3D Simulations of Pre-Ignition Transient of P80 SRM

The first three stages of the new small European launcher Vega are solid rocket motors characterized by a star-shaped finocyl region (close to the propulsive nozzle). Zefiro 16 (a prototype developed as a precursor of the three stages of Vega) static fire tests have evidenced pressure oscillations during ignition startup. This phenomenon has been analyzed by means of quasi-1D and 3D numerical models. The numerical results of both models have very good agreement with experimental data and they have allowed a complete explanation of pressure oscillation phenomenology. These studies have suggested that the use helium instead nitrogen as pressurizing gas could eliminate pressure oscillations. Instead the subsequent static fire tests of P80, Zefiro 23 and Zefiro 9 have been done with helium showing no pressure oscillations during ignition transient as numerical simulations have predicted. On the contrary a second firing of P80, made with nitrogen as pressurizing gas, has exhibited pressure oscillations [ref.14]. Therefore we have done numerical simulations of P80 ignition transient using nitrogen: because of their differences the comparison between Zefiro 16 and P80 is interesting.