CFD simulations of under-expanded hydrogen jets under high-pressure injection conditions

Abstract

Large-eddy simulations (LES) of hydrogen jets under highly under-expanded conditions are carried out. Computational fluid dynamics (CFD) analysis appears extremely useful to fully understand and optimize the hydrogen injection process, like in internal combustion engines. This work aims to analyze hydrogen high-pressure injection in the near-nozzle region, investigating the formation process and the structure of the Mach disks and the transition to turbulent jets, for nozzle pressure ratios (NPR) of 5.8 and 30. A real fluid model is utilized and compared against the simpler ideal gas model, for injections into an ambient pressure environment. Furthermore, hydrogen-air mixing evolution is investigated in the far-field region. Average quantities obtained from statistical analysis on LES simulations are compared with available data. The near nozzle region, except for the initial transient part, is better captured by accurate spatial discretization methods, while properly predicting far-field effects, like turbulence and acoustic effects, seems to be mostly related to time discretization schemes.

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

“…Further than in-house developed codes, basically three finite volume CFD codes were used. They are OpenFOAM, CONVERGE and STAR-CCM+ [59][60][61]. It should also be mentioned that some studies use the Lattice Boltzmann method [62,63].…”

“…The equation of state (EoS) (for a description of the pressure-volume-temperature (P-V-T) relationship) is crucial to the accuracy of the solution. Further than the ideal-gas EoS, Cubic EoS such as Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR) were widely applied due to their simplicity and reasonable accuracy [56,61,76,77,[91][92][93][94].…”

“…From a modelling point of view interesting comparisons between different CFD codes (such as OpenFOAM, Star CCM+ and CONVERGE) were carried out by various authors [61,112].…”

A New Generation of Hydrogen-Fueled Hybrid Propulsion Systems for the Urban Mobility of the Future

“…In this context, high-fidelity Large Eddy Simulations (LESs) of the turbulent under-expanded H2 jets can play a crucial role in the fundamental understanding and prediction of the physical mixing process, allowing the design of an optimized injector nozzle and associated injection strategies. In addition to high-resolution CFD simulations, the Reynolds-Averaged Navier-Stokes (RANS) modeling approach could also be employed as a cost-effective engineering tool to predict and explore several nozzle designs and pressure ratios [41][42][43][44]. Boundary and operating conditions are derived from reduced-order models (cf.…”

“…As a first step, LES fundamental studies have been conducted on nitrogen jets for validation of the developed injection model, and predictions [41] have been compared with experimental data [44,45]. An example is shown in Figure 4, where the contours of the density gradient of the nitrogen jet are presented at different time steps, with 5.8 bar of Nozzle Pressure Ratio (NPR) and 1 bar of ambient pressure, and the predicted axial density is compared for validation against the two reference studies.…”