scholarly journals IWC Analysis of Turbulent Plume Fires

2021 ◽  
Vol 65 (2-4) ◽  
pp. 196-200
Author(s):  
Francesco S. Ciani ◽  
Paolo Bonfiglio ◽  
Stefano Piva
Keyword(s):  
Spectral Analysis ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Power Law ◽  
Grid Size ◽  
Energy Spectra ◽  
Test Case ◽  
Wavenumber Domain ◽  
Taylor’S Hypothesis ◽  
Turbulent Plume

Plumes fires are characterized by a turbulent nature with a large number of different scales. LES is used to solve the largest structures and to model the smallest ones. Grid size and time steps become decisive to place a limit between solved and modelled turbulence. A spectral analysis, both in frequency and wavenumber domain of the specific turbulent kinetic energy is an instrument to check for the information investigated. Unfortunately, the spectra in the wavenumber domain can be difficult to achieve adequately, because the specific turbulent kinetic energy values should be available in many points. This issue can be overcome by identifying a correlation law between frequencies and wavenumbers. An approach to identify this correlation law can be to adopt the IWC method. Here, for a test case of a turbulent reacting plume of burning propane, specific turbulent kinetic energy is analysed both in frequency and wavenumber and a correlation law between them is identified by using the IWC method. A study has been performed to evaluate the grid dependency of the specific turbulent kinetic energy spectra, by assessing the extension of the Kolmogorov power law region. The correlation results are discussed and compared with the Taylor’s hypothesis.

scholarly journals Measurements of Enhanced Turbulent Mixing near Highways

2012 ◽  
Vol 51 (9) ◽  
pp. 1618-1632 ◽  
Author(s):  
Mark Gordon ◽  
Ralf M. Staebler ◽  
John Liggio ◽  
Paul Makar ◽  
Shao-Meng Li ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Traffic Flow ◽  
Power Law ◽  
Vertical Mixing ◽  
Weather Forecast ◽  
Early Morning ◽  
Highway Traffic ◽  
Vertical Diffusion ◽  
Global Environmental

AbstractIn August and September of 2010, measurements of turbulent fluxes and turbulent kinetic energy were made on highways in the Toronto area (Ontario, Canada). In situ turbulence measurements were made with a mobile laboratory while driving on the highway with traffic. Results demonstrate that the turbulent kinetic energy (TKE) spectrum is significantly enhanced on and near the highway by traffic for frequencies above 0.015 Hz. The decay of TKE with distance behind vehicles is well approximated by power-law curves. The strongest increase in TKE is seen while following heavy-duty trucks, primarily for frequencies above 0.7 Hz. From these results, a parameterization of on-road TKE enhancement is developed that is based on vehicle type and traffic-flow rate. TKE with distance downwind of the highway also decays following a power law. The enhancement of roadside TKE is shown to be strongly dependent on traffic flow. The effect of vehicle-induced turbulence on vertical mixing was studied by comparing parameterized TKE enhancement with the typical TKE predictions from the Global Environmental Multiscale weather forecast to predict the potential increase in vertical diffusion that results from highway traffic. It is demonstrated that this increase in TKE by traffic may be locally significant, especially in the early morning.

Local-Correlation Based Zero-Equation Transition Model for Turbomachinery

2019 ◽  
Author(s):  
Jatinder Pal Singh Sandhu
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Gamma Transition ◽  
Test Case ◽  
Transition Model ◽  
Bypass Transition ◽  
Local Correlation ◽  
New Model ◽  
Transition Prediction ◽  
Transition Mechanism

Abstract In this paper, we present a new local-correlation based zero-equation transition model. The new model, which is derived from the local-correlation based one-equation gamma transition model (Menter, F. R., Smirnov, P. E., Liu, T., and Avancha, R., A One-Equation Local Correlation-Based Transition Model, Flow, Turbulence and Combustion, vol. 95, 2015, pp. 583619.), does not require any additional equation to be solved, by defining a new variable, which captures the turbulent kinetic energy and intermittency collectively. The new model only adds three more source terms to the existing transport equation of turbulent kinetic energy. Hence the new model is straightforward to implement in already existing RANS solvers and reduces the computational memory requirement as compared to the other transition models. The transition prediction capability of the new model is tested and compared against the one-equation gamma transition model, especially for turbomachinery applications, where bypass transition is the primary transition mechanism, using a standard flat plate test case, and S809 airfoil. Preliminary results show that the new zero-equation transition model produces satisfactory results in terms of transition-location prediction.

