The characterization of the flowfield of a dump combustor
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To provide quality benchmark data (that can be used in numerical simulation comparisons) and to examine the effects of combustion on a typical ramjet engine flowfield, a water-cooled, stainless steel dump combustor model was developed. A two-component Laser Doppler Anemometer (LOA) was used to measure the mean and turbulent velocities in the axial and tangential directions and provide a comparison between combusting and isothermal flows. However, before any LOA measurements could be taken, the combustor had to be configured to run in a suitably stable mode.
Stability was identified by the pressure spectra obtained under various running conditions using piezoelectric pressure transducers wired to a spectrum analyzer. Operational parameters such as fuel composition, fuel injection location, acoustic configuration, and equivalence ratio were varied until instabilities were minimized. The optimal configuration ran with upstream fuel injection (premixed mode) at the duct center line and an orifice plate installed immediately upstream of the fuel injectors, with propane as the fuel.
Once stability was achieved, LOA data was taken. The results showed some significant differences between the reacting and nonreacting flows. The most significant effect was the difference between the inherent recirculation regions for each case. Combustion decreased the length of the region by approximately 50 percent, while increasing the maximum negative velocities. This made for a more compact, but stronger, recirculation region. Since the recirculation region acts as the main flame holder and is a major source of turbulence, the changes in this region significantly altered the dump combustor flowfield.
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