scholarly journals Measurements of turbulent diffusion in uniformly sheared flow

2014 ◽  
Vol 754 ◽  
pp. 488-514 ◽  
Author(s):  
Christina Vanderwel ◽  
Stavros Tavoularis
Keyword(s):  
Stereoscopic Particle Image Velocimetry ◽  
Turbulent Diffusivity ◽  
Relative Significance ◽  
Advection Diffusion Equation ◽  
Image Velocimetry ◽  
Planar Laser ◽  
The Mean ◽  
First Time ◽  
Diffusivity Tensor ◽  
Good Agreement

AbstractThe diffusion of a plume of dye in uniformly sheared turbulent flow in a water tunnel was investigated using simultaneous stereoscopic particle image velocimetry (SPIV) and planar laser-induced fluorescence (PLIF). Maps of the mean concentration and the turbulent concentration fluxes in planes normal to the plume axis were constructed, from which all components of the second-order turbulent diffusivity tensor were determined for the first time. Good agreement between the corresponding apparent and true diffusivities was observed. The turbulent diffusivity tensor was found to have strong off-diagonal components, whereas the streamwise component appeared to be counter-gradient. The different terms in the advection–diffusion equation were estimated from the measurements and their relative significance was discussed. All observed phenomena were explained by physical arguments and the results were compared to previous ones.

Enstrophy transport in swirl combustion

2019 ◽  
Vol 876 ◽  
pp. 715-732 ◽  
Author(s):  
Askar Kazbekov ◽  
Keishi Kumashiro ◽  
Adam M. Steinberg
Keyword(s):  
Isotropic Turbulence ◽  
Reynolds Numbers ◽  
The Other ◽  
Homogeneous Isotropic Turbulence ◽  
Relative Significance ◽  
Swirl Combustion ◽  
Image Velocimetry ◽  
Baroclinic Torque ◽  
Planar Laser ◽  
The Mean

The contributions of vortex stretching, dilatation, baroclinic torque and viscous diffusion to Reynolds-averaged enstrophy transport in turbulent swirl flames were experimentally measured using tomographic particle image velocimetry and $\text{CH}_{2}\text{O}$ planar laser induced fluorescence at jet Reynolds numbers of 26 000–51 000. The mean baroclinic torque was determined by subtracting the other terms in the enstrophy transport equation from the mean Lagrangian derivative. Enstrophy production from baroclinic torque was found to be significant relative to the other transport terms across all conditions studies. This result contrasts with direct numerical simulations of flames in homogeneous isotropic turbulence, which show a decreasing relative significance of baroclinic torque with increasing turbulence intensity (e.g. Bobbitt, Lapointe & Blanquart, Phys. Fluids, vol. 28 (1), 2016, 015101). Hence, the significance of baroclinic enstrophy production in flames is not determined entirely by the local turbulence and flame properties, but also depends on the configuration-specific pressure field.

scholarly journals Doppler temperatures from O(<sup>1</sup>D) airglow in the daytime thermosphere as observed by the Wind Imaging Interferometer (WINDII) on the UARS satellite

2002 ◽  
Vol 20 (2) ◽  
pp. 203-212 ◽  
Author(s):  
C. Lathuillère ◽  
W. A. Gault ◽  
B. Lamballais ◽  
Y. J. Rochon ◽  
B. H. Solheim
Keyword(s):  
Atmospheric Composition ◽  
Large Set ◽  
Temperature Variations ◽  
Data Processing Software ◽  
Imaging Interferometer ◽  
Composition And Structure ◽  
Instruments And Techniques ◽  
The Mean ◽  
First Time ◽  
Good Agreement

