A Comprehensive Numerical Study of Diesel Fuel Spray Formation with OpenFOAM 2011-01-0842
The accuracy and robustness of spray models and their
implementation in current commercial CFD codes vary substantially.
However, common features are that the resulting spray penetration
and levels of spray-generated turbulence - two factors that
strongly influence the rate of heat released during combustion -
are to a great extent grid size-dependent.
In the work presented here a new kind of spray model has been
implemented and thoroughly tested, under various ambient
conditions, in the open source code OpenFOAM. In addition, since
the turbulence model applied in simulations is known to strongly
affect spray penetration rates, results obtained using both the
standard k-ε and RNG k-ε models have been compared.
In the new spray model, designated VSB2, the traditional
Lagrangian parcel has been replaced by a so-called stochastic blob
containing droplets with a distribution of sizes, rather than a
number of uniform-sized droplets. These blobs do not interact with
the grid directly, but through bubbles of locally determined size.
One advantage of the VSB2 spray model is its less grid size
dependence due to the interaction with the gas phase in the bubbles
instead of the entire grid cell it currently occupies. Another
benefit of the model is its robustness, resulting from rigorous
calculation of equilibrium values for momentum and thermodynamic
(saturation and temperature) parameters affecting transfer rates
between the phases ensuring a bounded solution.
Results obtained using the code are compared here with
experimentally acquired data regarding spray penetration under
various ambient conditions. Qualitative comparisons of the evolving
spray shapes are also presented.