Analysis of small-scale scalar mixing processes in highly under-expanded jets

Buttay, Romain; Lehnasch, Guillaume; Mura, Arnaud

doi:10.1007/s00193-015-0599-7

Cited by 18 publications

(4 citation statements)

References 35 publications

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“…Seventh-order accurate weighted essentially non-oscillatory (WENO7) reconstruction of the characteristic fluxes was also adopted for simulating under-expanded jets. The shocks and discontinuities can be resolved using highly accurate and low-dissipation hybrid ENO schemes with shock detectors [65][66][67].…”

Section: Discretization Schemes and Solution Algorithmsmentioning

confidence: 99%

“…Figure 13 reports an example of SDR computed for an under-expanded methane jet. Some research used an SDR approach, concluding that a higher NPR favours a better and quicker air/fuel mixing [53,65,75]. This shows that NPR may substantially modify the mixing processes, which is not good news considering that high gaseous fuel injection pressures are typically not easily reachable due to intrinsic limitations in on-board gaseous fuel storage systems [114].…”

Section: Far Field-turbulent Mixingmentioning

confidence: 99%

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Under-Expanded Jets in Advanced Propulsion Systems—A Review of Latest Theoretical and Experimental Research Activities

Duronio,

Villante,

De Vita

2023

Energies

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The current ongoing rise in environmental pollution is leading research efforts toward the adoption of propulsion systems powered by gaseous fuels like hydrogen, methane, e-fuels, etc. Although gaseous fuels have been used in several types of propulsion systems, there are still many aspects that can be improved and require further study. For this reason, we considered it important to provide a review of the latest research topics, with a particular focus on the injection process. In advanced engine systems, fuel supply is achieved via enhanced direct injection into the combustion chamber. The latter involves the presence of under-expanded jets. Under-expanded jets are a particular kind of compressible flow. For this reason, the review initially provides a brief physical explanation of them. Next, experimental and numerical CFD investigation techniques are discussed. The last section of this manuscript presents an analysis of the jet’s structure. The injection parameters commonly used are examined; next, the characteristics of the near-nozzle field are reviewed and finally, the far-field turbulent mixing, which strongly affects the air–fuel mixture formation process, is discussed.

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Section: Discretization Schemes and Solution Algorithmsmentioning

confidence: 99%

Section: Far Field-turbulent Mixingmentioning

confidence: 99%

Under-Expanded Jets in Advanced Propulsion Systems—A Review of Latest Theoretical and Experimental Research Activities

Duronio,

Villante,

De Vita

2023

Energies

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“…Such a canonical flowfield is typical of the shock-mixing layer interactions that take place in compressible flows of practical interest [12]. For instance, supersonic jets at high nozzle-pressure ratio (NPR) give rise to complex cellular structures, where shocks and expansions waves interact with the turbulent outer shear layer [13]. It is also relevant to scramjet intakes and combustors, where shock waves interact with the shear layers issued from the injection systems.…”