Abstract. From 1992 to 1997, the WINDII interferometer on board the UARS satellite acquired a large set of thermospheric data from the O(1D) and O(1S) airglows. We report here for the first time on daytime O(1D) Doppler temperatures obtained with version 5.11 of the WINDII data processing software. Using a statistical analysis of the temperatures independently measured by the two WINDII fields of view, we estimate that the temperature variations larger than 40 K can be considered as geophysical. Comparisons of WINDII temperatures measured during magnetically quiet days with temperatures obtained by the MSIS-90 and DTM-94 thermospheric models show a 100 K bias. We demonstrate, however, that the modeled temperature variations represent very well the mean temperature variation observed by WINDII over 4 years. We also show that the observed latitudinal/local time variation is in very good agreement with the two empirical models. Finally, the temperature variations during a magnetically disturbed day are found to be qualitatively well represented in form by the models, but largely underestimated. The presence of non-thermal atoms and instrument related issues are discussed as possible explanations for the 100 K bias between the WINDII Doppler temperatures and the empirical models.Key words. Atmospheric composition and structure (air-glow and aurora; pressure, density and temperature; instruments and techniques)

Measurements of Periodic Reynolds Stress Oscillations in a Forced Turbulent Premixed Swirling Flame

2018 ◽  
Author(s):  
Christopher Douglas ◽  
Jamie Lim ◽  
Travis Smith ◽  
Benjamin Emerson ◽  
Timothy Lieuwen ◽  
...  
Keyword(s):  
Reynolds Stress ◽  
High Speed ◽  
Large Scale ◽  
Turbulent Transport ◽  
Stereoscopic Particle Image Velocimetry ◽  
Thermoacoustic Instability ◽  
Image Velocimetry ◽  
Planar Laser ◽  
Swirling Flame ◽  
Dynamics Simulations

This work is motivated by the thermoacoustic instability challenges associated with ultra-low emissions gas turbine combustors. It demonstrates the first use of high-speed dual-plane orthogonally-polarized stereoscopic-particle image velocimetry and synchronized OH planar laser-induced fluorescence in a premixed swirling flame. We use this technique to explore the effects of combustion and longitudinal acoustic forcing on the time- and phase-averaged flow field — particularly focusing on the behavior of the Reynolds stress in the presence of harmonic forcing. We observe significant differences between ensemble averaged and time averaged Reynolds stress. This implies that the large-scale motions are non-ergodic, due to coherent oscillations in Reynolds stress associated with the convection of periodic vortical structures. This result has important implications on hydrodynamic stability models and reduced order computational fluid dynamics simulations, which do show the importance of turbulent transport on the problem, but do not capture these coherent oscillations in their models.

Production Estimates for Scotian Shelf Copepods Based on Mass Specific P/B Ratios

1983 ◽  
Vol 40 (6) ◽  
pp. 749-753 ◽  
Author(s):  
M. John Tremblay ◽  
John C. Roff
Keyword(s):  
Body Mass ◽  
Secondary Production ◽  
Empirical Relationship ◽  
Copepod Species ◽  
Scotian Shelf ◽  
Adult Body Mass ◽  
Adult Body ◽  
The Mean ◽  
First Time ◽  
Good Agreement

We estimated annual secondary production by copepod species on the Emerald Bank, Scotian Shelf, for the first time. We tentatively ranked copepod species in order of importance based on production to biomass (P/B) ratios calculated from adult body mass using an empirical relationship. The significance of assessing species in terms of production rather than population biomass is demonstrated. The mean estimate of total copepod production (530 kJ∙m−2) is in good agreement with previous estimates of secondary production on the Scotian Shelf.

