- Author
-
Kent, J. H.
- Title
- Turbulent Jet Diffusion Flames.
- Coporate
- Sydney Univ., Australia
- Report
-
Thesis,
1972,
280 p.
- Keywords
-
turbulent jet flames
|
diffusion flames
|
data analysis
|
sampling
|
vapor phases
|
viscosity
|
thermal conductivity
|
numerical analysis
|
shear stress
- Identifiers
- K-epsilon modeling; field modeling
- Abstract
- An experimental and theoretical investigation into turbulent jet diffusion flames is conducted. The flow configuration is an axisymmetric hydrogen jet issuing into a coflowing stream. Tests are conducted at jet to stream velocity ratios of 10:1, 8:1, 5:1 and 2:1. A gas sampling and analysis system is developed for rapid on-line analysis of hydrogen, oxygen and water. The system is described and the effects of sample flow rate and sampling probe design are discussed. Composition measurements are presented for the above conditions on the centerline and across the flow at various axial stations for each condition. Temperature measurements are made and momentum flux distributions are also measured. The pollutant species nitric oxide is measured and it is discovered that peak production rate does not occur near stoichiometry as expected. Limited turbulence measurements are presented and turbulent concentration fluctuations are deduced from the sample compositions. The theoretical analysis is based on a method which expresses the effective turbulent viscosity in terms of turbulent kinetic energy and turbulence length scale. The method allows predictions of turbulence and concentraion fluctuations to be made in the flow as well as predictions of time mean velocities, temperatures and compositions. The boundary layer equations of momentum, enthalpy and species concentration, together with three auxiliary equations to describe turbulence and concentration fluctuations, are solved using a finite difference procedure. The theory is applied to isothermal jet mixing data and found to give good predictions. However, when applied to the present flame results, the theory overestimates the mixing rate by a factor of approximately 2. The explanation for this may lie in the apparently lower turbulence levels in the flame as compared with levels in isothermal jets. Another explanation is the possibility of a density-velocity fluctuation correlation affecting the turbulent shear stresses in the combustion situation where large density gradients are to be found.