Research On Bluff-body Modification And Combustion Performance In A Central Bluff-body Trapped Vortex Combustor

The central bluff-body trapped vortex combustor is an advanced vortex combustor which is proposed by Ramgen Power Systems for its research on Ramgen engine. When the fore-body and aft-body are installed in the combustor, a trapped vortex cavity can be formed. And the cavity is able to capture vortices to ensure stable combustion.For the deeper research on the possibility of reducing the total pressure loss coefficient at the outlet of the central bluff-body trapped vortex combustor, different forms of fore-bodies were designed. And the cold flow field of the central bluff-body trapped vortex combustor with different fore-bodies was simulated. The cold characteristics and performance parameters of these central bluff-body trapped vortex combustors were obtained. The results show that double vortex pairs can be formed in the trapped vortex cavity when the circular shape fore-body and V shape fore-body are adopted. When the pear shape fore-body is adopted, the vortex structure in the trapped vortex cavity will change from the double vortex pairs into the single vortex pair with the decrease of the rear end face width. Compared with the circular shape fore-body, the total pressure loss coefficient of the combustor can be reduced by 0.867% and 7.783% respectively when V shape and pear shape fore-bodies are adopted. The cold performance of the combustor is optimal when the rear end face width of the pear shape fore-body is 64mm.The experimental measurements were carried out to obtain the cold performance of the central bluff-body trapped vortex combustor with the optimal fore-body. The pressure loss coefficient, static pressure distribution and limit streamlines of the top wall were measured, and the flow characteristics in each experimental condition were simulated; so that, they could be compared with the experimental results. The research shows that the total pressure loss coefficient of the combustor increases with the increase of the incoming flow Mach number. Under all conditions, two low-pressure areas appear on the top wall of the trapped vortex cavity and trapped vortices are formed in the trapped vortex cavity too.The numerical simulation was carried out to obtain the combustion performance of the combustor. The numerical results show that the combustion efficiency decreases when the incoming flow velocity increases. When the excess air coefficient declines, the combustion efficiency declines. When the excess air coefficient decreases, the outlet temperature distribution factor (OTDF) reduces rapidly. The NOx mass fraction at the outlet decreases with the increase of the incoming flow velocity. The NOx mass fraction drops when the total excess air coefficient drops. The NOx mass fraction increases when the incoming flow total temperature increases. The combustion efficiency of the central bluff-body trapped vortex combustor is about 98%, under most conditions.