Measurements of Periodic Reynolds Stress Oscillations in a Forced Turbulent Premixed Swirling Flame

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Christopher Douglas ◽  
Jamie Lim ◽  
Travis Smith ◽  
Benjamin Emerson ◽  
Timothy Lieuwen ◽  
...  
Keyword(s):  
Reynolds Stress ◽  
High Speed ◽  
Large Scale ◽  
Turbulent Transport ◽  
Stereoscopic Particle Image Velocimetry ◽  
Thermoacoustic Instability ◽  
Image Velocimetry ◽  
Planar Laser ◽  
Swirling Flame ◽  
Dynamics Simulations

This work is motivated by the thermoacoustic instability challenges associated with ultra-low emissions gas turbine (GT) combustors. It demonstrates the first use of high-speed dual-plane orthogonally-polarized stereoscopic-particle image velocimetry (PIV) and synchronized OH planar laser-induced fluorescence in a premixed swirling flame. We use this technique to explore the effects of combustion and longitudinal acoustic forcing on the time- and phase-averaged flow field—particularly focusing on the behavior of the Reynolds stress in the presence of harmonic forcing. We observe significant differences between ensemble-averaged and time-averaged Reynolds stress. This implies that the large-scale motions are nonergodic, due to coherent oscillations in Reynolds stress associated with the convection of periodic vortical structures. This result has important implications on hydrodynamic stability models and reduced-order computational fluid dynamics simulations, which do show the importance of turbulent transport on the problem, but do not capture these coherent oscillations in their models.

Convergence of PIV Measurements at the Inlet of a Turbocharger Compressor

2019 ◽  
Author(s):  
Deb Banerjee ◽  
Ahmet Selamet ◽  
Rick Dehner ◽  
Keith Miazgowicz
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Turbulent Flow ◽  
Coefficient Of Variation ◽  
Particle Image ◽  
Flow Fields ◽  
Statistical Moment ◽  
Stereoscopic Particle Image Velocimetry ◽  
Image Velocimetry ◽  
The Mean

Abstract Particle Image Velocimetry has become a desirable tool to investigate turbulent flow fields in different engineering applications, including flames, combustion engines, and turbomachinery. The convergence characteristics of turbulent statistics of these flow fields are of prime importance since they help with the number of images (temporally uncorrelated) to be captured in order for the results to converge to a certain tolerance or with the assessment of the uncertainty of the measurements for a given number of images. The present work employs Stereoscopic Particle Image Velocimetry to examine the turbulent flow field at the inlet of an automotive turbocharger compressor without any recirculating channel. Optical measurements were conducted at five different mass flow rates spanning from choke to surge at a corrected rotational speed of 80 krpm. The velocity fields thus obtained were used to analyze the convergence of the mean (first statistical moment) and variance (second statistical moment) at different operating conditions. The convergence of the mean at a particular location in the flow field depends on the local coefficient of variation (COV). The number of required images for the mean to converge to a particular tolerance was also found to follow roughly a linear trend with respect to COV. While the convergence of the variance, on the other hand, did not appear to show any direct dependence on the coefficient of variation, it takes significantly more images than the mean to converge to the same level of tolerance.

scholarly journals Complex Flow Generation and Development in a Full-Scale Turbofan Inlet

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Tamara Guimarães ◽  
K. Todd Lowe ◽  
Walter F. O'Brien
Keyword(s):  
Secondary Flow ◽  
Full Scale ◽  
Stereoscopic Particle Image Velocimetry ◽  
Complex Flow ◽  
Mean Velocity ◽  
Ground Testing ◽  
Turbofan Engines ◽  
Flow Generation ◽  
Image Velocimetry ◽  
The Mean

The future of aviation relies on the integration of airframe and propulsion systems to improve aerodynamic performance and efficiency of aircraft, bringing design challenges, such as the ingestion of nonuniform flows by turbofan engines. In this work, we describe the behavior of a complex distorted inflow in a full-scale engine rig. The distortion, as in engines on a hybrid wing body (HWB) type of aircraft, is generated by a 21-in diameter StreamVane, an array of vanes that produce prescribed secondary flow distributions. Data are acquired using stereoscopic particle image velocimetry (PIV) at three measurement planes along the inlet of the research engine (Reynolds number of 2.4 × 106). A vortex dynamics-based model, named StreamFlow, is used to predict the mean secondary flow development based on the experimental data. The mean velocity profiles show that, as flow develops axially, the vortex present in the profile migrates clockwise, opposite to the rotation of the fan, and toward the spinner of the engine. The turbulent stresses indicate that the center of the vortex meanders around a preferred location, which tightens as flow gets closer to the fan, yielding a smaller radius mean vortex near the fan. Signature features of the distortion device are observed in the velocity gradients, showing the wakes generated by the distortion screen vanes in the flow. The results obtained shed light onto the aerodynamics of swirling flows representative of distorted turbofan inlets, while further advancing the understanding of the complex vane technology presented herein for advanced ground testing.

