Passive Scalar Concentration Field of Isolated Turbulent Puffs

2005 ◽  
Author(s):  
Elham Ghaem-Maghami ◽  
Hamid Johari
Keyword(s):  
Concentration Field ◽  
Passive Scalar ◽  
Scalar Concentration

Concentration Field Measurements Within Isolated Turbulent Puffs

2006 ◽  
Vol 129 (2) ◽  
pp. 194-199 ◽  
Author(s):  
E. Ghaem-Maghami ◽  
H. Johari
Keyword(s):  
Concentration Field ◽  
Spherical Geometry ◽  
Field Measurements ◽  
Axial Direction ◽  
Passive Scalar ◽  
Fast Response ◽  
Mie Scattering ◽  
Injection Volume ◽  
Scalar Concentration ◽  
Planar Laser

The structure of passive scalar concentration field within isolated turbulent puffs was measured using the planar laser Mie scattering technique. Puffs were generated by injecting seeded air through a 5-mm-diameter nozzle into a chamber with a weak air co-flow. The injection time and volume was varied by the use of a fast-response solenoid valve. Puffs were examined in the range of 25–55 diameters downstream of the nozzle. The Reynolds number based on the average velocity and nozzle diameter was 5000. The results indicate that as the injection volume increases, puffs evolve from a spherical geometry to that with a tail. The half-width of radial concentration profiles through the puff center decrease as the injection volume increases. On the other hand, the puff length in the axial direction increases with the injection volume. The volume of ambient fluid entrained by the puff, and normalized by the injected volume, decreases with increasing injection volume.

On the geometry of turbulent mixing

1999 ◽  
Vol 393 ◽  
pp. 123-147 ◽  
Author(s):  
EMMANUEL VILLERMAUX ◽  
CLAUDIA INNOCENTI
Keyword(s):  
Fractal Dimension ◽  
Scalar Field ◽  
Turbulent Mixing ◽  
Concentration Field ◽  
Volume Ratio ◽  
Passive Scalar ◽  
Global Features ◽  
Integral Scale ◽  
Scalar Dispersion ◽  
Concentration Threshold

We investigate the temporal evolution of the geometrical distribution of a passive scalar injected continuously into the far field of a turbulent water jet at a scale d smaller than the local integral scale of the turbulence. The concentration field is studied quantitatively by a laser-induced- fluorescence technique on a plane cut containing the jet axis. Global features such as the scalar dispersion from the source, as well as the fine structure of the scalar field, are analysed. In particular, we define the volume occupied by the regions whose concentration is larger than a given concentration threshold (support of the scalar field) and the surface in which this volume is enclosed (boundary of the support). The volume and surface extents, and their respective fractal dimensions are measured as a function of time t, and the concentration threshold is normalized by the initial concentration Cs/C0 for different injection sizes d. All of these quantities display a clear dependence on t, d and Cs, and their evolutions rescale with the variable ξ = (ut/d)(Cs/C0), the fractal dimension being, in addition, scale dependent. The surface-to-volume ratio and the fractal dimension of both the volume and the surface tend towards unity at large ξ, reflecting the sheet-like structure of the scalar at small scales. These findings suggest an original picture of the kinetics of turbulent mixing.

scholarly journals Wall-Modelled Large Eddy Simulations of Axial Turbine Rim Sealing

2020 ◽  
Author(s):  
Donato M. Palermo ◽  
Feng Gao ◽  
Dario Amirante ◽  
John W. Chew ◽  
Anna Bru Revert ◽  
...  
Keyword(s):  
Eddy Viscosity ◽  
Passive Scalar ◽  
Rotor Blades ◽  
Computational Time ◽  
Scalar Concentration ◽  
Large Eddy ◽  
Annulus Flow ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
Good Agreement

Abstract This paper presents WMLES simulations of a chute type turbine rim seal. Configurations with an axisymmetric annulus flow and with nozzle guide vanes fitted (but without rotor blades) are considered. The passive scalar concentration solution and WMLES are validated against available data in the literature for uniform convection and a rotor-stator cavity flow. The WMLES approach is shown to be effective, giving significant improvements over an eddy viscosity turbulence model, in prediction of rim seal effectiveness compared to research rig measurements. WMLES requires considerably less computational time than wall-resolved LES, and has the potential for extension to engine conditions. All WMLES solutions show rotating inertial waves in the chute seal. Good agreement between WMLES and measurements for sealing effectiveness in the configuration without vanes is found. For cases with vanes fitted the WMLES simulation shows less ingestion than the measurements, and possible reasons are discussed.

