Matching Study Of Air Injection Parameters In An Annular Central-bluff-body Trapped Vortex Combustor

In order to meet the tangential outflow of ram-rotor and to reduce the flow loss,the annular central bluff-body trapped vortex combustor was put forward by the company of Ramgen in the United States in 2007 in the study of the concept of new engines.The trapped vortex cavity air injection parameters have a decisive influence both on the vortex structure in the trapped vortex cavity and on the performance of the combustor.As the ignition source of the annular central bluff-body trapped vortex combustor,the difference and stability of the internal vortex structure directly influence the ignition and combustion of the combustor,and then determine the combustion performance and the pollutant emission performance of the combustor.The fluent software is adopted to simulate the cold flow field of an annular central bluff-body trapped vortex combustor in the paper.The research contents include the air injection position on afterbody,the matching study of the injection velocity both on afterbody and forebody and the matching study of the air injection size both on afterbody and forebody.In the paper the influence of the three air injection parameters both on the vortex distribution in the trapped vortex cavity and on the total pressure loss of combustor are mainly discussed.Numerical results show that the relatively stable vortex structure can all be formed in the trapped vortex cavity under different air injection position on afterbody,except the slightly different in size,shape and position of the vortex in the trapped vortex cavity;The average velocity of the flow field in the trapped vortex cavity increases with the air injection position moving inside,while the average static pressure and average turbulence intensity decreases with the air injection position moving inside.The two vortices in the trapped vortex cavity of the combustor are relatively regular and symmetrical at the injection velocity of 0.35Ma on forebody and the air injection velocity of 0.3Ma on afterbody,besides the core of the low pressure region is coincident with the vortex core under this air injection velocity matching scheme.The symmetry and uniformity of the vortex distribution decline when the air injection velocity is far away from the air injection velocity matching scheme mentioned above.The total pressure loss coefficient of the annular central bluff-body trapped vortex combustor under the air injection velocity of 0.35Ma on forebody and the air injection velocity of 0.3Ma on afterbody is lower than other air injection velocity matching schemes,and the value is 7.38%.The vortex distribution in the trapped vortex cavity is more regular and symmetrical when the forebody and the afterbody have the same or similar air injection size.Besides the total pressure loss of the combustor is lower with smaller air injection size of forebody.The equivalent aerodynamic width of the afterbody increases with the wider air injection size of forebody,causing greater aerodynamic resistance and narrower air flow area,thus the air friction exacerbate,therefore,the total pressure loss of the outlet is increased.