Aeroacoustics Analysis of Rifle Silencers Using Unsteady Overset CFD Methods*

Rifle silencers are used in both military and recreational applications to prevent hearing damage for firearm operators. The acoustic signature of a rifle firing is composed of both a spherical shock wake produced by the propellent combustion and an oblique shock wave form the projectile. Silencers reduce the peak sound pressure and intensity of the combustion shock by increasing the time over which the combustion gases are released from the barrel. Many silencer designs have been employed over the years, which varying degrees of success. While silencer manufactures conduct performance evaluations for new products, few studies have been published on the gas dynamic flow through a silencer. 

In this work, an unsteady overset CFD grid method was used to model the projectile traversing the rifle barrel and silencer. The air-standard approximation was applied, with the combustion event simulated as a short duration fluid addition in the bullet chamber at combustion temperatures and pressures. The increased pressure and temperature resulted in a one degree of freedom motion of the projectile. The near-field acoustic signature was analyzed and compared to sound probes from manufacturer tests. The CFD simulations indicated how geometric design features effect the silencer performance.