scholarly journals Turbulence Intensity and Length Scale Effects on Premixed Turbulent Flame Propagation

2021 ◽  
Author(s):  
Shrey Trivedi ◽  
R. S. Cant
Keyword(s):  
Strain Rate ◽  
Flame Propagation ◽  
Turbulence Intensity ◽  
Turbulent Flame ◽  
Integral Length Scale ◽  
Length Scale ◽  
Tangential Strain ◽  
Turbulent Flame Speed ◽  
Turbulence Length ◽  
Premixed Turbulent Flame

AbstractThe effects of varying turbulence intensity and turbulence length scale on premixed turbulent flame propagation are investigated using Direct Numerical Simulation (DNS). The DNS dataset contains the results of a set of turbulent flame simulations based on separate and systematic changes in either turbulence intensity or turbulence integral length scale while keeping all other parameters constant. All flames considered are in the thin reaction zones regime. Several aspects of flame behaviour are analysed and compared, either by varying the turbulence intensity at constant integral length scale, or by varying the integral length scale at constant turbulence intensity. The turbulent flame speed is found to increase with increasing turbulence intensity and also with increasing integral length scale. Changes in the turbulent flame speed are generally accounted for by changes in the flame surface area, but some deviation is observed at high values of turbulence intensity. The probability density functions (pdfs) of tangential strain rate and mean flame curvature are found to broaden with increasing turbulence intensity and also with decreasing integral length scale. The response of the correlation between tangential strain rate and mean flame curvature is also investigated. The statistics of displacement speed and its components are analysed, and the findings indicate that changes in response to decreasing integral length scale are broadly similar to those observed for increasing turbulence intensity, although there are some interesting differences. These findings serve to improve current understanding of the role of turbulence length scales in flame propagation.

Comparison of a spectral model for premixed turbulent flame propagation to DNS and experiments

2000 ◽  
Vol 4 (3) ◽  
pp. 241-264 ◽  
Author(s):  
Mark Ulitsky ◽  
Chaouki Ghenaï ◽  
Iskender Gökalp ◽  
Lian-Ping Wang ◽  
Lance R Collins
Keyword(s):  
Flame Propagation ◽  
Turbulent Flame ◽  
Spectral Model ◽  
Premixed Turbulent Flame

scholarly journals High-Fidelity Simulations of a Linear HPT Vane Cascade Subject to Varying Inlet Turbulence

2017 ◽  
Author(s):  
Richard Pichler ◽  
Richard D. Sandberg ◽  
Gregory Laskowski ◽  
Vittorio Michelassi
Keyword(s):  
Heat Flux ◽  
Turbulence Intensity ◽  
Side Surface ◽  
Suction Side ◽  
Transition Process ◽  
Length Scale ◽  
Length Scales ◽  
Inflow Turbulence ◽  
High Turbulence ◽  
Turbulence Length

The effect of inflow turbulence intensity and turbulence length scales have been studied for a linear high-pressure turbine vane cascade at Reis = 590,000 and Mis = 0.93, using highly resolved compressible large-eddy simulations employing the WALE turbulence model. The turbulence intensity was varied between 6% and 20% while values of the turbulence length scales were prescribed between 5% and 20% of axial chord. The analysis focused on characterizing the inlet turbulence and quantifying the effect of the inlet turbulence variations on the vane boundary layers, in particular on the heat flux to the blade. The transition location on the suction side of the vane was found to be highly sensitive to both turbulence intensity and length scale, with the case with turbulence intensity 20% and 20% length scale showing by far the earliest onset of transition and much higher levels of heat flux over the entire vane. It was also found that the transition process was highly intermittent and local, with spanwise parts of the suction side surface of the vane remaining laminar all the way to the trailing edge even for high turbulence intensity cases.

Hydrogen–Air–Steam Deflagration Experiment Simulated Using Different Turbulent Flame-Speed Closure Models

2018 ◽  
Vol 4 (3) ◽  
Author(s):  
Holler Tadej ◽  
Ed M. J. Komen ◽  
Kljenak Ivo
Keyword(s):  
Flame Propagation ◽  
Nuclear Power ◽  
Large Scale ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Energy Output ◽  
Combustion Model ◽  
Turbulent Flame Speed ◽  
Modeling Approach ◽  
Combustion Models

The paper presents the computational fluid dynamics (CFD) combustion modeling approach based on two combustion models. This modeling approach was applied to a hydrogen deflagration experiment conducted in a large-scale confined experimental vessel. The used combustion models were Zimont's turbulent flame-speed closure (TFC) model and Lipatnikov's flame-speed closure (FSC) model. The conducted simulations are aimed to aid identifying and evaluating the potential hydrogen risks in nuclear power plant (NPP) containment. The simulation results show good agreement with experiment for axial flame propagation using the Lipatnikov combustion model. However, substantial overprediction in radial flame propagation is observed using both combustion models, which consequently results also in overprediction of the pressure increase rate and overall combustion energy output. As assumed for a large-scale experiment without any turbulence inducing structures, the combustion took place in low-turbulence regimes, where the Lipatnikov combustion model, due to its inclusion of quasi-laminar source term, has advantage over the Zimont model.

Lateral dispersion in random cylinder arrays at high Reynolds number

2008 ◽  
Vol 600 ◽  
pp. 339-371 ◽  
Author(s):  
YUKIE TANINO ◽  
HEIDI M. NEPF
Keyword(s):  
Turbulence Intensity ◽  
Turbulent Diffusion ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Laboratory Data ◽  
Integral Length Scale ◽  
Length Scale ◽  
Linear Superposition ◽  
Cylinder Diameter ◽  
The Mean

Laser-induced fluorescence was used to measure the lateral dispersion of passive solute in random arrays of rigid, emergent cylinders of solid volume fraction φ=0.010–0.35. Such densities correspond to those observed in aquatic plant canopies and complement those in packed beds of spheres, where φ≥0.5. This paper focuses on pore Reynolds numbers greater than Res=250, for which our laboratory experiments demonstrate that the spatially averaged turbulence intensity and Kyy/(Upd), the lateral dispersion coefficient normalized by the mean velocity in the fluid volume, Up, and the cylinder diameter, d, are independent of Res. First, Kyy/(Upd) increases rapidly with φ from φ =0 to φ=0.031. Then, Kyy/(Upd) decreases from φ=0.031 to φ=0.20. Finally, Kyy/(Upd) increases again, more gradually, from φ=0.20 to φ=0.35. These observations are accurately described by the linear superposition of the proposed model of turbulent diffusion and existing models of dispersion due to the spatially heterogeneous velocity field that arises from the presence of the cylinders. The contribution from turbulent diffusion scales with the mean turbulence intensity, the characteristic length scale of turbulent mixing and the effective porosity. From a balance between the production of turbulent kinetic energy by the cylinder wakes and its viscous dissipation, the mean turbulence intensity for a given cylinder diameter and cylinder density is predicted to be a function of the form drag coefficient and the integral length scale lt. We propose and experimentally verify that lt=min{d, 〈sn〉A}, where 〈sn〉A is the average surface-to-surface distance between a cylinder in the array and its nearest neighbour. We farther propose that only turbulent eddies with mixing length scale greater than d contribute significantly to net lateral dispersion, and that neighbouring cylinder centres must be farther than r* from each other for the pore space between them to contain such eddies. If the integral length scale and the length scale for mixing are equal, then r*=2d. Our laboratory data agree well with predictions based on this definition of r*.

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