TITLE : FREE 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 case considered is the turbulent diffusion flame of a round jet of hydrogen in a co-flowing air stream, as studied experimentally by Kent and Bilger (14th Int. Symp. Combustion, p615, 1975).

FLOW DETAILS :

• The case considered is the turbulent diffusion flame for hydrogen issuing from a 7.62mm diameter nozzle into a co-flowing stream of air.

• The flame is unconfined and buoyancy and radiation effects are negligible.

• The ratio of the jet-discharge velocity to the free-stream velocity is 10. The jet-discharge velocity is 151.1 m/s.

• The free-stream temperature is 288K, which is the same as the jet- discharge temperature.

MAIN FEATURES OF CFD MODEL:

• Turbulence is represented via the k-e turbulence model, and the turbulent Schmidt number is taken as 0.9.
• Calculations are made with 2 different combustion models: (a) fast-chemistry model with a one-step global irreversible hydrogen reaction to form H2O; (b) as (a) but with an assumed double-delta probability density function to account for the influence of concentration fluctuations;
• The calculations employ variable specific heats and heats of reaction.
• The flow is treated as weakly compressible.
• The calculation is performed using parabolic marching integration with a cylindrical-polar expanding mesh.
• A forward step size of 5% of the local jet radius is employed together with 40 radial grid cells.
• For simplicity, uniform profiles are used at the inlet plane.
• A fixed-pressure condition is used at the free boundary.

  1. TURBULENT DIFFUSION FLAME: TEMPERATURE CONTOURS ( DEG K )
  2. TURBULENT DIFFUSION FLAME: TEMPERATURE PROFILES AT Z/D=40
  3. TURBULENT DIFFUSION FLAME: TEMPERATURE PROFILES AT Z/D=80
  4. TURBULENT DIFFUSION FLAME: AXIAL TEMPERATURE DISTRIBUTION
  5. TURBULENT DIFFUSION FLAME: MOLE-FRACTION PROFILES AT Z/D=40
  6. TURBULENT DIFFUSION FLAME: MOLE-FRACTION PROFILES AT Z/D=80
  7. TURBULENT DIFFUSION FLAME: AXIAL COMPOSITION DISTRIBUTION