scholarly journals On the internal vorticity and density structures of miscible thermals

2013 ◽  
Vol 722 ◽  
Author(s):  
B. Zhao ◽  
A. W. K. Law ◽  
A. C. H. Lai ◽  
E. E. Adams
Keyword(s):  
Particle Image ◽  
Initial Density ◽  
Density Distributions ◽  
Image Velocimetry ◽  
Buoyancy Convection ◽  
Planar Laser ◽  
Self Similar ◽  
The Mean ◽  
Subsequent Motion ◽  
Density Excess

AbstractMiscible thermals are formed by instantaneously releasing a finite volume of buoyant fluid into stagnant ambient. Their subsequent motion is then driven by the buoyancy convection. The gross characteristics (e.g. overall size and velocity) of a thermal have been well studied and reported to be self-similar. However, there have been few studies concerning the internal structure. Here, turbulent miscible thermals (with initial density excess of 5 % and Reynolds number around 2100) have been investigated experimentally through a large number of realizations. The vorticity and density fields were quantified separately by particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques. Ensemble-averaged data of the transient development of the miscible thermals are presented. Major outcomes include: (i) validating Turner’s assumption of constant circulation within a buoyant vortex ring; (ii) measuring the vorticity and density distributions within the miscible thermal; (iii) quantifying the effect of baroclinicity on the generation and destruction of vorticity within the thermal; and (iv) identifying the significantly slower decay rate of the peak density as compared to the mean.

Verification of Fully Developed Flow Entering Diffuser and Particle Image Velocimetry Procedures

2013 ◽  
Vol 465-466 ◽  
pp. 1352-1356 ◽  
Author(s):  
Normayati Nordin ◽  
Zainal Ambri Abdul Karim ◽  
Safiah Othman ◽  
Vijay R. Raghavan
Keyword(s):  
Particle Image ◽  
Abrupt Change ◽  
Laser Sheet ◽  
Settling Chamber ◽  
Mean Velocity ◽  
Fully Developed Flow ◽  
3 Dimensional ◽  
Image Velocimetry ◽  
The Mean ◽  
Good Agreement

3-Dstereoscopic PIV is capable of measuring 3-dimensional velocity components. Itinvolves a very sophisticated routine during setup, calibration, measurementand data processing phases. This paper aims to verify the 3-D stereoscopic PIVmeasurement procedures and to prove that the flow entering thediffuser is a fully developed flow. A diffuser inlet of rectangularcross-section, 130 mm x 50 mm is presently considered. For verification, thevelocities from PIV are compared with the velocities from pitot static probeand theory. The mean velocity obtained using pitot static probe is 2.44 m/s,whereas using PIV is 2.46 m/s. It thus gives the discrepancy of 0.8%. There isalso a good agreement between the mean velocity measured by PIV and theoreticalvalue with the discrepancy of 1.2%. This minor discrepancy is mainly due touncertainties in the experiments such as imperfect matching of coordinatesbetween the probe and laser sheet, unsteadiness of flow, variation in density andless precision in calibration. Basically, the operating procedures of 3-Dstereoscopic PIV have successfully been verified. Nevertheless, the flowentering diffuser is not perfectly developed due to the imperfect joining ductand the abrupt change of inlet cross-section introduced. Therefore, improvementto the existing rig is proposed by means of installing settling chamber withmultiple screens arrangement and contraction cone.

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