Section: Introductionmentioning

confidence: 99%

On the role of bulk viscosity in compressible reactive shear layer developments

Boukharfane

Ferrer

Mura

et al. 2019

European Journal of Mechanics - B/Fluids

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a b s t r a c tDespite 150 years of research after the reference work of Stokes, it should be acknowledged that some confusion still remains in the literature regarding the importance of bulk viscosity effects in flows of both academic and practical interests. On the one hand, it can be readily shown that the neglection of bulk viscosity (i.e., κ = 0) is strictly exact for mono-atomic gases. The corresponding bulk viscosity effects are also unlikely to alter the flowfield dynamics provided that the ratio of the shear viscosity µ to the bulk viscosity κ remains sufficiently large. On the other hand, for polyatomic gases, the scattered available experimental and numerical data show that it is certainly not zero and actually often far from negligible. Therefore, since the ratio κ/µ can display significant variations and may reach very large values (it can exceed thirty for dihydrogen), it remains unclear to what extent the neglection of κ holds.The purpose of the present study is thus to analyze the mechanisms through which bulk viscosity and associated processes may alter a canonical turbulent flow. In this context, we perform direct numerical simulations (DNS) of spatially-developing compressible non-reactive and reactive hydrogen-air shear layers interacting with an oblique shock wave. The corresponding flowfield is of special interest for various reactive high-speed flow applications, e.g., scramjets. The corresponding computations either neglect the influence of bulk viscosity (κ = 0) or take it into consideration by evaluating its value using the EGlib library. The qualitative inspection of the results obtained for two-dimensional cases in either the presence or the absence of bulk viscosity effects shows that the local and instantaneous structure of the mixing layer may be deeply altered when taking bulk viscosity into account. This contrasts with some mean statistical quantities, e.g., the vorticity thickness growth rate, which do not exhibit any significant sensitivity to the bulk viscosity. Enstrophy, Reynolds stress components, and turbulent kinetic energy (TKE) budgets are then evaluated from three-dimensional reactive simulations. Slight modifications are put into evidence on the energy transfer and dissipation contributions. From the obtained results, one may expect that refined large-eddy simulations (LES) may be rather sensitive to the consideration of bulk viscosity, while Reynolds-averaged Navier-Stokes (RANS) simulations, which are based on statistical averages, are not. (A. Mura). structure of the fluid as well as the flowfield conditions. However, acoustic absorption measurements performed at room temperature have shown that the ratio of the volume to the shear viscosity κ/µ may be up to thirty for hydrogen at room temperature [2], and recent analyses of reactive multicomponent high-speed flows have confirmed that it is not justified to neglect it, except for the sake of simplicity [3]. The dilatational viscosity is important in describing sound attenuation in gaseous media, and the absorption o...

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“…Using turbulence-resolving shock-capturing simulations, we have examined the turbulence statistics, turbulence budgets, conditional statistics and energy spectrum in multi-fluid Density effects on multi-fluid STI 937 STI and found that the nonlinear effects from the density variations significantly change the turbulence properties in both physical and spectral spaces. The relation between velocity and a passive scalar field has also been studied by Buttay, Lehnasch & Mura (2016) and Boukharfane, Bouali & Mura (2018). Other studies (Jin et al 2015;Huete et al 2017) used LIA and shock-capturing simulations to investigate the interaction of a reactive premixed mixture with shock and turbulence.…”

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confidence: 99%

Density effects on post-shock turbulence structure and dynamics

2019

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Turbulence structure resulting from multi-fluid or multi-species, variable-density isotropic turbulence interaction with a Mach 2 shock is studied using turbulence-resolving shock-capturing simulations and Eulerian (grid) and Lagrangian (particle) methods. The complex roles density play in the modification of turbulence by the shock wave are identified. Statistical analyses of the velocity gradient tensor (VGT) show that the density variations significantly change the turbulence structure and flow topology. Specifically, a stronger symmetrization of the joint probability density function (PDF) of second and third invariants of the anisotropic velocity gradient tensor, PDF(Q * , R * ), as well as the PDF of the vortex stretching contribution to the enstrophy equation, are observed in the multi-species case. Furthermore, subsequent to the interaction with the shock, turbulent statistics also acquire a differential distribution in regions having different densities. This results in a nearly symmetrical PDF(Q * , R * ) in heavy fluid regions, while the light fluid regions retain the characteristic tear-drop shape. To understand this behavior and the return to "standard" turbulence structure as the flow evolves away from the shock, Lagrangian dynamics of the VGT and its invariants are studied by considering particle residence times and conditional particle variables in different flow regions. The pressure Hessian contributions to the VGT invariants transport equations are shown to be not only affected by the shock wave, but also by the density in the multi-fluid case, making them critically important to the flow dynamics and turbulence structure. arXiv:1908.05327v1 [physics.flu-dyn]

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Analysis of small-scale scalar mixing processes in highly under-expanded jets

Cited by 18 publications

References 35 publications

Under-Expanded Jets in Advanced Propulsion Systems—A Review of Latest Theoretical and Experimental Research Activities

Under-Expanded Jets in Advanced Propulsion Systems—A Review of Latest Theoretical and Experimental Research Activities

On the role of bulk viscosity in compressible reactive shear layer developments

Density effects on post-shock turbulence structure and dynamics

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