Abstract
High-resolution direct numerical simulations are conducted for under-expanded cryogenic hydrogen gas jets to characterize the nearfield flow physics. The basic flow features and jet dynamics are analyzed in detail, revealing the existence of four stages during early jet development, namely, (a) initial penetration, (b) establishment of near-nozzle expansion, (c) formation of downstream compression, and (d) wave propagation. Complex acoustic waves are formed around the under-expanded jets. The jet expansion can also lead to conditions for local liquefaction from the pressurized cryogenic hydrogen gas release. A series of simulations are conducted with systematically varied nozzle pressure ratios and systematically changed exit diameters. The acoustic waves around the jets are found to waken with the decrease in the nozzle pressure ratio. The increase in the nozzle pressure ratio is found to accelerate hydrogen dispersion and widen the regions with hydrogen liquefaction potential. The increase in the nozzle exit diameter also widens the region with hydrogen liquefaction potential but slows down the evolution of the flow structures.
Highlights
Hydrogen is being increasingly used as an alternative fuel for vehicles and aircraft propulsion
High-resolution multi-component direct numerical simulations have been conducted for under-expanded cryogenic hydrogen jets to characterize the near-field flow physics
The potential of liquefaction in the cryogenic hydrogen gas jet is analyzed through the dynamics of pressure evolution during the complex expansion–compression processes
Summary
Hydrogen is being increasingly used as an alternative fuel for vehicles and aircraft propulsion. Experimental studies on underexpanded cryogenic hydrogen jets were first conducted by Veser et al.1 They measured hydrogen concentration along the streamwise centerline for the inflow temperature from 35 K onward. Friedrich et al. conducted a series of experimental investigations with cryogenic hydrogen at temperatures of 34 K–65 K to study the behavior of cryogenic jets They proposed a correlation for predicting the dependence of hydrogen concentration on the nozzle diameters and the cryogenic reservoir conditions. Hamzehloo and Aleiferis numerically investigated the effects of ambient pressure on the instantaneous evolution of the nearfield shock wave structures and tip vortices of hydrogen and methane jets. The detailed nearfield flow structures and transient physics of the under-expanded cryogenic hydrogen jets are analyzed for the first time using high-resolution direct numerical simulations (DNSs). As the measurements of Hecht and Panda only covered the far field, no direct comparison will be made with the experimental data
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