Turbulent Premixed Combustion Research at CCSE

Low-swirl Burner

LBNL-EETD Low-Swirl Burner Ongoing CCSE research includes study of a low-swirl burner experiment in LBNL's EETD laboratory. Simulation issues related to turbulent premixed flames are discussed here, and background on the EETD laboratory flames is discussed here. The low-swirl burner experiment is constructed very similar to the V-flame, except that no rod is required across the inflow and small swirlers jet high-speed air (35-40 percent sound speed) tangentially clockwise along the inside of the nozzle. The swirling flow exits the nozzle and expands outward, creating a local deficit in axial velocity that is used to sustain a premixed turbulent flame above the nozzle exit plane. The photo is of a two-jet swirl burner from the EETD laboratory, and a stable bowl-shaped flame is apparent above the nozzle exit. The bluish color is fluoresence from the CH flame radical, and is blurred due to time-averaging over the camera shutter speed. The instantaneous flame surface is quite wrinkled and time-dependent.

Nozzle simulations

Correct simulations of such a flame requires a full simulation of the fluid, from the turbulence grid and swirl jets on through the nozzle exit, and up through the flame. In the figures below, an animation shows the simulated evolution of the premixed fuel upward though the vertical midplane of the nozzle. The blue colored activity is dilution due to the high-speed air jets. The animation was taken well after nozzle had flushed its initial volume of air. The animation on the right depicts the magnitude of the vertical velocity at the exit plane of the swirl nozzle as a function of time, where red represents strong upward flow. It is apparent that the swirling flow remains rather confined to the outside edges of the nozzle, and the inner core of fuel is moving at relatively constant, low rate.

Fuel [orange] and air [blue] inside nozzle.
(Mouse over for animation/click for QuickTime)

Axial velocity at nozzle exit plane.
(Mouse over for animation/click for QuickTime)

Methane flame simulation

Flame surface (volumetric rendering of temperature gradient field)
(Mouse over for animation/click for QuickTime)

The compressible nozzle simulation above provide the inflow boundary data for a low Mach number simulation with 20 species and 84 chemical reactions. The simulations are a work-in-progress, and remain to be completed or analyzed. Below, we see animations of the fuel concentration, and the location of the carbon monoxide during the start-up transient phase of the simulation. We see the methane enter the domain through a central core, while the edges are part of the swirling flow and expand rapidly downstream of the inflow. The carbon monoxide concentration, which peaks at the flame surface, illustrates the shape of the flame surface. Initially, the flame is a circular disk (seen here edge-on), but rapidly distorts with the turbulent inflow. A large-scale vortical pattern is developing to hold the flame in a quasi-steady location, and the flame surface areas increases dramatically.


Methane concentration in vertical midplane. (Mouse over for animation/click for QuickTime)	CO at flame surface in vertical midplane. (Mouse over for animation/click for QuickTime)

The adaptive low Mach number simulation code, an extension of CCSE code IAMR for incompressible flows, is not presently available for release. For more information about the adaptive methodology for low Mach number combustion modeling applications, or about these calculations, contact Marc Day or John Bell of CCSE.

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