Combustion Research and Flow Technology, Inc.

Video showing simulation of the oscillating flame mode of a partially premixed CH4/air–air jet flame just prior to global flame blowout, followed by the actual global flame blow-out of the same system.

Problem:

Combustion Research and Flow Technology, Inc. (CRAFT Tech) was asked to model flame extinction and blow-out effects in aircraft propulsion and power generation systems. Turbulence–flame, or turbulence–chemistry, interactions in these systems are difficult to model accurately. Large-eddy simulation (LES) can directly simulate the evolution of large turbulent scales in the flow, but it removes the small scales through a spatial filtering process. Adding a subgrid model can restore these crucial small-scale effects.

Solution:

CRAFT Tech adopted a database-driven modeling approach, which used statistics from an advanced turbulent combustion model that were pre-computed and stored in a database. Flame statistics and extinction limits from a linear-eddy model/counter flow (LEM-CF) formulation were used to develop the database-driven LES subgrid combustion model. The model was implemented in ANSYS Fluent as a user-defined-function to simulate piloted, partially premixed flames. This method succeeded in capturing flame temperature suppression due to local flame extinction, and in predicting the global blow-out limit. It also identified an oscillating flame mode just prior to global extinction.

Business Benefit:

This advanced modeling approach implemented within ANSYS Fluent may be used by commercial power system manufacturers to design new gas turbines that reduce pollutant emissions and increase efficiency while avoiding lean blow-out conditions as identified by the modeling approach. This formulation also enables aircraft engine manufacturers to reduce emissions and avoid engine flame out conditions, especially for high performance systems.

Software used: