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Abstract
This article analyzes the response of bluff-body stabilized flames to transverse acoustic waves. Data were obtained for bluff-body flames at flow velocities of 50 m/s and 100 m/s with inlet air temperatures ranging from 475–750 K. Two different modes of acoustic excitation were applied, corresponding to velocity and pressure nodes/antinodes along the combustor centerline. High-speed imaging and phase-locked particle image velocimetry (PIV) were used to characterize the spatio-temporal flame front and velocity field response. The key objective of the study is to compare measurements of the fluctuating velocity and flame wrinkling using the G-equation, e.g., to compare how the ensemble averaged unsteady flame wrinkling gain/phase predicted by solving the G-equation using the measured velocity field as inputs compares to the measured values. These results show good qualitative agreement between the comparisons and measurements, and quite good quantitative accuracy in many of the cases. These comparisons also enable insight into the features controlling the unsteady flame wrinkling; for example, it enables insight into the relative contributions of acoustic and vortical disturbances on the flame wrinkling characteristics, whose different propagation velocities lead to interference patterns and oscillatory flame wrinkle amplitude characteristics.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the U.S. Air Force (Contract FA-8650-07-M-2784, Contract monitor Barry Kiel) and the U.S. Department of Energy (Contract DEFG26-07NT43069 and DE-NT5054, Contract Monitors: Mark Freeman and Richard Wenglarz) for their financial support of this research.
Notes
1The measurements for both velocity and flame edge are prone to large errors close to the edge of their respective image boundaries at the edge of the laser sheet. Where the flame edge data is used as input, the predictions use only local data and the velocity field prediction is only shown farther downstream. Where the velocity field is used as an input, the flame edge prediction is initiated at the bluff body. The velocity data in the region x/λ c < 0.1 is extrapolated from points close to x/λ c > 0.1 based on a polynomial fit of their behavior. These extrapolated values are not used for the local comparison in the velocity field validation study.