Numerical modelling of accidental gas release in a gas turbine enclosure- Evaluation of notional nozzle models and dispersion modelling using RANS, URANS and LES methods
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Typ
Examensarbete för masterexamen
Program
Publicerad
2019
Författare
Forsell, Martin
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
In the event of an accidental gas leak in an industrial facility it is important that
gas is not collected in a cloud of sufficiently large size and concentration that an
explosion could occur. When evaluating the effect of an accidental gas release, the
leak and the dispersion of potentially explosive gases must be modelled in a manner
that is accurate and conservative.
The work presented in this report can be divided into two main parts. The first
part concerns the modelling of the leak itself and what shape of the leak hole is
appropriate to use. Jets exiting from circular, rectangular and elliptic orifices of
different aspect ratios have been evaluated. Ways to model the hypersonic nearfield
of the leak using notional nozzle submodels have been compared to a simulation of
an equivalent hypersonic jet. Methane is used for modelling the leaked gas as it is
the main constituent of natural gas.
The second part concerns ways to model the turbulent mixing of the leaked gas with
ambient air. Two turbulence modelling approaches have been evaluated: URANS
and LES. Steady RANS was found to not be a suitable approach for simulating the
flow in the gas turbine enclosure even with no leak implemented.
Results indicate that the circular shape is the preferable choice regarding leak hole
shape.The notional nozzle model called the Adiabatic expansion approach appears
to be both conservative and highly accurate.
Simulations of the gas leak in a gas turbine enclosure using LES in combination
with the Adiabatic expansion approach produces a considerably smaller explosive
gas cloud volume compared to when URANS is used with the same notional nozzle
model. This effect was not seen however when comparing URANS and LES when
the Sonic jet approach was used as a notional nozzle. This could be due to the lower
velocity of the jet produced with the Sonic jet approach which in turn might cause
less turbulent mixing.
Beskrivning
Ämne/nyckelord
URANS , LES , mixing , leak , notional nozzle , accidental gas release , fictional nozzle , submodel , methane jet