Evaluation of the Turbulence Model Effects on the Flow Field and Sound Pressure Levels Generated by Small Caliber Weapons System

Abstract

Estimation of the flow field around the projectile is crucial to predict the high-intensity noise. In this study, the effects of turbulence models on the flow field and far-field noise generated during the blast flow of a small caliber gun were investigated numerically. In this context, the numerical simulations of the influence of different turbulence models were performed for two different ammunition models, where in one case the projectile at the muzzle of the barrel had a subsonic velocity, and in the other case the projectile's initial velocity was supersonic. The small caliber 9x19 mm gun was selected in accordance with this purpose. To predict the far-field noise in numerical modeling, Ffowcs Williams and Hawkings acoustic analogies (FW-H) equations were solved in twodimensional, axisymmetric, transient conditions. To see the effects of turbulence models on results, k-epsilon models (Standard, RNG, Realizable), Standard k-omega, Spalart-Allmaras and LES turbulence models were used. Also, to model the moving projectile where the ballistic domain changed with time, a dynamic mesh model was used. The results of the numerical simulation obtained on the RNG k-epsilon turbulence model, in comparison with the experimental results, give better agreement for projectiles with a subsonic initial velocity. For projectiles that have supersonic velocity, the best results are given by numerical simulations where Spalart-Allmaras turbulence model was used. Therefore, by assuming two-dimensional and single-phase gas, where the chamber pressure and temperature are known and angular momentum of projectile is neglected, these models can be used as a quick tool to estimate the far-field noise from a small-caliber gun during the design stage.