A submerged annular conical aerospike nozzle for a design Mach number of 2.0 has been numerically studied under over-expanded condition. Particular attention has been paid to the flow separation characteristics in aerospike nozzle for underwater propulsion application. The detailed Navier- Stokes flow computations were utilized to elucidate the gas-water interactions under the framework of a Volume of fluid model. The calculation results show that,the intermittently necking/bulging or necking/back-attack ph...