Theory of premixed flame propagation in large-scale turbulence
An investigation into the feedback between a downward-propagating laminar premixed flame and a turbulent flow of low intensity and large length scale is presented. Closed-form, analytical expressions are obtained at the leading order for the turbulent burning velocity, variation of turbulent kinetic energies, and root-mean-square vorticity fluctuations. These expressions involve the character of the excitation turbulence introduced far upstream-its integral length scale, intensity, and autocorrelation function-and aspects of the chemically-reactive flow. Calculations show that a finite value of the turbulence length scale gives the greatest turbulent burning velocity. Also, gas expansion across the flame is found to enhance flame wrinkling and give greater turbulent flame speeds. It is shown how buoyancy counteracts the tendency for gas expansion to increase transverse components of the turbulent flame speeds. It is shown how buoyancy counteracts the tendency for gas expansion to increase transverse components of the turbulent kinetic energy, pressure fluctuations, and vorticity generation across the wrinkled flame. Strong readjustments in turbulent kinetic energy components are shown to occur in the downstream hydrodynamic zone. It is established that the flame can induce anisotropy in initially isotropic turbulence. An iteration method is formulated for obtaining series solutions to the fully nonlinear feedback problem. It is shown that coefficients of odd powers of intensity in the series solutions are zero for excitation fields which are isotropically turbulent or periodic, so that solutions of the nonlinear problem describing turbulent kinetic energy profiles and the turbulent burning velocity are expected to depend on the square of the turbulence intensity of the excitation field for these cases.
- Research Organization:
- Princeton Univ., NJ (USA)
- OSTI ID:
- 6234252
- Resource Relation:
- Other Information: Ph.D. Thesis
- Country of Publication:
- United States
- Language:
- English
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