Conditional Sampling of Turbulence Intensities and Reynolds Stress in Premixed Turbulent Flames

Abstract

Abstrac–-A two-color LDA technique has been developed for conditional sampling of turbulence intensity and Reynolds stress in premixed turbulent flame. To sample conditionally in the unburned reactants, silicone oil aerosol which burned and evaporated by combustion is used to seed the flow. Conventional AI₂O₃ seed particles are used to sample unconditionally through the flame. A conditional analysis method is developed to deduce conditioned data in the burned products from the unconditioned data. Comparison of the conditioned and unconditioned data obtained in a lean ethylene/air v-flame shows that the so-called "flame-generated turbulence" and the increase in Reynolds stress within the flame brush are caused primarily by intermittent measurements in the reactants and in the products. Using an intermittency model for the flame turbulence, the contributions due to intermittency are shown to be proportional to the difference between the conditioned mean velocities. The conditioned fluctuation intensities in the product are generally higher than those in the reactants indicating production of turbulence by the flame. The fluctuations in the products show rapid decay beyond the turbulent flame region.