A simple algebraic model for the Favre averaged scalar dissipation rate, c, in high Damkohler number premixed flames is obtained from its transport equation by balancing leading order terms. Recently proposed models dominant terms are revisited and revised. The incorporates essential physics of turbulent flames, namely, dilatation influence on turbulence-scalar interaction, chemical reactions, processes. realizability analysis carried out to show that always unconditionally realizable....

Scalar dissipation rate is a central quantity in turbulent flame modeling as it closely related to the reaction rate. It well known that turbulence-scalar interaction plays vital role flows with scalar mixing and thus on This process characterized by tensor inner product between gradient vector turbulence strain found depend strongly Damköhler number, Da. Two direct numerical simulation data sets are analyzed detail order understand physics of Da dependence. The alignment most compressive...

Three-dimensional direct numerical simulation (DNS) of turbulent combustion under moderate and intense low-oxygen dilution (MILD) conditions has been carried out inside a cuboid with inflow outflow boundaries on the upstream downstream faces, respectively. The initial inflowing mixture turbulence fields are constructed carefully to be representative MILD involving partially mixed pockets unburned burned gases. kinetics modeled using skeletal mechanism for methane-air combustion, including...

We highlight the critical role of data in developing sustainable combustion technologies for industries requiring high-density and localized energy sources. Combustion systems are complex difficult to predict, high-fidelity simulations out reach practical because computational cost. Data-driven approaches artificial intelligence offer promising solutions, enabling renewable synthetic fuels meet decarbonization goals. discuss open challenges associated with availability fidelity data,...

The interaction of turbulence with progress variable, c, field in a premixed flame is studied. This characterized by the correlation c,ieijc,j¯, where overbar denotes an appropriate averaging process, c,i gradient c spatial direction i and eij strain rate. importance this term recognized via transport equation for square magnitude scalar turbulent flames. It also shown that above forms natural part tangential rate which appears surface density, Σ, equation. well known negative signifying...

Stereoscopic particle image velocimetry and planar laser induced fluorescence measurements of hydroxyl radical are simultaneously applied to measure, respectively, local turbulence intensities flame front position in premixed ethylene-air flames stabilized on a bluff body. Three different equivalence ratios, 0.55, 0.63, 0.7, three Reynolds numbers, 14 000, 17 21 considered. Laser were made for five configurations within the ranges above corresponding cold flows. By comparing hot flows,...

Abstract A strategy to extract turbulence structures from direct numerical simulation (DNS) data is described along with a systematic analysis of geometry and spatial distribution the educed structures. DNS dataset decaying homogeneous isotropic at Reynolds number ${\mathit{Re}}_{\lambda } = 141$ considered. bandpass filtering procedure shown be effective in extracting enstrophy dissipation their smallest scales matching filter width, $L$ . The these characterized classified through use two...

The validity of the commonly used flame marker for heat release rate (HRR) visualization, namely reaction OH + CH2O ⇔ HCO H2O is re-examined. This done both methane–air and multi-component fuel–air mixtures lean stoichiometric conditions. Two different methods are to identify HRR correlations, it found that correlations vary strongly with stoichiometry. For methane mixture there exist alternative markers, while fuel above correlation be inadequate. Alternative markers visualization thus...

Direct numerical simulations of Moderate or Intense Low-oxygen Dilution combustion inside a cubical domain are performed. The computational is specified with inflow and outflow boundary conditions in one direction periodic the other two directions. inflowing mixture constructed carefully preprocessing step has spatially varying fraction reaction progress variable fields. Thus, this includes range thermo-chemical states for given value. kinetics modelled using 58-step skeletal mechanism...

This study focuses on the modelling of turbulent lifted jet flames using flamelets and a presumed Probability Density Function (PDF) approach with interest in both flame lift-off height brush structure. First, flamelet models used to capture contributions from premixed non-premixed modes partially combustion are assessed Direct Numerical Simulation (DNS) data for hydrogen flame. The joint PDFs mixture fraction Z progress variable c, including their statistical correlation, obtained copula...

The scalar dissipation rate transport in both the corrugated flamelet and thin reaction zone regimes is studied using three-dimensional direct numerical simulation (DNS) databases for freely propagating statistically planar turbulent premixed flames. Both flames have comparable Reynolds number but flame representing combustion regime has a global Damköhler number, Da>1, whereas second Da<1. It demonstrated that of its molecular diffusive strong Da dependence. contributions...

The sound emission from open turbulent flames is dictated by the two-point spatial correlation of rate change fluctuating heat release rate. This in premixed can be represented well using Gaussian-type functions and unstrained laminar flame thermal thickness used to scale length scale, which about a quarter planar thickness. its are observed less influenced fuel type or stoichiometry turbulence Reynolds Damkohler numbers. time for deduced τ c /34 on an average, where direct numerical...

Abstract Kinetic energy and reactive scalar spectra in turbulent premixed flames are studied from compressible three-dimensional direct numerical simulations (DNS) of a temporally evolving rectangular slot-jet flame, statistically one-dimensional configuration. The correspond to lean hydrogen–air mixture at an equivalence ratio 0.7, preheated 700 K 1 atm, three DNS considered with fixed jet Reynolds number 10 000 Damköhler varying between 0.13 0.54. For the study spectra, motivated by need...