Slitty bluff body is widely used as a high-performance flame holder in power industry. To understand the flame stability mechanism, the evolution of the near wake over a slitty bluff body in cold state was numerically investigated using the renormalization group (RNG) k-ε model at Reynolds number of 470,000. The coherent structure of the near wake was identified by the vortex shedding simulation. To explain the vortex shedding, a mechanism that single vortex of large size suddenly immerses two shear layers was proposed. To quantitatively compare the near wakes at different gap ratio, a vortex shedding character dimension was first proposed. This character dimension has positive correlation with flame stability. Particle-image velocimetry (PIV) measurements in a close wind tunnel were also carried out to confirm the observation from the numerical study. The evidence shows that the numerical results are of good agreement with the cold-state experiments.
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