Verlag des Forschungszentrums Jülich
JUEL-3930
Wang, Boliang; Rehm, Werner
Recent DDT simulations and criteria based on experimental and numerical results for hydrogen safety studies
III, 59 S., 2001
In this report, we will first briefly describe the phenomena, underlying mechanisms and
necessary criteria of DDT, then summarize the experimental work on hydrogen
explosion performed at the SWL of RWTH Aachen. Then we will explain the CFD
codes SHOCKIN and AIXCO as well as the applications in the simulation of DDT
processes.
Studies performed at the SWL include three topics: 1) self-ignition phenomena;
2) DDT mechanisms in axis-symmetric geometry with periodic obstacles or a single
obstacle; and 3) detonation formation at the entrance to narrow gaps. A database of
ignition delay times and schlieren records has been set up for hydrogen-air-steam/CO2
mixtures. Excellent photographs conceming shock reflections and ignition were
produced providing good materials for the validation of computer codes.
Based on the preparatory work at the SWL, a new two-dimensional CFD code
(SHOCKIN), which describes the feedback of the flow fields with chemical reactions,
has been successfully developed. This code takes into account all species and
elementary reactions defined by the user, or uses a two-step kinetic model for the global
reaction processes. First test cases for validation of the calculations were carried out for
experimental results with schlieren pictures. The results show that the code works quite
well. It was then used to simulate hydrogen events in a reactor containment. With the
assumptions applied, it is concluded from the simulation results that the most probable
ignition position is at the axis of symmetry in those test cases studied. The test cases
demonstrated that it will be possible to define DDT conditions in large-scale geometries
initiated by shock wave reflection and focusing effects.
Improvements to the AIXCO code, developed at the Institute of Mechanics of
the RWTH Aachen for the numerical simulation of three-dimensional compressible
reactive flows, have been made in three respects at ISRl: 1) enabling a temperature
gradient in the computation domain as an initial condition for the SW ACER
mechanism, 2) enabling a shock front at any position in the computation domain as an
initial condition, and 3) introduction of a temperature switch concept which takes the
"hot spots" effect into account. With the improved AIXCO, spontaneous DDT induced
by temperature gradients (SWACER mechanism), DDT by shock reflections and DDT
by a "hot spot" ahead of a flame front were achieved.
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