scholarly journals Bottlenecks in turbulent kinetic energy spectra predicted from structure function inflections using the Von Kármán-Howarth equation

2015 ◽  
Vol 92 (3) ◽  
Author(s):  
Gabriel G. Katul ◽  
Costantino Manes ◽  
Amilcare Porporato ◽  
Elie Bou-Zeid ◽  
Marcelo Chamecki
Keyword(s):  
Kinetic Energy ◽  
Structure Function ◽  
Turbulent Kinetic Energy ◽  
Energy Spectra ◽  
Von Karman ◽  
Von Kármán

Assessment Measures for LES Applications

2006 ◽  
Author(s):  
I. Celik ◽  
M. Klein ◽  
J. Janicka
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Power Spectra ◽  
Grid Size ◽  
Large Eddy Simulations ◽  
Large Eddy ◽  
Modeling Errors ◽  
The Common ◽  
Assessment Measures ◽  
Molecular Viscosity

Anticipating that Large Eddy Simulations will increasingly become the future engineering tool for research, development and design, it is deemed necessary to formulate some quality assessment measures that can be used to judge the resolution of turbulent scales and the accuracy of predictions. In this context some new and refined measures are proposed above and beyond those already published by the authors in the common literature. These new measures involve (a) fraction of total turbulent kinetic energy, (b) relative grid size with respect to Kolmogorov or Taylor scales, (c) relative effective sub-grid/numerical viscosity with respect to molecular viscosity, and (d) some property related to power spectra of turbulent kinetic energy. In addition, an attempt is made to segregate the contributions from numerical and modeling errors. Proposed measures are applied to various benchmark cases, and validated against fully resolved LES and/or DNS whenever possible. Along the same line of thinking, the authors present a perspective for verification of under-resolved direct numerical simulations.

How white is the sky? 

2021 ◽  
Author(s):  
Nedjeljka Žagar ◽  
Žiga Zaplotnik ◽  
Valentino Neduhal
Keyword(s):  
Kinetic Energy ◽  
Gravity Wave ◽  
Power Law ◽  
Gravity Waves ◽  
Global Analysis ◽  
Vertical Motion ◽  
Energy Spectra ◽  
Horizontal Wind ◽  
Unified Framework ◽  
Inertia Gravity Waves

<p>The energy spectrum of atmospheric horizontal motions has been extensively studied in observations and numerical simulations. Its canonical shape includes a transition from the -3 power law at synoptic scale to -5/3 power law at mesoscale. The transition is taking place at scales around 500 km that can be seen as the scale where energy associated with quasi-linear inertia-gravity waves exceeds the balanced (or Rossby wave) energy. In contrast to the horizontal spectrum, the spectrum of kinetic energy of vertical motions is poorly known since the vertical motion is not an observed quantity of the global observing system and vertical kinetic energy spectra from non-hydrostatic models are difficult to validate.</p> <p>Traditionally, vertical velocities associated with the Rossby and gravity waves have been treated separately using the quasi-geostrophic omega equations and polarization relations for the stratified Boussinesq fluid in the (x,z) plane, respectively. In the tropics, the Rossby and gravity  wave regimes are difficult to separate and their frequency gap, present in the extra-tropics, is filled with the Kelvin and mixed Rossby-gravity waves. A separate treatment of the Rossby and gravity wave regimes makes it challenging to quantify energies of their vertical motions and vertical momentum fluxes. A unified treatment and wave interactions is performed by high-resolution non-hydrostatic models but their understanding requires the toolkit of theory. </p> <p>This contribution presents a unified framework for the derivation of vertical velocities of the Rossby and inertia-gravity waves and associated kinetic energy spectra. Expressions for the Rossby and gravity wave vertical velocities are derived using the normal-mode framework in the hydrostatic atmosphere that can be considered applicable up to the scale around 10 km. The derivation involves the analytical evaluation of divergence of the horizontal wind associated with the Rossby and inertia-gravity eigensolutions of the linearized primitive equations. The new framework is applied to the global analysis data of the ECMWF system. Results confirm that the tropical vertical kinetic energy spectra associated with inertia-gravity waves are on average indeed white. Deviations from the white spectrum are discussed for latitude and altitude bands.</p>

Numerical Predictions and Experiment Results for a 1m Diameter Methane Fire

2005 ◽  
Author(s):  
Amalia R. Black
Keyword(s):  
Experimental Data ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Turbulence Model ◽  
Vertical Velocity ◽  
Grid Size ◽  
Closure Models ◽  
Filter Width ◽  
Numerical Predictions ◽  
Temporal Filter

