CAREER: A New Understanding of Flame Dynamics and Turbulence-Chemistry Interaction from 2D/3D/4D Spatio-Temporal Measurements

Ohio State University, The, Columbus OH

Investigators

Abstract

The objective of this research is to quantify the time-dependent coupling among the highly unsteady flowfield, species concentrations, local temperature, and reaction rates in turbulent flames. Turbulent flows are inherently time-varying, three-dimensional phenomena, and when coupled with chemical reactions, create a highly dynamic system occurring on multiple length and time scales. Turbulent combustion dynamics are not well understood, which limits the development of both advanced control strategies and predictive numerical models for engineering applications. Current combustion models have difficulty in accurately predicting the time-dependent relationship between the fluctuating turbulent flowfield, reactive scalar mixing, and the complex flame chemistry over a broad range of conditions. Measurements performed under this research program will resolve physical and chemical processes in both space and time and will be used to assess common assumptions found in time-dependent combustion models and guide future approaches. Understanding both the temporal and spatial behavior of turbulent combustion environments is critical for improving modern energy-conversion systems. Intellectual Merit: The proposed research is rooted in a new class of multi-dimensional, high-repetition rate (> 10 kHz) laser diagnostic measurements of velocity, temperature, species concentrations, and reaction rates that have not been available previously. Scalar transport and mixing within turbulent flames, along with individual turbulence-chemistry interactions will be tracked in "real time". Specific research contributions include fully-resolved, four-dimensional (three spatial dimensions and time) temperature and species concentration gradients to analyze the competition between large-scale turbulent transport and small-scale mixing and chemical reaction. Space-time correlations and the governing length and time scales for the velocity and multiple reactive scalar fields will be determined under varying flow conditions. Simultaneous high-speed velocity and scalar measurements will yield flow-flame interactions in time, detailing how species transport, turbulent mixing, and local reaction rates are modified by and coupled to the fluctuating turbulence. Finally, new temporal data and statistics (e.g., fluctuations, correlations, time-scales, and power spectra) derived from the velocity/scalar measurements will serve as improved assessment tools for large-eddy simulation (LES) models. The PI will collaborate with researchers at Sandia National Laboratories and colleagues through the International Workshop on Measurement and Computation of Turbulent Non-Premixed Flames and to assess, validate, and improve the predictive capabilities of current LES approaches. Broader Impacts: A successful project will lead to a new understanding of combustion dynamics, which will have significant impact in the development of predictive combustion models and perhaps lead to improved combustion control within highly transient environments. Both of these factors have the potential to yield improvements in efficiency, flame stability, and pollutant output in combustion systems. Because turbulent combustion processes account for more than 85% of the world's energy usage, improvements in efficiency and lowered emissions have important implications in terms of environmental sustainability and energy security. The research program is heavily integrated into a series of educational and outreach activities with three objectives (1) increasing the interest of pre-college students in pursuing a career in science and engineering through local outreach, (2) fostering active learning (and teaching) at the collegiate level and (3) increasing students- ability to visualize physical concepts, thus making the transition from theory to application more achievable for the individual student. One component of the outreach plan is a series of interactive teaching modules will be developed and delivered at a local mastery-based high school which specializes in a STEM-based curriculum targeted for students living in high poverty areas. These modules are intended to cultivate interests in scientific and engineering disciplines within minority students who have had little exposure to science and math-based careers.