Evidence for supercritical mixing layers in the ECN Spray A

Falgout, Zachary; Rahm, Mattias; Wang, Zhenkan; Linne, Mark

doi:10.1016/j.proci.2014.06.109

Cited by 55 publications

(17 citation statements)

References 11 publications

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“…Also, Agarwal and Trujillo [63] demonstrated the effects of nozzle imperfection on generating stronger radial velocity components with shorter liquid core and faster primary atomization. With relevance to the high temperature and pressure environment in Spray A, Falgout et al [64] reported evidences on the existence of supercritical effects in the mixing layer, thereby supporting the hypothesis which was previously investigated in [65][66][67] and theoretically established in [68,69]. On the other hand, recent observations by Crua at al.…”

Section: Introductionsupporting

confidence: 53%

Large-Eddy Simulation of ECN Spray A: Sensitivity Study on Modeling Assumptions

et al. 2020

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In this study, various mixing and evaporation modeling assumptions typically considered for large-eddy simulation (LES) of the well-established Engine Combustion Network (ECN) Spray A are explored. A coupling between LES and Lagrangian particle tracking (LPT) is employed to simulate liquid n-dodecane spray injection into hot inert gaseous environment, wherein Lagrangian droplets are introduced from a small cylindrical injection volume while larger length scales within the nozzle diameter are resolved. This LES/LPT approach involves various modeling assumptions concerning the unresolved near-nozzle region, droplet breakup, and LES subgrid scales (SGS) in which their impact on common spray metrics is usually left unexplored despite frequent utilization. Here, multi-parametric analysis is performed on the effects of (i) cylindrical injection volume dimensions, (ii) secondary breakup model, particularly Kelvin–Helmholtz Rayleigh–Taylor (KHRT) against a no-breakup model approach, and (iii) LES SGS models, particularly Smagorinsky and one-equation models against implicit LES. The analysis indicates the following findings: (i) global spray characteristics are sensitive to radial dimension of the cylindrical injection volume, (ii) the no-breakup model approach performs equally well, in terms of spray penetration and mixture formation, compared with KHRT, and (iii) the no-breakup model is generally insensitive to the chosen SGS model for the utilized grid resolution.

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Section: Introductionsupporting

confidence: 53%

Large-Eddy Simulation of ECN Spray A: Sensitivity Study on Modeling Assumptions

et al. 2020

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“…A common feature of all simulations is the formation of high |∇| magnitude (HDGM) regions which result from the species diffusional mixing. The HDGM observation is entirely consistent with experiments conducted under high- fully turbulent flow conditions [38,39,40,41] and detected [42] in the Engine Combustion Network Spray A Sandia data [43] that was obtained at an ambient  of 60 atm and ambient  of 900 K (compare with the free-stream conditions of Tables 1 and 2). This latter data is described on the Sandia web site [43] as "The Spray A condition is a low-temperature combustion condition relevant to engines that use moderate EGR" which is entirely consistent with the composition listed in Table 2.…”

Section: Brief Description Of Previous Results Obtained From Analyzinsupporting

confidence: 87%

Evaluation of mixture-fraction-based turbulent-reaction-rate model assumptions for high-pressure reactive flows

Bellan

2017

Combustion and Flame

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Several assumptions of atmospheric-pressure (atmospheric-) single-phase turbulent reaction rate models are examined for high- reactive flows having turbulent characteristics. The study uses a Direct Numerical Simulation (DNS) database described elsewhere [1]. This database was obtained with a model combining multi-species mixing under high- conditions, a real-gas equation of state (EOS) and a single-step chemical reaction. The database, created in the configuration of a temporal mixing layer, probes the effect of the initial Reynolds number, Re 0  of the initial pressure,  0 , and of the initial composition of the two mixing-layer streams. The reaction is initiated in a turbulent flow and in each simulation the computations are pursued past a time when a maximum average-volumetric  is attained,  * . The examination of the vorticity and enstrophy equations at a time before reaction initiation and also at  *  highlights the pivotal role of the high density-gradient magnitude regions [1] in producing turbulence and the crucial role at  *  of the baroclinic effect representing the misalignments of gradients of thermodynamic variables. Compared to the classical mixture fraction equation, the results show that the mixture fraction obeys an equation in which there is an additional diffusion term having a larger r.m.s. magnitude than that of the mixture-fraction typical diffusion term. An assessment of the Conditional Source-term Estimation (CSE) model assumptions found that, using an accurate mixture fraction probability density function (PDF), one can obtain a very good representation of the turbulent reaction rate in the most intense reaction regions, however the quality of the predictions of CSE deteriorated significantly when a common model for the PDF, the -PDF, was used despite the -PDF being constructed with the accurate moments extracted from the DNS. In the regions of minimal reaction, the CSE model using the exact PDF extracted from the DNS does not provide an accurate representation of the turbulent reaction rate, a fact which is attributed to the combined effect of lack of correlation between fluctuations of the reaction rate and of the mixture fraction, and to the strong correlation of the thermodynamic variables through the real-gas EOS in regions of colder and denser fluid.

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“…Falgout et al [46] has also provided evidence of dense-fluid mixing layers using ballistic imaging of the same diesel fuel injector at the same chamber conditions. A thickened turbulent n-dodecane-nitrogen mixing layer was found to evolve with a cellular structure characteristic of gas jets.…”

Section: Introductionmentioning

confidence: 92%

Liquid jet breakup regimes at supercritical pressures

Dahms

Oefelein

2015

Combustion and Flame

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Previously, a theory has been presented that explains how discrete vapor-liquid interfaces become diminished at certain high-pressure conditions in a manner that leads to well known qualitative trends observed from imaging in a variety of experiments. Rather than surface tension forces, transport processes can dominate over relevant ranges of conditions. In this paper, this framework is now generalized to treat a wide range of fuel-oxidizer combinations in a manner consistent with theories of capillary flows and extended corresponding states theory. Different flow conditions and species-specific molecular properties are shown to produce distinct variations of interfacial structures and local free molecular paths. These variations are shown to occur over the operating ranges in a variety of propulsion and power systems. Despite these variations, the generalized analysis reveals that the envelope of flow conditions at which the transition from classical sprays to diffusion-dominated mixing occurs exhibits a characteristic shape for all liquid-gas combinations. For alkane-oxidizer mixtures, it explains that these conditions shift to higher pressure flow conditions with increasing carbon number and demonstrates that, instead of widely assumed classical spray atomization, diffusion-dominated mixing may occur under relevant high-pressure conditions in many modern devices.

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Evidence for supercritical mixing layers in the ECN Spray A

Cited by 55 publications

References 11 publications

Large-Eddy Simulation of ECN Spray A: Sensitivity Study on Modeling Assumptions

Large-Eddy Simulation of ECN Spray A: Sensitivity Study on Modeling Assumptions

Evaluation of mixture-fraction-based turbulent-reaction-rate model assumptions for high-pressure reactive flows

Liquid jet breakup regimes at supercritical pressures

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