Abstract: The numerical simulation accuracy of interior ballistics of ultrahigh firing rate guns depends on the accuracy of calculating the drag force acting on projectile nose. In order to improve the numerical simulation accuracy of interior ballistics of ultrahigh firing rate gun, the secondary development tool UDF is used to couple FLUENT and the classic interior ballistic (CIB) model for the calculation of flow field in front of projectile. The nose drag force of the second launched projectile is obtained, and the variation law of nose drag force at different firing rates is analyzed. The simulated results show that the propellant gas flow field distribution can be obtained by the two-way coupling of FLUENT and CIB model, and the accuracy of calculating the nose drag force is improved. The nose drag force increases quickly after launching, and then decreases after it reaches a maximum value until the projectile leaves the muzzle. This variation law is common at different firing rates. When the firing rate reduces, the increased amplitude of nose drag force decreases at the earlier stage of projectile movement, and its decreased amplitude also decreases at the later stage of projectile movement.

Key words: ordnance science and technology, interior ballistics, ultrahigh firing rate gun, numerical simulation, FLUENT, two-way coupling