Research Papers: Flows in Complex Systems

A Numerical Analysis of Hydrogen Underexpanded Jets Under Real Gas Assumption

[+] Author and Article Information
Francesco Bonelli

e-mail: francesco.bonelli@unibas.it

Annarita Viggiano

e-mail: annarita.viggiano@unibas.it

Vinicio Magi

e-mail: vinicio.magi@unibas.it

School of Engineering,
niversity of Basilicata,
Potenza 85100, Italy

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received October 12, 2012; final manuscript received August 6, 2013; published online September 12, 2013. Assoc. Editor: John Abraham.

J. Fluids Eng 135(12), 121101 (Sep 12, 2013) (11 pages) Paper No: FE-12-1512; doi: 10.1115/1.4025253 History: Received October 12, 2012; Revised August 06, 2013

This work examines the fluid dynamic structure of underexpanded gas jets by using a high-performance computing (HPC) methodology in order to untangle the question of whether it is necessary to include the real gas assumption dealing with hydrogen jets. The answer to this question is needed in order to guarantee accurate numerical simulations of such jets in practical engineering applications, such as direct-injection hydrogen engines. An axial symmetric turbulent flow model, which solves the Favre-averaged Navier–Stokes equations for a multicomponent gas mixture, has been implemented and validated. The flow model has been assessed by comparing spreading and centerline property decay rates of subsonic jets at different Mach numbers with those obtained by both theoretical considerations and experimental measurements. Besides, the Mach disk structure of underexpanded jets has been recovered, thus confirming the suitability and reliability of the computational model. To take into account the effects of real gases, both van der Waals and Redlich–Kwong equations of state have been implemented. The analysis of a highly underexpanded hydrogen jet with total pressure equal to 75 MPa, issuing into nitrogen at 5 MPa, shows that the use of real gas equations of state affects significantly the jet structure in terms of temperature, pressure, and Mach number profiles along the jet centerline and also in terms of jet exit conditions, with differences up to 38%.

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Fig. 1

Schematic of underexpanded sonic jet

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Fig. 2

Hydrogen compressibility factor versus pressure for different values of temperature: Redlich–Kwong EoS and NIST data [36]

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Fig. 3

Computational domain for subsonic nitrogen jets. The grid lines are shown every 16th and 8th grid point in the computational domain (at the top) and in the blow up (at the bottom), respectively.

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Fig. 4

Subsonic nitrogen jets: grid independence analysis in terms of normalized centerline velocity profile

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Fig. 5

Subsonic nitrogen jets: comparison of numerical results (lines) and experimental data [16] (symbols) in terms of normalized centerline velocity profiles

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Fig. 6

Subsonic air jet: comparison of numerical results (lines) and experimental data [17] (symbols) in terms of normalized centerline velocity profiles and grid independence analysis

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Fig. 7

Subsonic nitrogen jets: velocity profiles in similarity coordinates

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Fig. 8

Subsonic nitrogen jets: spreading rates for the subsonic jets

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Fig. 9

Underexpanded air jet: grid independence analysis in terms of centerline pressure

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Fig. 10

Shadowgraph field of the air underexpanded jet

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Fig. 11

Temperature (a) and pressure (b) along the air underexpanded jet centerline

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Fig. 12

Radial temperature (a) and radial pressure (b) distribution of the air underexpanded jet at x/Din = 1.28

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Fig. 13

Underexpanded hydrogen jet: grid independence analysis in terms of centerline pressure

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Fig. 14

Temperature, pressure, and Mach number contour plots for the hydrogen jet: ideal (a), van der Waals (b), Redlich-Kwong (c)

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Fig. 15

Temperature, pressure, and Mach number along the hydrogen underexpanded jet centerline




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