity fields to determine the statistically dominant features of the single and tandem jet configurations at equivalent velocity ratios. The velocity fields are then reconstructed using the truncated POD modes to provide further insight into the shear layer and wake vortices that drive these configurations. Vortex identification algorithms are applied to the reconstructed velocity fields to determine the statistical characteristics of the vortices, including their centroids, populations, areas, and strengths, each of which exhibit largely different dependencies on jet configuration and velocity ratio. Several of the investigated metrics are found to exhibit different behaviors below and above a velocity ratio of unity, and also as a function of increasing velocity ratio between 1 and 2, implying that several transitions mechanisms are present in the low velocity ratio regime investigated herein.

Influence of Drag-Reducing Surfactant Additives on Vortex Structures and Turbulent Events in a Channel Flow

Volume 1 ◽  
2004 ◽  
Author(s):  
Feng-Chen Li ◽  
Yasuo Kawaguchi ◽  
Takehiko Segawa ◽  
Koichi Hishida
Keyword(s):  
Particle Image ◽  
Velocity Fields ◽  
Vortex Structures ◽  
Instantaneous Velocity ◽  
Two Dimensional ◽  
Instantaneous Velocity Field ◽  
Contour Maps ◽  
Image Velocimetry ◽  
Swirling Strength ◽  
Characteristic Angle

The characteristics of vortex structures and turbulent events of drag-reducing surfactant (CTAC) solution flows in a two-dimensional channel have been studied using particle image velocimetry (PIV) to measure the instantaneous velocity fields in a streamwise-wall-normal plane. Through visualizing the instantaneous velocity field, contour maps of the swirling strength and instantaneous value of uv, the characteristic angle of vortex packets was quantified, and it was shown that the drag-reducing CTAC additive reduced both the strength and frequency of turbulent bursts near the wall, and that the characteristics of vortex structures and bursts were not only dependent on drag-reduction level but also on concentration of additive. Based on the quantified parameters characterizing turbulent events in a wall-bounded turbulent flow, a model of turbulent contribution to the friction factor, fT, was proposed. It was obtained that fT was linearly proportional to the product of frequency and strength of turbulent events.

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