Study On The Effect Of Flame Characteristic Quantities On The Fast Cook-off Ammunition

Fast cook-off is an indispensable part of ammunition thermal safety assessment.In order to study the influence of flame characteristics on the fast cook-off,a pool fire combustion model of cook-off specimens is established based on experimental research.The flame characteristics around the specimens are simulated by FDS software,and the calculated non-uniform flame characteristics are added to FLUENT as boundary conditions to simulate the fast cook-off response characteristics.In addition,according to the pool fire combustion model of the cookoff specimen,the matching between the pool fire size and the cook-off specimen and the influence of the location of the cook-off specimen on the response results are studied by using FDS software,and some important conclusions are obtained,which are of reference value for the study of the fast cook-off test method and simulation.The specific research conclusions are as follows:For the specimens filled with fused cast B explosives of three specifications,the response results of fast cook-off are explosion and its intensity response.Before ignition,only the B explosive about 2mm on the surface layer melts,the internal temperature of the grain is very low,and the central temperature is the same as that before the test.The average temperature of the flame increases with the increase of the size in the oil pool.With the increase of the charge quantity,the burning time prolongs and the response intensity increases;when the large bomb loaded with FOX-7 pressure explosive is loaded,the result of the fast cook-off response is combustion reaction,and the average flame temperature in the burning process is more than800℃;According to the pool fire combustion model of the cook-off specimen,important parameters such as flame temperature,total flame heat flux,and radiation heat flux can be calculated by FDS software.The changes of temperature and heat flux at different positions on the surface of the cook-off bomb can be obtained,which can be used as a boundary condition to embed it into FLUENT for fast cook-off simulation.The radiant heat flux plays a leading role in the fast cook-off process,and the proportion of radiant heat flux increases with the increase of the size of the oil pool.Under the conditions studied in this paper,the radiative heat flux accounts for more than 90% of the total heat flux,and the convective heat flux accounts for less than 10%.The oil pool area and the length-width ratio of the oil pool are important factors that affect the flame structure.With the increase of the length-width ratio of the oil pool,the flame structure changes from a cone-like structure to a flat cone-shaped thin structure.Therefore,it can be known that in the fast cook-off,the structure of the oil pool is not suitable to use a large ratio of length to width,usually about 1.3;There is a reasonable matching relationship between the sample size and the tank size.Under the condition that the structure of the oil pool is determined,the placement position and offset of the cook-off specimen are important factors affecting the temperature around the specimen.For the oil pool whose size is determined,the appropriate height and offset can be obtained by simulation calculation.