Experimental study of combustion: the turbulent structure of a reacting shear layer formed at a rearward-facing step

Thesis/Dissertation · Thu Jan 01 04:00:00 EST 1981

OSTI ID:6056912

Pitz, R W

A premixed propane-air flame is stabilized in a turbulent free shear layer formed at a rearward-facing step. The mean and rms averages of the turbulent velocity flow field are determined by LDV for both reacting (phi = 0.57) and non-reacting flows (Re = 1.5 x 10/sup 4/ to 3.7 x 10/sup 4/ based on step height). The reacting flow is visualized by high speed schlieren photography. Large scale structures dominate the reacting shear layer. The growth of the large scale structures is tied to the propagation of the flame. The linear growth rate of the reacting shear layer defined by the mean velocity profiles is unchanged by combustion but the virtual origin is shifted downstream. The reacting shear layer based on the mean velocity profiles is shifted toward the recirculation zone and the reattachments lengths are shortened by 30%. The edge of the flame controlled by the large scale structure development propagates faster into the incoming reactants than the boundary of the shear layer given by the mean velocity flow field. This results in non-Gaussian behavior above the shear layer. The velocity probability density function is positively skewed from the impelling effect of the large scale structures expanding between the top of the shear layer and the flame boundary. Under combustion, measurements of the passing frequency of the large scale structures from LDV spectra indicate that the coalescence rate is sharply reduced. The pairing process in the reacting shear layer is nearly eliminated as a growth mechanism. The reacting shear layer grows primarily by entrainment of fluid and heat expansion.

• OSTI ID: 6056912
• Country of Publication: United States
• Language: English

Related Subjects

090110* -- Hydrocarbon Fuels-- Properties-- (1979-1989)
10 SYNTHETIC FUELS
ALKANES
CHEMICAL REACTIONS
COMBUSTION
FLAMES
HYDROCARBONS
ORGANIC COMPOUNDS
OXIDATION
PROPANE
THERMOCHEMICAL PROCESSES
TURBULENCE
VELOCITY