scholarly journals Incipient thermal choking and stable shock-train formation in the heat-release region of a scramjet combustor. Part II: Large eddy simulations

2015 ◽  
Vol 162 (4) ◽  
pp. 907-920 ◽  
Author(s):  
Johan Larsson ◽  
Stuart Laurence ◽  
Iván Bermejo-Moreno ◽  
Julien Bodart ◽  
Sebastian Karl ◽  
...  
Keyword(s):  
Heat Release ◽  
Large Eddy Simulations ◽  
Shock Train ◽  
Scramjet Combustor ◽  
Large Eddy

scholarly journals Linear-eddy subgrid model for reacting large-eddy simulations - Heat release effects

1997 ◽  
Author(s):  
William Calhoon, Jr. ◽  
Suresh Menon ◽  
William Calhoon, Jr. ◽  
Suresh Menon
Keyword(s):  
Heat Release ◽  
Large Eddy Simulations ◽  
Subgrid Model ◽  
Large Eddy

Confinement effects in shock wave/turbulent boundary layer interactions through wall-modelled large-eddy simulations

2014 ◽  
Vol 758 ◽  
pp. 5-62 ◽  
Author(s):  
Iván Bermejo-Moreno ◽  
Laura Campo ◽  
Johan Larsson ◽  
Julien Bodart ◽  
David Helmer ◽  
...  
Keyword(s):  
Turbulent Flows ◽  
Separation Bubble ◽  
Incident Shock ◽  
Large Eddy Simulations ◽  
Periodic Case ◽  
Shock Train ◽  
Mean Flow ◽  
Lateral Confinement ◽  
Large Eddy ◽  
Shock System

AbstractWe present wall-modelled large-eddy simulations (WLES) of oblique shock waves interacting with the turbulent boundary layers (TBLs) (nominal$\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\delta _{99}=5.4\ \mathrm{mm}$and${\mathit{Re}}_{\theta }\approx 1.4\times 10^4$) developed inside a duct with an almost-square cross-section ($45\ \mathrm{mm}\times 47.5\ \mathrm{mm}$) to investigate three-dimensional effects imposed by the lateral confinement of the flow. Three increasing strengths of the incident shock are considered, for a constant Mach number of the incoming air stream$M\approx 2$, by varying the height (1.1, 3 and 5 mm) of a compression wedge located at a constant streamwise location that spans the top wall of the duct at a 20° angle. Simulation results are first validated with particle image velocimetry (PIV) experimental data obtained at several vertical planes (one near the centre of the duct and three near one of the sidewalls) for the 1.1 and 3 mm-high wedge cases. The instantaneous and time-averaged structure of the flow for the stronger-interaction case (5 mm-high wedge), which shows mean flow reversal, is then investigated. Additional spanwise-periodic simulations are performed to elucidate the influence of the sidewalls, and it is found that the structure and location of the shock system, as well as the size of the separation bubble, are significantly modified by the lateral confinement. A Mach stem at the first reflected interaction is present in the simulation with sidewalls, whereas a regular shock intersection results for the spanwise-periodic case. Low-frequency unsteadiness is observed in all interactions, being stronger for the secondary shock reflections of the shock train developed inside the duct. The downstream evolution of secondary turbulent flows developed near the corners of the duct as they traverse the shock system is also studied.

Large-Eddy Simulations of a Normal Shock Train in a Constant-Area Isolator

AIAA Journal ◽  
2014 ◽  
Vol 52 (3) ◽  
pp. 539-558 ◽  
Author(s):  
Brandon Morgan ◽  
Karthik Duraisamy ◽  
Sanjiva K. Lele
Keyword(s):  
Large Eddy Simulations ◽  
Normal Shock ◽  
Shock Train ◽  
Constant Area ◽  
Large Eddy

Understanding partial fuel stratification for low temperature gasoline combustion using large eddy simulations

2020 ◽  
pp. 146808742092104
Author(s):  
Priya Priyadarshini ◽  
Aimilios Sofianopoulos ◽  
Sotirios Mamalis ◽  
Benjamin Lawler ◽  
Dario Lopez-Pintor ◽  
...  
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Direct Injection ◽  
Large Eddy Simulations ◽  
Compression Ignition ◽  
Load Range ◽  
Injection Strategy ◽  
Compression Ignition Engines ◽  
Fuel Stratification ◽  
Large Eddy

