TITLE : CONFINED TURBULENT DIFFUSION FLAME
BY : CHAM Development Team - M R Malin
FOR : Validation of Gaseous Combustion Models
PURPOSE OF THE CALCULATIONS:
- The main objective of the calculations is to validate the
turbulent combustion models provided in the extended SCRS
attachment for gaseous combustion.
- The experimental data to be simulated are the zero-swirl results for
the gas-fired turbulent combustion chamber of Owen et al (16th Int.
Symp. Combustion, p105, 1976).
FLOW DETAILS :
- The geometry comprises a 12.2cm diameter axisymmetric combustor
into which natural gas (96% CH4) is injected centrally and axially
to mix and burn with a heated, coaxial annular air stream.
- The chamber length is taken as 4 diameters in the CFD simulations.
- Coaxial fuel and air streams are admitted separately into the
combustor and then burn in a turbulent diffusion flame. The inlet
fuel/air velocity ratio is 0.05.
- The fuel jet enters through a pipe of 6.3cm diameter at a
temperature of 288 K. The air jet enters through an annulus at a
temperature of 750 K. The furnace walls are presumed isothermal
at a temperature of 600 K.
- The inlet fuel/air equivalence ratio is 0.9, and the combustor
operating pressure is 3.8 atmospheres.
MAIN FEATURES OF CFD MODEL:
- Turbulence is represented via the k-e turbulence model.
- Calculations are made with 4 different combustion models:
(a) fast-chemistry model with a one-step global irreversible
methane reaction to form CO2 and H2O;
(b) as (a) but with an assumed double-delta probability density
function to account for the influence of concentration
(c) eddy-break-up finite-rate chemistry model with a one-step
global irreversible methane reaction (CEBU=6.0); and
(d) as (c) but with a two-step global reaction mechanism involving
the intermediate CO (CEBU1=6.0 and CEBU2=1.0).
- The calculations employ variable specific heats and heats of reaction.
- The flow is treated as weakly compressible.
- Radiative heat transfer is modelled via the P1 spherical-harmonics
approximation for a gray medium. The wall emissivity is taken as 0.9
and the optical thickness as 0.25 based on furnace diameter.
- A cylindrical-polar mesh is used with 30 radial by 40 axial cells.
1. OWEN FURNACE TWO-STEP EBU MODEL: VELOCITY VECTORS ( M/S )
2. OWEN FURNACE TWO-STEP EBU MODEL: TEMPERATURE CONTOURS ( DEG K )
3. OWEN FURNACE: TEMPERATURE PROFILES AT Z/D=0.6
4. OWEN FURNACE: TEMPERATURE PROFILES AT Z/D=1.99
5. OWEN FURNACE: CO2 MOLE FRACTION PROFILES AT Z/D=2.84
6. OWEN FURNACE: CO MOLE FRACTION PROFILES AT Z/D=2.84