| Whether the slitted bluff body can be successfully used as flameholder in aircraft afterburner or not depends on its drag and flameholding ability, which requires less drag and better flame stabilization at high temperature and high speed. These characteristics intimately relate to the coherent structure of large vortex over the slitted bluff body, about which numerous questions remain. The focus of present paper is explaining the coherent structure and vortex shedding dynamics in the wake over bluff body, and studying the flameholding mechanism numerically and experimentally. The basic theory or data to optimize slitted bluff body will be proposed through the investigation, which is fundamental to carry on further experiment at high speed. The wake regions after a triangle bluff body and different V shape bluff bodies were investigated numerically using the RNG k -εmodel at Reynolds number of 470000. The numerical results are of good agreement with the previous experiments. The comparison between RNG k -εmodel and large eddy simulation also indicates that RNG k -εmodel is adequate in computing the bluff body flow. The evidence shows that the V shape slitted bluff body has the best flameholding ability and the lowest drag at a gap ratio of 36%. The evolution of the coherent structure over slitted bluff body was investigated: The coherent structure is divided by the gap flow, which deflects to one side, into two zones called the primary recirculation zone and the secondary recirculation zone, vortex shedding in the primary recirculation zone stimulates absolute instability in the near wake. To explain the vortex shedding, a mechanism that single vortex of large dimension suddenly immerses between two shear layers was proposed. Cold state experiment in an open tunnel was carried out to measure the total pressure loss coefficient and minus x-component velocity zone, the experiment results confirm the observation from the numerical study. Particle image velocimetry measurements in a close wind tunnel were also carried out to investigate the wake structure after a slitted bluff body with different gap ratios and different slitted bluff bodies with the same gap ratio. The researcher investigated the statistical character and structure of the turbulent shear flow of the near wake, and its dynamic mechanism like vorticity concentration, transport and evolution et al. Of particular significance to the theory in flow over bluff body and the experiment analysis methods was the definition of vortex shedding character dimension, which was first proposed by the researcher to analyze the time-dependent wake flow quantitatively. Using the ensemble-averaged mean, flow structure comparison among different bluff bodies was made by analyzing the experiment data, the flameholding and drag characteristics of slitted bluff body were forecasted. The flameholding mechanism was studied in time-dependent viewpoint on the basis of the investigation on wake structure in cold state. The researcher discovered that the gap flow makes the turbulent energy distribution wider, on the other hand, makes the vortex shedding character dimension longer, prolongs the elapsed time between the fuel gas in gap flow and shear layers gets in and out the recirculation zone, creates favourable condition for flame stabilization in the gap flow, and intensifys the firing support between the two shear layers. All the evidence proves that the slitted bluff body is a high efficiency flameholder with low drag. The flameholding mechanism was confirmed by the combustion experiment at low speed. Using the equilibrium state concept, topologic method and energy method, the transition of the wake over slitted bluff body was investigated, which was confirmed by the particle image velocimetry measurements, the nonlinear dynamics and vortex evolution mechanism in wake transition from layer flow to turbulent flow was proposed.
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