Comparisons between numerical predictions and experimental data for a methane fire have been performed. Vertical velocity and turbulent kinetic energy measurements along the centerline of the fire were used to validate the models in the SIERRA/Fuego fire code. Two different turbulence treatments, a steady RANS solution with a model for buoyancy generated turbulence, and an unsteady solution with closure models based on a temporal filter width were used. Solution sensitivity to grid size has been examined for both approaches. The results indicate strong sensitivities to the turbulence model.

scholarly journals Boundary-layer turbulent processes and mesoscale variability represented by Numerical Weather Prediction models during the BLLAST campaign

2016 ◽  
Author(s):  
Fleur Couvreux ◽  
Eric Bazile ◽  
Guylaine Canut ◽  
Yann Seity ◽  
Marie Lothon ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Sensible Heat Flux ◽  
Grid Size ◽  
Global Model ◽  
Sensible Heat ◽  
Mesoscale Variability ◽  
Order Of Magnitude

Abstract. This study evaluates the ability of three operational models, AROME, ARPEGE and ECMWF, to predict the boundary-layer turbulent processes and mesoscale variability observed during the Boundary Layer Late-Afternoon and Sunset Turbulence (BLLAST) field campaign. AROME is a 2.5 km limited area non-hydrostatic model operated over France, ARPEGE a global model with a 10 km grid-size over France and ECMWF a global model with a 16 km grid-size. We analyze the representation of the vertical profiles of temperature and humidity and the time evolution of near surface atmospheric variables as well as the radiative and turbulent fluxes for a total of 12 24h-long Intensive Observing Periods. Special attention is paid to the evolution of the turbulent kinetic energy that was sampled by a combination of independent instruments. For the first time, this variable, which is a central variable in the turbulence scheme used in AROME and ARPEGE, is evaluated with observations. In general, the 24h-forecasts succeed in reproducing the variability from one day to the other in term of cloud cover, temperature, boundary-layer depth. However, they exhibit some systematic biases, in particular a cold bias within the daytime boundary layer for all models. An overestimation of the sensible heat flux is noted for two points in ARPEGE, partly related to an inaccurate simplification of surface characteristics and over-predominance of forests. AROME shows a moist bias within the daytime boundary layer, consistently with overestimated latent heat fluxes. ECMWF presents a dry bias at 2 m above surface and also overestimates the sensible heat flux. The high-resolution model AROME better resolves the vertical structures, in particular the strong daytime inversion and the evening thin stable boundary layer. This model is also capable to capture the peculiar observed features, such as the orographically-driven subsidence and a well-defined maximum in water vapor mixing ratio in the upper part of the residual layer that arises during the evening due to mesoscale advection. The mesoscale variability is analyzed and the order of magnitude is also well reproduced in AROME. AROME provides a good simulation of the diurnal variability of the turbulent kinetic energy while ARPEGE shows a right order of magnitude.

scholarly journals On the influence of turbulent kinetic energy level on accuracy of k − ε and LRR turbulence models

2018 ◽  
Vol 45 (2) ◽  
pp. 139-149
Author(s):  
Djordje Novkovic ◽  
Jela Burazer ◽  
Aleksandar Cocic ◽  
Milan Lecic
Keyword(s):  
Kinetic Energy ◽  
Theoretical Analysis ◽  
Turbulent Kinetic Energy ◽  
Turbulent Flows ◽  
Cross Sections ◽  
Turbulence Models ◽  
Velocity Profiles ◽  
Navier Stokes ◽  
Test Case ◽  
Reynolds Stresses

This paper presents research regarding the influence of turbulent kinetic energy (TKE) level on accuracy of Reynolds averaged Navier?Stokes (RANS) based turbulence models. A theoretical analysis of influence TKE level on accuracy of the RANS turbulence models has been performed according to the Boussinesq hypothesis definition. After that, this theoretical analysis has been investigated by comparison of numerically and experimentally obtained results on the test case of a steady-state incompressible swirl-free flow in a straight conical diffuser named Azad diffuser. Numerical calculations have been performed using the OpenFOAM CFD software and first and secondorder closure turbulence models. TKE level, velocity profiles and Reynolds stresses have been calculated downstream in four different cross sections of the diffuser. Certain conclusions about modeling turbulent flows by ?? ??? and LRR turbulence models have been made by comparing the velocity profiles, TKE distribution and Reynolds stresses on the selected cross sections.

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