NUMERICAL STUDY OF A HIGHLY UNDEREXPANDED HYDROGEN JET

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NUMERICAL STUDY OF A HIGHLY UNDER-EXPANDED
HYDROGEN JET

• B P Xu, J P Zhang, J X WEN, S Dembele
• and J Karwatzki
• Faculty of Engineering, Kingston
  UniversityFriars venue, Roehampton Vale, London,
  SW15 3DW, UK

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Very High Pressure Hydrogen Storage

• The Fuel cell vehicles (FCV) currently in trial
  use are mounted with hydrogen containers
  pressurized up to 400 bar and yield a driving
  range of 300-350 km per filling - roughly half of
  the gasoline vehicles driving range.
• Industry is developing containers for up to 700
  bar pressurization.
• Need to gain insight of such release and its
  potential for ignition

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Schematic diagram of free jet flow shock structure
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Two Modelling Approaches

• Pseudo-source approach (Ewan and Modie 1985)
• Leak modelled from downstream as a sonic jet with
  the same mass flow rate

• Numerically solving the under-expanded shock
  structure
• Results used as inflow for the subsequent large
  eddy simulation of the jet

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Simulation of the Under-expanded Shock Structure

• Commercial code CFX
• Total energy model take into the kinetic energy
  of high speed flows
• The k-? based shear stress turbulence (SST)
  model
• A TVD type high resolution discretisation scheme
  to represent sharp gradients without numerical
  oscillations
• A global 2nd accuracy, which switches to a 1st
  order upwind scheme locally to prevent
  non-physical oscillations
• The 2nd order backward Euler scheme to define the
  discretisation algorithm for the transient term.

Validation of the code for supersonic application
is available through CFX Vendor, now part ANSYS
Europe
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Simulation of the free hydrogen jet

• KIVA-LES (modified for LES from KIVA-3V)
• Finite volume based ALE (Arbitrary
  Lagrangian-Eulerian) method
• the 2nd order Crank-Nicolson scheme for the
  diffusion terms and the terms associated with
  pressure wave propagation
• The 2nd order MacCormack method for the
  convective terms in the rezone phase
• A 2nd order centred scheme for the convection
  term in the momentum equation.
• 17.  
• B B P Xu, J X Wen, S Dembele, Large eddy
  simulation of plane impinging jets, submitted to
  Physics of Fluids.
• 18.   B P Xu and J X Wen, Validation of a new
  droplet collision model in LES of non-evaporating
  diesel fuel sprays, submitted to Int. J of
  Multiphase Flow.

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Real Gas Property

• Abel-Noble EOS (Equation of State)

For hydrogen, b1.5510-5 (m3/mole), valid for
Plt1600atm and 200ltTlt 350K

• Van der Waals EOS

This EoS has been reported to reproduce a large
part of the experiment thermodynamic data on
hydrogen within 0.1 and practically all data
within 0.5.
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Comparison of density as a function of pressure
for constant temperatures
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Choked Flow Nozzle Dynamics

• Table 1. Initial data in the high-pressure jet
  simulation

• Assuming isentropic flow
• T from Van der Waals EoS

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530
K Mohamed and M Paraschivoiu, Real gas simulation
of hydrogen release from a high-pressure chamber,
Int J of Hydrogen Energy, 30 (2005).
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• Release pressure 200 Bar

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• Release pressure 20 bar

• At very high pressure ratios (such as the
  previous one), only one Mach disk
• Several Mach disks at relatively lower pressure
  ratios

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Predicted pressure, velocity, temperature and
hydrogen mass concentrations at the centreline
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The free hydrogen jet (with KIVA-LES)
Instantaneous density
Mean velocity
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Normalized values of main axial velocity, axial
turbulent intensity and hydrogen mass fraction
on the centreline
Normalized values of main axial velocity and
hydrogen mass density versus distance to the
centreline at different Z positions.
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Conclusion

• The predicted flow pattern and Mach number
  distribution within the shock structure are in
  line with previous experimental observation and
  theoretical analysis.
• Apparent air entrainment is found after these
  shock structures, implying that the widely used
  pseudo-source approach may incur some errors for
  such jet simulations.
• The hydrogen release temperature is lower than
  the vessel temperature when the container
  pressure is below a certain value (e.g. 530 bar
  in the current configuration). The situation is
  different for higher vessel pressures.
• A combustible cloud could be formed above the
  leak source within a very short period of time
  (about 0.1s).

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ACKNOWLEDGEMENT

• We gratefully acknowledge the helpful discussion
  with Vincent Tam, Peter Cumber and Marius
  Paraschvoiu.
• Jet flame simulation is already ongoing
• Work will continue jointly with BP and HSL
  through the EC funded HYFIRE project in several
  areas concerning fire and explosion safety of
  hydrogen.

FUTURE WORK