Suppression of combustion instability by geometrical design of the bluff-body stabilizer

Abstract

Passive control methods were used to suppress combustion instability in a combustor with a bluff-body stabilizer. The instabilities in this combustor are excited by interaction between vortices shed downstream of the stabilizer and the combustion chamber acoustic modes. The passive control methodology was to change the geometrical design of the stabilizer in a manner that will disrupt the formation or reduce the coherence of the wake vortices, thus eliminating the source of the instability excitation. Two geometrical designs were tested and compared to the regular baseline disk stabilizer. The first was a corrugated stabilizer that promotes the shedding of longitudinal vortices from the stabilizer`s base. These vortices induce azimuthal instability in the axisymmetric wake vortices and accelerates their breakdown. The second configuration was a multistep cone that was shown to enhance the production of small-scale turbulence in the flow. Both methods were effective in the suppression of the pressure oscillations and reduced significantly the range of unstable combustion without adversely affecting the lean and rich flammability limits. The optimal configuration was the multistepped cone stabilizer. The orientation of the stabilizers and the effect of central ventilations were studied as well as the instability mode characteristics. 16 refs.