The development of gasoline compression ignition engines operating in a low temperature combustion mode depends heavily on robust control of the heat release profile. Partial fuel stratification is an effective method for controlling the heat release by creating a stratified mixture prior to autoignition, which can be beneficial for operation across a wide load range. In this study, three-dimensional large eddy simulations were used to model a double direct injection strategy for which 80% of the fuel was injected during the intake stroke, and 20% of the fuel was injected at varying timing during the compression stroke. The simulations replicated a set of experiments performed at Sandia National Laboratories on a 1-L single-cylinder research engine using E10 gasoline (gasoline fuel containing 10% vol. ethanol). The objective of this study is to analyze the effects of the double direct injection strategy on the compositional and thermal stratification of the mixture, and understand the best use of this operating strategy. The modeling results indicated that by retarding the start of the second injection, the mixture stratification increases, which can be used to control the autoignition timing and the combustion phasing. Ignition and CA50 (crank angle of 50% mass fraction burned) are dictated by the mass concentration of the richest zones in the combustion chamber, as well as their location. The richer zones have the lowest temperatures before ignition primarily due to evaporative cooling from direct fuel injection. Overall, this study enhances the understanding of partial fuel stratification that can be used for controlling the heat release in gasoline compression ignition engines.

A comparative study of gasoline skeletal mechanisms under partial fuel stratification conditions using large eddy simulations

2021 ◽  
pp. 146808742110313
Author(s):  
Gaurav Guleria ◽  
Dario Lopez-Pintor ◽  
John E Dec ◽  
Dimitris Assanis
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Chemical Kinetic ◽  
Large Eddy Simulations ◽  
Low Temperature Combustion ◽  
Fuel Stratification ◽  
Large Eddy ◽  
Kinetic Mechanisms ◽  
Temperature Combustion ◽  
Research Grade

Partial fuel stratification (PFS) is a low temperature combustion strategy that can alleviate high heat release rates of traditional low temperature combustion strategies by introducing compositional stratification in the combustion chamber using a split fuel injection strategy. In this study, a three-dimensional computational fluid dynamics (CFD) model with large eddy simulations and reduced detailed chemistry was used to model partial fuel stratification at three different stratified conditions. The double direct injection strategy injects 80% of the total fuel mass at −300 CAD aTDC and the remaining 20% of the fuel mass is injected at three different timings of −160, −50, −35 CAD to create low, medium, and high levels of compositional stratification, respectively. The PFS simulations were validated using experiments performed at Sandia National Laboratories on a single-cylinder research engine that operates on RD5-87, a research-grade E10 gasoline. The objective of this study is to compare the performance of three different reduced chemical kinetic mechanisms, namely SKM1, SKM2, and SKM3, at the three compositional stratification levels and identify the most suitable mechanism to reproduce the experimental data. Zero-dimensional chemical kinetic simulations were also performed to further understand differences in performance of the three reduced chemical kinetic mechanisms to explain variations in CFD derived heat release profiles. The modeling results indicate that SKM3 is the most suitable mechanism for partial fuel stratification modeling of research-grade gasoline. The results also show that the autoignition event progresses from the richer to the leaner compositional regions in the combustion chamber. Notably, the leaner regions that have less mass per unit volume, can contribute disproportionately more toward heat release as there are more cells at leaner equivalence ratio ranges. Overall, this study illuminates the underlying compositional stratification phenomena that control the heat release process in PFS combustion.

Incipient thermal choking and stable shock-train formation in the heat-release region of a scramjet combustor. Part I: Shock-tunnel experiments

2015 ◽  
Vol 162 (4) ◽  
pp. 921-931 ◽  
Author(s):  
S.J. Laurence ◽  
D. Lieber ◽  
J. Martinez Schramm ◽  
K. Hannemann ◽  
J. Larsson
Keyword(s):  
Heat Release ◽  
Shock Tunnel ◽  
Shock Train ◽  
Scramjet Combustor
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