Simultaneous Density-Velocity Measurements in Premixed Turbulent Flames to Assess a Theoretical Model (Experimental).

Density and velocity are measured simultaneously for the first time in premixed turbulent flames using the techniques of Rayleigh scattering and laser velocimetry. The flame configuration used in this study represents a significant improvement over the previous studies in that extraneous sources of turbulence have been eliminated. Mean quantities, density-velocity correlations, Favre averaged velocities and conditioned velocity measurements are used to assess the Bray-Moss-Libby model for premixed turbulent flames. Three of the five terms involved in turbulent kinetic energy budget in the flame are directly measured for the first time and compared with predictions of the model. The influence of heat release also is studied for the first time. The structure of the flame is shown to consist of hemi-spherical wrinkled laminar flamelets that propagate at the mean tangential velocity of the flow. The flame is found to generate turbulence and the amount of flame generated turbulence is found to increase with heat release as predicted by the model. The trends of variation of the three terms of Turbulent kinetic energy balance measured (dilatation, diffusion and convection) agree with model predictions. Counter-gradient diffusion increases with heat release. The scalar quantities such as scalar flux, r.m.s. density fluctuations, normalized time scales of reactants and products agree well with model predictions. The inferred reaction rate w is found to agree with the predicted trends. Significant differences between experimental results and model predictions that were identified are: (a) It was discovered that there are slow moving products that result from the curved shape of the flamelets and which represent an additional source of turbulence not considered by the model, (b) Mean flame properties deviate from being one-dimensional as assumed by the model, (c) The model does not predict even the trend of variation of conditioned velocity fluctuations correctly, and (d) One closure relation used by the model is not valid. Overall the model is found to be very successful in predicting trends of variation of most quantities correctly. Certain model improvements are suggested.PhDAerospace engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161099/1/8621292.pd