Large-Eddy Simulation of Time Evolution and Instability of Highly Underexpanded Sonic Jets

Abstract

High-pressure jet injection into quiescent air is a challenging fluid dynamics problem in the field of aerospace engineering. Although plenty of experimental, theoretical, and numerical studies have been conducted to explore this flow, there is a dearth of literature detailing the flow evolution and instability characteristics, which is vital to the mixing enhancement design and jet noise reduction. In this paper, a density-based solver for compressible supersonic flow, astroFoam, is developed based on the OpenFOAM library. Large-eddy simulations of highly underexpanded jets with nozzle pressure ratios from 5.60 to 11.21 at a Reynolds number around 10 5 are carried out with a highresolution grid. A grid-convergence study has been conducted to confirm the fidelity of the large-eddy simulation results. The large-eddy simulation results have also been validated against available literature data in terms of the time-averaged near-field properties of underexpanded jets. The turbulent transition processes are revealed based on the instantaneous flow features and are quantitatively resolved according to the jet penetration and maximum width. The vorticity analysis is conducted to understand the turbulent transition mechanism, and it is found that the vortex stretching term plays a leading role on the distortion of the vortex rings in the near field of the jets. The dominant instability modes of jets, visualized by helicity, are quantitatively revealed based on the spectrum and relative phase of pressure fluctuation. The single helical modes corresponding to a phase angle close to 180 deg with the 1 1 helices are dominant for nozzle pressure ratios of 5.60 and 7.47, whereas the complex and multiple helices for the other two higher nozzle pressure ratios are due to the superposition of the single and double helical modes. In addition, the performance of the coarse mesh and different subgrid-scale models on capturing the dominant instability characteristics in large-eddy simulation of underexpanded jets is investigated.

Flow characteristic of highly underexpanded jets from various nozzle geometries

“…The density-based compressible solver astroFoam, which is developed based on the open-source CFD (Computational Fluid Dynamics) package OpenFOAM 2.3.0, is used to solve the above equations. The astroFoam solver is well established and validated in our previous LES of underexpand hydrogen [35] and nitrogen [36] jets issuing from circular nozzles, thus only the main aspects of the astroFoam solver are described here for concision. In astroFoam, the convection-diffusion equation is solved by semi-discrete KT (Kurganov and Tadmor) scheme [39] for shock capturing and turbulence resolving.…”

“…Hamzehloo and Aleiferis [33] focused on the flow characteristics of the underexpanded hydrogen jets, and then compared the mixing characteristics of hydrogen jets with the methane jets at various NPR [34]. Li et al [35] investigated the differences of flow structures and screech characteristics between the underexpanded hydrogen and nitrogen jets using LES, and also explored the turbulence transition mechanism and three-dimensional instability of underexpanded jets at different NPR [36]. These studies show that the LES technique is capable of capturing the salient flow structures and dynamics in supersonic underexpanded jets.…”

LES Study of Flame Stabilization in DLR Hydrogen Supersonic Combustor with Strut Injection

“…An in-house code AstroFoam, which was developed based on the OpenFoam V 3.0 platform, was used in the present study. AstroFoam has been used in previous studies for simulating multicomponent supersonic flow, particularly for capturing shock waves and resolving turbulent eddies with high resolution [9,10] . AstroForm adopts the Kurganov and Tadmor (KT) scheme [11] which is a second-order semi-discrete non-staggered, and central-upwind scheme.…”

Numerical Investigation on Flame Stabilization in DLR Hydrogen Supersonic Combustor with Strut Injection

“…An in-house code, AstroFoam, which was developed based on the OpenFoam platform, was used in the present study. AstroFoam has been used in the previous studies for simulating multicomponent supersonic flows and can capture shock waves and resolve turbulent eddies with high resolutions (Li et al, 2016a(Li et al, , 2016b. AstroForm adopts the second-order, semidiscrete, non-staggered, central-upwind, Kurganov and Tadmor (KT) scheme (Kurganov and Tadmor, 2000), which has been implemented in the OpenFoam framework (Greenshields et al, 2009) in order to capture the flow discontinuities (e.g., shock waves) with nonoscillatory and low-dissipation features.…”