Wall-Modelled Large Eddy Simulations of Axial Turbine Rim Sealing

2021 ◽  
Author(s):  
Donato Maria Palermo ◽  
Feng Gao ◽  
Dario Amirante ◽  
John W. Chew ◽  
Anna Bru Revert ◽  
...  
Keyword(s):  
Eddy Viscosity ◽  
Passive Scalar ◽  
Rotor Blades ◽  
Computational Time ◽  
Scalar Concentration ◽  
Large Eddy ◽  
Annulus Flow ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
Good Agreement

Abstract This paper presents WMLES simulations of a chute type turbine rim seal. Configurations with an axisymmetric annulus flow and with nozzle guide vanes fitted (but without rotor blades) are considered. The passive scalar concentration solution and WMLES are validated against available data in the literature for uniform convection and a rotor-stator cavity flow. The WMLES approach is shown to be effective, giving significant improvements over an eddy viscosity turbulence model, in prediction of rim seal effectiveness compared to research rig measurements. WMLES requires considerably less computational time than wall-resolved LES, and has the potential for extension to engine conditions. All WMLES solutions show rotating inertial waves in the chute seal. Good agreement between WMLES and measurements for sealing effectiveness in the configuration without vanes is found. For cases with vanes fitted the WMLES simulation shows less ingestion than the measurements, and possible reasons are discussed.

Simulation of the Scalar Transport above and within the Amazon Forest Canopy

Atmosphere ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1631
Author(s):  
Edivaldo M. Serra-Neto ◽  
Hardiney S. Martins ◽  
Cléo Q. Dias-Júnior ◽  
Raoni A. Santana ◽  
Daiane V. Brondani ◽  
...  
Keyword(s):  
Forest Canopy ◽  
Passive Scalar ◽  
Scalar Transport ◽  
Amazon Forest ◽  
Large Eddy Simulation Model ◽  
Turbulence Structures ◽  
Wind Speeds ◽  
Eddy Simulation ◽  
Scalar Concentration ◽  
Passive Scalar Transport

The parallelized large-eddy simulation model (PALM) was used to understand better the turbulent exchanges of a passive scalar above and within a forested region located in the central Amazon. Weak (2 ms−1) and strong (6 ms−1) wind conditions were simulated. A passive scalar source was introduced to the forest floor for both simulations. The simulations reproduced the main characteristics of the turbulent flow and of the passive scalar transport between the forest and the atmosphere. Noteworthily, strong and weak wind conditions presented different turbulence structures that drove different patterns of scalar exchange both within and above the forest. These results show how passive scalar concentration is influenced by the wind speed at the canopy top. Additionally, higher wind speeds are related to stronger sweep and ejection regimes, generating more intense plumes that are able to reduce the passive scalar concentration inside the forest canopy. This work was the first that used PALM to investigate scalar transport between the Amazon rainforest and the atmosphere.

scholarly journals Peripheral mixing of passive scalar at small Reynolds number

2009 ◽  
Vol 624 ◽  
pp. 151-158 ◽  
Author(s):  
G. BOFFETTA ◽  
F. DE LILLO ◽  
A. MAZZINO
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Passive Scalar ◽  
Peripheral Region ◽  
Direct Numerical Simulations ◽  
Small Reynolds Number ◽  
Two Dimensional ◽  
Dispersion Modelling ◽  
Low Reynolds Numbers ◽  
Scalar Concentration

Mixing of a passive scalar in the peripheral region close to a wall is investigated by means of accurate direct numerical simulations of both a three-dimensional Couette channel flow at low Reynolds numbers and a two-dimensional synthetic flow. In both cases, the resulting phenomenology can be understood in terms of the theory recently developed by Lebedev & Turitsyn (Phys. Rev. E, vol. 69, 2004, 036301). Our results prove the robustness of the identified mechanisms responsible for the persistency of scalar concentration close to the wall with important consequences in completely different fields ranging from microfluidic applications to environmental dispersion modelling.

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