vida: multi-physics low Mach number reacting flow solverIn a continual push to improve the operability and performance of combustion devices, high-fidelity simulation methods for turbulent combustion are emerging as critical elements in the design process. Multi-physics large-eddy simulation based methodologies can accurately predict mixing, study flame structure and stability, and even predict product and polutant concentrations at design and off-design conditions.

Cascade’s multi-physics variable density flow solver vida provides an enabling technology for high-fidelity les of mixing and reacting flows in low-Mach number regimes. vida’s formulation decouples pressure from density and temperature, removing any acoustic re-strictions on the time step. This property combined with an implicit fractional step method results in a very efficient time integration method. Coupled with a novel double-Poisson formulation (Ham, 2007), vida does not require any outer iteration during the time-advancement, dramatically increasing the efficiency and robustness of the solver.

vida uses the flamelet progress-variable chemistry model in which a turbulent flame is described as an ensemble of laminar flamelets using a presumed pdf. A major advantage of the flamelet-based models are their simplicity and ability to efficiently account for complex chemical kinetics by pre-computing the thermo-chemical relationships and tabulating them for easy retrieval while keeping the computational cost tractable.

In addition, the Lagrangian spray models in the vida solver allow for the coupled simulation of liquid-phase fuel spray and evapo-ration. The Lagrangian spray modeling is built on the Cascade infrastructure’s massively parallel particle tracking implementation for unstructured grids, allowing the load-balanced simulation of mil-lions of independent droplet trajectories. State-of-the-art models for droplet breakup and evaporation are available in the vida solver.

vida has been applied to a wide variety of mixing and reacting flow problems including combustor problems with very complex geom-etries. Among those are investigation of flame stability in a model augmentor of a military jet engine, simulation of a co-axial combus-tor, flame-holding study in a gas-turbine premixer, and simulation of a low power jet engine with liquid fuel.

Top Left: Instantaneous Temperature contours at mid- and axial planes from les of the co-axial combustor experimentally studied by Owen et al. Low-speed methane enters the combustion chamber through the central pipe and a non-swirling high-speed-high temperature air enters through the outer annulus.

Top right: Snapshot of iso-surfaces of temperature and fuel sprays in near injector regions of the Pratt & Whitney gas turbine engine combustor

Bottom right: Snapshots of instantaneous temperature at the combustor mid-plane from variable-density simulations of the reacting jet engine combustor of Pratt & Whitney at cruise conditions.

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