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**1 - 10**of**10**### Iowa State University Digital Repository @ Iowa State University

, 2010

"... Bioethanol production from lignocellulosic feedstock using aqueous ammonia pretreatment and simultaneous saccharification and fermentation (SSF): process development and optimization ..."

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Bioethanol production from lignocellulosic feedstock using aqueous ammonia pretreatment and simultaneous saccharification and fermentation (SSF): process development and optimization

### Modeling flame brush thickness in premixed turbulent combustion By

"... Turbulent flame brush thickness is a characteristic measure of the transition zone between the burned and unburned states of a premixed flame. It may be interpreted as the square root of flame position variance, and must be accurately described if the flow properties and heat release characteristics ..."

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Turbulent flame brush thickness is a characteristic measure of the transition zone between the burned and unburned states of a premixed flame. It may be interpreted as the square root of flame position variance, and must be accurately described if the flow properties and heat release characteristics of a premixed flame are to be captured. In this work the transport equation for the flame brush thickness is presented and new modeling approaches to the unclosed production and dissipation terms are suggested. To validate and test these approaches, a series of direct numerical simulations (DNS) of turbulent level set propagation are performed. These simulations provide the data needed to set the constants in the RANS-type production and dissipation closure models. The resulting transport equation for the flame brush thickness accurately describes transient cases and thus offers an improved means of predicting flame properties in non-equilibrium regions, e.g., near burner nozzles or flame stabilizers. 1.

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"... Modeling of the wrinkling of premixed turbulent flames in the thin reaction zones regime for large eddy simulation ..."

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Modeling of the wrinkling of premixed turbulent flames in the thin reaction zones regime for large eddy simulation

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"... Coupling tabulated chemistry with large-eddy simulation of turbulent reactive flows ..."

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Coupling tabulated chemistry with large-eddy simulation of turbulent reactive flows

### DNS of Turbulent Primary Atomization Using a Level Set/Vortex Sheet Method

"... Modeling the primary atomization of turbulent liquid jets and sheets still remains an unsolved problem. Considering numerical grid resolutions typical for Large Eddy Simulations, the large scale liquid structures during primary breakup are well resolved, whereas all small scale structures are unreso ..."

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Modeling the primary atomization of turbulent liquid jets and sheets still remains an unsolved problem. Considering numerical grid resolutions typical for Large Eddy Simulations, the large scale liquid structures during primary breakup are well resolved, whereas all small scale structures are unresolved and thus require modeling. To help in the derivation of such subgrid models, DNS of the turbulent breakup of surfaces have been performed using the Level Set/Vortex Sheet method. To address the volume/mass errors inherent in the standard level set approach, a Refined Level Set Grid method is presented. LES filtering techniques consistent with the general scaling symmetries of the level set equation are discussed and applied to the DNS results. The influence of key parameters on the turbulent breakup, like the Weber number and the turbulent Weber number are explored, and a closure for the turbulent production term of the subgrid phase interface length scale is proposed. ∗Corresponding Author 1

### Open Access Some Basic Issues of the Averaged G-Equation Approach to Premixed Turbulent Combustion Modeling

"... Abstract: In a recently developed and widely used premixed turbulent flame model, the so-called G-equation is averaged and combined with a balance equation for the variance G 2 G G ()2, where G is an averaged G-field. The goal of this communication is to discuss certain basic issues relevant to the ..."

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Abstract: In a recently developed and widely used premixed turbulent flame model, the so-called G-equation is averaged and combined with a balance equation for the variance G 2 G G ()2, where G is an averaged G-field. The goal of this communication is to discuss certain basic issues relevant to the G- and 2 G -equations and, in particular, to stress that the latter equation is ill defined, because the G- and G-equations are physically meaningful at different surfaces. Moreover, by analyzing simple examples, it is shown that a widely accepted association of the scalar G with the so-called distance function does not allow us to consider the G-equation to be physically meaningful in the entire flow field.

### Open Access Large-Eddy Simulation for Combustion Systems: Modeling Approaches for Partially Premixed Flows

"... Abstract: Combustion models often appear in forms that are customized for specific applications. This process of custo-mization produces modeling approaches that tend to be very different from one another in terms of cost, accuracy, and ap-plicability. For example, many combustion models have been d ..."

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Abstract: Combustion models often appear in forms that are customized for specific applications. This process of custo-mization produces modeling approaches that tend to be very different from one another in terms of cost, accuracy, and ap-plicability. For example, many combustion models have been developed to describe either the asymptotic premixed or the asymptotic non-premixed combustion limit. These idealized regimes are chosen as the basis for modeling approaches be-cause the associated combustion physics are understood sufficiently well to be cast in a framework that accounts for how turbulence and chemistry interact. Partially premixed regimes and regimes that involve transitions between premixed and non-premixed behavior, however, are not very well understood. Consequently, most readily available modeling ap-proaches do not account for these mixed regimes in a very careful fashion. This presents a particular challenge to further model development, since these partially premixed and transition processes are very important in realistic combustion de-vices. In this review, the particular challenges associated with modeling partially premixed combustion in LES will be discussed and the applicability of common LES combustion models to partially premixed processes will be assessed.

### 3. DATES COVERED 4. TITLE AND SUBTITLE

, 2006

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