Large-Eddy Simulation of Subsonic Jets

Vuorinen, Ville; Wehrfritz, Armin; Yu, Jingzhou; Kaario, Ossi; Larmi, Martti; Boersma, Bendiks Jan

doi:10.1088/1742-6596/318/3/032052

Cited by 10 publications

(8 citation statements)

References 8 publications

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“…Figure 11 also reveals that the current computational study was able to capture Kelvin-Helmholtz (K-H) type instabilities which are created due to significant shear forces. These types of instabilities have also been noticed earlier in both subsonic and supersonic jets (Vuorinen et al, 2011;Vuorinen et al, 2014b). After formation of the initial vortex ring, annular shear layer are producing K-H instabilities continuously; however, in some snapshots of Figure 11 these instabilities cannot be identified.…”

Section: K-h Type Instabilitysupporting

confidence: 60%

“…After formation of the initial vortex ring, annular shear layer are producing K-H instabilities continuously; however, in some snapshots of Figure 11 these instabilities cannot be identified. This may be because they were concealed by the excessive amount of turbulent scales (Vuorinen et al, 2011). The counter-rotating secondary vortex ring, that was discussed earlier, created a concave tip in the under-expanded jets with NPR=6.5 and 8.5 as can be seen at t=30 μs in Figure 11.…”

Section: K-h Type Instabilitymentioning

confidence: 74%

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LES and RANS modelling of under-expanded jets with application to gaseous fuel direct injection for advanced propulsion systems

Hamzehloo

Aleiferis

2019

International Journal of Heat and Fluid Flow

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A density-based solver with the classical fourth-order accurate Runge-Kutta temporal discretization scheme was developed and applied to study under-expanded jets issued through millimeter-size nozzles for applications in highpressure direct-injection (DI) gaseous-fuelled propulsion systems. Both large eddy simulation (LES) and Reynoldsaveraged Navier-Stokes (RANS) turbulence modelling techniques were used to evaluate the performance of the new code. The computational results were compared both quantitatively and qualitatively against available data from the literature. After initial evaluation of the code, the computational framework was used in conjunction with RANS modelling (k-ω SST) to investigate the effect of nozzle exit geometry on the characteristics of gaseous jets issued from millimeter-size nozzles. Cylindrical nozzles with various length to diameter ratios, namely 5, 10 and 20, in addition to a diverging conical nozzle, were studied. This study is believed to be the first to provide a direct comparison between RANS and LES within the context of nozzle exit profiling for advanced high-pressure injection systems with the formation of under-expanded jets. It was found that reducing the length of the straight section of the nozzle by 50% resulted in a slightly higher level of under-expansion (~2.6% higher pressure at the nozzle exit) and ~1% higher mass flow rate. It was also found that a nozzle with 50% shorter length resulted in ~6% longer jet penetration length. At a constant nozzle pressure ratio (NPR), a lower nozzle length to diameter ratio resulted in a noticeably higher jet penetration. It was found that with a diverging conical nozzle, a fairly higher penetration length could be achieved if an under-expanded jet formed downstream of the nozzle exit compared to a jet issued from a straight nozzle with the same NPR. This was attributed to the radial restriction of the flow and consequently formation of a relatively smaller reflected shock angle. With the conical nozzle used in this study and a 30 bar injection pressure, an under-expanded hydrogen jet exhibited ~60% higher penetration length compared to an under-expanded nitrogen jet at 100 μs after start of injection. Moreover, the former jet exhibited ~22% higher penetration compared to a nitrogen jet issued through the conical profile with 150 bar injection pressure.

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Section: K-h Type Instabilitysupporting

confidence: 60%

Section: K-h Type Instabilitymentioning

confidence: 74%

LES and RANS modelling of under-expanded jets with application to gaseous fuel direct injection for advanced propulsion systems

Hamzehloo

Aleiferis

2019

International Journal of Heat and Fluid Flow

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“…An explicit, density based approach is employed along with the classical 4th-order accurate Runge-Kutta time integration scheme. Among other validation studies (e.g., turbulent channel flow), the solver was validated by Vuorinen et al 16 for turbulent subsonic jets and also laminar flows.…”

Section: B Les Based On Scale Selective Discretizationmentioning

confidence: 99%

“…1,4,[10][11][12][13][14] The presence of the Mach disk has also been reported for conditions which are relevant for combustion engines by White and Milton. 12 The numerical framework for LES of subsonic and incompressible turbulent jets is well established [15][16][17][18][19][20][21][22] and the recent studies have focused on supersonic conditions. [23][24][25][26][27][28][29][30] A review on the classical and the state-of-the-art numerical methods for high-speed flows can be found in the review article by Pirozzoli.…”

Section: Introductionmentioning

confidence: 99%

“…As a numerical tool, we have implemented a density based 4th-order Runge-Kutta finite volume (FV) solver using the OpenFOAM R library. 16 The FVmethod on an unstructured grid framework is chosen since the method should be eventually applied in complex geometries. The results are qualitatively compared with planar laser induced fluorescence (PLIF) experiments.…”

Section: Introductionmentioning

confidence: 99%

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Large-eddy simulation of highly underexpanded transient gas jets

Vuorinen¹,

Yu²,

Tirunagari³

et al. 2013

Physics of Fluids

157

142

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Large-eddy simulations (LES) based on scale-selective implicit filtering are carried out in order to study the effect of nozzle pressure ratios on the characteristics of highly underexpanded jets. Pressure ratios ranging from 4.5 to 8.5 with Reynolds numbers of the order 75 000-140 000 are considered. The studied configuration agrees well with the classical picture of the structure of highly underexpanded jets. Similarities and differences between simulation and experiments are discussed by comparing the concentration field structures from LES and planar laser induced fluorescence data. The transient stages, leading eventually to the highly underexpanded state, are visualized and investigated in terms of a phase diagram revealing the shock speeds and duration of the transient stages. For the studied nozzle pressure ratio range, the Mach disk dimensions are found to be in good agreement with literature data and experimental observations. It is observed how the nozzle pressure ratio influences the Mach disk width, and thereby the slip line separation, which leads to co-annular jets with inner and outer shear layers at higher pressure ratios. The improved mixing with increasing pressure ratio is demonstrated by the probability density functions of the concentration. The coherent structures downstream of the Mach disk are identified using proper orthogonal decomposition (POD). The structures indicate a helical mode originating from the shear layers of the jet. Despite the relatively low energy content of the dominant POD modes, the frequencies of the POD time coefficients explain the dominant frequencies in the pressure fluctuation spectra. C

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